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to Engineering Evaluation 14-E16, Dominion Flooding Hazard Reevaluation Report for Millstone, Units 2 and 3, in Response to 50.54(F) Information Request Regarding Near-Term Task Force Recommendation 2.1: Flooding, Pp. 2-172 Through the End
	ML15078A208
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Site:	Millstone
Issue date:	03/12/2015
From:	; Dominion Nuclear Connecticut, Zachry Nuclear Engineering
To:	; Dominion Nuclear Connecticut, Office of Nuclear Reactor Regulation
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ML15078A203	List: ML15078A204; ML15078A205; ML15078A206; ML15078A207; ML15078A208;
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C IJRY DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.7. Ice-Induced FloodingThis section evaluates the potential of ice effects to contribute to flooding at MPS.2.7.1. MethodThe criteria for ice-induced flooding is provided in NUREG/CR-7046, Appendix G (NRC 2011). Twoice-induced events may lead to flooding at the site and are recommended and discussed inNUREG/CR-7046, Appendix G including:1. Ice jams or dams that form upstream of a site that collapse, causing a flood wave; and2. Ice jams or dams that form downstream of a site that result in backwater flooding.With respect to ice-induced flooding at MPS, the HHA used the following steps:1. Review historical ice events and information on backwater effects due to ice jams in theNiantic River near MPS.2. Evaluate historical salinity levels of the Niantic River and Long Island Sound to assess thefeasibility of the formation of ice jams in the Niantic River near MPS.3. Calculate flood elevations which could result at MPS from potential ice jams upstream ordownstream in the Niantic River.2.7.2. Results2.7.2.1. Review of Historical Ice EventsThe USACE maintains records of historical ice jams and dams on the Ice Jam Database (USACE,2012), which can be queried (using state/city/river name) to obtain information regarding historicalice events. There are no records of historical ice jams on the Niantic River or on the Long IslandSound in the USACE Ice Jam Database.2.7.2.2. Salinity of Water in Niantic River at MillstoneThe mean salinity of surface water in the Niantic River near MPS ranges from approximately 27.4 to30.3 psu (practical salinity unit), based on the data retrieved from the Long Island Sound ResourceCenter (University of Connecticut and the Connecticut DEP, 2004). According to the National Snowand Ice Data Center (NSIDC, 2013), a psu is nearly equivalent to a ppt (parts per thousand). Salinityin water has the potential to reduce the freezing point to be lower than 32 OF (0 0C) (NOAA, 2013).For example, the freezing point is 30 OF when the salinity is 17 ppt (NOAA, 2013).Although the salinity in water reduces the freezing point to be lower than 32 OF (0 0C), and reducesthe likelihood of ice jams near Millstone, the potential for ice jam formation on the Niantic River wasconservatively not disregarded based on possible extended period of time of low air temperature inthe region.EE 14-El 6, REV. 1 2-172EE 14-E16, REV.12-172

(-I DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.7.2.3. Flood Elevation due to Ice JamMPS is located along the shore of the Niantic Bay in the Long Island Sound, which does not containstructures downstream of the site where an ice jam can occur. Therefore, the potential for flooding tooccur at MPS as a result of a downstream ice jam is not significant.The closest structure upstream of MPS is the Amtrak Niantic River Bridge, which is locatedapproximately 0.8 miles upstream (see Figure 2.7-1). The maximum water depth above normal riverelevation resulting from an ice jam at the Amtrak Niantic River Bridge was conservatively calculatedto be equal to the bridge clearance of 16 feet (Amtrak, 2013). It is assumed that the ice daminstantaneously fails and the resulting flood wave was conservatively translated directly from theAmtrak Niantic River Bridge to the vicinity of MPS without consideration of flood wave attenuationwithin the Niantic Bay. It is assumed that the ice dam fails and the peak flow resulting from the floodwave was conservatively translated directly from the Amtrak Niantic River Bridge to the vicinity ofMPS without consideration of flood wave attenuation (i.e. decrease of discharge) within the NianticBay. The resultant peak flow from the ice dam failure was calculated using two empirical dambreach peak flow equations that use metric units (i.e., m, m3/s) as follows:Bureau of Reclamation: Qp = 19.1 (hw)1"85 Eq-1 (Wahl, 2004)Kirkpatrick: Qp = 1.268 (hw + 0.3)25 Eq-2 (Wahl, 2004)Where:Qp = Dam breach peak flow;hw = Head water.The dam breach peak flow (Qp) was calculated using the bridge clearance of 16 feet. The resultsshowed that the peak dam breach flow using the Bureau of Reclamation resulted in a greater peakflow than the Kirkpatrick equation. Therefore, the peak flow of 12,645 cfs was selected as the icedam breach peak flow calculated for the ice dam failure at the Amtrak Niantic River Bridge.The resultant rise in water level at Millstone was calculated using the Manning Formula (Chow,1959) for channel depth calculation:Q=A 1.4-9R2/3s]/2nWhere:A = cross section area (square-feet);n = Manning's n roughness;R = hydraulic radius (the cross sectional area of flow divided by the wetted perimeter);S = Slope of energy lineA rectangle channel with a bottom width equal to the Niantic Bay width at water surface elevationzero NAVD88 in the vicinity of Millstone and vertical walls at both sides of the channel (Figure 2.7-1)was assumed to calculate the normal depth using the Manning Formula. Therefore, the floodplainslopes and the Niantic Bay bathymetry (i.e., flow area below water surface elevation zero NAVD88)was conservatively ignored in the normal depth calculation. The resulting rise in water level at MPSwas conservatively estimated to be 2.9 feet, which is well below site grade at MPS (see Section 3).EE 14-El 6, REV.12-173 a C DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.This estimate is conservative because attenuation of the flood wave is not considered. Niantic Bay,located immediately downstream of the Amtrak Niantic River Bridge, significantly increases in areanear MPS, which would result in significant attenuation of the flood wave. This would be anticipatedto greatly reduce the size of the flood wave due to the failure of an upstream ice jam before itreached MPS.Note that the Amtrak Niantic River Bridge is a movable structure, which can be raised in the event ofan ice jam formation. As a result, ice jams can be released by raising the bridge structure.2.7.3. ConclusionsThe USACE Ice Jam Database (USACE, 2012) does not include records of ice jams occurring onthe Niantic River. MPS's location at the downstream-most end of the Niantic Bay creates conditionswhich are unlikely to sustain a downstream ice dam due to both water salinity and channelmorphology. Therefore, the potential for flooding to occur at MPS as a result of a downstream icejam is not significant.The failure of a conservatively-estimated hypothetical upstream ice jam would not exceed theprotected elevation at MPS (see Section 3).EE 14-El 6, REv. 1 2-174EE 14-El 6, REV.12-174 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.7.4. References2.7.4-1 Amtrak, 2013. Amtrak -Niantic River Bridge, ARRA Project Overview(http://www.amtrak.com/ccurl/377/521/Niantic-River-Bridqe-Replacement-Fact-Sheet.pdf -web page printed on 3/6/13).2.7.4-2 Chow, 1959. Ven Te Chow, "Open-Channel Hydraulics," reprint of the 1959 Edition,McGraw Book Company, Inc, 1959.2.7.4-3 NOAA, 2013. "JetStream -Online School for Weather -Sea Water," National Climatic andOceanic Administration (http://www.srh.noaa.gov/jetstream/ocean/seawater.htm -webpage printed on 1-1 9-2013).2.7.4-4 NRC 2011. "Design Basis Flood Estimation for Site Characterization at Nuclear PowerPlants -NUREG/CR-7046", U.S. Nuclear Regulatory Commission, November 2011.2.7.4-5 NSIDC, 2013. National Snow and Ice Data Center (NSIDC). Salinity and Brine(http://nsidc.org/cryosphere/seaice/characteristics/brine_salinity.html -web page printed3/7/13).2.7.4-6 University of Connecticut and the Connecticut DEP, 2004. Long Island SoundResource Center, prepared by the University of Connecticut and the ConnecticutDepartment of Environmental and Protection (DEP) with the support of researchers andorganizations throughout the Long Island Sound watershed. Niantic River 2004(http://www.lisrc.uconn.edu/eelgrass/LocationData.html -web page printed on 3/6/13).2.7.4-7 USACE, 2012. Ice Jam Database, U.S. Army Corps of Engineers, Ice EngineeringResearch Group, Cold Regions Research and Engineering Laboratory, 2012.2.7.4-8 Wahl, 2004. Tony L. Wahl, "Uncertainty of Predictions of Embankment Dam BreachParameters," Journal of Hydraulic Engineering ASCE, May 2004.EE 14-El 6, REV. 1 2-175EE 14-E16, REV.12-175 Z AM jilpfDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.7-1: Location of First Structure Upstream of MPS: Amtrak Niantic River BridgeA§*Msftfthea n3,ki*Legend* Miwone Power StatonEE 14-El 6, REV. 1 2-176EE 14-E16, REV.12-176 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.8. Channel Migration or DiversionThis section of the report evaluates the potential for natural channels to meander or otherwisechange alignment in a manner that could flood or otherwise affect Structures, Systems, andComponents (SSCs) important to safety at MPS. NUREG/CR-7046 (NRC, 2011) includes thefollowing statement in Section 3.8-Flooding Resulting from Channel Migration or Diversion:Natural channels may migrate or divert either away from or toward the site. The relevantevent for flooding is diversion of water towards the site. There are no well-establishedpredictive models for channel diversions. Therefore, it is not possible to postulate a probablemaximum channel diversion event. Instead, historical records and hydrogeomorphologicaldata should be used to determine whether an adjacent channel, stream, or river hasexhibited the tendency to meander towards the site.2.8.1. MethodThe channel migration and diversion flooding evaluation followed the HHA approach described inNUREG/CR-7046, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plantsin the United States of America (NRC, 2011). With respect to channel migration and diversion, theHHA used the following two steps:1. Review historical records and hydrogeomorphological data to assess whether the NianticRiver has exhibited the tendency to meander towards the site.2. Evaluate the foundation type at critical structures and shoreline protection features to assesspotential susceptibility to erosion caused by possible channel migration.2.8.2. Results2.8.2.1. Review of Historical RecordsA literature review did not yield evidence suggesting there have been significant historical diversionsof the Niantic River near Millstone or the small unnamed coastal stream east of Millstone for morethan 50 years. A comparison of a 1958 USGS Topographic map (USGS, 1958) and a 2012 USGSTopographic map (USGS, 2012) illustrates continuity of the river course for more than 50 years, seeFigures 2.8-1 and 2.8-2. Note that a former quarry located south of Millstone shown in the 1958USGS Topographic map (Figure 2.8-1) has been decommissioned (Figure 2.8-2). The area of theformer quarry has been flooded to be the plant cooling water discharge area.Millstone is located at the mouth of the Niantic Bay where the bay opening is approximately 2.1 mileswide. NUREG/CR-7046 (NRC, 2011) includes the following statement in Section 3.8-FloodingResulting from Channel Migration or Diversion:Because most channel diversion occurs during high flows when the stream or river overflowits banks, flood data, particularly stage, may also prove useful in the determination.The Niantic River watershed is approximately 31 square-miles. High flows in the Niantic Riverdissipate quickly in the Long Island Sound; therefore, high velocity overflows of the banks of the rivernear Millstone that could result in channel diversion or severe erosion are not anticipated. As aresult, channel diversion is not expected to occur near Millstone due to high riverine flows in theNiantic River. The small coastal stream near Millstone is not expected to produce high flows thatEE 14-El 6, REV.12-177 DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.could result in channel diversion toward Millstone due to its limited drainage area of 87 acres (seeSection 2.2).2.8.2.2. Review of foundation Types and Susceptibility to ErosionThe foundations for a majority of the critical structures including the reactor containment are onbedrock. However, the emergency generator, waste disposal enclosure, and turbine building, arefounded on dense basal till which overlies rock. The control building is founded on structural backfilloverlying till and bedrock. Generally, bedrock is highest on the eastern portion of the site and dips tothe west towards Long Island Sound. MPS is located on till that contains silt, sand, and stony fill;artificial fill, and bedrock. Subsurface explorations included in the MPS-3 FSAR (Dominion, 2014)generally show that till, when present, ranges from depths of 0 to 20 feet and rests on top ofbedrock.The soils and rock underlying the site are strong, stable materials that are not susceptible to loss ofstrength, subsidence, or other instabilities during earthquake motion. The soil and bedrock atMillstone are of very low permeability (Dominion, 2014).2.8.3. ConclusionsA review of historical data indicates that the Niantic River has not exhibited a tendency to meandertowards the site. High flows in the Niantic River dissipate quickly in the Long Island Sound,therefore, high velocity overflows of the banks of the river near Millstone that could result in channeldiversion or severe erosion are not anticipated. In addition, most of the site's critical structures arefounded on bedrock or structural backfill overlain on bedrock, and the shoreline is protected by arobust riprap revetment. Given these conditions, channel migration as a result of riverine flooding isnot considered to be a potential contributor to flooding at Millstone.2.8.4. References2.8.4-1 Dominion, 2014. Millstone Power Station Final Safety Analysis Report (MPS-3 FSAR), Rev.25.2.2.8.4-2 USGS, 1958. U.S. Geological Survey (USGS), Niantic Quadrangle 7.5-Minute SeriesHistorical Topographic Map, revised on 1958 and topography surveyed in 1934.2.8.4-3 USGS, 2012. USGS, Niantic Quadrangle 7.5-Minute Series Topographic Map, contoursbased on National Elevation Dataset, 2012.2.8.4-4NRC, 2011. "Design Basis Flood Estimation for Site Characterization at Nuclear PowerPlants -NUREG/CR-7046", U.S. Nuclear Regulatory Commission, November 2011.EE 14-El 6, REV. 1 2-178EE 14-E16, REV.12-178 ZACHIitYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.8-1:1958 Historical Topographic MapEE 14-El 6, REV. 1 2-179EE 14-E16, REV.12-179 ZACHFIYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zuchry Nuclear Engineering, Inc.Figure 2.8-2: 2012 Current Topographic MapEE 14-El 6, REV. 1 2-180EE 14-E16, REV.12-180 EIW DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.9. Combined Effect FloodsAn evaluation of the combined external flood effects associated with coastal flooding at MPS wasperformed. The combined flood effects were evaluated for both deterministic (Probable MaximumStorm Surge) and probabilistic flood analyses (associated with a flood annual exceedanceprobability of 1 E-6).2.9.1 MethodThe HHA approach described in NUREG/CR-7046 (NRC, 2011) was used for the evaluation of theeffects of the combined external flood effects at MPS. Deterministic combined effect flooding wasevaluated first, followed by a refined probabilistic combined effect flooding which is judged torepresent the most accurate estimate of flooding potential at MPS.2.9.1.1. Deterministic Combined Effect FloodMPS is subject to coastal flood hazards including storm surge, wind-generated waves and tsunamis.The coupled ADCIRC + SWAN model was used to simulate storm surge and waves due to thedeterministic PMSS and the probabilistic storm surge. The following approach to deterministicallycombining external flood hazards was used consistent with NUREG/CR-7046:H.1 -Floods Caused by Precipitation EventsThe following criteria for floods caused by precipitation events (NUREG/CR-7046, Appendix H,Section H.1) were evaluated.* Alternative 1 -A combination of mean monthly base flow, median soil moisture, antecedent orsubsequent rain, the PMP, and waves induced by 2-year wind speed applied along the criticaldirection;" Alternative 2 -A combination of mean monthly base flow, probable maximum snowpack, a 100-year snow-season rainfall, and waves induced by 2-year wind speed applied along the criticaldirection; and* Alternative 3 -A combination of mean monthly base flow, a 100-year snowpack, snow-seasonPMP, and waves induced by 2-year wind speed applied along the critical direction.The PMF was calculated for the small intermittent stream located approximately 200 feet east of theIndependent Spent Fuel Storage Installation (ISFSI) (Section 2.2). The small intermittent stream'swatershed is 87 acres (about 0.14 square miles) and terminates at the Millstone Road embankmentwithout a visible outlet to Long Island Sound. The resulting PMF elevation on the small coastalstream (due in large part to the access road embankment obstruction) near Millstone is 11.2 feet(Section 2.2), which is approximately 12.8 feet below the MPS3 site grade of 24.0 feet (Dominion,2014a) and approximately 2.8 feet below the MPS2 site grade of 14.0 feet (Dominion, 2014b).Significant wave propagation toward MPS is not expected due to the distance and the land use andland cover (e.g., woods and security barriers) between MPS and the small coastal stream and theavailable vertical margin or freeboard between MPS site grade and the PMF flood elevation.Additionally, flood velocities are anticipated to be very low because flooding is impounded by theMillstone Road embankment, limiting the potential for scour and erosion. Therefore, combined effectfloods caused by precipitation events (NUREG/CR-7046, Appendix H, Section H.1) are notconsidered further.EE 14-El 6, REV.12-181 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.The results of the dam failure section (Section 2.3) indicate that the potential for flooding at MPSresulting from upstream dam failure is not applicable based on the lack of dams within the Millstonelocal drainage basin and the watershed contributing to the small coastal stream.H.3 -Floods along the Shores of Open and Semi-Enclosed Bodies of WaterDue to the shore-side location of MPS, criteria for shore-side location combined events wereevaluated (Appendix H, Section H.3.1):-Probable maximum surge and seiche with wind-wave activity;-Antecedent 10 percent exceedance high tide.The antecedent 10 percent exceedance high tide elevation includes the calculated sea levelanomaly and the expected sea level rise in accordance with ANS 2.8 (ANS, 1992). Sea levelanomaly and the expected sea level rise were calculated in the Deterministic PMSS section (Section2.4).Wave action at MPS was calculated using SWAN, which is a component of the coupledADCIRC+SWAN model. Figure 2.9-6 provides the model bathymetric and topographic contoursused to model the combined storm surge and wind-wave activity. Both the MPS2 and MPS3 intakeswere identified as safety-related structures pertinent to the calculation of wave effects duringcombined event scenarios, as well as the MPS2 and MPS3 turbine buildings. Due to the structuregeometry of the intakes, as shown in Figure 2.9-1 and Figure 2.9-2, respectively, wave effects will beapplied against vertical walls.Wave effects include inundation (resulting in hydrostatic and hydrodynamic loads) and wavebreaking (resulting in slash and spray and wave loads). Unbroken waves in front of a verticalstructure located in relatively deep water result in an elevated, reflected standing wave (Goda,2010). This is due to reflection and transformation of non-breaking waves at a vertical face, wherethere can be an upward flow (vertical shift, referred to here as runup) that can be higher than theheight of the unbroken wave. Reflected wave crest elevations due to non-breaking waves werecalculated using the Sainflou Formula1 as presented in the USACE Coastal Engineering Manual(CEM) (USACE, 2006) for predicting wave forces on a vertical structure.The calculated "standing" (also referred to as "reflected") wave crest height is added to the PMSSstillwater elevation, to calculate the elevation of the standing wave crests at both intake structuresand turbine buildings.H.4 -Floods along the Shores of Enclosed Bodies of WaterThe criteria for floods along the shore of enclosed bodies of water (NUREG/CR-7046, Appendix H,Section H.4) do not apply to MPS since the site is not located on an enclosed body of water.1 In the case of irregular waves, wave height, H, should be taken as the characteristic wave height (USACE,2006). For the purposes of this evaluation, Hs, the significant wave height, is used.EE 14-E16, REV.12-182 EIW DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.H.5 -Floods Caused by TsunamisCombined flood effects associated with tsunamis are included as part of the analyses required byNUREG/CR-7046 (Appendix H, Section H.5). Considering MPS's hydrologic setting (i.e., the smallstream has a small watershed, no outlet to Long Island Sound and no hydraulic route for upstreamtsunami propagation exists) and based on the results of the PMF and Dam Failure, combinations oftsunami and small stream flooding are insignificant. Therefore, the single combined effect floodalternative for a shore location was used:Alternative H.5.1 -Combination of Probable Maximum Tsunami (PMT) run-up and antecedent10 percent exceedance high tide.Evaluation of the potential for tsunamis at the MPS site concluded that the PMT results in lower floodelevations than the PMSS. PMT maximum flood elevations are locally as high as 14.7 feet near theMPS2 and MPS3 intake structures, including the 10 percent exceedance high tide. The PMTmaximum flood elevation is a result of a far-field source (i.e., Cumbre Vieja subaerial landslide).Although the PMT run-up elevation is bounded (i.e., less than) by the storm surge stillwaterelevation, tsunamis may be associated with high velocity flow. Therefore, hydrodynamic andhydrostatic loading due to the PMT is evaluated in this section.2.9.1.2 Combined Effect Flood with Probabilistic Storm SurgqeIn addition to applying the combined flood effects presented above to the deterministic floodanalyses, the combined flood effects were also evaluated for the probabilistically-determined stormsurge corresponding to the annual exceedance probability (AEP) of 1 E-6. The combined effects forthe probabilistic analyses were assumed to be consistent with NUREG/CR-7046 (NRC, 2011) andANS 2.8 (ANS, 1992) for a shore location, including:* Storm surge corresponding to the to the AEP of 1 E-6 (Section 2.4);* Coincident wind-wave activity.While NUREG/CR-7046 (NRC, 2011) does not contain specific guidance for probabilistic inputs tocombined effect scenarios, ANSI/ANS 2.8 infers that the acceptable average exceedance probabilityfor combined effect flooding should be on the order of 1E-6 for design basis floods (ANSI, 1992).While the tidal component of the probabilistic surge does not include the 10-percent exceedancehigh tide (as used as input for the deterministic surge), the combination of the exceedanceprobability of the tidal condition used with the probabilistic storm surge parameters, equals anexceedance probability of 1 E-6. Using a probabilistic input to the combined effect scenario with anexceedance probability equal to the exceedance probability of the combined effect flooding, istherefore considered conservative.2.9.1.3 Hydrostatic Force and Hydrodynamic Loading and DebrisResulting flood depths were used to develop hydrostatic force and hydrodynamic loads. The flooddepths used for the calculation of hydrodynamic, hydrostatic and impact loads include increases indepth that may occur as a result of erosion and scour.EE 14-El 6, REV.12-183 Sp DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Hydrostatic LoadsHydrostatic loads are those caused by water above or below the ground surface, free or confinedwhich is either stagnant or moves at velocities less than 5 feet per second (fps) (ASCE, 2010).These loads are equal to the product of the water pressure multiplied by the surface area on whichthe pressure acts. The hydrostatic lateral forces (per linear foot of surface) were calculated usingASCE guidance.Flow VelocityFloodwater flow velocities include velocity components due to flooding and wind-generated waves.Estimating design flood velocities in coastal flood hazard areas is subject to considerableuncertainty. Flood velocities were estimated conservatively by assuming that floodwaters canapproach from the most critical direction relative to the site and by assuming that flow velocities canbe high (FEMA, 2011). The upper bound flood velocity (FEMA, 2011) was used to calculatehydrodynamic and impact loads.Hydrodynamic LoadsWater flowing around a building (or structure) imposes loads on the building. Hydrodynamic loads,which are a function of flow velocity and structure geometry, include frontal impact on the upstreamface, drag along the sides and suction at the downstream side. Hydrodynamic loads calculated hereused steady-state flow velocities consistent with FEMA guidance (FEMA, 2011; FEMA, 2012). Notethat the hydrodynamic loads applied above are for rigid structures. Dividing the horizontal drag forceby the building width yields a force per length (pounds per linear foot). The maximum forces at thebottom of the intakes were calculated using the area of the uniform pressure distribution.Hydrodynamic forces for low velocity flow (less than 10 feet per second) were analyzed as anequivalent hydrostatic force. Resultant force acts at a distance of H/2 above the ground.Debris Impact LoadsDebris impact loads are imposed on a building (or structure) by objects carried by moving water.The loads are influenced by where the impacted structure is located in the potential debris stream,specifically if it is:" immediately adjacent to or downstream from another building;* downstream from large floatable objects; or* among closely spaced buildings.Debris impact loads at the water surface were calculated using the guidelines described in FEMAP-259 (FEMA, 2012) and by considering debris weight recommended in ASCE-7-1 0 (ASCE, 2010).Per ASCE 7-10 (ASCE, 2010), in coastal areas debris weights may range from 1,000 to 2,000pounds. A debris object weight of 1,000 pounds is a reasonable average for flood-borne debris(representing trees, logs and other large woody debris (ASCE, 2010). A debris weight of 2,000pounds was conservatively used.EE 14-El 6, REV. 1 2-184EE 14-E16, REV.12-184 Z NW M 14DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Wave LoadsLoads due to broken waves are similar to hydrodynamic loads from flowing or surging water. Theforces from breaking waves are the largest and most severe; therefore this load condition was usedas the design wave load (FEMA, 2011). The three breaking wave load conditions (FEMA, 2011)include: a) waves breaking against submerged small diameter piles; b) waves breaking againstsubmerged walls; and c) wave slam, where the top of the wave strikes against a vertical wall. Theterm "wave slam" refers to the action of wave crest striking the elevated portion of a structure(FEMA, 2011). Wave slam is only calculated for elevated structures.The maximum breaking wave pressures and loads on vertical walls were calculated for structures atMPS (ASCE, 2010). The calculations apply to the condition where the space behind the wall is dry(e.g., the interior of a building). The loads are applied as shown in Figure 2.9-3 (FEMA, 2011).2.9.1.1.1 Tsunami LoadingThe results of the tsunami simulations indicate that the highest predicted runup elevations in thevicinity of the MPS site result from the subaerial landslide (extreme flank failure) of the CVV. TheCVV results in maximum water levels of approximately 14.7 feet, MSL at MPS2 and MPS3 (seeSection 2.6). Fluid density of tsunami flow is assumed to be 1.2 times the density of freshwater, 2.33slugs per cubic foot, based on a sediment volume concentration of 10% in seawater (FEMA, 2008).Hydrostatic LoadsThe hydrostatic lateral forces (per linear foot of surface) were calculated at both the MPS2 andMPS3 intakes (FEMA, 2008). These loads are equal to the product of the water pressure multipliedby the surface area on which the pressure acts.Hydrodynamic ForcesHydrodynamic forces were calculated at both the MPS2 and MPS3 intakes based on FEMAguidance (FEMA, 2008). Resultant hydrodynamic forces are applied at approximately the centroid ofthe wetted surface of the structure.Impulsive ForcesImpulsive forces are caused by the leading edge of the surge water (i.e. tsunami wave) impacting astructure. The impulsive forces are conservatively estimated as 1.5 times the hydrodynamic force(FEMA, 2008).Debris Impact ForcesThe debris impact forces were calculated at both the MPS2 and MPS3 intakes based on FEMAguidance (FEMA, 2008).Two types of waterborne debris were analyzed, a log and a 20-foot heavy shipping container. Theeffective stiffness and mass of a log is 2.4x1 06 newton per meter and 450 kilograms respectively(FEMA, 2008). The effective stiffness and mass of a 20-foot long heavy shipping container is1.7xl 09 Newtons per meter and 2,400 kilograms respectively (FEMA, 2008).EE 14-El 6, REV.12-185 Z ow DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.9.2. Results2.9.2.1. Combined Effect Flood: DeterministicThe shore location combined effects flood alternative consists of the combination of 1) the PMSS, 2)the antecedent 10% exceedance high tide, and 3) coincident wind-wave activity.The PMSS and Antecedent 10 Percent Exceedance High Tide:The maximum stillwater elevation of 25.8 feet2, MSL (Section 2.4) was used in the determination ofmaximum water level resulting from combined effects of storm surge and wind-driven wave activity.The resulting stage hydrograph (with waves) for the deterministic PMSS is shown in Figure 2.9-4.Estimated wind speed and duration based on ADCIRC results are shown on Figure 2.9-5.Coincident wind-wave activityWind wave effects at the MPS2 and MPS3 buildings were determined based on the maximumsignificant wave heights presented in Figure 2.9-7. While there will be wave effects at the MPS1reactor building and turbine building, these are no longer safety-related structures. These structureswill also significantly dissipate wave action that could otherwise affect both MPS2 and MPS3. Asshown in Figure 2.9-7, waves on the eastern portion of the site are not of substantial height (i.e. lessthan 0.5 meters) and are travelling in a northeast direction. The presence of non-safety relatedbuildings such as the MPS2 maintenance shop and other warehouse buildings would significantlydissipate any wave generation and wave energy that could impact the eastern portion of the site.The combination of wave direction and dissipation of wave energy due to the MPS1 buildings andother non-safety related structures indicate that wave effects are negligible on the southern andeastern portions of MPS. Therefore, wave effects were calculated on the western portion of the sitewhere waves will impact the MPS2 and MPS3 intakes and turbine buildings. Significant waveheights and peak periods at these locations were extracted from the deterministic PMSSADCIRC+SWAN model, as shown in Table 2.9-1. Figure 2.9-9 presents the locations of each nodefor the SWAN output locations.Reflected wave crest heights and elevations are presented in Table 2.9-2, and correspond to 17.9feet at the MPS2 intake, and 16.2 feet at the MPS3 intake, respectively. Maximum elevationsassociated with reflected wave crests are 43.7 feet, MSL at the MPS2 intake, and 42.0 feet, MSL atthe MPS3 intake. The MPS2 intake would be overtopped by approximately 4.7 feet, for a period ofapproximately 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months . Non-breaking wave overtopping due to the significant wave height will havea non-impulsive, (i.e.,"green water") overtopping effect. Smaller waves and broken waves againstthe intake structure will result in splash and spray on the structure, but will not result in significantovertopping effects.As shown in Figure 2.9-7, there is a significant decrease in wave height once waves propagate ontothe site grade on the western portion of MPS. The dissipation in wave height is largely due to frictionof land and uneven topography. Non-breaking wave heights near the MPS2 turbine building are2 25.8 feet MSL is inclusive of model uncertainty (i.e. 0.78 feet), wave setup, and the difference between thepeak simulated tide elevation at Watch Hill, RI and the antecedent water level of 1.026 feet: 23,3' MSL(Section 2.4) + 0.7' setup + 0.78' model uncertainty + 1.026' tidal difference = 25.8' MSL."EE 14-E16, REV.12-186 EW DOMINION FLOODING HAZARD REEVALUATION REPORT FORZ'ACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.approximately 5.4 feet. The maximum wave height at the MPS3 Turbine building was calculatedusing the relationship of depth-limited wave heights (0.78 x depth; ANS, 1992), resulting in a waveheight of 1.4 feet. The reflected wave crest height at the MPS2 turbine building is 6.7 feet and 1.9feet at the MPS3 turbine building, as shown in Table 2.9-2. The maximum standing wave crestelevations are 32.5 feet and 27.7 feet, MSL, respectively.2.9.2.2. Combined Effect Flood: Probabilistic Storm SurgeThe combined effects for the 1 E-6 Annual Exceedance Probability Probabilistic Storm Surge resultsfrom a combination of 1) the storm surge corresponding to the 1,000,000-year recurrence interval, 2)the mean high tide with sea level rise, and 3) coincident wind-wave activity.Stillwater ElevationThe stillwater level resulting from the combination of the storm surge corresponding to the1,000,000-year recurrence interval and mean high tide with sea level rise was calculated to be 21.0feet, MSL including aleatory variability and epistemic uncertainty at the 1 E-6 AEP level and 50-yearsea level rise projections.Since wave heights were initially developed using the ADCIRC+SWAN models based on themodeled stillwater elevation of 16.8 feet, MSL, wave heights in this model are biased lower and arenot inclusive of uncertainty. Therefore, a second ADCIRC+SWAN model simulation was performedto include the uncertainty effects by adding 4.249 feet to the initial static water level. The stagehydrograph (with waves) from a representative storm that results in an elevation corresponding tothe 1,000,000-year recurrence interval inclusive of uncertainty factors is shown in Figure 2.9-10. Acomparison between the two model simulations shows that wave heights are slightly higher usingthe model inclusive of error uncertainty.Coincident Wind-Wave ActivityWave heights and periods from the probabilistic storm surge SWAN model are included in Table 2.9-3. The SWAN results indicate that at the MPS2 intake, wave heights are approximately 6.3 feet witha peak period of 4.3 seconds. At the MPS3 intake wave heights are approximately 7.0 feet with acorresponding peak period of 7.3 seconds. Reflected wave crest heights and elevations arepresented in Table 2.9-4, and correspond to 7.8 feet at the MPS2 intake, and 7.7 feet at the MPS3intake, respectively. Maximum elevations associated with reflected wave crests are 28.7 feet, MSLat the MPS2 intake, and 28.7 feet, MSL at the MPS3 intake which will not result in overtopping of theintake structures. While there may be a portion of waves breaking against the intakes, this wouldresult in splash and spray on the structures, and not result in any significant overtopping.Under the probabilistic storm surge stillwater elevation, MPS3 is not exposed to flooding as the sitegrade of 24 feet, MSL is above the stillwater elevation of 21 feet, MSL. While there will be waveeffects at MPS1, these are no longer safety-related structures, and the presence of MPS1 willsignificantly decrease wave heights affecting MPS2. As shown in Figure 10, wave heights on theeastern portion of the site are not of substantial height (i.e. less than 0.5 meters). The SWAN modeldoes not currently include detail inclusive of all MPS buildings, however, the presence of non-safetyrelated buildings (such as the MPS2 maintenance shop, MPS2 Maintenance Snubber Shop, HealthFacility, the Fire Water Tanks, Security Operations Center, and Refuel Outage Building) wouldsignificantly dissipate any wave generation and wave energy that could impact the eastern portion ofthe site (i.e. the MPS2 reactor building). Due to the dissipation of wave energy by the various non-EE 14-El 6, REV.12-187 MW DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.safety related buildings, the wave effects are considered negligible on the eastern side of the MPS2reactor building. Therefore, wave effects were evaluated on the western portion of the site wherewaves will impact the MPS2 turbine building. Wave heights at these locations were extracted fromthe probabilistic ADCIRC+SWAN model, as shown in Table 3. As shown in Figure 9, there is asignificant reduction in wave height once the waves propagate onto the site grade. This is due tobottom friction effects and steep changes in topography. Wave heights are dissipated toapproximately 2.8 feet with a 9.1 second peak period. Reflected wave crest elevations weredetermined using the Sainflou formulas for fully head on reflected wave crests. The results arepresented in Table 4. The reflected wave crest at the MPS2 Turbine building is 3.4 feet, with amaximum elevation of 24.4 feet, MSL. While this elevation is about 2.4 feet above the flood wallelevation of 22 feet, MSL, the siding of the flood wall will prevent water resulting from splash effectsfrom entering the building (Dominion, 2014a). Splash effects are due to the reflected wave crestsovertopping the flood wall at the turbine building.2.9.2.3. Hydrostatic Force and Hydrodynamic Loading and DebrisTypical hydrostatic and hydrodynamic forces were calculated for the controlling deterministiccombined flood effects and the probabilistic combined flood effects. Calculation equations,constants, and corresponding units were described in Section 2.4. Typical hydrostatic andhydrodynamic forces were calculated at the area near MPS2, the area near MPS3, the MPS2 intakestructure and the MPS3 intake structure. The foot of the MPS2 and MPS3 intake structures is atelevation -30.0 feet, MSL (Dominion, 2014b and Dominion, 2014a, respectively).Hydrostatic LoadsThe maximum stillwater water elevation of 25.8 feet3, MSL for the deterministic combined effect floodwas used, and results in a depth of flood water of 11.8 feet at MPS2 turbine building, 1.8 feet at theMPS3 turbine building and 55.8 feet at the intake structures. The typical hydrostatic forces werecalculated as:Location Hydrostatic Load (lb/ft) Elevation (feet MSL)MPS2 Turbine Building 4,456 17.9MPS3 Turbine Building 104 24.6Intake Structures 99,636 -11.4The pressure at the bottom of the intakes was determined to be 3,571 psf.The maximum stillwater elevation of 21.0 feet, MSL for the probabilistic combined effect flood wasused and results in a depth of flood water of 7 feet at the MPS2 turbine building and 51 feet at the3 25.8 feet MSL is inclusive of model uncertainty (i.e. 0.78 feet), wave setup, and the difference between thepeak simulated tide elevation at Watch Hill, RI and the antecedent water level of 1.026 feet: 23,3' MSL(Section 2.4) + 0.7' setup + 0.78' model uncertainty + 1.026' tidal difference = 25.8' MSL.EE 14-El 6, REV.12-188 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.intake structures. The area near MPS3 is not flooded for the probabilistic combined effect flood.The typical hydrostatic forces were calculated as:Location Hydrostatic Load (lb/ft) Elevation (feet MSL)MPS2 Turbine Building 1,568 16.3MPS3 Turbine Building N/A N/AIntake Structures 83,232 -13The pressure at the bottom of the intakes was determined to be 3,264 psf.Flow VelocityFor the intake structures, the flood depth used to calculate the flow velocity, the hydrodynamic forceand debris loads on the MPS2 and MPS3 intakes was selected based on the elevations at theconfluence of the sloped intake channel and the bay (MPS, 1989 and Dominion, 2014b). Theseelevations are -16 feet, MSL for MPS3 intake and -15 feet, MSL for MPS2 intake. An upper boundflow velocity was calculated to be 36.2 feet per second at the MPS2 intake and 36.7 feet per secondat the MPS3 intake for the deterministic combined effects flood.An upper bound flow velocity was calculated to be 19.5 feet per second at MPS2 turbine buildingand 7.6 feet per second at the MPS3 turbine building for the controlling deterministic combinedeffects flood.An upper bound flow velocity was calculated to be 15.0 feet per second at the MPS2 turbinebuilding, 34.0 feet per second at the MPS2 intake structure and 34.5 feet per second at the MPS3intake structure for the probabilistic combined effects flood.Hydrodynamic LoadsThe hydrodynamic loading analysis was calculated along various buildings throughout the site (seeTable 2.9-5) for the controlling deterministic combined effect flood. The hydrodynamic loading variesfrom 5,436 pounds per linear foot to 6,089 pounds per linear foot near MPS2 for the controllingdeterministic combined effect flood. The hydrodynamic loading varies from 135 pounds per linearfoot to 207 pounds per linear foot near MPS3 for the controlling deterministic combined effect flood.The hydrodynamic forces at MPS3 were analyzed as an equivalent hydrostatic force because theflood flow velocity was less than 10 feet per second. The hydrodynamic loading was calculated tobe 66,498 pounds per linear foot at the MPS2 intake structure and 70,023 pounds per linear foot atthe MPS3 intake structures. The hydrodynamic loading near MPS2 acts at elevation 19.9 feet, MSL.The hydrodynamic loading near MPS3 acts at elevation 24.9 feet MSL. The hydrodynamic loadingat the intake structures acts at elevation -2.1 feet, MSL.The hydrodynamic loading analysis was calculated along various buildings throughout the site (seeTable 2.9-6) for the probabilistic storm surge. The hydrodynamic loading varies from 1,962 poundsper linear foot to 2,747 pounds per linear foot near MPS2 for the controlling probabilistic combinedeffect flood. The hydrodynamic loading near MPS2 act at elevation 17.5 feet, MSL. TheEE 14-E16, REV.12-189 A C H IRY DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.hydrodynamic loading was calculated to be 51,760 pounds per linear foot at the MPS2 intakestructure and 54,774 pounds per linear foot at the MPS3 intake structure. The hydrodynamic loadingat the intake structures acts at elevation -4.5 feet, MSL.Debris Impact LoadsTypical debris impact loads on exterior portions of structures (for debris weight of 2,000 pounds)were calculated for the deterministic PMSS as 40,560 pounds near MPS2, 3,952 pounds near MPS3and 75,296 pounds for the MPS2 intake structure and 76,336 pounds for the MPS3 intake structurefor the controlling deterministic combined effects flood.Debris impact loads on exterior portions of structures were calculated for the probabilistic stormsurge as 31,200 pounds near MPS2, 70,720 pounds at the MPS2 intake structure and 71,760pounds at the MPS3 intake structure for the probabilistic combined effects flood.Wave LoadsLoads due to non-breaking waves were calculated as the hydrostatic and hydrodynamic loadsdescribed above.For the deterministic PMSS, the typical breaking wave load on vertical walls was calculated as55,696 pounds per foot near MPS2, 1,296 pounds per foot near MPS3 and 1,245,456 pounds perfoot for the intake structures for the controlling deterministic combined effects flood.For the probabilistic storm surge, the maximum breaking wave load on vertical walls was calculatedas 19,600 pounds per foot near MPS2 and 1,040,400 pounds per foot for the intake structures forthe probabilistic combined effects flood.2.9.2.3.1 Tsunami LoadingTypical hydrostatic and hydrodynamic forces were calculated at the area near MPS2, the MPS2intake structure and the MPS3 intake structure. The inundation extent along the MPS2 Turbinebuilding was approximately 630 feet (see Section 2.6). The MPS2 intake structure is approximately80 feet wide. The MPS3 intake structure is approximately 135 feet wide.Hydrostatic LoadsThe maximum water surface elevation of 14.7 feet MSL for the tsunami at MPS2 and MPS3 (Section2.6) results in a depth of flood water of 0.7 feet at MPS2 and 44.7 feet at the intake structures. Thearea near MPS3 is not flooded due to the tsunami. The typical hydrostatic forces were calculatedas:Location Hydrostatic Load (lb/ft) Elevation (feet MSL)MPS2 Turbine Building 18.4 14.2MPS3 Turbine Building N/A N/AMPS2 Intake Structure 74,954 -15.1MPS3 Intake Structure 74,954 -15.1EE 14-El 6, REV.12-190 MWAM JJRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYFOMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Hydrodynamic ForcesThe hydrodynamic loading was calculated to be 326 pounds per linear foot near MPS2 and 20,961pounds per linear foot at the intake structures. The hydrodynamic loading near MPS2 acts atelevation 14.5 feet, MSL. The hydrodynamic loading at the intake structures acts at elevation -7.7feet, MSL.Impulsive ForcesThe impulsive force was calculated to be 489 pounds per linear foot near MPS2 and 31,441 poundsper linear foot at the intake structures.Debris Impact ForcesThe maximum flow velocity of 1.05 meters per second (3.4 feet per second) was calculated inSection 2.6. The debris loads was calculated to be 15,515 pounds for a log and 953,593 pounds fora heavy shipping container at the MPS2 and MPS3 intake structures.2.9.3. ConclusionsA summary of combined event scenario maximum water elevations are presented in Table 2.9-7.MPS is considered to be a shore location because riverine and dam failure-induced flooding hasbeen demonstrated to be negligible. Both deterministic and a refined probabilistic combined effectflood analyses were performed for this combination:o The resulting stillwater elevation for the deterministic analysis is 25.8 feet, MSL. This elevationis the combination of the modeled stillwater elevation of 23.3 feet MSL, wave setup of 0.7 feet,uncertainty (i.e. 0.78 feet) and the difference between the peak simulated tide elevation atWatch Hill, RI and the antecedent water level of 1.026 feet, which includes applicable sea levelrise. The results of the reflected wave crest elevations at the MPS2 and MPS3 intakes are43.7 feet and 42.0 feet, MSL, respectively. Reflected wave crest elevations on the westernsides of the MPS2 and MPS3 turbine buildings are 32.5 feet and 27.7 feet, MSL, respectively.As shown in Figure 2.9-4, the peak of the deterministic surge occurs between 2.1 and 2.15days of storm simulation (i.e., where day 15 marks the start of the storm simulation withrepresentation of dynamic tide conditions).o The resulting stillwater elevation for the probabilistic analysis is 21.0 feet, MSL. This elevationis the combination of the modeled stillwater (i.e., including wave setup) elevation of 16.8 feetMSL and the uncertainty effects of 4.249 feet., which include consideration of applicable sealevel rise An additional ADCIRC+SWAN model was run for the probabilistic storm surge toaccount for model uncertainty. This model was run with a condition of adding 4.2 feet to thestarting static water level. The results of the reflected wave crest elevations at the MPS2 andMPS3 intakes are 28.8 feet and 28.7 feet, MSL, respectively. Reflected wave crest elevationsat the western side of the MPS2 turbine building is 24.4 feet, MSL. The probabilistic stormsurge stillwater elevation does not inundate MPS3. As shown in Figure 2.9-10, the peak of theprobabilistic surge occurs slightly after 2.1 days of storms simulation (i.e., where day 0 marksthe start of the storm simulation under static tide conditions).EE 14-E16, REV.12-191 o C DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.9.4. References2.9.3-1 ANS, 1992. American National Standard for Determining Design Basis Flooding at PowerReactor Sites (ANSI/ANS 2.8-1992).2.9.3-2 ASCE, 2010. "Minimum Design Loads for Buildings and Other Structures," ASCE/SEI 7-10,American Society of Civil Engineers (ASCE), 2010.2.9.3-3 Dominion, 2014a. Millstone Power Station Unit 3, Final Safety Analysis Report (FSAR),Revision 25.2.2.9.3-4 Dominion, 2014b. Millstone Power Station Unit 2, Final Safety Analysis Report (FSAR),Revision 30.2.2.9.3-5 FEMA, 2008. "Guidelines for Design of Structures for Vertical Evacuation from Tsunamis,"FEMA P646, June 2008.2.9.3-6 FEMA, 2011. "Coastal Construction manual: Principles and Practices of Planning, Siting,designing, Constructing and Maintaining Residential Buildings in Coastal Areas," FEMA 55,2011.2.9.3-7 FEMA, 2012. "Engineering Principles and Practices for Retrofitting Flood-Prone ResidentialStructures," FEMA-P-259, 2012.2.9.3-8 Goda, 2010. "Random Seas and Design of Maritime Structures," Advanced Series onOcean Engineering -Volume 33, 3rd Edition, Y. Goda, 2010.2.9.3-9 MPS, 1989. "Shorefront & Dredging Plan & Details," Drawing Number 12179-BCY-11A-3SH 1, July 11, 1989.2.9.3-10 NRC, 2011. Design Basis Flood Estimation for Site Characterization at Nuclear PowerPlants -NUREG/CR-7046, United States Nuclear Regulatory Commission, November2011.2.9.3-11 USACE, 2006. Coastal Engineering Manual -Part VI, Chapter 5, "Fundamentals ofDesign," EM 1110-2-1100, U.S. Army Corps of Engineers, June 2006.EE 14-El 6, REV. 1 2-192EE 14-E16, REV.12-192 Zac HA 14RYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.TaTable 2.9-1: Deterministic SWAN ResultsSignificant Peak WaveLocation Wave Height Period(feet) (seconds)MPS2 Intake 15.1 9.4MPS2 Turbine Building 5.4 8.9MPS3 Intake 13.9 9.4MPS3 Turbine Building 2.8 9.4ible 2.9-2: Deterministic Sainflou Reflected Wave Crest ResuReflected ReflectedWave CrestLocation Wave Crest ElevatHeight (feet) (feet, MSL)MPS2 Intake 17.9 43.7MPS2 Turbine Building 6.7 32.5MPS3 Intake 16.2 42.0MPS3 Turbine Building 1.9 27.7Table 2.9-3: Probabilistic SWAN ResultsSignificant Peak WaveLocation Wave Height Period(feet) (seconds)MPS2 Intake 6.3 4.3MPS2 Turbine Building 2.8 9.1MPS3 Intake 7.0 7.3MPS3 Turbine Building N/A N/AItsTable 2.9-4: Probabilistic Sainflou Reflected Wave Crest ResultsReflected ReflectedWave CrestLocation Wave Crest ElevatHeigt (fet) ElevationHeight (feet) (feet, MSL)MPS2 Intake 7.8 28.8MPS2 Turbine Building 3.4 24.4MPS3 Intake 7.7 28.7MPS3 Turbine Building N/A N/AEE 14-El 6, REV. 1 2-193EE 14-El 6, REV.12-193 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 2.9-5: Hydrodynamic loading for the controlling deterministic combined effect floodBuilding Name Width in North -South Direction (feet) Depth (feet) Width to Height Ratio Cd Velocity (ft/sec) Fdyn (Ib/ft) dh Fdh (lb/ft)Auxiliary 165 11.8 14.0 1.3 19.5 5,654Bldg 118 (Control Bldg East, Unit 1) 30 11.8 2.5 1.25 19.5 5,436c0 Enclosure 80 11.8 6.8 1.25 19.5 5,436Fire Pump House 65 11.8 5.5 1.25 19.5 5,436Intake 80 11.8 6.8 1.25 19.5 5,436Turbine 315 11.8 26.7 1.4 19.5 6,089Aux Building 1.8 -7.6Control Building 91 1.8 50.6 1.75 7.6 1.575 181DWST 40 1.8 22.2 1.4 7.6 1.26 145EDG Building 60 1.8 33.3 1.5 7.6 1.35 156ESF Building 150 1.8 83.3 1.8 7.6 1.62 187Fuel Building 75 1.8 41.7 1.75 7.6 1.575 181o Hydrogen Recombiner Building 60 1.8 33.3 1.5 7.6 1.35 156Intake 95 1.8 52.8 1.75 7.6 1.575 181Maint Shop 150 1.8 83.3 1.8 7.6 1.62 187RWST 60 1.8 33.3 1.5 7.6 1.35 156Service Bldg. 1.8 --7.6 --Steam Valve Building 85 1.8 47.2 1.75 7.6 1.575 181Turbine Building 355 1.8 197.2 2 7.6 1.8 207Waste Disposal 80 1.8 44.4 1.75 7.6 -1.575 181Building Name Width in East -West Direction (feet) Depth (feet) Width to Height Ratio Cd Velocity (ft/sec) Fdyn (lb/ft) dh Fdh (Ib/ft)Auxiliary 85 11.8 7.2 1.25 19.5 5,436Bldg 118 (Control Bldg East, Unit 1) 11.8 -19.5 -(n Enclosure 175 11.8 14.8 1.3 19.5 5,654Fire Pump House 20 11.8 1.7 1.25 19.5 5,436Intake 70 11.8 5.9 1.25 19.5 5,436Turbine 11.8 19.5Aux Building 110 1.8 61.1 1.75 7.6 1.575 181Control Building 120 1.8 66.7 1.75 7.6 1.575 181DWST 40 1.8 22.2 1.4 7.6 1.26 145EDG Building 80 1.8 44.4 1.75 7.6 1.575 181ESF Building 50 1.8 27.8 1.4 7.6 1.26 145Fuel Building 1.8 --7.6 -W Hydrogen Recombiner Building 1.8 --7.6 --Intake 120 1.8 66.7 1.75 7.6 1.575 181Maint Shop 110 1.8 61.1 1.75 7.6 1.575 181RWST 60 1.8 33.3 1.5 7.6 1.35 156Service Bldg. 30 1.8 16.7 1.3 7.6 1.17 135Steam Valve Building 1.8 -7.6Turbine Building _ 1.8 -7.6Waste Disposal 115 1.8 63.9 1.75 7.6 1.575 181EE 14-E16, REV. 1 2-194EE 14-E16, REV.12-194 ZACIHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 2.9-6: Hydrodynamic loading for the controlling probabilistic combined effect floodBuilding Name Width in North -South Direction (feet) Depth (feet) Width to Height Ratio Cd Velocity (ft/sec) Fdyn (Ib/ft)Auxiliary 165 7 23.6 1.4 15.0 2,198Bldg 118 (Control Bldg East, Unit 1) 30 7 4.3 1.25 15.0 1,962U) Enclosure 80 7 11.4 1.25 15.0 1,962(LFire Pump House 65 7 9.3 1.25 15.0 1,962Intake 80 7 11.4 1.25 15.0 1,962Turbine 315 7 45.0 1.75 15.0 2,747Aux Building 0 -Control Building 91 0DWST 40 0EDG Building 60 0ESF Building 150 0C' Fuel Building 75 0-Hydrogen Recombiner Building 60 0Intake 95 0Maint Shop 150 0RWST 60 0Service Bldg. 0Steam Valve Building 85 0Turbine Building 355 0Waste Disposal 80 0Building Name Width in East -West Direction (feet) Depth (feet) Width to Height Ratio Cd Velocity (ft/sec) Fd n lb/ftAuxiliary 85 7 12.1 1.3 15.0 2,041Bldg 118 (Control Bldg East, Unit 1) 7 -15.0 -(n Enclosure 175 7 25.0 1.4 15.0 2,198Fire Pump House 20 7 2.9 1.25 15.0 1,962Intake 70 7 10.0 1.25 15.0 1,962Turbine 7 --Aux Building 110 0Control Building 120 0DWST 40 0EDG Building 80 0ESF Building 50 0Fuel Building _ 0Co Hydrogen Recombiner Building 0Intake 120 0Maint Shop 110 0RWST 60 0Service Bldg. 30 0Steam Valve Building 0Turbine Building 0Waste Disposal 115 0EE 14-E16, REV.12-195 wACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 2.9-7: Summary of Reflected Wave Crest Elevations at MPSDeterministic PMSS Probabilistic Storm SurgeLocationReflected ReflectedRaeflete Wave Crest Reflet Wave CrestWave Crest Wave CrestElevation ElevationHeight (feet) (feet, MSL) Height (feet) (feet, MSL)MPS2 Intake 17.9 43.7 7.8 28.8MPS2 Turbine Building 6.7 32.5 3.4 24.4MPS3 Intake 16.2 42.0 7.7 28.7MPS3 Turbine Building 1.9 27.7 N/A N/AEE 14-El 6, REV. 1 2-196EE 14-E16, REV.12-196 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-1: MPS2 Intake Structure Layout(Figure from Dominion, 2014b)EE 14-El 6, REV. 1 2-197EE 14-El 6, REV.12-197 9ACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-2: MPS3 Intake Structure Layout+43.0 FEET MSL-+41.2 FEET MSLLS+39.0 FEET MSL4 14.5 FEET MSL+ "11.5 FEET MSL-7.0 FEET MSLFEET MSL-30 FEET MSLINCIDENT WAVE-WAVE HEIGHT: 16.2 FEETWAVE PERIOD: 9.0 SECONDS0 5 10 15 20 25I I I I ! ISCALE-FEET(Figure from Dominion, 2014a)EE 14-E16, REV. 1 2-198EE 14-El 6, REV.12-198 ZACHry ule E IYcDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-3: Wave load schematicDOW -uo WillTmb* fi c*"w #A014 owE(Figure from FEMA, 2011)EE 14-El 6, REV. 1 2-199EE 14-El 6, REV.12-199 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-4: Stage Hydrograph (Surge +Wave Setup) for Deterministic PMSSWater Surface Elevation at MPS Intake~104..'Uciwa,U(USt1~a'NOW.-/15 15.25 15.5 15.7516 16.25 16.5 16.75Day (Simulated Date)17 17.25 17.5 17.75 18EE 14-E16, REV. 1 2-200EE 14-E16, REV.12-200 Z'ACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-5: Wind Speed vs Time for the Deterministic PMSSWind Speed at MPS Intake656055504540E-35(/ 30C3: 252015105015 15.25 15.5 15.7516 16.25 16.5 16.75 17 17.25 17.5 17.75 18Days in May, 2003EE 14-E16, REV. 1 2-201EE 14-E16, REV.12-201 ZAC lear Ee Inc.DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachiy Nuclear Engineering, Inc.Negative values indicate topographic contours.Negative values indicate topographic contours.EE 14-E16, REV.12-202 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.lnur 2-9 Mavimujm Ainnlfirant Wava Hpinht anti f'nrrmqnnndiinn WavA flirmifinn- notorminiatir, PMQ-EE 14-E16, REV. 1 2-203EE 14-E16, REV.12-203 ZAChrHulerEgnernIYcDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-8: Maximum Significant Wave Height and Corresponding Wave Direction- Probabilistic Storm Surge + 4.2Cgad* Irsifial I ,aEE 14-El 6, REV. 1 2-204EE 14-E16, REV.12-204 ZAyNa iDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zschry Nuclear Engineering, Inc.EE 14-.E16, REv. 1 2-205EE 14-E16, REV.12-205 Z'ACHRiYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-10: Stage Hydrographs (Surge +Wave Setup) for Probabilistic Storm + 4.2 Feet Initial Water LevelWater Surface Elevation at MPS near Intake Structures0-wLU2221201918171615141312111098765432100.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00Time (days)EE 14-E16, REV. 1 2-206EE 14-E16, REV.12-206 Z M" DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.3.0 COMPARISON OF CURRENT AND REEVALUATED FLOOD CAUSINGMECHANISMSThis section provides a comparison of current and reevaluated flood causing mechanisms atMPS identified in Enclosure 2 of the NRC RFI letter pursuant to Title 10 CFR 50.54(f) datedMarch 12, 2012.An assessment of the current design basis flood elevation is provided relative to the beyonddesign basis, reevaluated flood elevation. A conclusion of whether or not the current designbasis flood bounds the reevaluated flood hazard is provided for each flood mechanism at eachof MPS2 and MPS3. The FSAR for MPS3 (Dominion 2014a) is used as a source of currentdesign basis information for flooding. MPS2, constructed before MPS3, also providesinformation on current design basis information for flooding (Dominion 2014b). The MPSFlooding Walkdown report, which was reviewed and approved by the NRC, also containsinformation describing the current design basis (Dominion Nuclear Connecticut, 2012).Summary tables are provided in Table 3.0-1 and Table 3.0-2 for MPS2 and MPS3, respectively.A detailed LIP comparison at MPS3 is provided in Table 3.0-3.As discussed below, the following reevaluated external flood mechanisms exceed the currentdesign basis flood elevation at one or more areas of MPS2 and/or MPS3:* Local Intense Precipitation (see Section 3.1);* Storm Surge (see Section 3.4);* Tsunami (see Section 3.5);* Combined Effect Flooding (see Section 3.9).Interim flood protection measures for the safety-related and important-to-safety SSCs aredescribed in Section 4 of this report.EE 14-El 6, REV. 1 3-1EE 14-E16, REV. 13-1 OWIACLIRY DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.3.1. Local Intense PrecipitationCurrent Design BasisThe FSAR for MPS2 summarizes flooding due to LIP. Runoff was calculated using the RationalMethod, based on a rainfall intensity of 9.4 inches per hour (Dominion, 2014b). A total runoffflow of 60 cubic feet per second (cfs) was calculated and compared to the capacity of the stormdrain (i.e., catch basin number 9 outfall to Niantic Bay) of 8.8 cfs. Excess runoff was toaccumulate in the yard area until it reaches Elevation 14.5 feet MSL and overtop a site accessroadway, into Jordan Cove and Niantic Bay. Site grade at MPS2 is 14.0 feet MSL; therefore,the flood depth is 0.5 feet. The FSAR also notes that the MPS2 rainfall event would notproduce a more significant flood than the flood associated with the storm surge (see Section3.4).MPS3 uses HMR-51 and 52 to calculate the flooding due to LIP (Dominion, 2014a). The one-hour PMP was calculated as 17.4 inches and the six-hour PMP was calculated to be 26.0inches. The LIP analysis was performed using one-dimensional methods: a rainfall-runoffanalysis was performed using the USACE HEC-1 computer program (predecessor to HEC-HMS) and water surface elevations were calculated using HEC-2 (predecessor to HEC-RAS).The calculation assumed no credit for the storm drain system and zero infiltration. The plantarea was divided into individual drainage basins and the resulting computed runoff values wererouted through "channels" based on site topography and project features such as buildings,roadways, and railroad tracks. Computed maximum water surface elevations (in feet, MSL) foreach structure are summarized below (reprinted from Table 2.4-11 of Dominion 2014a):Auxiliary Building 24.85Control Building 24.27Emergency Generator Enclosure 24.27Main Steam Valve Building 24.85Hydrogen Recombiner Building 24.85Auxiliary Building 24.85Engineered Safety Features Building 24.85Fuel Building 24.85RWST/SIL Valve Enclosure 24.85Demineralized Water Storage Tank Block House 24.85Although some of the above water surface elevations exceed the typical door sill elevation atMPS3 of 24.50 feet MSL, no affects upon safety-related equipment were anticipated due toinsignificant leakage rates through doors.EE 14-E16, REV. 13-2 MW AM 1HIRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Reevaluation ResultsThe reevaluation used a two-dimensional hydrodynamic computer program to develop floodlevels due to the LIP. A site-specific meteorology study was performed to develop the localProbable Maximum Precipitation (PMP) as an input to the LIP analysis. The site-specific PMPvalues are more refined than generic Hydrometeorological Report Nos. 51 and 52 and are usedconsistent with the Hierarchical Hazard Assessment (HHA) approach. Resulting maximumflood depths and maximum LIP flood elevations vary by location.Maximum LIP elevations at MPS3 are below the current licensing basis values. Maximum LIPelevations at the MPS3 Control Building and the Emergency Generator Enclosure are 24.2 feetMSL and 24.0 feet MSL, respectively (compared to the current design basis value of 24.27 feetMSL at both locations). The maximum LIP elevations for the remainder of MPS3 locationsidentified above are 24.8 feet MSL or less, which is at least 0.05 feet below the current designbasis maximum LIP elevation.Maximum LIP elevations at MPS2 locally exceed the current licensing basis values. MaximumLIP elevations at MPS2 range from El. 14.3 feet MSL at Flood Gate No. 20 (Item 218) situatedat the intake structure to El. 17.5 feet MSL at Flood Gate No. 13 (Item 211) at the northernperimeter of the Containment Enclosure building. The LIP maximum flood elevations in theimmediate vicinity of MPS3 range from EI.1 4.0 feet MSL at Door WP-1 4-7A (Item. 302) to locallyas high as El. 24.8 feet MSL at Door A-24-6 (Item 357) in the alleyway south of the ServiceBuilding (Building No. 317). Table 2.1-7 presents the maximum LIP flood depths and elevationsat many door locations throughout MPS.Please refer to Section 4.0 for a discussion of interim actions that have been developed torespond to LIP flooding.3.2. Probable Maximum Flood in Streams and RiversCurrent Design BasisThe MPS3 FSAR (Dominion, 2014a) states that: "There are no major rivers or streams in thevicinity of Millstone Point, nor are there any watercourses on the site." The MPS3 FSARacknowledges the number of small brooks which flow into Jordan Cove, east of MPS, butconcludes that: "In each area, local topography precludes flooding of any portion of the sitefrom the landward side." Detailed analyses or calculations were not performed. The MPS2FSAR similarly concludes that, due to the limited drainage area of the Niantic River, riverineflooding would not result in flooding of MPS. (Dominion, 2014b).Reevaluation ResultsThe reevaluation addresses the potential for flooding at MPS due to the Probable MaximumFlood (PMF) on the small unnamed coastal stream near MPS. Riverine flooding in the NianticRiver was not analyzed because flooding from the Niantic River is expected to dissipate intoNiantic Bay and have a negligible effect on MPS.As described in Section 2.2, the PMF peak flow rate in the small coastal stream near MPS wascalculated to be 1,100 cfs. The peak PMF water surface elevation at MPS is 11.2 feet MSL,which is below MPS site grade at MPS2 of 14 feet MSL (Dominion, 2014b) and MPS3 siteEE 14-El 6, REV. 13-3 OIA C H IRY DOMINION FLOODING HAZARD REEVALUATION REPORT FORZAC H KYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.grade of 24 feet MSL (Dominion, 2014a). Therefore, the current design basis flood evaluation isconsidered to be consistent with the conclusions of the reevaluated flood hazard evaluation andfurther action is not necessary.3.3. Dam FailuresCurrent Design BasisThe FSARs for MPS2 and MPS3 do not include calculation of flood elevations due to damfailure because there are no dams on the Niantic River and no major rivers or streams in thevicinity of MPS (Dominion 2014b, Dominion 2014a).Reevaluation ResultsThe local drainage area of MPS and the 87-acre watershed contributing to a small coastalstream located approximately 200 feet east of the ISFSI were evaluated for potential damfailures as part of the flood hazard re-evaluation. The review of the databases did not identifyany dams within the local drainage basins near MPS. Additionally, any upstream dam failureflows that reach Niantic Bay will dissipate quickly in Niantic Bay (i.e., Long Island Sound) and nosignificant increase in water surface elevation in Niantic Bay is expected.Therefore, the current design basis flood evaluation is considered to be consistent with theconclusions of the reevaluated flood hazard evaluation and further action is not necessary.3.4. Probable Maximum Storm SurgeCurrent Design BasisMPS2:The MPS2 FSAR describes potential flooding due to the PMH (Dominion 2014b). The PMHwas developed using NOAA technical report HUR 7-97 which has been superseded by NWS-23. The PMH parameters are as follows:* Central pressure index = 27.26 inches (Peripheral pressure 30.56 inches)Radius of maximum winds = 48 nautical milesForward speed of translation = 15 knotsMaximum gradient wind = 123 miles per hourMaximum (overwater) wind speed = 124 miles per hour (108 knots)The track of the PMH was generally northwestward across Long Island and Long Island Sound,with landfall occurring east of New Haven, Connecticut. Other combinations of storm size andforward speed were evaluated but did not result in higher surges than the PMH presentedabove. The calculated surge components were:Wind setup = 12.41 feet;EE 14-El 6, REV. 13-4 ZA C H IRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.* Water level rise due to pressure drop = 2.20 feet;Astronomical tide = 2.50 feet;Initial rise (forerunner) = 1.00 feet;Total surge stillwater level increase = 18.11 feet.The initial rise value was based on several discussions with the Atomic Energy Commission(AEC), predecessor to the NRC. The FSAR notes that the AEC accepted a PMH total stillwatersurge elevation of 18.2 feet MSL. Wave action was also calculated and combined with stormsurge, as described in Section 3.9.MPS2 is generally protected by gates and walls to an elevation of 22.0 feet MSL. The MPS2intake structure has service water pump motors and associated equipment that are alsoprotected to an elevation of 22.0 feet MSL. The MPS2 walkdown report notes that one servicewater pump motor is protected to Elevation 26.5 feet MSL (Dominion Nuclear Connecticut,2012).MPS3:The MPS3 FSAR also uses NOAA technical report HUR 7-97 to develop the PMH (Dominion2014a). Nine different PMH candidate combinations were evaluated. The surge analysis useda computerized bathystrophic storm surge model. The highest surge resulted from thefollowing PMH parameters:Central pressure index = 27.26 inches (Peripheral pressure 30.56 inches)Radius of maximum winds = 48 nautical milesForward speed of translation = 15 knotsMaximum gradient wind = 124 to 131 miles per hour (108 to 114 knots)In addition, the surge was combined with an astronomical tide (10 percent exceedance hightide) of 2.4 feet above MSL and an initial rise of 1.0 foot. The hurricane track followed a similarpath as the MPS2 PMH. The resulting maximum surge stillwater elevation was calculated to be19.7 feet MSL. Wave action was also evaluated, as described in Section 3.9.The safety-related structures and equipment at MPS3 are protected from flooding by the sitegrade elevation of 24 feet MSL, with the exception of the circulating and service water pumphouse (i.e., intake structure). The seaward wall of the intake structure is constructed towithstand the forces of a standing wave, or clapotis, with a maximum crest elevation of 41.2 feetMSL.Reevaluation ResultsThe reevaluation performed detailed analyses of the PMH and storm surge consistent with theHHA approach. First, the PMH was developed deterministically and the resulting PMSS wascalculated using a two-dimensional hydrodynamic program, ADCIRC. As a second step,EE 14-El 6, REV. 13-5 EIW DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.refinement of the analysis was performed by completing a probabilistic storm surge calculation,supported by a site-specific hurricane meteorology and climatology study. Several additionalADCIRC simulations were performed to support a Joint Probability Method-Optimum Samplingcalculation of very low probability storm surge. At an annual exceedance probability ofapproximately 1 E-6 (i.e., return period of 1,000,000 years), the storm surge stillwater elevationat MPS was calculated to be 21.0 ft MSL. The stillwater elevation was then used as an input tothe combined effect analysis to develop final maximum flood levels at MPS-see Section 3.9.3.5. SeicheCurrent Design BasisThe FSARs for MPS2 and MPS3 do not include calculation of flood elevations due to seiche(Dominion 2014b, Dominion 2014a). The MPS2 FSAR does not discuss seiche. The MPS3FSAR sections on surge and seiche focus on storm surge.Reevaluation ResultsSeiche within two surface water bodies at MPS were analyzed for reevaluation, including: 1)the Long Island Sound and 2) the discharge basin (former quarry). Seiche was found to poseno flood risk to MPS based on the screening analysis performed using Merian's formula andliterature review. Indications of resonance that could lead to significant seiche developmentwere not found. Therefore, the current design basis flood evaluation is considered to beconsistent with the conclusions of the reevaluated flood hazard evaluation and further action isnot necessary.3.6. TsunamiCurrent Design BasisThe MPS3 FSAR notes that the North Atlantic coastline has an extremely low probability oftsunamis (Dominion 2014a). Thus, analyses of flooding and drawdown were not discussed inthe MPS3 FSAR. The MPS2 FSAR does not discuss tsunami potential (Dominion 2014b).Reevaluation ResultsThe tsunami flooding reevaluation analysis concluded that there is a regional tsunami hazardpotential at MPS. Numerical modeling was then performed to account for the complexgeography in and around Long Island Sound (see Section 2.6).Several tsunamigenic sources were assessed. The analysis indicated the highest predictedrunup elevations in the vicinity of MPS result from the subaerial landslide (extreme flank failure)of the CVV. Other tsunamigenic sources, such as the near-field submarine mass failure, do notresult in flooding at MPS.Propagation of the initial CVV surface waves across the Atlantic Ocean and into Long IslandSound results in maximum water levels of approximately 14.7 feet MSL near MPS as shownbelow:EE 14-El 6, REV. 13-6 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Maximum Water Maximum Water Maximum Depth Depth of Water Time fromSurface Surface of Water Above Above MPS3 TsunamigenicElevation at MPS Elevation on the MPS2 Average Average Site Source Event toMPS2 and MPS3 Eastern Side of Site Grade (14 ft Grade (24 ft Tsunami(feet MSL) the Site (feet MSL) MSL) Reaching MPSMSL) (hr)14.7 12.0 0.7 0.0 8.7As shown on Figure 2.6-19, inundation areas are highest in areas west of MPS2 and MPS3, inthe vicinity of the parking areas, storage buildings, and wooded areas north and west of theintake structures. MPS is protected from flooding due to high water in these areas primarily bytopography, but also by buildings not important to safety and security barriers.However, maximum flood elevations of 14.7 feet MSL are predicted at the intake structures andat MPS2. In these areas, shallow flooding above average MPS2 site grade of 14 feet ispossible (up to 0.7 feet).A warning time of at least 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months from the initiating tsunamigenic event is predicted.Additionally, the NOAA National Tsunami Warning Center (NTWC) provides tsunami detection,forecasts, and warnings for the U.S. including the Atlantic coast. NTWC operates 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months perday, with a goal of issuing tsunami warnings within five minutes of an earthquake (NTWC,2014).MPS3 is not impacted by flooding due to tsunami, owing to the higher average site grade atMPS3 of 24 ft MSL.See Section 4.0 for a discussion of interim actions planned or taken in response to tsunamihazard.3.7. Ice-Induced FloodingThe criteria for ice-induced flooding is provided in NUREG/CR-7046, Appendix D (NRC 2011).Two ice-induced events may lead to flooding at MPS and are recommended and discussed inNUREG/CR-7046, Appendix D including:1. Ice jams or dams that form upstream of a site that collapse, causing a floodwave; and2. Ice jams or dams that form downstream of a site that result in backwater flooding.The MPS3 FSAR (Dominion, 2014a) does not specifically discuss the potential for flooding dueto upstream or downstream ice jams. It does note that there is no history of ice in Niantic Bay orin the area of the circulating and service water pumphouse. The MPS3 FSAR describespreventive measures to recirculate water to prevent icing near the circulating and service waterpumphouse, as well as features of the pumphouse that prohibit ice from entering thepumphouse. The MPS2 FSAR (Dominion, 2014b) notes that the formation of ice in front of theintake structure is highly unlikely and also discusses a recirculation procedure that can be usedto limit icing.EE 14-E16, REV. 13-7 ZI CW DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Reevaluation ResultsThe re-evaluation concluded that the MPS's location at the downstream-most end of the NianticBay creates conditions which are unlikely to sustain a downstream ice dam due to both watersalinity and channel morphology. Therefore, the potential for flooding to occur at MPS as aresult of a downstream ice jam is not significant.The failure of a conservatively-estimated hypothetical upstream ice jam would not exceed theprotected elevation at MPS. The resulting rise in water level at Millstone was conservativelyestimated to be 2.9 feet (see Section 2.7).Safety-related structures at MPS3 are flood-protected up to a minimum elevation 24.0 feetexcept for the service water pumps and pump motors located in the intake structure, which areflood protected to elevation 25.5 feet (Dominion, 2014a). MPS2 is passively (i.e., does notrequire manual actions) flood protected up to the average site grade elevation of 14 feetNGVD29, except for the service water pump motors and associated electrical and controlequipment located in the intake structure, which are flood protected to elevation 22 feetNGVD29 (Dominion 2014b). The estimated freeboard to the protected elevation in the MPS2intake structure is:MPS2 Intake Structure El. 22 feet -2.9 feet = 19.1 feetand the estimated freeboard to the protected elevation in the MPS3 intake structure is:MPS3 Intake Structure El. 25.5 feet -2.9 feet = 22.6 feetThe lowest protected elevation at MPS2 is:MPS2 average site grade El. 14 feet -2.9 feet = 11.1 feetTherefore, the current design basis flood evaluation is considered to be consistent with theconclusions of the reevaluated flood hazard evaluation and further action is not necessary.3.8. Channel Migration or DiversionThe MPS3 FSAR (Dominion, 2014a) states that: "There are no channel diversions to the coolingwater supply which would have any effect on safety related equipment." Detailed analyses orcalculations were not performed. The MPS2 FSAR does not discuss channel migration ordiversion (Dominion, 2014b).Reevaluation ResultsThe reevaluation concluded that the Niantic River has not exhibited a tendency to meander.Long Island Sound also serves to dissipate high flows in the river. The geology and foundationmaterials at the site are resistant to erosion. The shoreline near MPS is protected with riprap.Given these conditions, channel migration or diversion is not considered to be a potentialcontributor to flooding at MPS. Therefore, the current design basis flood evaluation isconsidered to be consistent with the conclusions of the reevaluated flood hazard evaluation andfurther action is not necessary.EE 14-E16, REV. 13-8 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.3.9. Combined Effect FloodingCurrent Desiqn BasisMPS2:The MPS2 FSAR describes coincident wave action combined with the PMSS elevation of 18.1feet (Dominion, 2014b). The FSAR reports the wind would be from the southeast during thepeak of the surge and MPS1 would "shield" MPS2 (other than the intake structure) from directwave attack. The maximum PMSS stillwater depth of 4.1 feet was calculated from the MPS2 Iaverage ground elevation near plant buildings of 14.0 feet MSL. A maximum, depth-limitedwave of 3.2 feet could be generated anywhere around MPS2 buildings, producing a maximumrunup elevation of 25.1 feet MSL. While this is 3.1 feet above the top of the flood gates andflood walls protecting MPS2, the minimum elevation of the exterior concrete walls of thecontainment building, auxiliary building, and warehouse building is up to elevation 54.5 feetMSL. The turbine building and the enclosure building are protected by metal siding which iscontinuous over the exterior flood walls and sealed at the interface between the flood wall andsiding with waterproof caulked connections. Therefore, the FSAR concluded that the waverunup elevation of 25.1 feet MSL does not result in adverse effects on any safety-relatedequipment.A maximum wave level of 42.5 feet MSL was calculated at the vertical wall of the intakestructure, which is open to the coast. The maximum water level inside the intake structurecaused by the standing wave condition was calculated to be 26.5 feet MSL. The analysisconsidered the profile of the incident wave, in-leakage through the louvers and system headloss. The service water system is the only safety-related system in the intake structure. Theservice water pump motors and electrical equipment are protected to elevation 22 feet MSL,with one exception: The MPS2 walkdown report notes that one service water pump is protectedthrough installation of protection for the service water motor to elevation 26.5 feet MSL(Dominion Nuclear Connecticut, 2012).The FSAR notes the intake structure and vicinity is designed to be stable against all forces fromwave action, including buoyancy and scour. The shores are protected by post-tensionedreinforced concrete walls founded upon bedrock. Areas immediately back of the walls areprotected by riprap designed for the PMH condition. The maximum pressure at the foot of theintake structure was calculated to be 3,960 pounds per square foot and the stability of thestructure was found to be stable under such conditions. The louvers in the front of the intakestructure are capable of withstanding a maximum pressure of 1,120 pounds per square foot dueto pressure from a nonbreaking wave.MPS3:The MPS3 FSAR (Dominion, 2014a) discusses the calculation of deep water waves, shallowwater waves, wave shoaling, refraction, and resulting runup. The FSAR notes that thetopography and configuration of Millstone Point protects the MPS3 area from open ocean wavesand breaking waves during the period of peak tidal flooding when the winds are from thesoutheast. The FSAR indicates very large deepwater maximum waves approaching orexceeding 100 feet are reduced to 10 to 16 feet in maximum height by the time waves near theMillstone Point shoreline.EE 14-El 6, REV. 13-9 MZWA IJRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRI~YFoo.ozoMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Three transects were used to calculate runup: two at the west side of MPS3, including theintake structure, and one at the east side of the structure. The calculation used Saville'smethod of composite slopes using wave steepness, structure type, and depth at the structuretoe as input values. The maximum calculated runup value was 23.8 feet MSL. The maximumwater level on the intake structure was calculated to be 41.2 feet MSL, based on a maximumwave height of 16.2 feet.MPS3 safety-related structures are protected by the site grade elevation of 24 feet MSL. Waveaction only effects the intake structure, which is designed to withstand the PMH, includingresultant loading. Service water pumps and pump motors inside the intake structurepumphouse are housed in individual watertight cubicles. The cubicles are watertight up toelevation 25.5 feet MSL. Access openings below 23.8 feet MSL are fitted with watertight doorscapable of withstanding the maximum hydrostatic loading. The seaward wall of the intakestructure is reinforced concrete designed to withstand the standing wave or clapotis up to 41.2feet MSL. Maximum wave loading was calculated to be 3,642 pounds per square foot.Maximum uplift pressure on the pumphouse floor was calculated to be 863 pounds per squarefoot.Reevaluation ResultsThe reevaluation evaluated combined effect flooding based on the combination of floodsprovided in NUREG/CR-7046, Appendix H. These combined effect floods were considered tobe appropriate for MPS. Riverine hazards were screened-out.The stillwater level resulting from the combination of the storm surge corresponding to the 1 E-6annual exceedance probability (i.e., 1,000,000-year-return period) and mean high tide with sealevel rise was calculated to be 21.0 feet, MSL. This elevation is the combination of the modeledstillwater (i.e., including wave setup) elevation of 16.8 feet MSL and the uncertainty effects of4.249 feet., which include consideration of applicable sea level rise. Thus, the stillwater levelincludes wind setup, aleatory variability and epistemic uncertainty and 50-year sea level riseprojections. MPS3 is not exposed to flooding as the site grade of 24 feet, MSL is above thestillwater elevation of 21 feet, MSL. Due to the dissipation of wave energy by the MPS1buildings and lack of inundation on the eastern portion of the site, the wave effects areconsidered negligible on the eastern side of the MPS2. The reflected wave crest at the westside of MPS2 is 3.4 feet, with a maximum elevation of 24.4 feet, MSL. This elevation is about2.4 feet above the flood wall elevation of 22 feet, MSL at MPS2.MPS2 and MPS3 each have intake structures west of the main building complex that are ocean-front structures. Wave heights are approximately 6.3 feet at the MPS2 intake. At the MPS3intake, wave heights are approximately 7.0 feet. Reflected wave crest heights are 7.8 feet atMPS2 intake and 7.7 feet at MPS3 intake, respectively. Maximum elevations associated withreflected wave crests are 28.8 feet, MSL outside the MPS2 intake, and 28.7 feet, MSL outsidethe MPS3 intake which will not result in overtopping of the intake structures. While there maybe a portion of waves breaking against the intakes, this would result in splash and spray on thestructures, and not result in any significant overtopping. The effect of wave action on outside ofthe intake structures on components inside the Intake Structures will be further evaluated -seeSection 4.0 for more information.Hydrostatic, hydrodynamic, and debris loading forces were conservatively developed for theProbabilistic combined effect flooding scenario, which bounds the tsunami scenario. TheseEE 14-El 6, REV. 13-10 ZI Cw DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.forces are anticipated to be localized to the area around the MPS2 and MPS3 Intake Structures,as well as the west side of MPS2. Hydrostatic forces at the Intakes are estimated to beapproximately 83,232 pounds per foot, acting at an elevation of -13 feet MSL. The pressure atthe bottom of the intakes was estimated to be 3,264 pounds per square foot.The hydrodynamic loading varies from 1,962 pounds per linear foot to 2,747 pounds per linearfoot near MPS2 for the controlling probabilistic combined effect flood. The hydrodynamicloading near MPS2 act at elevation 17.5 feet, MSL. The hydrodynamic loading was calculatedto be 51,760 pounds per linear foot at the MPS2 intake structure and 54,774 pounds per linearfoot at the MPS3 intake structure. The hydrodynamic loading at the intake structures acts atelevation -4.5 feet, MSL. The maximum breaking wave load on vertical walls was calculated as19,600 pounds per foot near MPS2 and 1,040,400 pounds per foot for the intake structures,based on a conservative upper bound water velocity up to 34.5 feet per second. Debris impactloads on exterior portions of structures were calculated as 31,200 pounds for the west side ofMPS2, 70,720 pounds at the MPS2 intake structure, and 71,760 pounds at the MPS3 intakestructure. Debris impact loads act at the water surface elevation.Impact forces for flood loading conditions are not discussed in detail for the current licensingbasis and differing methodologies used for the reevaluation make it difficult to provide specificcomparisons to the current design basis for loading. Please refer to Section 4 for moreinformation.3.10. References3.10-1 Dominion, 2014a. Millstone Power Station Final Safety Analysis Report (MPS-3 FSAR),Rev. 25.2.3.10-2 Dominion, 2014b. Millstone Power Station Final Safety Analysis Report (MPS-2 FSAR),Rev. 30.2.3.10-3 Dominion Nuclear Connecticut, 2012. Millstone Power Station Units 2 and 3, FloodingWalkdowns Results Report for Resolution of Fukushima Near-Term Task ForceRecommendation 2.3: Flooding, November, 20123.10-4 NRC, 2011. "Design Basis Flood Estimation for Site Characterization at Nuclear PowerPlants -NUREG/CR-7046", U.S. Nuclear Regulatory Commission, November 2011.3.10-5 NTWC, 2014. National Oceanic and Atmospheric Administration, National WeatherService, National Tsunami Warning Center, "User's Guide for the Tsunami WarningSystem in the U.S. National Tsunami Warning Center Area-of-Responsibility," UpdatedJuly, 2014.EE 14-El 6, REV. 1 3-11EE 14-E16, REV. 13-11 ZACIH-RYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 3.0-1: Summary of the Comparison of Current and Reevaluated Flood CausingMechanisms for MPS2Flooding Flood Critical Current Current Flood ReevaluatedMechanism Structure (Per FSAR) Design Basis Protection Flood LevelFlood Level Elevation (MSL) (MSL)(MSL) [2]Combined MPS2, except Intake 21 .3 ft 22 ft 21.0 ft at east sideEffects Structure (Stillwater plus of MPS2;wave crest) 24.4 ft at west side25.1 ft of MPS2(Wave runup)MPS2 Intake Structure 26.5 ft 22 ft Wave runup up to(standing wave except 26.5 ft (at 28.8 ft at theinside Intake exept Intake structureone serviceStructure) water pumpmotor)Storm Surge Diesel Generator & 18.2 ft 22 ft 21 .0 ft(Stillwater Intake Structure [3]Elevation)Local Containment & 14.5 ft 14.5 ft 14.3 ft to 17.5 ftIntense Enclosure Building, (22 ft if the Flood [1]Precipitation Aux Building, EDG Gates areBuildings, Control closed)Building, TurbineBuilding, IntakeStructure, Fire PumpHouse, and RSSTTsunami Intake Structures No Flooding 14.5 ft 14.7 ft(including Expected (22 ft if the Floodwave runup) Gates areclosed)Flooding in No Flooding Expected No Flooding No Flooding 11.2 ftStreams Expected Expected (No Floodingand Rivers Expected -BelowSite Grade)Upstream No Flooding Expected No Flooding No Flooding No FloodingDam Expected Expected ExpectedFailuresNotes are located on the next pageEE 14-El 6, REV. 13-12 Z'ACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 3.0-1 (Continued): Summary of the Comparison of Current and Reevaluated FloodCausing Mechanisms for MPS2Flooding Flood Critical Current Current Flood ReevaluatedMechanism Structure (Per FSAR) Design Basis Protection Flood LevelFlood Level Elevation (MSL) (MSL)(MSL) [2]Seiche No Flooding Expected No Flooding No Flooding No FloodingExpected Expected ExpectedIce Induced No Flooding Expected No Flooding No Flooding No FloodingFlooding Expected Expected ExpectedChannel No Flooding Expected No Flooding No Flooding No FloodingMigration or Expected Expected ExpectedDiversionNotes:[1] Flood level is location dependent;[2] Flood Protection Elevation 22 ft. assumes that there is sufficient warning time to closeall MPS2 flood gates;[3] Current Design Basis Flood Level considers stillwater level plus wave runup. Waveaction in conjunction with wave runup is projected to cause higher levels in somelocations and was independently calculated.EE 14-El 6, REV. 1 3-13EE 14-El 6, REV. 13-13 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 3.0-2: Summary of the Comparison of Current and Reevaluated Flood CausingMechanisms for MPS3Flooding Flood Critical Current Current Flood ReevaluatedMechanism Structure (Per FSAR) Design Protection Flood LevelBasis Flood Elevation (MSL) (MSL)Level (MSL)Combined Intake Structure 23.8 ft (near 24 ft (25.5 ft for 21.0 ft (stillwaterEffects MPS3 except SW Pumps) elevation -siteat front of grade protectsIntake against waveStructure) runup except at41.2 ft (at Intake)seaward wall 28.7 ft at Intakeof IntakeStructure)[2]Storm Surge Intake Structure 19.7 ft 24 ft (25.5 ft for 21.0 ft(Stillwater [2] SW Pumps)Elevation)Local Aux Building, Control 24.85 ft Typical door sill Up to 24.8 ft;Intense Building, DWST Block except elevation is 24.5 24.2 ft at ControlPrecipitation House, Emergency 24.27 ft at ft -No affects Building; 24.0 ft atGenerator Enclosure, Control upon safety- EmergencyESF Building, Fuel Building and related GeneratorBuilding, Hydrogen Emergency equipment EnclosureRecombiner Building, Generator anticipated forMSV Building, and Enclosure. water levels up (See Table 3.0-3)RWST/SIL Valve to El. 24.85 ft.Enclosure (See Table [1]3.0-3)Tsunami Intake Structure No flooding 24 ft (25.5 ft for 14.7 ft(including Expected SW Pumps) (No floodingwave runup) expected)Flooding in No Flooding Expected No Flooding No Flooding 11.2 ftStreams Expected Expected (No Floodingand Rivers Expected -BelowSite Grade)Upstream No Flooding Expected No Flooding No Flooding No FloodingDam Expected Expected ExpectedFailuresSeiche No Flooding Expected No Flooding No Flooding No FloodingExpected Expected ExpectedNotes are located on next pageEE 14-El 6, REV. 13-14 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 3.0-2 (Continued): Summary of the Comparison of Current and Reevaluated FloodCausing Mechanisms for MPS3Flooding Flood Critical Current Current Flood ReevaluatedMechanism Structure (Per FSAR) Design Basis Protection Flood LevelFlood Level Elevation (MSL) (MSL)(MSL)Ice Induced No Flooding Expected No Flooding No Flooding No FloodingFlooding Expected Expected ExpectedChannel No Flooding Expected No Flooding No Flooding No FloodingMigration or Expected Expected ExpectedDiversionNotes:[1] Flood level is location dependent;[2] Current Design Basis Flood Level considers stillwater level plus wave runup. Waveaction in conjunction with wave runup is projected to cause higher levels in somelocations and was independently calculated.EE 14-El 6, REV. 1 3-15EE 14-El 6, REV. 13-15 ZACHIRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 3.0-3: Summary of the Comparison of Current and Reevaluated LIP for MPS3Building Current Design Reevaluated Representative RepresentativeBasis Maximum Flood FLO-2D Grid LocationMaximum Flood Elevation ElementElevation(feet, MSL) (feet, MSL)Auxiliary 24.85 24.57 43655 Aux Building DoorBuilding A-24-1Control, 24.27 24.24 45449 Control BuildingBuilding Door -C-24-1Emergency 24.27 24.08 43336 EDG BuildingGenerator Door -EG-24-1EnclosureMain Steam 24.85 24.50 50744 Steam ValveValve Building Building Door -SV-24-3Hydrogen 24.85 24.19 51892 HydrogenRecombiner Recombiner DoorBuilding HR-24-5Auxiliary 24.85 24.78 48433 Aux Building DoorBuilding A-24-6Engineered 24.85 24.20 49907 ESF BuildingSafety Door -SF-24-2FeaturesBuildingFuel Building 24.85 24.50 44888 Fuel BuildingDoor -F-24-4RWST/SIL 24.85 24.26 49042 North Side ofValve StructureEnclosureDemineralized 24.85 24.23 48170 South Side ofWater Storage StructureTank BlockHouseEE 14-El 6, REV. 1 3-16EE 14-El 6, REV. 13-16 EW DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACH-RYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.4.0 INTERIM EVALUATION AND ACTIONSThis section identifies the interim evaluation and actions taken or planned prior to thecompletion of the integrated assessment to address any greater flooding hazards relative to theCLB. Identification of interim actions was requested in Enclosure 2 of the NRC RFI letterpursuant to Title 10 CFR 50.54(f) dated March 12, 2012.Combined Effects Flooding due to storm surge is the bounding event that exceeds the CurrentLicensing Basis Flood Level. The proposed interim evaluations and actions to address thisflooding concern are discussed in Section 4.1. Additionally, unique flooding concerns associatedwith Local Intense Precipitation resulting from the Site Specific Probable Maximum Precipitation,and a Tsunami resulting from the subaerial landslide (extreme flank failure) of the Cumbre ViejaVolcano will be discussed in Sections 4.2 and 4.3, respectively.4.1. Combined Effects FloodingThe Combined Effects Flooding considers two different approaches to storm surge (probabilisticand deterministic analysis), and investigates structural loading due to flooding. The basis for thissection of the Flood Hazard Reevaluation Report will rely on the probabilistic analysis approachonly. The Combined Effects Flooding analysis produced stillwater elevations of 21.0 ft MSL,which are above the CLB stillwater elevations for both MPS2 and MPS3, however, this level isbelow current flood protection levels.The combined effects flooding results due to wave action vary across the site. Due to thedissipation of wave energy acting on MPS1 and the lack of inundation on the east side of thesite, no significant wave activity is expected in these areas. Therefore, MPS2 is bounded undercurrent flood protection levels on the east side of the plant. MPS3 (with the exception of theIntake Structure) is unaffected by wave activity based on the general site grade of 24.0 ft MSL.The west side of the MPS2 Turbine Building and both MPS2 and MPS3 Intake structures maybe subjected to flooding levels higher than the current license basis. The reflected wave crest,imposed on top of the stillwater level, creates a periodic wave that reaches an elevation of 24.4ft MSL on the west side of the MPS2 Turbine Building and causes a BDB flooding elevation of28.6 ft MSL and 28.7 ft MSL on the MPS2 and MPS3 Intake Structures (external floodingelevations), respectively. Additionally there are loads on the west side of the MPS2 TurbineBuilding from hydrostatic loading, hydrodynamic loading, debris impact, and wave impact thatneed further evaluation. The same types of loadings are seen on the Intake structures, exceptthe loadings at the Intake Structures are of a larger magnitude and there is an additionalcombined effect loading introduced from the tsunami. Based on these results, in the event thateither one or both Intake Structures become inoperable due to Combined Effects Flooding, theplanned interim action is to invoke Millstone's FLEX strategies to respond to a loss of ultimateheat sink (UHS) event.In addition to flood gates, the west side of the MPS2 Turbine Building has a concrete wall up to22 ft MSL. On the exterior of the building, metal siding overlaps this wall and extends up to theparapet of the Turbine Building. The probabilistic storm surge is created by the ProbableMaximum Hurricane (PMH), which has wind characteristics of a Category 4/5 hurricane on theSaffir-Simpson Hurricane Wind Scale. Based on the different hurricane parameters (such asEE 14-El 6, REV. 14-1 EWA C DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.wind, wind generated debris, etc.), in addition to flooding, relying on the siding to keep floodwaters out of the Turbine Building will be further evaluated in the Integrated Assessment.The Combined Effects hazard (caused by the PMH) would be identified in advance bymeteorological forecasting. There are current measures (procedure driven) that would beinvoked by the site to prepare for these events. Some of the existing features includeadjustments to staffing, power levels, various tank levels, and the installation of flood protectionbarriers in preparation for hurricane surge and loss of power on site.Potential flooding inside the MPS2 Turbine Building has been considered and abnormaloperations procedures have been updated to prepare for such an event. To mitigate flooding inthe Turbine Building (due to flood water bypassing floodgates) the following preparatory actionswill be taken in advance of an approaching storm in accordance with existing stationprocedures.The following equipment will be staged in the Turbine Building condenser pit:* Self-powered pumps* Electric pumps with generators" Air-driven diaphragm pumps* Hoses to direct water outsideAdditionally a BDB AFW pump will be staged at the Turbine Building Railway Access.Operations will request that sandbag walls (at least 2 feet high) be established at the followinglocations:* Outside the 125VDC Swithgear room door" Inside the Machine Shop to West Service Corridor door* Inside Service Building Hallway door between the men's locker room and the ServiceBuilding elevator area* Inside the Control Building northwest door* Outside East entrance to TDAFW Pump Room door" Outside TDAFW Pump Room to Outside double doorsTherefore, an integrated assessment will be performed in response to the results of theCombined Effects flood hazards for MPS2 and MPS3. The assessment will validateexisting and/or develop new mitigating strategies in response to combined effects floodingwhich may compromise existing flood protection and challenge SSCs in the MPS2 TurbineBuilding. Additionally, the MPS2 and MPS3 Intake Structures will be evaluated based onincreased flood levels and new/increased structural loading.4.2. Local Intense PrecipitationThe LIP calculation, following Hydrometeorological Report (HMR) No. 52 methodologyendorsed by the 10 CFR 50.54(f) letter, produced results which were above the current floodEE 14-El 6, REV. 14-2 Z 9w DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRY oorR+-,MILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.protection levels on site for an extended period of time. As an immediate action, a site specificLIP calculation was performed, relying on modern day technology and methodology (instead ofthe HMR No. 52 methodology). The results indicated that the flood levels at MPS3 are belowthose for the current LIP model considered in the MPS3 FSAR. Based on this no further actionis required for MPS3. The results for MPS2 are above the CLB, but are bounded by flood levelsfor the CLB storm surge.The interim action will be to review, revise, and include necessary steps to enhance theapplicable station abnormal weather procedures for mitigation of a BDB potential flooding eventdue to a local intense precipitation (LIP) event. The procedure update will implement existingstation flood protection features (for example closing flood gates) based on a notification of animminent LIP event and include an entry condition (trigger event) to initiate required actions.4.3. TsunamiThe controlling tsunami wave (generated from the subaerial landslide (extreme flank failure) ofthe Cumbre Vieja Volcano) impacts the south side of the plant at an elevation of 14.7 ft MSL,which is above the current site grade of MPS2 (14.0 ft MSL). Other potential tsunami sourcesinvestigated produced results which are below the current site grade. The flood levels producedfrom the tsunami are bounded by storm surge; however the warning time on the tsunami is lessthan that of a storm surge. The tsunami is predicted to take an estimated 8.7 hours8.101852e-5 days 0.00194 hours 1.157407e-5 weeks 2.6635e-6 months to reachMPS from the initiation of the event.The interim action will be to review, revise, and include necessary steps to enhance theapplicable station abnormal weather procedures for prevention and mitigation of a potentialflooding event due to a tsunami. The procedure updates will implement existing station floodprotection features (for example closing flood gates) based on a notification of an imminenttsunami and include an entry condition (based on a tsunami warning from NOAA's/NWSNational Tsunami Warning Center) to initiate required actions.4.4. All other Flood Causing MechanismsProbable Maximum Flood in Streams and Rivers, Dam Failure, Seiche, Ice Induced Flooding,and Channel Migration/Diversion evaluations produced results that are either below currentdesign basis, do not challenge existing flood protection features, or are not a threat to generatea new flooding condition for Millstone Power Station. Therefore, no further evaluation or interimactions are required for these flood-causing mechanisms.4.5. ConclusionBased on the scenarios discussed in Section 4.1, an Integrated Assessment will be performedthat addresses any concerns from the Combined Effects event. Sections 4.2 and 4.3 will beresolved as an interim action with improvements to station procedures currently in place. Thisand other identified interim actions will provide flood protection until the Integrated Assessmentcan be performed. All interim actions will be entered into the Dominion corrective actionprogram.EE 14-El 6, REV. 1 4-3EE 14-E16, REV. 14-3 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.5.0 ADDITIONAL ACTIONSThere are no additional actions beyond those discussed in Section 4.0. During the developmentof the Integrated Assessment, additional actions may be required, which will be developed andaddressed in the Integrated Assessment, or will be identified in a Condition Report andaddressed appropriately.EE 14-E16, REv. 1 5-1EE 14-El 6, REV. 15-1 Appendix AFLO-2D Technical DescriptionZachry EE 14-E16, Rev. 1Page Al of A7 FLO-2D TECHNICAL DESCRIPTION1. Model DescriptionThe FLO-2D Pro Model, Build No. 14.03.07 (FLO-2D) computer program was developed byFLO-2D Software, Inc., Nutrioso, Arizona. FLO-2D is a combined two-dimensional hydrologicand hydraulic model that is designed to simulate river and overbank flows as well as unconfinedflows over complex topography and variable roughness, split channel flows, mud/debris flowsand urban flooding. FLO-2D is a physical process model that routes rainfall-runoff and floodhydrographs over unconfined flow surfaces using the dynamic wave approximation to themomentum equation. FLO-2D moves flood volume on a series of tiles (grid) for overland flow orthrough stream segments for channel routing.Application of the model requires knowledge of the site, the watershed (and coastal, asappropriate) setting, goals of the study, and engineering judgment.2. Model ComponentsFLO-2D has components to simulate overland flow, channel/riverine flow including flow throughculverts, flow exchange between a channel and the floodplain, buildings and obstructions,rainfall-runoff and levees. The model also has components to simulate street flow, spatiallyvariable rainfall and infiltration, evaporation, sediment transport, and levee and dam breachfailures.Overland Flow SimulationThis FLO-2D component simulates overland flow and computes flow depth, velocities, impactforces, static pressure and specific energy for each grid. Predicted flow depth and velocitybetween grid elements represent average hydraulic flow conditions computed for a small timestep. For unconfined overland flow, FLO-2D applies the equations of motion to compute theaverage flow velocity across a grid element (cell) boundary. Each cell is defined by 8 sidesrepresenting the eight potential flow directions (the four compass directions and the fourdiagonal directions). The discharge sharing between cells is based on sides or boundaries inthe eight directions. At runtime, the model sets up an array of side connections that are onlyaccessed once during a time step. The surface storage area or flow path can be modified forobstructions including buildings and levees. Rainfall and infiltration losses can add or subtractfrom the flow volume on the floodplain surface.Channel Flow SimulationThis component simulates channel flow in one-dimension. The channel is represented bynatural, rectangular or trapezoidal cross sections. Discharge between channel grid elementsare defined by average flow hydraulics of velocity and depth. Flow transition betweensubcritical and supercritical flow is based on the average conditions between two channelelements. River channel flow is routed with the dynamic wave approximation to the momentumequation. Channel connections can be simulated by assigning channel confluence elements.Channel -floodplain InterfaceThis FLO-2D component exchanges channel flow with the floodplain grid elements in aseparate routine after the channel, street and floodplain flow subroutines have beenZachry EE 14-E16, Rev. 1Page A2 of A7 completed. An overbank discharge is computed when the channel conveyance capacity isexceeded. The channel-floodplain flow exchange is limited by the available exchange volumein the channel or by the available storage volume on the floodplain. Flow exchange betweenstreets and floodplain are also computed during this subroutine. The diffusive wave equation isused to compute the velocity of either the outflow from the channel or the return flow to thechannel.Floodplain Surface Storage Area Modification and Flow ObstructionThis FLO-2D component enhances detail by enabling the simulation of flow problemsassociated with flow obstructions or loss of flood storage. This is achieved by the application ofcoefficients (Area reduction factors (ARFs) and width reduction factors (WRFs)) that modify theindividual grid element surface area storage and flow width. ARFs can be used to reduce theflood volume storage on grid elements due to buildings or topography and WRFs can beassigned to any of the eight flow directions in a grid element to partially or completely obstructflow paths in all eight directions simulating floodwalls, buildings or berms. Floodplainmodifications due to buildings and/or storage basins can also be achieved by manuallymodifying grid element elevations.Rainfall -Runoff SimulationRainfall can be simulated in FLO-2D. The storm rainfall is discretized as a cumulative percent ofthe total. This discretization of the storm hyetograph is established through local rainfall data orthrough regional drainage criteria that defines storm duration, intensity and distribution. Rain isadded in the model using an S-curve to define the percent depth over time. The rainfall isuniformly distributed over the grid system and once a certain depth requirement (0.01-0.05 ft) ismet, the model begins to route flow.Hydraulic Structures and Storm DrainsHydraulic structures including bridges and culverts and storm drains may be simulated in FLO-2D using the hydraulic structures component. Discharge through round and rectangular culvertswith potential for inlet and outlet control can be computed using equations based onexperimental and theoretical results from the U.S. Department of Transportation procedures(Hydraulic Design of Highway Culverts; Publication Number FHWA-NHI-01-020 revised May,2005). The equations include options for box and pipe culverts and take into account differententrance types for box culverts (wingwall flare 30 to 70 degrees, wingwall flare 90 or 15 degreesand wingwall flare 0 degrees) and three entrance types for pipe culverts (square headwall,socket end with headwall and socket end projecting).Storm drains are modeled using the EPA SWMM Model. FLO-2D is linked to the EPA SWMMModel at runtime to exchange surface water and storm drain conveyance. FLO-2D computesthe surface water depth at grid elements prescribed with storm drains and computes thedischarge inflow to the storm drain based on input storm drain geometry. The EPA SWMMmodel then computes the pipe network flow distribution and potential return flow to the surfacewater.LeveesThis FLO-2D component confines flow on the floodplain surface by blocking one of the eightflow directions. A levee crest elevation can be assigned for each of the eight flow directions in agiven grid element. The model predicts levee overtopping. When the flow depth exceeds theZachry EE 14-E16, Rev. 1Page A3 of A7 levee height, the discharge over the levee is computed using the broad-crested weir flowequation with a 3.1 coefficient. Weir flow occurs until the tailwater depth is 85% if the headwaterdepth. At higher flows, the water is exchanged across the levees using the difference in watersurface elevations.3. Governing EquationsThe general constitutive fluid equations include the continuity equation, and the equation ofmotion (dynamic wave momentum equation):c h V-h+ a =1at e.x8bt v 8V I 8vSr = Soex gc- gatwhere h is the flow depth and V is the depth-averaged velocity in one of the eight flow directionsx. The excess rainfall intensity (i) may be nonzero on the flow surface. The friction slopecomponent Sf is based on Manning's equation. The other terms include the bed slope (S,),pressure gradient and convective and local acceleration terms.The equations of motion in FLO-2D are applied by computing the average flow velocity across agrid element boundary one direction at time. There are eight potential flow directions, the fourcompass directions (north, east, south and west) and the four diagonal directions (northeast,southeast, southwest and northwest). Each velocity computation is essentially one-dimensionalin nature and is solved independently of the other seven directions. The stability of this explicitnumerical scheme is based on strict criteria to control the magnitude of the variablecomputational timestep.4. Model Implementation4.1 AssumptionsThe inherent assumptions in a FLO-2D simulation are as follows:o Grid element is represented by a single elevation, n-value, flow deptho Steady flow for the duration of the timestepo Hydrostatic pressure distributiono 1-dimensional channel flow (no secondary currents, no vertical velocity distributions)o Rapidly varying flow such as hydraulic jumps or shock waves are smoothed out inmodel calculations. Subcritical and supercritical flow transitions are assimilated intothe average hydraulic conditions between two grid elements.4.2 Spatial and Temporal Discretization SchemesThe solution domain in the FLO-2D model is discretized into uniform, square gridelements. The differential form of the continuity and momentum equations in the FLO-Zachry EE 14-E16, Rev. 1Page A4 of A7 2D model is solved with a central, finite difference numerical scheme. This explicitalgorithm solves the momentum equation for the flow velocity across the grid elementboundary one element at a time.4.3 Interpolation MethodsGrid element elevation data is based on imported digital terrain (DTM) points orelevation points that are added to the working region. Interpolation methods available inFLO-2D include:o Using a user specified minimum number of closest DTM points within the vicinityof a grid element to compute the grid elevation;o Using a user specified radius of interpolation which defines a circle around eachgrid element node to select DTM points for use in computing the grid elementelevation; ando Using an inverse distance weighting formula exponent to assign elevations to thegrid element from the DTM points4.4 Solution Procedures and Convergence CriteriaThe solution algorithm incorporates the following steps:1. The average flow geometry, roughness and slope between two grid elements arecomputed.2. The flow depth dx for computing the velocity across a grid boundary for the nexttimestep (i+1) is estimated from the previous timestep i using a linear estimate (theaverage depth between two elements).÷X d x+33. The first estimate of the velocity is computed using the diffusive wave equation. Theonly unknown variable in the diffusive wave equation is the velocity for overland, channelor street flow.4. The predicted diffusive wave velocity for the current timestep is used as a seed in theNewton-Raphson solution to solve the full dynamic wave equation for the solutionvelocity. It should be noted that for hyperconcentrated sediment flows such as mud anddebris flows, the velocity calculations include the additional viscous and yield stressterms.5. The discharge Q across the boundary is computed by multiplying the velocity by thecross sectional flow area. For overland flow, the flow width is adjusted by the widthreduction factors (WRFs).Zachry EE 14-E16, Rev. 1Page A5 of A7

6. The incremental discharge for the timestep across the eight boundaries (or upstreamand downstream channel elements) are summed,A -Q +QQQ+/-Q-0+QQ+Q,, +QO.and the change in volume (net discharge x timestep) is distributed over the availablestorage area within the grid or channel element to determine an incremental increase inthe flow depth.A~d' = A.QO At ..-A!,,ýfwhere AQx is the net change in discharge in the eight floodplain directions for the gridelement for the timestep At between time i and i + 1.7. The numerical stability criteria are then checked for the new grid element flow depth. Ifany of the stability criteria are exceeded, the simulation time is reset to the previoussimulation time, the timestep increment is reduced, all the previous timestepcomputations are discarded and the velocity computations begin again.8. The simulation progresses with increasing timesteps until the stability criteria areexceeded.The convergence criteria for the solution in FLO-2D are +/- 0.01 ft/s for velocity and +/- 0.01 ftfor depth.4.5 Timestep SelectionFLO-2D has a variable timestep that varies depending on whether the numerical stabilitycriteria are not exceeded or not. Timesteps generally range from 0.1 second to 30seconds. The model starts with the a minimum timestep equal to 1 second andincreases it until the numerical stability criteria exceeded, then the timestep isdecreased. If the stability criteria continue to be exceeded, the timestep is decreaseduntil a minimum timestep is reached. If the minimum timestep is not small enough toconserve volume or maintain numerical stability, then the minimum timestep can bereduced, the numerical stability coefficients can be adjusted or the input data can bemodified. The timesteps are a function of the discharge flux for a given grid element andits size. Small grid elements with a steep rising hydrograph and large peak dischargerequire small timesteps. Accuracy is not compromised if small timesteps are used, butthe computational time can be long if the grid system is large.5 Input Data RequirementsThe major design inputs to the FLO-2D computer model are:o Digital terrain model of the land surface,Zachry EE 14-E16, Rev. 1Page A6 of A7 o inflow hydrograph and/or rainfall data,o Manning's roughness coefficient ando Soil hydrologic properties such as the SCS curve number.The digital terrain model of the land surface is used in creating the elevation grid systemover which flow is routed. The specific design inputs depend on the modeling purpose andthe level of detail desired.6 Output DetailsFLO-2D model outputs include:o Maximum flow depths at each grid element;o Maximum velocity at each grid element;o Maximum water surface elevation at each grid element;o Time the peak water surface elevations and velocities occur;o The discharge hydrograph overtopping a levee within a grid element;o The discharge hydrograph through a hydraulic structure; ando Maximum flow depth and water surface elevation in channel segments.References1. FLO-2D Software, Inc, 2014. FLO-2D Pro Reference Manual, Nutrioso, Arizona,www.flo-2d.com2. FLO-2D Software, Inc, 2011. FLO-2D Model Validation for Version 2009 and upprepared for FEMA, June 2011.Zachry EE 14-E16, Rev. 1Page A7 of A7 Appendix BFLO-2D Grid Elements ResultsPageB1 -Grid Element NumberB2 -Ground Elevations (feet, MSL)B3 -Maximum Flow Depth (feet)B4 -Maximum Water Surface Elevation (feet, MSL)B5 -Maximum Flow Velocity (feet per second)B6 -Maximum Flow Velocity VectorB2B3B4B5B6B7Note: Pages B2 through B7 are not numbered. In lieu of numbering, page numbers are identified above.Zachry EE 14-E16, Rev. 1Page B I of B7 BI -GRID ELEMENT NUMBERFeetI B2 -GROUND ELEVATIONS (FEET, MSL)NN ____________________________NS1) MAW0 Photo (Mourn & Creed. 20128) for referenc only asA 1h0,, bukkns aO an 01,09,. aoo" .Use but"0 0,*hw0ft0.. 11000 (paw. & Creed. 2012.) for .01.0.0 to actual2) S118tegiC b00011, (Ram0) # 344 Uses same1 FLO-2D gridak00 as fter, #34301w4 111,0#393 uses sameo FLO.2D WW1040.0001 as hem, Ar 3110. Rem # 344 and ha0m1# 393 am1 001101,040in004.. map loo loplay 00,Z =:=z~~LogondLiii ~ 00000.0110050,110.11,4--L0,~00, 000,0, 00,S0000~~000~~0 125 250 500 750 1.000Feet B3 -MAXIMUM FLOW DEPTH (FEET)N ____________Feet B4 -MAXIMUM WATER SURFACE ELEVATION (FEET, MSL)r~IFeet B5 -MAXIMUM FLOW VELOCITY (FEET PER SECOND)NosN ___________________,0Feet B6 -MAXIMUM FLOW VELOCITY VECTOR Appendix CBuilding LocationsNote: Pages C2 to CIO are not numbered due to their size.Zachry EE 14-E16, Rev. 1Page C1 of C10 r? r --~ ~ -( -- t f/j ,-~-1KI1jAIS~wa STATION DIIIOZG UNOM.0 *llEEL-=VU C -/.5-0~SCALE f.200!STHE COWECTlCUT LOT IS POM R_MILLSTONE POINT

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1- v -B', so' H- H,.,r ,,,-,-, -T I r+/-÷-t+÷÷÷+/-+/-4++/-H÷H-+/-r A'+I÷-++÷-*+/-+H--f+/-7-- A C " m CAF /X p-?-ASCALE f-5d Appendix DExtended Third-Party ReviewZachry EE 14-E16, Rev. 1Page Dl of Dl11 GZAGeoEnvironmental, Inc.Engineers andScientistsDecember 15, 2014File No. 01.0171382.13Zachry Nuclear Engineering, Inc.14 Lord's Hill RdStonington, CT 06378Attention: Mr. Michael KerstProject ManagerRe:Transmittal and Response to Third Party Review CommentsDominion Nuclear Flood Hazard Re-Evaluation Project

Dear Mr. Kerst,

249 Vanderbilt AvenueNorwood, Massachusetts02062781-278-3700FAX 781-278-5701www.gza.comThe purpose of this letter is to transmit and provide responses to the independent peer review ofthe External Flood Hazard Re-Evaluation hurricane and surge calculation methodology by Dr.Donald T. Resio (Attachment 2). It is GZA's opinion that Dr. Resio's review of External FloodHazard Re-Evaluation hurricane and surge calculation methodology used at Surry Power Station(SPS) is valid for hurricane and surge calculations for Millstone Power Station (MPS) because theanalyses were performed by GZA in parallel using nearly identical methodological approaches. Itis important to note that extension of this review to the MPS calculations is limited tomethodology only, as Dr. Resio has not specifically reviewed the MPS calculations or theassociated results. A summary of Dr. Resio's experience and qualifications is provided inAttachment 1.Dr. Resio performed a focused review of the following calculations, which represent elements ofa step-wise assessment of the coastal flooding hazard at SPS:* Calculation No.14-028, Rev. 0 -Probable Maximum Hurricane for Surry Power Station0 Calculation No.14-116, Rev. 0 -Deterministic Probable Maximum Storm Surge forSurry Power Station0 Calculation No.14-117, Rev. 0 -Probabilistic Storm Surge for Surry Power StationGZA's calculations for MPS follow the identical process:0 Calculation No.14-034, Rev. 0 -Probable Maximum Hurricane for Millstone PowerStation0 Calculation No.14-162, Rev. 0 -Deterministic Probable Maximum Storm Surge forMillstone Power Station* Calculation No.14-161, Rev. 0 -Probabilistic Storm Surge for Millstone Power StationIn addition the calculation documentation, Dr. Resio's review was informed by discussions withGZA during a series of teleconferences between May of 2014 and December of 2014. Thisreview culminated in the opinion summary provided as Attachment 2. In general, Dr. Resio'scomments and recommendations were considered by GZA prior to finalizing each calculationabove. A summary of Dr. Resio's comments for each calculation and GZA discussion follows:Zachry EE 14-E16, Rev. 1Page D2 of D1 1 December 15, 2014Page 2File No. 01.0171382.13CL~Calculation No.14-028, Rev. 0 -"Probable Maximum Hurricane for Surry Power Station"Overall, Dr. Resio concurred with the employed methodology and results associated with thiscalculation. Items highlighted by Dr. Resio's review judged by GZA to require additionaldiscussion are as follows." On Page 2 of Attachment 2, Dr. Resio notes that it is difficult to validate the WRTsynthetic data as being representative of extreme conditions. GZA agrees with thisposition, and points to the fact that available historical data do not characterize theseextremes due to a paucity of data relative to the range of ammal exceedance probabilitiesbeing considered. Expert meteorologists and climatologists were retained to support thiscalculation, and their review of these data highlighted general consistency with availablehistorical data and a slight conservative bias with respect to storm intensity and generalsurge generation potential. Therefore, the synthetic WRT data are considered to be aneffective tool for characterizing extreme hurricanes affecting the SPS vicinity." On Page 3 of Attachment 2, Dr. Resio comments on sensitivity of the GPD function tothreshold selection. While GZA agrees that probability estimates derived from GPD fitscan be sensitive to the selected threshold, it is important to note that the GPD functionwas not used to develop the 3M data set; therefore, sensitivity of the GPD fits to selectedthresholds would not affect the scaling function used to calculate PMH intensities, norwould it affect maximum wind speed probabilities derived from the 3M data set itself.GPD functions were only used to evaluate error in the development of the data setextension (i.e., the 3M data set) through direct comparison to the synthetic WRT data.Calculation No.14-116, Rev. 0 -"Deterministic Probable Maximum Storm Surge for SurryPower Station"Overall, Dr. Resio concurred with the employed methodology and results associated with thiscalculation. One item highlighted by Dr. Resio's review judged by GZA to require additionaldiscussion follows.On Page 3 of Attachment 2, Dr. Resio comments on comparing SLOSH and ADCIRC todemonstrate consistency between the models. While absolute results may differ betweenthe models due to model resolution and/or other contributing factors, similar parametersensitivities are expected. This expectation is confirmed by the results of theProbabilistic Storm Surge calculation, which shows similar parameter-specificsensitivities between SLOSH and ADCIRC despite different absolute maximumstillwater elevation estimates.Calculation No.14-117, Rev. 0 -"Probabilistic Storm Surge for Surry Power Station"Overall, Dr. Resio concurred with the employed methodology and results associated with thiscalculation. It is noted that Dr. Resio adjusted his comments related to utilizing BayesianQuadrature to recognize the use of Response Surface methodology during a December 4, 2014telephone conversation. Items highlighted by Dr. Resio's review judged by GZA to requireadditional discussion are as follows:Zachry EE 14-E16, Rev. 1Page D3 of D1 1 December 15, 2014File No. 01.0171382.13 Page 3cz'I" On Page 4 of Attachment 2, Dr. Resio comments on demonstrating consistency inprobability mass as parameter-specific probabilities transition to the surge-frequencyresponse. GZA recognizes the desire to verify the recovery of all probability massreflective of the probability level considered in this analysis (i.e., IE-6 annual exceedanceprobability, or AEP, level). A comparison of the storm parameter definitions associatedwith this calculation and the univariate probability density functions presented in thePMH calculation shows that, while not all probability mass is directly recovered, massassociated with storm parameter responsible for extreme surge elevations has beencompletely represented. Probability mass that has not been considered is limited to morefrequent, lower-risk level characteristics (e.g., maximum wind speeds below 70 knots andstorms traveling east-of-north). Exclusion of this probability mass is analogous toexcluding contributions to the surge-frequency relationship from extra-tropical events.With respect to storm parameter combinations with probabilities smaller than 1-in-3,000,000, it is important to note that maximum wind speeds equal to or above bearing-specific PMH levels have been included in certain cases (i.e., to promote conservatism).As such, the 1-in-3,000,000 lower probability threshold is shown to be adequatelyconservative such that lower-probability storms would not contribute to the 1E-6 AEPlevel." On page 4 of Attachment 2, Dr. Resio comments on evaluating aleatory variability (i.e.,note: Figure 59, which is specifically referenced in Dr. Resio's review, has changed toFigure 60 in the final version of the calculation): This method of characterization (i.e.,via a linear functional fit, as opposed to a more complex functional fit) was necessary, asthe FEMA tool employed to distribute uncertainty requires this simplification. Asdemonstrated by Figure 60, the linear fit, which is necessitated by the uncertaintyadjustment formulations, is conservative for the majority of the wind speed range (i.e.,over-estimates the maximum wind speed difference at the 95% confidence limit between90 and approximately 138 knots).In consideration of the attached review summary and the additional discussion presented above,GZA considers the peer review of Calculation No.14-028, 14-116 and 14-117 to be complete.As previously indicated, the methodologies used to develop these calculations are consistent withthe methodologies used to develop MPS Calculation No.14-034, 14-162 and 14-161. Inconsideration of these consistencies, GZA also considers the peer reviews of the methodologiesused to develop MPS Calculation No.14-034, 14-162 and 14-161 to be complete.Very truly yours,GZA GEOENVIRONMENTAL, INC.Michael A. Mobile, Ph.D.Originator/Daniel C. Stapleton, P.E.VerifierZachry EE 14-E16, Rev. 1Page D4 of D1 1 December 15, 2014Page 4File No. 01.0171382.13MAM/DCS:krAttachments1. Summary of Experience and Qualifications, Donald T. Resio2. Peer Review of Storm Surge Analysis at Surry Power Station in VirginiaOnZXZachry EE 14-E16, Rev. 1Page D5 of D1 1 . Summary of Experience and Qualifications, Donald T. ResioDr. Resio's credentials as a subject matter expert are summarized as follows:Dr. Resio is currently a Professor of Ocean Engineering at the University of North Florida (UNF) and theDirector of the Taylor Engineering Research Institute (TERI). A biographical sketch available on theNRC's website' states the following with respect to Dr. Resio's background as of 2010 (i.e., prior totaking his position at UNF): "Dr. Resio was appointed to the position of Senior Technologist (ST) inMay 1994. This position represents the highest technical rank in the DoD civil service, with less thanforty such positions authorized within the Army. Dr. Resio has been involved in performing anddirecting engineering and oceanographic research for over 30 years. He serves as the technical leader forthe Coastal Military Engineering program and is the Technical Manager (TM) for a recent successfullycompleted Advanced Technology Concept Demonstration (ACTD) for military logistics. He alsoconducts/directs research that spans a wide range of environmental and engineering areas within theCorps Civil Works Program. In this capacity he directs the MORPHOS project aimed at improving thepredictive state of the art for winds, waves, currents, surges, and coastal evolution due to storms. Mostrecently, Dr. Resio has been selected as the co-leader (with Professor Emeritus Robert Dean of theUniversity of Florida) for the IPET Task 5a (analysis of wave and surge effects, overtopping and relatedforces on levees during Katrina) and as the leader of the Risk Analysis team for the South LouisianaHurricane Protection Project, including consideration of the effects of climatic variability on hurricanecharacteristics in the Gulf of Mexico. Dr. Resio led the team that developed the new technical approachfor hurricane risk assessment along US coastlines and is now leading an effort sponsored by the NuclearRegulatory Agency to extend this approach to the estimation of hazards for Nuclear Power Plants incoastal areas. Recently, under the sponsorship of the Department of Homeland Security, Dr. Resio led ateam of researchers in the development of innovative methods for the rapid repair of levee breaches. Thiswork appears to offer new options for improved flood mitigation in many areas of the US."from information associated with the Regulatory Information Conference, 2010: http://vwww.nc.gov/public-involve/conference-symposia/ric/past/2010/bio/resiodpdfZachry EE 14-E16, Rev. 1Page D6 of D1 1 UNIVERSITYofUNFNORTH FLORIDA.Attachment 2: Peer Review of Storm Surge Analysis at Surry Power Stationin VirginiaResearch Agreement #1309-001October 30, 2014Prepared for:GZA GeoEnvironmental, Inc.249 Vanderbilt AvenueNorwood, MA 02062POC: Michael MobileI UNF Drive, Science & Engineering Building 50, Suite 3200, Jacksonville, Florida 32224An Equal OpportunitY / Equal Access /Affirmative Action InstitutionZachry EE 14-E16, Rev. 1Page D7 of D1 1 Review of Zachry Nuclear, Inc.Professor Donald T. ResioUniversity of North Florida1. IntroductionThis report presents a review of three documents pertaining to the estimation of waterlevels produced by the "controlling storm" at the Dominion/Sunry Power Station in Virginia.The first report contains material which describes the theoretical and empirical basis for thedefinition of the controlling storm and its deterministic and probabilistic attributes. The secondreport provides a deterministic analysis of the Probable Maximum Storm Surge (PMSS) resultingfrom the combination of meteorological parameters generating the PMSS at the SPS. The thirdreport provides a probabilistic analysis of storm surge for Surny Power Station (SPS) using stateof the art numerical models combined with the probabilities of meteorological parametersdeveloped in the first report. This analysis focuses on the very-low probability range of AnnualExceedance Probability (AEP) for still water at the SPS site.2. Review of Report Entitled "Probable Maximum Hurricane for Surry Power Station"This report documents the approach used in developing Probable Maximum Hurricane(PMiH) parameters for Dominion/Surry Power Station (SPS) and the approach used to developprobabilistic representations of parameters to be used in Probable Maximum Storm Surgecalculations and for probabilistic (JPM) calculations at this site.2.1 Review of PMH Parameter DevelopmentStep 1: Develop A Rationale for Selection of the Controlling Event for the PMIH.Identify the controlling meteorological event. This involved a relatively straightforward analysisof tropical and extratropical storms in this areas and it was determyned that, for the extreme rangeof low probability considered, hurricanes would be the dominant contributor to the maximumsurge at this site. This is an easy ease to make and should be readily accepted.Step 2: Develop parameters Based on NWS 23 Report. Utilize NWS 23 (1979) todevelop a set of meteorological parameters for the PMH in the area of the SPS. An initial reviewof parameters developed in the 1979 report (NWS 23) suggested that the storm characteristics forthe PMH hi this area as estimated in that study were quite intense and might not berepresentative of local conditions at the SPS, primarily due to the inclusion in NWS 23 ofheadings that do not produce maximum surges at the SPS.One factor that could use some additional discussion in this section is the treatment ofmaximum wind speed as the defining factor for storin intensity instead of the more conventional(at least in terms of storm surge generation) pressure differential. A table or graph showing therelationship between tile two (which might be a family of curves depending on latitude, stormPage 1Zachry EE 14-E16, Rev. 1Page D8 of D1 1 size and forward speed) would be extremely helpful in understanding the transition from oneparameter space to the other.Step 3: Part I Development of Deterministic PMH Parameters. Most of the stormparameters were analyzed in a fashion that produced values very consistent with the NWS 23valued. The one exception is the treatment of storm intensity. Motivated by the existence of astrong co-variation between storm heading directions and storm intensities a site-specific studywas undertaken to examine storm behavior in this area in more detail. A set of synthetic stormswas created by WindRisk Tech (WRT) using a well validated model developed by Emanuel et al.(2004). This set of storms was used to create a scaling function for storm intensity as a functionof storm heading. The maximum of this directional function was set to be equal to the NSW 23value for this area. Unfortunately, the manner in which this is written makes it sound like aprobabilistic development of a maximum wind speed rather than a dimensionless scalingfunction which is used to allow natural variability of the NWS maximum wind speed withrespect to storm heading direction. I recommend that this section be recast in terms of using theresults from the WRT simulations to scale the maximum wind speeds for hurricanes approachingfrom different directions, rather than introducing any probabilistic terms into this analysis whichmight be misunderstood. Such a misunderstanding might then necessitate a discussion ofprobability levels, sources of uncertainty and other related non-deterministic aspects of thisanalysis. The WRT methodology is robust; however, it is difficult to argue that this method forgenerating synthetic storms is correct in an absolute sense for prediction of extremes, since thedata for local comparison of such extremes is very sparse.Step 3: Part 1 Development of Probabilistic PMH Parameter Framework. This section isstraightforward in its development but the joint probability information could be displayed in aclearer fashion. An equation for p(xl,x2,x3,x4...) should be written with any jointly varyingterms written as such and graphical diagrams or equations should be presented to demonstrateclearly the final probability distributions, cumulative distributions, and complementarydistributions. Such information would really help reviewers if it were placed in the finalsummary section.Two small points that might be considered for changing are as follows:a. On Page 24, it is implied that information on central pressures is Ihnited to the1979-2012 time frame due to lack of data. Most hurricanes that passed close to the US east coasthave central pressure data back into the 1950s or so. Perhaps the intent here is to make theanalysis somewhat consistent in a climatological sense, due to changes in weather patterns, butthis is not how the comment is posed.b. The FEMA report for this area (from the USACE-Vickery study) does contain someinformation on storm sizes and should probably be referenced as a relevant source of data. Thedata there seem fairly consistent with the results presented in the WRT analyses.Step 4: Development of Joint Probabilities for Hurricane. Once the synthetic storm set isdeveloped and included within the methodology for estimating joint probabilities for the JPMapproach, a careful analysis of univariate and multivariate probabilities is performed as part ofthis report. This section is very thorough in its treatment of these different terms. One questionPage 2Zachry EE 14-E16, Rev. 1Page D9 of D11 which might be asked relative to this work is the application of tile GPD in estimating hurricanewind speeds. The GPD can be quite sensitive to the choice of the chosen threshold value. Manystudies perform analyses using at least 3 different thresholds to investigate this potential sourceof variation. Since NRC reviewers are well aware of this potential issue, it would probably be agood idea to be proactive on this issue and perform these analyses before their review. Lookingat the shape of the curve, I do not think that there will be a large sensitivity, but it should bequantified.Summary of Review of Probable Maximum Hurricane for Surry Power StationOverall, this is a very high-level analysis and is carefully performed. A few minor points asnoted should be addressed, but I do not think any of the issues raised in this review willsignificantly affect the PMH parameter or probabilistic results. Some relevant points include thefollowing:I. The upper ranges of the rmax reach relatively large sizes for all heading angles, 28.4 -41.7 nm.2. The vnax values are developed to include a storm-heading dependence which is used todeterministically scale the NWS 23 values of windspeed, which seems reasonable.3. Upper and lower bounds on forward speeds seems reasonable.4. The range of storm bearings for surge simulation seems sufficiently broad to cover theentire ranged needed.3. Review of Report 2 Entitled "Deterministic Probable Maximum Storm Surge for SurryPower Station"This report presents the deterministic analysis of the Probable Maximum Storm Surge(PMSS) for Surry Power Station, including the combined effects of storm surge, antecedentwater level, waves and river flood. It relies on report I for all estimates of all meteorologicalparameters associated with a set of hurricane parameters shown to be capable of producing thehighest storm surges reasonably expected at this site.The modeling approach seems straightforward and uses state of the art methods andmodels to perform all estimates. The SLOSH model was used as a screening tool to select asmall set of storms for detailed simulation with the ADCIRC model. There is always thepossibility of mismatched physics producing storms which are not ordered in the same sequencewhen using results from different models. The ADCIRC model is forced by a slightly differentwind field formulation than that used in the SLOSH model, however, for low values of theHolland B parameter, the net differences in winds should be relatively small. Since the valuesused here (characteristic of this region) range from 1.08 to 1.37, this should be the case here.Thus the differences in the ordering seem to relatively small. It is recommended that theADCIRC results be plotted against the SLOSH results at the sites of interest (SPS Discharge siteand SPS Intake site) to make this point graphically.Page 3Zachry EE 14-E16, Rev. 1Page D1IO of D1l1 Fifteen ADCIRC simulations were utilized to cover the range of parameter combinationsfound to produce the largest combined water levels at the Surry Power Station. Given that themaximum wind speeds are reasonably defined as a finction of storm heading, this set ofcombinations appears to cover the range needed for this purpose. A plot of the parameters in Table 4as a fiunction of the heading along with the maximum conditions defined as a function of heading inReport I would help make the point that the simulated storms constitute a set that should provide agood estimate of the maximum surges.4. Review of Report 3 Entitled "Probabilistic Storm Surges for Surry Power Station"As in Report 2, the hydrodynamic models are state of the art and are executed in astraightforward manner, so there should be no problems with the results firom these models.This report describes the effort to produce a probabilistic analysis of storm surge (JPM study)for Surry Power Station, using a Bayesian Quadrature method typical of many FEMA applicationstoday. In this approach, a joint probability of storm parameters is taken from Report 1; however,documentation of the joint probability density functions is lacking. Since the Bayesian Quadrature isused to define the probabilities of the 20 individual ADCIRC simulations, the individual probabilitymasses defined for each of the storms needs to be shown somewhere in a table hi order to enable areviewer to validate the probability estimates. These masses are determined by a Monte Carlomethod and some assumptions pertaining to the correlation lengths of different parameters. Thesecorrelation lengths should be clearly specified and hiformation on all the probability masses shouldbe included somewhere in the report, particularly since the description suggests that there might besome constraints on the event combinations. It is essential to be able to check that the complementaryprobabilities sum to one where appropriate. I tend to agree with the motivation to discretize the eventcount in defining the probabilities such that less than 1/3,000,000 is equal to zero, but it is moredefensible in a probabilistic method to let these small values (even when a number of them aresummed) actually shown to be negligible. In Section 6.2.6 (Identification of the OS Storm Set),paragraph 2 is not very clear. More information on the selection process and the application of theSurge-Stat program would be very helpfil to reviewers.The treatment of epistemic uncertainty is consistent with previous studies in this area. Thetreatment of aleatory uncertainty seems adequate and provides the magnitude of increase that seemstypical for inclusion of this type of uncertainty. The variation of surge level with vmax is clear, as isthe equation to parameterize it. However, the curve for the aleatory variation of surge elevation lookslike it is not well fit with a linear equation. Since the curve extends beyond the region of primarycontribution to the probabilities, it is recommended that Figure 59 be redone to focus on the region ofprimary contribution to the probabilities. It is verny likely that this difference in aleatory fitting is nota problem due to the range of probabilities that are affected here, but this should be checked.Donald T. Resio, Ph.D.Page 4Zachry EE 14-E16, Rev. 1Page D1 1 o D1 I Serial No. 15-106Docket Nos. 50-336/423ATTACHMENT 2MILLSTONE NTTF 2.1: FLOODING HAZARD RE-EVALUATIONINTERIM ACTIONS PLANDOMINION NUCLEAR CONNECTICUT, INC.MILLSTONE POWER STATION UNITS 2 AND 3 Serial No. 15-106Docket Nos. 50-336/423Attachment 2, Page 1 of 11Section 4.1Verify procedures are in place to initiate FLEX strategies in responseto a loss of ultimate heat sink if either one or both Millstone PowerStation (MPS) Intake Structures becomes inoperable due tocombined effects flooding.June 30, 20152 Section 4.2 Review/revise, the applicable station abnormal weather andoperational procedures for mitigation of a Beyond Design Basis June30 2015(BDB) potential flooding event due to a local intense precipitation(LIP) event for MPS Unit 2 (MPS2).3 Section 4.3 Revise applicable abnormal weather and operational procedures formitigation of a BDB potential flooding event due to a tsunami for June 30, 2015MPS2.4 Section 4.5 Perform Integrated Assessment of the flood hazards for MPS2 and March 12, 2017MPS3. (may changebased onguidance fromthe NRC)'A

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+{{#Wiki_filter:C IJRY DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.7. Ice-Induced FloodingThis section evaluates the potential of ice effects to contribute to flooding at MPS.2.7.1. MethodThe criteria for ice-induced flooding is provided in NUREG/CR-7046, Appendix G (NRC 2011). Twoice-induced events may lead to flooding at the site and are recommended and discussed inNUREG/CR-7046, Appendix G including:1. Ice jams or dams that form upstream of a site that collapse, causing a flood wave; and2. Ice jams or dams that form downstream of a site that result in backwater flooding.With respect to ice-induced flooding at MPS, the HHA used the following steps:1. Review historical ice events and information on backwater effects due to ice jams in theNiantic River near MPS.2. Evaluate historical salinity levels of the Niantic River and Long Island Sound to assess thefeasibility of the formation of ice jams in the Niantic River near MPS.3. Calculate flood elevations which could result at MPS from potential ice jams upstream ordownstream in the Niantic River.2.7.2. Results2.7.2.1. Review of Historical Ice EventsThe USACE maintains records of historical ice jams and dams on the Ice Jam Database (USACE,2012), which can be queried (using state/city/river name) to obtain information regarding historicalice events. There are no records of historical ice jams on the Niantic River or on the Long IslandSound in the USACE Ice Jam Database.2.7.2.2. Salinity of Water in Niantic River at MillstoneThe mean salinity of surface water in the Niantic River near MPS ranges from approximately 27.4 to30.3 psu (practical salinity unit), based on the data retrieved from the Long Island Sound ResourceCenter (University of Connecticut and the Connecticut DEP, 2004). According to the National Snowand Ice Data Center (NSIDC, 2013), a psu is nearly equivalent to a ppt (parts per thousand). Salinityin water has the potential to reduce the freezing point to be lower than 32 OF (0 0C) (NOAA, 2013).For example, the freezing point is 30 OF when the salinity is 17 ppt (NOAA, 2013).Although the salinity in water reduces the freezing point to be lower than 32 OF (0 0C), and reducesthe likelihood of ice jams near Millstone, the potential for ice jam formation on the Niantic River wasconservatively not disregarded based on possible extended period of time of low air temperature inthe region.EE 14-El 6, REV. 1 2-172EE 14-E16, REV. 12-172
+(-I DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.7.2.3. Flood Elevation due to Ice JamMPS is located along the shore of the Niantic Bay in the Long Island Sound, which does not containstructures downstream of the site where an ice jam can occur. Therefore, the potential for flooding tooccur at MPS as a result of a downstream ice jam is not significant.The closest structure upstream of MPS is the Amtrak Niantic River Bridge, which is locatedapproximately 0.8 miles upstream (see Figure 2.7-1). The maximum water depth above normal riverelevation resulting from an ice jam at the Amtrak Niantic River Bridge was conservatively calculatedto be equal to the bridge clearance of 16 feet (Amtrak, 2013). It is assumed that the ice daminstantaneously fails and the resulting flood wave was conservatively translated directly from theAmtrak Niantic River Bridge to the vicinity of MPS without consideration of flood wave attenuationwithin the Niantic Bay. It is assumed that the ice dam fails and the peak flow resulting from the floodwave was conservatively translated directly from the Amtrak Niantic River Bridge to the vicinity ofMPS without consideration of flood wave attenuation (i.e. decrease of discharge) within the NianticBay. The resultant peak flow from the ice dam failure was calculated using two empirical dambreach peak flow equations that use metric units (i.e., m, m3/s) as follows:Bureau of Reclamation: Qp = 19.1 (hw)1"85  Eq-1 (Wahl, 2004)Kirkpatrick: Qp = 1.268 (hw + 0.3)25 Eq-2 (Wahl, 2004)Where:Qp = Dam breach peak flow;hw = Head water.The dam breach peak flow (Qp) was calculated using the bridge clearance of 16 feet. The resultsshowed that the peak dam breach flow using the Bureau of Reclamation resulted in a greater peakflow than the Kirkpatrick equation. Therefore, the peak flow of 12,645 cfs was selected as the icedam breach peak flow calculated for the ice dam failure at the Amtrak Niantic River Bridge.The resultant rise in water level at Millstone was calculated using the Manning Formula (Chow,1959) for channel depth calculation:Q=A 1.4-9R2/3s]/2nWhere:A = cross section area (square-feet);n = Manning's n roughness;R = hydraulic radius (the cross sectional area of flow divided by the wetted perimeter);S = Slope of energy lineA rectangle channel with a bottom width equal to the Niantic Bay width at water surface elevationzero NAVD88 in the vicinity of Millstone and vertical walls at both sides of the channel (Figure 2.7-1)was assumed to calculate the normal depth using the Manning Formula. Therefore, the floodplainslopes and the Niantic Bay bathymetry (i.e., flow area below water surface elevation zero NAVD88)was conservatively ignored in the normal depth calculation. The resulting rise in water level at MPSwas conservatively estimated to be 2.9 feet, which is well below site grade at MPS (see Section 3).EE 14-El 6, REV. 12-173 a C DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.This estimate is conservative because attenuation of the flood wave is not considered. Niantic Bay,located immediately downstream of the Amtrak Niantic River Bridge, significantly increases in areanear MPS, which would result in significant attenuation of the flood wave. This would be anticipatedto greatly reduce the size of the flood wave due to the failure of an upstream ice jam before itreached MPS.Note that the Amtrak Niantic River Bridge is a movable structure, which can be raised in the event ofan ice jam formation. As a result, ice jams can be released by raising the bridge structure.2.7.3. ConclusionsThe USACE Ice Jam Database (USACE, 2012) does not include records of ice jams occurring onthe Niantic River. MPS's location at the downstream-most end of the Niantic Bay creates conditionswhich are unlikely to sustain a downstream ice dam due to both water salinity and channelmorphology. Therefore, the potential for flooding to occur at MPS as a result of a downstream icejam is not significant.The failure of a conservatively-estimated hypothetical upstream ice jam would not exceed theprotected elevation at MPS (see Section 3).EE 14-El 6, REv. 1 2-174EE 14-El 6, REV. 12-174 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.7.4. References2.7.4-1 Amtrak, 2013. Amtrak -Niantic River Bridge, ARRA Project Overview(http://www.amtrak.com/ccurl/377/521/Niantic-River-Bridqe-Replacement-Fact-Sheet.pdf -web page printed on 3/6/13).2.7.4-2 Chow, 1959. Ven Te Chow, "Open-Channel Hydraulics," reprint of the 1959 Edition,McGraw Book Company, Inc, 1959.2.7.4-3 NOAA, 2013. "JetStream -Online School for Weather -Sea Water," National Climatic andOceanic Administration (http://www.srh.noaa.gov/jetstream/ocean/seawater.htm -webpage printed on 1-1 9-2013).2.7.4-4 NRC 2011. "Design Basis Flood Estimation for Site Characterization at Nuclear PowerPlants -NUREG/CR-7046", U.S. Nuclear Regulatory Commission, November 2011.2.7.4-5 NSIDC, 2013. National Snow and Ice Data Center (NSIDC). Salinity and Brine(http://nsidc.org/cryosphere/seaice/characteristics/brine_salinity.html -web page printed3/7/13).2.7.4-6 University of Connecticut and the Connecticut DEP, 2004. Long Island SoundResource Center, prepared by the University of Connecticut and the ConnecticutDepartment of Environmental and Protection (DEP) with the support of researchers andorganizations throughout the Long Island Sound watershed. Niantic River 2004(http://www.lisrc.uconn.edu/eelgrass/LocationData.html -web page printed on 3/6/13).2.7.4-7 USACE, 2012. Ice Jam Database, U.S. Army Corps of Engineers, Ice EngineeringResearch Group, Cold Regions Research and Engineering Laboratory, 2012.2.7.4-8 Wahl, 2004. Tony L. Wahl, "Uncertainty of Predictions of Embankment Dam BreachParameters," Journal of Hydraulic Engineering ASCE, May 2004.EE 14-El 6, REV. 1 2-175EE 14-E16, REV. 12-175 Z AM jilpfDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.7-1: Location of First Structure Upstream of MPS: Amtrak Niantic River BridgeA&sect;*Msftfthea n3,ki*Legend* Miwone Power StatonEE 14-El 6, REV. 1 2-176EE 14-E16, REV. 12-176 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.8. Channel Migration or DiversionThis section of the report evaluates the potential for natural channels to meander or otherwisechange alignment in a manner that could flood or otherwise affect Structures, Systems, andComponents (SSCs) important to safety at MPS. NUREG/CR-7046 (NRC, 2011) includes thefollowing statement in Section 3.8-Flooding Resulting from Channel Migration or Diversion:Natural channels may migrate or divert either away from or toward the site. The relevantevent for flooding is diversion of water towards the site. There are no well-establishedpredictive models for channel diversions. Therefore, it is not possible to postulate a probablemaximum channel diversion event. Instead, historical records and hydrogeomorphologicaldata should be used to determine whether an adjacent channel, stream, or river hasexhibited the tendency to meander towards the site.2.8.1. MethodThe channel migration and diversion flooding evaluation followed the HHA approach described inNUREG/CR-7046, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plantsin the United States of America (NRC, 2011). With respect to channel migration and diversion, theHHA used the following two steps:1. Review historical records and hydrogeomorphological data to assess whether the NianticRiver has exhibited the tendency to meander towards the site.2. Evaluate the foundation type at critical structures and shoreline protection features to assesspotential susceptibility to erosion caused by possible channel migration.2.8.2. Results2.8.2.1. Review of Historical RecordsA literature review did not yield evidence suggesting there have been significant historical diversionsof the Niantic River near Millstone or the small unnamed coastal stream east of Millstone for morethan 50 years. A comparison of a 1958 USGS Topographic map (USGS, 1958) and a 2012 USGSTopographic map (USGS, 2012) illustrates continuity of the river course for more than 50 years, seeFigures 2.8-1 and 2.8-2. Note that a former quarry located south of Millstone shown in the 1958USGS Topographic map (Figure 2.8-1) has been decommissioned (Figure 2.8-2). The area of theformer quarry has been flooded to be the plant cooling water discharge area.Millstone is located at the mouth of the Niantic Bay where the bay opening is approximately 2.1 mileswide. NUREG/CR-7046 (NRC, 2011) includes the following statement in Section 3.8-FloodingResulting from Channel Migration or Diversion:Because most channel diversion occurs during high flows when the stream or river overflowits banks, flood data, particularly stage, may also prove useful in the determination.The Niantic River watershed is approximately 31 square-miles. High flows in the Niantic Riverdissipate quickly in the Long Island Sound; therefore, high velocity overflows of the banks of the rivernear Millstone that could result in channel diversion or severe erosion are not anticipated. As aresult, channel diversion is not expected to occur near Millstone due to high riverine flows in theNiantic River. The small coastal stream near Millstone is not expected to produce high flows thatEE 14-El 6, REV. 12-177 DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.could result in channel diversion toward Millstone due to its limited drainage area of 87 acres (seeSection 2.2).2.8.2.2. Review of foundation Types and Susceptibility to ErosionThe foundations for a majority of the critical structures including the reactor containment are onbedrock. However, the emergency generator, waste disposal enclosure, and turbine building, arefounded on dense basal till which overlies rock. The control building is founded on structural backfilloverlying till and bedrock. Generally, bedrock is highest on the eastern portion of the site and dips tothe west towards Long Island Sound. MPS is located on till that contains silt, sand, and stony fill;artificial fill, and bedrock. Subsurface explorations included in the MPS-3 FSAR (Dominion, 2014)generally show that till, when present, ranges from depths of 0 to 20 feet and rests on top ofbedrock.The soils and rock underlying the site are strong, stable materials that are not susceptible to loss ofstrength, subsidence, or other instabilities during earthquake motion. The soil and bedrock atMillstone are of very low permeability (Dominion, 2014).2.8.3. ConclusionsA review of historical data indicates that the Niantic River has not exhibited a tendency to meandertowards the site. High flows in the Niantic River dissipate quickly in the Long Island Sound,therefore, high velocity overflows of the banks of the river near Millstone that could result in channeldiversion or severe erosion are not anticipated. In addition, most of the site's critical structures arefounded on bedrock or structural backfill overlain on bedrock, and the shoreline is protected by arobust riprap revetment. Given these conditions, channel migration as a result of riverine flooding isnot considered to be a potential contributor to flooding at Millstone.2.8.4. References2.8.4-1 Dominion, 2014. Millstone Power Station Final Safety Analysis Report (MPS-3 FSAR), Rev.25.2.2.8.4-2 USGS, 1958. U.S. Geological Survey (USGS), Niantic Quadrangle 7.5-Minute SeriesHistorical Topographic Map, revised on 1958 and topography surveyed in 1934.2.8.4-3 USGS, 2012. USGS, Niantic Quadrangle 7.5-Minute Series Topographic Map, contoursbased on National Elevation Dataset, 2012.2.8.4-4NRC, 2011. "Design Basis Flood Estimation for Site Characterization at Nuclear PowerPlants -NUREG/CR-7046", U.S. Nuclear Regulatory Commission, November 2011.EE 14-El 6, REV. 1 2-178EE 14-E16, REV. 12-178 ZACHIitYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.8-1:1958 Historical Topographic MapEE 14-El 6, REV. 1 2-179EE 14-E16, REV. 12-179 ZACHFIYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zuchry Nuclear Engineering, Inc.Figure 2.8-2: 2012 Current Topographic MapEE 14-El 6, REV. 1 2-180EE 14-E16, REV. 12-180 EIW DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.9. Combined Effect FloodsAn evaluation of the combined external flood effects associated with coastal flooding at MPS wasperformed. The combined flood effects were evaluated for both deterministic (Probable MaximumStorm Surge) and probabilistic flood analyses (associated with a flood annual exceedanceprobability of 1 E-6).2.9.1 MethodThe HHA approach described in NUREG/CR-7046 (NRC, 2011) was used for the evaluation of theeffects of the combined external flood effects at MPS. Deterministic combined effect flooding wasevaluated first, followed by a refined probabilistic combined effect flooding which is judged torepresent the most accurate estimate of flooding potential at MPS.2.9.1.1. Deterministic Combined Effect FloodMPS is subject to coastal flood hazards including storm surge, wind-generated waves and tsunamis.The coupled ADCIRC + SWAN model was used to simulate storm surge and waves due to thedeterministic PMSS and the probabilistic storm surge. The following approach to deterministicallycombining external flood hazards was used consistent with NUREG/CR-7046:H.1 -Floods Caused by Precipitation EventsThe following criteria for floods caused by precipitation events (NUREG/CR-7046, Appendix H,Section H.1) were evaluated.* Alternative 1 -A combination of mean monthly base flow, median soil moisture, antecedent orsubsequent rain, the PMP, and waves induced by 2-year wind speed applied along the criticaldirection;" Alternative 2 -A combination of mean monthly base flow, probable maximum snowpack, a 100-year snow-season rainfall, and waves induced by 2-year wind speed applied along the criticaldirection; and* Alternative 3 -A combination of mean monthly base flow, a 100-year snowpack, snow-seasonPMP, and waves induced by 2-year wind speed applied along the critical direction.The PMF was calculated for the small intermittent stream located approximately 200 feet east of theIndependent Spent Fuel Storage Installation (ISFSI) (Section 2.2). The small intermittent stream'swatershed is 87 acres (about 0.14 square miles) and terminates at the Millstone Road embankmentwithout a visible outlet to Long Island Sound. The resulting PMF elevation on the small coastalstream (due in large part to the access road embankment obstruction) near Millstone is 11.2 feet(Section 2.2), which is approximately 12.8 feet below the MPS3 site grade of 24.0 feet (Dominion,2014a) and approximately 2.8 feet below the MPS2 site grade of 14.0 feet (Dominion, 2014b).Significant wave propagation toward MPS is not expected due to the distance and the land use andland cover (e.g., woods and security barriers) between MPS and the small coastal stream and theavailable vertical margin or freeboard between MPS site grade and the PMF flood elevation.Additionally, flood velocities are anticipated to be very low because flooding is impounded by theMillstone Road embankment, limiting the potential for scour and erosion. Therefore, combined effectfloods caused by precipitation events (NUREG/CR-7046, Appendix H, Section H.1) are notconsidered further.EE 14-El 6, REV. 12-181 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.The results of the dam failure section (Section 2.3) indicate that the potential for flooding at MPSresulting from upstream dam failure is not applicable based on the lack of dams within the Millstonelocal drainage basin and the watershed contributing to the small coastal stream.H.3 -Floods along the Shores of Open and Semi-Enclosed Bodies of WaterDue to the shore-side location of MPS, criteria for shore-side location combined events wereevaluated (Appendix H, Section H.3.1):-Probable maximum surge and seiche with wind-wave activity;-Antecedent 10 percent exceedance high tide.The antecedent 10 percent exceedance high tide elevation includes the calculated sea levelanomaly and the expected sea level rise in accordance with ANS 2.8 (ANS, 1992). Sea levelanomaly and the expected sea level rise were calculated in the Deterministic PMSS section (Section2.4).Wave action at MPS was calculated using SWAN, which is a component of the coupledADCIRC+SWAN model. Figure 2.9-6 provides the model bathymetric and topographic contoursused to model the combined storm surge and wind-wave activity. Both the MPS2 and MPS3 intakeswere identified as safety-related structures pertinent to the calculation of wave effects duringcombined event scenarios, as well as the MPS2 and MPS3 turbine buildings. Due to the structuregeometry of the intakes, as shown in Figure 2.9-1 and Figure 2.9-2, respectively, wave effects will beapplied against vertical walls.Wave effects include inundation (resulting in hydrostatic and hydrodynamic loads) and wavebreaking (resulting in slash and spray and wave loads). Unbroken waves in front of a verticalstructure located in relatively deep water result in an elevated, reflected standing wave (Goda,2010). This is due to reflection and transformation of non-breaking waves at a vertical face, wherethere can be an upward flow (vertical shift, referred to here as runup) that can be higher than theheight of the unbroken wave. Reflected wave crest elevations due to non-breaking waves werecalculated using the Sainflou Formula1 as presented in the USACE Coastal Engineering Manual(CEM) (USACE, 2006) for predicting wave forces on a vertical structure.The calculated "standing" (also referred to as "reflected") wave crest height is added to the PMSSstillwater elevation, to calculate the elevation of the standing wave crests at both intake structuresand turbine buildings.H.4 -Floods along the Shores of Enclosed Bodies of WaterThe criteria for floods along the shore of enclosed bodies of water (NUREG/CR-7046, Appendix H,Section H.4) do not apply to MPS since the site is not located on an enclosed body of water.1 In the case of irregular waves, wave height, H, should be taken as the characteristic wave height (USACE,2006). For the purposes of this evaluation, Hs, the significant wave height, is used.EE 14-E16, REV. 12-182 EIW DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.H.5 -Floods Caused by TsunamisCombined flood effects associated with tsunamis are included as part of the analyses required byNUREG/CR-7046 (Appendix H, Section H.5). Considering MPS's hydrologic setting (i.e., the smallstream has a small watershed, no outlet to Long Island Sound and no hydraulic route for upstreamtsunami propagation exists) and based on the results of the PMF and Dam Failure, combinations oftsunami and small stream flooding are insignificant. Therefore, the single combined effect floodalternative for a shore location was used:Alternative H.5.1 -Combination of Probable Maximum Tsunami (PMT) run-up and antecedent10 percent exceedance high tide.Evaluation of the potential for tsunamis at the MPS site concluded that the PMT results in lower floodelevations than the PMSS. PMT maximum flood elevations are locally as high as 14.7 feet near theMPS2 and MPS3 intake structures, including the 10 percent exceedance high tide. The PMTmaximum flood elevation is a result of a far-field source (i.e., Cumbre Vieja subaerial landslide).Although the PMT run-up elevation is bounded (i.e., less than) by the storm surge stillwaterelevation, tsunamis may be associated with high velocity flow. Therefore, hydrodynamic andhydrostatic loading due to the PMT is evaluated in this section.2.9.1.2 Combined Effect Flood with Probabilistic Storm SurgqeIn addition to applying the combined flood effects presented above to the deterministic floodanalyses, the combined flood effects were also evaluated for the probabilistically-determined stormsurge corresponding to the annual exceedance probability (AEP) of 1 E-6. The combined effects forthe probabilistic analyses were assumed to be consistent with NUREG/CR-7046 (NRC, 2011) andANS 2.8 (ANS, 1992) for a shore location, including:* Storm surge corresponding to the to the AEP of 1 E-6 (Section 2.4);* Coincident wind-wave activity.While NUREG/CR-7046 (NRC, 2011) does not contain specific guidance for probabilistic inputs tocombined effect scenarios, ANSI/ANS 2.8 infers that the acceptable average exceedance probabilityfor combined effect flooding should be on the order of 1E-6 for design basis floods (ANSI, 1992).While the tidal component of the probabilistic surge does not include the 10-percent exceedancehigh tide (as used as input for the deterministic surge), the combination of the exceedanceprobability of the tidal condition used with the probabilistic storm surge parameters, equals anexceedance probability of 1 E-6. Using a probabilistic input to the combined effect scenario with anexceedance probability equal to the exceedance probability of the combined effect flooding, istherefore considered conservative.2.9.1.3 Hydrostatic Force and Hydrodynamic Loading and DebrisResulting flood depths were used to develop hydrostatic force and hydrodynamic loads. The flooddepths used for the calculation of hydrodynamic, hydrostatic and impact loads include increases indepth that may occur as a result of erosion and scour.EE 14-El 6, REV. 12-183 Sp DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Hydrostatic LoadsHydrostatic loads are those caused by water above or below the ground surface, free or confinedwhich is either stagnant or moves at velocities less than 5 feet per second (fps) (ASCE, 2010).These loads are equal to the product of the water pressure multiplied by the surface area on whichthe pressure acts. The hydrostatic lateral forces (per linear foot of surface) were calculated usingASCE guidance.Flow VelocityFloodwater flow velocities include velocity components due to flooding and wind-generated waves.Estimating design flood velocities in coastal flood hazard areas is subject to considerableuncertainty. Flood velocities were estimated conservatively by assuming that floodwaters canapproach from the most critical direction relative to the site and by assuming that flow velocities canbe high (FEMA, 2011). The upper bound flood velocity (FEMA, 2011) was used to calculatehydrodynamic and impact loads.Hydrodynamic LoadsWater flowing around a building (or structure) imposes loads on the building. Hydrodynamic loads,which are a function of flow velocity and structure geometry, include frontal impact on the upstreamface, drag along the sides and suction at the downstream side. Hydrodynamic loads calculated hereused steady-state flow velocities consistent with FEMA guidance (FEMA, 2011; FEMA, 2012). Notethat the hydrodynamic loads applied above are for rigid structures. Dividing the horizontal drag forceby the building width yields a force per length (pounds per linear foot). The maximum forces at thebottom of the intakes were calculated using the area of the uniform pressure distribution.Hydrodynamic forces for low velocity flow (less than 10 feet per second) were analyzed as anequivalent hydrostatic force. Resultant force acts at a distance of H/2 above the ground.Debris Impact LoadsDebris impact loads are imposed on a building (or structure) by objects carried by moving water.The loads are influenced by where the impacted structure is located in the potential debris stream,specifically if it is:" immediately adjacent to or downstream from another building;* downstream from large floatable objects; or* among closely spaced buildings.Debris impact loads at the water surface were calculated using the guidelines described in FEMAP-259 (FEMA, 2012) and by considering debris weight recommended in ASCE-7-1 0 (ASCE, 2010).Per ASCE 7-10 (ASCE, 2010), in coastal areas debris weights may range from 1,000 to 2,000pounds. A debris object weight of 1,000 pounds is a reasonable average for flood-borne debris(representing trees, logs and other large woody debris (ASCE, 2010). A debris weight of 2,000pounds was conservatively used.EE 14-El 6, REV. 1 2-184EE 14-E16, REV. 12-184 Z NW M 14DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Wave LoadsLoads due to broken waves are similar to hydrodynamic loads from flowing or surging water. Theforces from breaking waves are the largest and most severe; therefore this load condition was usedas the design wave load (FEMA, 2011). The three breaking wave load conditions (FEMA, 2011)include: a) waves breaking against submerged small diameter piles; b) waves breaking againstsubmerged walls; and c) wave slam, where the top of the wave strikes against a vertical wall. Theterm "wave slam" refers to the action of wave crest striking the elevated portion of a structure(FEMA, 2011). Wave slam is only calculated for elevated structures.The maximum breaking wave pressures and loads on vertical walls were calculated for structures atMPS (ASCE, 2010). The calculations apply to the condition where the space behind the wall is dry(e.g., the interior of a building). The loads are applied as shown in Figure 2.9-3 (FEMA, 2011).2.9.1.1.1 Tsunami LoadingThe results of the tsunami simulations indicate that the highest predicted runup elevations in thevicinity of the MPS site result from the subaerial landslide (extreme flank failure) of the CVV. TheCVV results in maximum water levels of approximately 14.7 feet, MSL at MPS2 and MPS3 (seeSection 2.6). Fluid density of tsunami flow is assumed to be 1.2 times the density of freshwater, 2.33slugs per cubic foot, based on a sediment volume concentration of 10% in seawater (FEMA, 2008).Hydrostatic LoadsThe hydrostatic lateral forces (per linear foot of surface) were calculated at both the MPS2 andMPS3 intakes (FEMA, 2008). These loads are equal to the product of the water pressure multipliedby the surface area on which the pressure acts.Hydrodynamic ForcesHydrodynamic forces were calculated at both the MPS2 and MPS3 intakes based on FEMAguidance (FEMA, 2008). Resultant hydrodynamic forces are applied at approximately the centroid ofthe wetted surface of the structure.Impulsive ForcesImpulsive forces are caused by the leading edge of the surge water (i.e. tsunami wave) impacting astructure. The impulsive forces are conservatively estimated as 1.5 times the hydrodynamic force(FEMA, 2008).Debris Impact ForcesThe debris impact forces were calculated at both the MPS2 and MPS3 intakes based on FEMAguidance (FEMA, 2008).Two types of waterborne debris were analyzed, a log and a 20-foot heavy shipping container. Theeffective stiffness and mass of a log is 2.4x1 06 newton per meter and 450 kilograms respectively(FEMA, 2008). The effective stiffness and mass of a 20-foot long heavy shipping container is1.7xl 09 Newtons per meter and 2,400 kilograms respectively (FEMA, 2008).EE 14-El 6, REV. 12-185 Z ow DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.9.2. Results2.9.2.1. Combined Effect Flood: DeterministicThe shore location combined effects flood alternative consists of the combination of 1) the PMSS, 2)the antecedent 10% exceedance high tide, and 3) coincident wind-wave activity.The PMSS and Antecedent 10 Percent Exceedance High Tide:The maximum stillwater elevation of 25.8 feet2, MSL (Section 2.4) was used in the determination ofmaximum water level resulting from combined effects of storm surge and wind-driven wave activity.The resulting stage hydrograph (with waves) for the deterministic PMSS is shown in Figure 2.9-4.Estimated wind speed and duration based on ADCIRC results are shown on Figure 2.9-5.Coincident wind-wave activityWind wave effects at the MPS2 and MPS3 buildings were determined based on the maximumsignificant wave heights presented in Figure 2.9-7. While there will be wave effects at the MPS1reactor building and turbine building, these are no longer safety-related structures. These structureswill also significantly dissipate wave action that could otherwise affect both MPS2 and MPS3. Asshown in Figure 2.9-7, waves on the eastern portion of the site are not of substantial height (i.e. lessthan 0.5 meters) and are travelling in a northeast direction. The presence of non-safety relatedbuildings such as the MPS2 maintenance shop and other warehouse buildings would significantlydissipate any wave generation and wave energy that could impact the eastern portion of the site.The combination of wave direction and dissipation of wave energy due to the MPS1 buildings andother non-safety related structures indicate that wave effects are negligible on the southern andeastern portions of MPS. Therefore, wave effects were calculated on the western portion of the sitewhere waves will impact the MPS2 and MPS3 intakes and turbine buildings. Significant waveheights and peak periods at these locations were extracted from the deterministic PMSSADCIRC+SWAN model, as shown in Table 2.9-1. Figure 2.9-9 presents the locations of each nodefor the SWAN output locations.Reflected wave crest heights and elevations are presented in Table 2.9-2, and correspond to 17.9feet at the MPS2 intake, and 16.2 feet at the MPS3 intake, respectively. Maximum elevationsassociated with reflected wave crests are 43.7 feet, MSL at the MPS2 intake, and 42.0 feet, MSL atthe MPS3 intake. The MPS2 intake would be overtopped by approximately 4.7 feet, for a period ofapproximately 3 hours. Non-breaking wave overtopping due to the significant wave height will havea non-impulsive, (i.e.,"green water") overtopping effect. Smaller waves and broken waves againstthe intake structure will result in splash and spray on the structure, but will not result in significantovertopping effects.As shown in Figure 2.9-7, there is a significant decrease in wave height once waves propagate ontothe site grade on the western portion of MPS. The dissipation in wave height is largely due to frictionof land and uneven topography. Non-breaking wave heights near the MPS2 turbine building are2 25.8 feet MSL is inclusive of model uncertainty (i.e. 0.78 feet), wave setup, and the difference between thepeak simulated tide elevation at Watch Hill, RI and the antecedent water level of 1.026 feet: 23,3' MSL(Section 2.4) + 0.7' setup + 0.78' model uncertainty + 1.026' tidal difference = 25.8' MSL."EE 14-E16, REV. 12-186 EW DOMINION FLOODING HAZARD REEVALUATION REPORT FORZ'ACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.approximately 5.4 feet. The maximum wave height at the MPS3 Turbine building was calculatedusing the relationship of depth-limited wave heights (0.78 x depth; ANS, 1992), resulting in a waveheight of 1.4 feet. The reflected wave crest height at the MPS2 turbine building is 6.7 feet and 1.9feet at the MPS3 turbine building, as shown in Table 2.9-2. The maximum standing wave crestelevations are 32.5 feet and 27.7 feet, MSL, respectively.2.9.2.2. Combined Effect Flood: Probabilistic Storm SurgeThe combined effects for the 1 E-6 Annual Exceedance Probability Probabilistic Storm Surge resultsfrom a combination of 1) the storm surge corresponding to the 1,000,000-year recurrence interval, 2)the mean high tide with sea level rise, and 3) coincident wind-wave activity.Stillwater ElevationThe stillwater level resulting from the combination of the storm surge corresponding to the1,000,000-year recurrence interval and mean high tide with sea level rise was calculated to be 21.0feet, MSL including aleatory variability and epistemic uncertainty at the 1 E-6 AEP level and 50-yearsea level rise projections.Since wave heights were initially developed using the ADCIRC+SWAN models based on themodeled stillwater elevation of 16.8 feet, MSL, wave heights in this model are biased lower and arenot inclusive of uncertainty. Therefore, a second ADCIRC+SWAN model simulation was performedto include the uncertainty effects by adding 4.249 feet to the initial static water level. The stagehydrograph (with waves) from a representative storm that results in an elevation corresponding tothe 1,000,000-year recurrence interval inclusive of uncertainty factors is shown in Figure 2.9-10. Acomparison between the two model simulations shows that wave heights are slightly higher usingthe model inclusive of error uncertainty.Coincident Wind-Wave ActivityWave heights and periods from the probabilistic storm surge SWAN model are included in Table 2.9-3. The SWAN results indicate that at the MPS2 intake, wave heights are approximately 6.3 feet witha peak period of 4.3 seconds. At the MPS3 intake wave heights are approximately 7.0 feet with acorresponding peak period of 7.3 seconds. Reflected wave crest heights and elevations arepresented in Table 2.9-4, and correspond to 7.8 feet at the MPS2 intake, and 7.7 feet at the MPS3intake, respectively. Maximum elevations associated with reflected wave crests are 28.7 feet, MSLat the MPS2 intake, and 28.7 feet, MSL at the MPS3 intake which will not result in overtopping of theintake structures. While there may be a portion of waves breaking against the intakes, this wouldresult in splash and spray on the structures, and not result in any significant overtopping.Under the probabilistic storm surge stillwater elevation, MPS3 is not exposed to flooding as the sitegrade of 24 feet, MSL is above the stillwater elevation of 21 feet, MSL. While there will be waveeffects at MPS1, these are no longer safety-related structures, and the presence of MPS1 willsignificantly decrease wave heights affecting MPS2. As shown in Figure 10, wave heights on theeastern portion of the site are not of substantial height (i.e. less than 0.5 meters). The SWAN modeldoes not currently include detail inclusive of all MPS buildings, however, the presence of non-safetyrelated buildings (such as the MPS2 maintenance shop, MPS2 Maintenance Snubber Shop, HealthFacility, the Fire Water Tanks, Security Operations Center, and Refuel Outage Building) wouldsignificantly dissipate any wave generation and wave energy that could impact the eastern portion ofthe site (i.e. the MPS2 reactor building). Due to the dissipation of wave energy by the various non-EE 14-El 6, REV. 12-187 MW DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.safety related buildings, the wave effects are considered negligible on the eastern side of the MPS2reactor building. Therefore, wave effects were evaluated on the western portion of the site wherewaves will impact the MPS2 turbine building. Wave heights at these locations were extracted fromthe probabilistic ADCIRC+SWAN model, as shown in Table 3. As shown in Figure 9, there is asignificant reduction in wave height once the waves propagate onto the site grade. This is due tobottom friction effects and steep changes in topography. Wave heights are dissipated toapproximately 2.8 feet with a 9.1 second peak period. Reflected wave crest elevations weredetermined using the Sainflou formulas for fully head on reflected wave crests. The results arepresented in Table 4. The reflected wave crest at the MPS2 Turbine building is 3.4 feet, with amaximum elevation of 24.4 feet, MSL. While this elevation is about 2.4 feet above the flood wallelevation of 22 feet, MSL, the siding of the flood wall will prevent water resulting from splash effectsfrom entering the building (Dominion, 2014a). Splash effects are due to the reflected wave crestsovertopping the flood wall at the turbine building.2.9.2.3. Hydrostatic Force and Hydrodynamic Loading and DebrisTypical hydrostatic and hydrodynamic forces were calculated for the controlling deterministiccombined flood effects and the probabilistic combined flood effects. Calculation equations,constants, and corresponding units were described in Section 2.4. Typical hydrostatic andhydrodynamic forces were calculated at the area near MPS2, the area near MPS3, the MPS2 intakestructure and the MPS3 intake structure. The foot of the MPS2 and MPS3 intake structures is atelevation -30.0 feet, MSL (Dominion, 2014b and Dominion, 2014a, respectively).Hydrostatic LoadsThe maximum stillwater water elevation of 25.8 feet3, MSL for the deterministic combined effect floodwas used, and results in a depth of flood water of 11.8 feet at MPS2 turbine building, 1.8 feet at theMPS3 turbine building and 55.8 feet at the intake structures. The typical hydrostatic forces werecalculated as:Location Hydrostatic Load (lb/ft) Elevation (feet MSL)MPS2 Turbine Building 4,456 17.9MPS3 Turbine Building 104 24.6Intake Structures 99,636 -11.4The pressure at the bottom of the intakes was determined to be 3,571 psf.The maximum stillwater elevation of 21.0 feet, MSL for the probabilistic combined effect flood wasused and results in a depth of flood water of 7 feet at the MPS2 turbine building and 51 feet at the3 25.8 feet MSL is inclusive of model uncertainty (i.e. 0.78 feet), wave setup, and the difference between thepeak simulated tide elevation at Watch Hill, RI and the antecedent water level of 1.026 feet: 23,3' MSL(Section 2.4) + 0.7' setup + 0.78' model uncertainty + 1.026' tidal difference = 25.8' MSL.EE 14-El 6, REV. 12-188 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.intake structures. The area near MPS3 is not flooded for the probabilistic combined effect flood.The typical hydrostatic forces were calculated as:Location Hydrostatic Load (lb/ft) Elevation (feet MSL)MPS2 Turbine Building 1,568 16.3MPS3 Turbine Building N/A N/AIntake Structures 83,232 -13The pressure at the bottom of the intakes was determined to be 3,264 psf.Flow VelocityFor the intake structures, the flood depth used to calculate the flow velocity, the hydrodynamic forceand debris loads on the MPS2 and MPS3 intakes was selected based on the elevations at theconfluence of the sloped intake channel and the bay (MPS, 1989 and Dominion, 2014b). Theseelevations are -16 feet, MSL for MPS3 intake and -15 feet, MSL for MPS2 intake. An upper boundflow velocity was calculated to be 36.2 feet per second at the MPS2 intake and 36.7 feet per secondat the MPS3 intake for the deterministic combined effects flood.An upper bound flow velocity was calculated to be 19.5 feet per second at MPS2 turbine buildingand 7.6 feet per second at the MPS3 turbine building for the controlling deterministic combinedeffects flood.An upper bound flow velocity was calculated to be 15.0 feet per second at the MPS2 turbinebuilding, 34.0 feet per second at the MPS2 intake structure and 34.5 feet per second at the MPS3intake structure for the probabilistic combined effects flood.Hydrodynamic LoadsThe hydrodynamic loading analysis was calculated along various buildings throughout the site (seeTable 2.9-5) for the controlling deterministic combined effect flood. The hydrodynamic loading variesfrom 5,436 pounds per linear foot to 6,089 pounds per linear foot near MPS2 for the controllingdeterministic combined effect flood. The hydrodynamic loading varies from 135 pounds per linearfoot to 207 pounds per linear foot near MPS3 for the controlling deterministic combined effect flood.The hydrodynamic forces at MPS3 were analyzed as an equivalent hydrostatic force because theflood flow velocity was less than 10 feet per second. The hydrodynamic loading was calculated tobe 66,498 pounds per linear foot at the MPS2 intake structure and 70,023 pounds per linear foot atthe MPS3 intake structures. The hydrodynamic loading near MPS2 acts at elevation 19.9 feet, MSL.The hydrodynamic loading near MPS3 acts at elevation 24.9 feet MSL. The hydrodynamic loadingat the intake structures acts at elevation -2.1 feet, MSL.The hydrodynamic loading analysis was calculated along various buildings throughout the site (seeTable 2.9-6) for the probabilistic storm surge. The hydrodynamic loading varies from 1,962 poundsper linear foot to 2,747 pounds per linear foot near MPS2 for the controlling probabilistic combinedeffect flood. The hydrodynamic loading near MPS2 act at elevation 17.5 feet, MSL. TheEE 14-E16, REV. 12-189 A C H IRY DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.hydrodynamic loading was calculated to be 51,760 pounds per linear foot at the MPS2 intakestructure and 54,774 pounds per linear foot at the MPS3 intake structure. The hydrodynamic loadingat the intake structures acts at elevation -4.5 feet, MSL.Debris Impact LoadsTypical debris impact loads on exterior portions of structures (for debris weight of 2,000 pounds)were calculated for the deterministic PMSS as 40,560 pounds near MPS2, 3,952 pounds near MPS3and 75,296 pounds for the MPS2 intake structure and 76,336 pounds for the MPS3 intake structurefor the controlling deterministic combined effects flood.Debris impact loads on exterior portions of structures were calculated for the probabilistic stormsurge as 31,200 pounds near MPS2, 70,720 pounds at the MPS2 intake structure and 71,760pounds at the MPS3 intake structure for the probabilistic combined effects flood.Wave LoadsLoads due to non-breaking waves were calculated as the hydrostatic and hydrodynamic loadsdescribed above.For the deterministic PMSS, the typical breaking wave load on vertical walls was calculated as55,696 pounds per foot near MPS2, 1,296 pounds per foot near MPS3 and 1,245,456 pounds perfoot for the intake structures for the controlling deterministic combined effects flood.For the probabilistic storm surge, the maximum breaking wave load on vertical walls was calculatedas 19,600 pounds per foot near MPS2 and 1,040,400 pounds per foot for the intake structures forthe probabilistic combined effects flood.2.9.2.3.1 Tsunami LoadingTypical hydrostatic and hydrodynamic forces were calculated at the area near MPS2, the MPS2intake structure and the MPS3 intake structure. The inundation extent along the MPS2 Turbinebuilding was approximately 630 feet (see Section 2.6). The MPS2 intake structure is approximately80 feet wide. The MPS3 intake structure is approximately 135 feet wide.Hydrostatic LoadsThe maximum water surface elevation of 14.7 feet MSL for the tsunami at MPS2 and MPS3 (Section2.6) results in a depth of flood water of 0.7 feet at MPS2 and 44.7 feet at the intake structures. Thearea near MPS3 is not flooded due to the tsunami. The typical hydrostatic forces were calculatedas:Location Hydrostatic Load (lb/ft) Elevation (feet MSL)MPS2 Turbine Building 18.4 14.2MPS3 Turbine Building N/A N/AMPS2 Intake Structure 74,954 -15.1MPS3 Intake Structure 74,954 -15.1EE 14-El 6, REV. 12-190 MWAM JJRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYFOMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Hydrodynamic ForcesThe hydrodynamic loading was calculated to be 326 pounds per linear foot near MPS2 and 20,961pounds per linear foot at the intake structures. The hydrodynamic loading near MPS2 acts atelevation 14.5 feet, MSL. The hydrodynamic loading at the intake structures acts at elevation -7.7feet, MSL.Impulsive ForcesThe impulsive force was calculated to be 489 pounds per linear foot near MPS2 and 31,441 poundsper linear foot at the intake structures.Debris Impact ForcesThe maximum flow velocity of 1.05 meters per second (3.4 feet per second) was calculated inSection 2.6. The debris loads was calculated to be 15,515 pounds for a log and 953,593 pounds fora heavy shipping container at the MPS2 and MPS3 intake structures.2.9.3. ConclusionsA summary of combined event scenario maximum water elevations are presented in Table 2.9-7.MPS is considered to be a shore location because riverine and dam failure-induced flooding hasbeen demonstrated to be negligible. Both deterministic and a refined probabilistic combined effectflood analyses were performed for this combination:o The resulting stillwater elevation for the deterministic analysis is 25.8 feet, MSL. This elevationis the combination of the modeled stillwater elevation of 23.3 feet MSL, wave setup of 0.7 feet,uncertainty (i.e. 0.78 feet) and the difference between the peak simulated tide elevation atWatch Hill, RI and the antecedent water level of 1.026 feet, which includes applicable sea levelrise. The results of the reflected wave crest elevations at the MPS2 and MPS3 intakes are43.7 feet and 42.0 feet, MSL, respectively. Reflected wave crest elevations on the westernsides of the MPS2 and MPS3 turbine buildings are 32.5 feet and 27.7 feet, MSL, respectively.As shown in Figure 2.9-4, the peak of the deterministic surge occurs between 2.1 and 2.15days of storm simulation (i.e., where day 15 marks the start of the storm simulation withrepresentation of dynamic tide conditions).o The resulting stillwater elevation for the probabilistic analysis is 21.0 feet, MSL. This elevationis the combination of the modeled stillwater (i.e., including wave setup) elevation of 16.8 feetMSL and the uncertainty effects of 4.249 feet., which include consideration of applicable sealevel rise An additional ADCIRC+SWAN model was run for the probabilistic storm surge toaccount for model uncertainty. This model was run with a condition of adding 4.2 feet to thestarting static water level. The results of the reflected wave crest elevations at the MPS2 andMPS3 intakes are 28.8 feet and 28.7 feet, MSL, respectively. Reflected wave crest elevationsat the western side of the MPS2 turbine building is 24.4 feet, MSL. The probabilistic stormsurge stillwater elevation does not inundate MPS3. As shown in Figure 2.9-10, the peak of theprobabilistic surge occurs slightly after 2.1 days of storms simulation (i.e., where day 0 marksthe start of the storm simulation under static tide conditions).EE 14-E16, REV. 12-191 o C DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.2.9.4. References2.9.3-1 ANS, 1992. American National Standard for Determining Design Basis Flooding at PowerReactor Sites (ANSI/ANS 2.8-1992).2.9.3-2 ASCE, 2010. "Minimum Design Loads for Buildings and Other Structures," ASCE/SEI 7-10,American Society of Civil Engineers (ASCE), 2010.2.9.3-3 Dominion, 2014a. Millstone Power Station Unit 3, Final Safety Analysis Report (FSAR),Revision 25.2.2.9.3-4 Dominion, 2014b. Millstone Power Station Unit 2, Final Safety Analysis Report (FSAR),Revision 30.2.2.9.3-5 FEMA, 2008. "Guidelines for Design of Structures for Vertical Evacuation from Tsunamis,"FEMA P646, June 2008.2.9.3-6 FEMA, 2011. "Coastal Construction manual: Principles and Practices of Planning, Siting,designing, Constructing and Maintaining Residential Buildings in Coastal Areas," FEMA 55,2011.2.9.3-7 FEMA, 2012. "Engineering Principles and Practices for Retrofitting Flood-Prone ResidentialStructures," FEMA-P-259, 2012.2.9.3-8 Goda, 2010. "Random Seas and Design of Maritime Structures," Advanced Series onOcean Engineering -Volume 33, 3rd Edition, Y. Goda, 2010.2.9.3-9 MPS, 1989. "Shorefront & Dredging Plan & Details," Drawing Number 12179-BCY-11A-3SH 1, July 11, 1989.2.9.3-10 NRC, 2011. Design Basis Flood Estimation for Site Characterization at Nuclear PowerPlants -NUREG/CR-7046, United States Nuclear Regulatory Commission, November2011.2.9.3-11 USACE, 2006. Coastal Engineering Manual -Part VI, Chapter 5, "Fundamentals ofDesign," EM 1110-2-1100, U.S. Army Corps of Engineers, June 2006.EE 14-El 6, REV. 1 2-192EE 14-E16, REV. 12-192 Zac HA 14RYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.TaTable 2.9-1: Deterministic SWAN ResultsSignificant Peak WaveLocation Wave Height Period(feet) (seconds)MPS2 Intake 15.1 9.4MPS2 Turbine Building 5.4 8.9MPS3 Intake 13.9 9.4MPS3 Turbine Building 2.8 9.4ible 2.9-2: Deterministic Sainflou Reflected Wave Crest ResuReflected ReflectedWave CrestLocation Wave Crest ElevatHeight (feet) (feet, MSL)MPS2 Intake 17.9 43.7MPS2 Turbine Building 6.7 32.5MPS3 Intake 16.2 42.0MPS3 Turbine Building 1.9 27.7Table 2.9-3: Probabilistic SWAN ResultsSignificant Peak WaveLocation Wave Height Period(feet) (seconds)MPS2 Intake 6.3 4.3MPS2 Turbine Building 2.8 9.1MPS3 Intake 7.0 7.3MPS3 Turbine Building N/A N/AItsTable 2.9-4: Probabilistic Sainflou Reflected Wave Crest ResultsReflected ReflectedWave CrestLocation Wave Crest ElevatHeigt (fet) ElevationHeight (feet) (feet, MSL)MPS2 Intake 7.8 28.8MPS2 Turbine Building 3.4 24.4MPS3 Intake 7.7 28.7MPS3 Turbine Building N/A N/AEE 14-El 6, REV. 1 2-193EE 14-El 6, REV. 12-193 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 2.9-5: Hydrodynamic loading for the controlling deterministic combined effect floodBuilding Name Width in North -South Direction (feet) Depth (feet) Width to Height Ratio Cd Velocity (ft/sec) Fdyn (Ib/ft) dh Fdh (lb/ft)Auxiliary 165 11.8 14.0 1.3 19.5 5,654Bldg 118 (Control Bldg East, Unit 1) 30 11.8 2.5 1.25 19.5 5,436c0 Enclosure 80 11.8 6.8 1.25 19.5 5,436Fire Pump House 65 11.8 5.5 1.25 19.5 5,436Intake 80 11.8 6.8 1.25 19.5 5,436Turbine 315 11.8 26.7 1.4 19.5 6,089Aux Building 1.8 -7.6Control Building 91 1.8 50.6 1.75 7.6 1.575 181DWST 40 1.8 22.2 1.4 7.6 1.26 145EDG Building 60 1.8 33.3 1.5 7.6 1.35 156ESF Building 150 1.8 83.3 1.8 7.6 1.62 187Fuel Building 75 1.8 41.7 1.75 7.6 1.575 181o Hydrogen Recombiner Building 60 1.8 33.3 1.5 7.6 1.35 156Intake 95 1.8 52.8 1.75 7.6 1.575 181Maint Shop 150 1.8 83.3 1.8 7.6 1.62 187RWST 60 1.8 33.3 1.5 7.6 1.35 156Service Bldg. 1.8 --7.6 --Steam Valve Building 85 1.8 47.2 1.75 7.6 1.575 181Turbine Building 355 1.8 197.2 2 7.6 1.8 207Waste Disposal 80 1.8 44.4 1.75 7.6 -1.575 181Building Name Width in East -West Direction (feet) Depth (feet) Width to Height Ratio Cd Velocity (ft/sec) Fdyn (lb/ft) dh Fdh (Ib/ft)Auxiliary 85 11.8 7.2 1.25 19.5 5,436Bldg 118 (Control Bldg East, Unit 1) 11.8 -19.5 -(n Enclosure 175 11.8 14.8 1.3 19.5 5,654Fire Pump House 20 11.8 1.7 1.25 19.5 5,436Intake 70 11.8 5.9 1.25 19.5 5,436Turbine 11.8 19.5Aux Building 110 1.8 61.1 1.75 7.6 1.575 181Control Building 120 1.8 66.7 1.75 7.6 1.575 181DWST 40 1.8 22.2 1.4 7.6 1.26 145EDG Building 80 1.8 44.4 1.75 7.6 1.575 181ESF Building 50 1.8 27.8 1.4 7.6 1.26 145Fuel Building 1.8 --7.6 -W Hydrogen Recombiner Building 1.8 --7.6 --Intake 120 1.8 66.7 1.75 7.6 1.575 181Maint Shop 110 1.8 61.1 1.75 7.6 1.575 181RWST 60 1.8 33.3 1.5 7.6 1.35 156Service Bldg. 30 1.8 16.7 1.3 7.6 1.17 135Steam Valve Building 1.8 -7.6Turbine Building _ 1.8 -7.6Waste Disposal 115 1.8 63.9 1.75 7.6 1.575 181EE 14-E16, REV. 1 2-194EE 14-E16, REV. 12-194 ZACIHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 2.9-6: Hydrodynamic loading for the controlling probabilistic combined effect floodBuilding Name Width in North -South Direction (feet) Depth (feet) Width to Height Ratio Cd Velocity (ft/sec) Fdyn (Ib/ft)Auxiliary 165 7 23.6 1.4 15.0 2,198Bldg 118 (Control Bldg East, Unit 1) 30 7 4.3 1.25 15.0 1,962U) Enclosure 80 7 11.4 1.25 15.0 1,962(LFire Pump House 65 7 9.3 1.25 15.0 1,962Intake 80 7 11.4 1.25 15.0 1,962Turbine 315 7 45.0 1.75 15.0 2,747Aux Building 0 -Control Building 91 0DWST 40 0EDG Building 60 0ESF Building 150 0C' Fuel Building 75 0-Hydrogen Recombiner Building 60 0Intake 95 0Maint Shop 150 0RWST 60 0Service Bldg. 0Steam Valve Building 85 0Turbine Building 355 0Waste Disposal 80 0Building Name Width in East -West Direction (feet) Depth (feet) Width to Height Ratio Cd Velocity (ft/sec) Fd n lb/ftAuxiliary 85 7 12.1 1.3 15.0 2,041Bldg 118 (Control Bldg East, Unit 1) 7 -15.0 -(n Enclosure 175 7 25.0 1.4 15.0 2,198Fire Pump House 20 7 2.9 1.25 15.0 1,962Intake 70 7 10.0 1.25 15.0 1,962Turbine 7 --Aux Building 110 0Control Building 120 0DWST 40 0EDG Building 80 0ESF Building 50 0Fuel Building _ 0Co Hydrogen Recombiner Building 0Intake 120 0Maint Shop 110 0RWST 60 0Service Bldg. 30 0Steam Valve Building 0Turbine Building 0Waste Disposal 115 0EE 14-E16, REV. 12-195 wACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 2.9-7: Summary of Reflected Wave Crest Elevations at MPSDeterministic PMSS Probabilistic Storm SurgeLocationReflected ReflectedRaeflete Wave Crest Reflet Wave CrestWave Crest Wave CrestElevation ElevationHeight (feet) (feet, MSL) Height (feet) (feet, MSL)MPS2 Intake 17.9 43.7 7.8 28.8MPS2 Turbine Building 6.7 32.5 3.4 24.4MPS3 Intake 16.2 42.0 7.7 28.7MPS3 Turbine Building 1.9 27.7 N/A N/AEE 14-El 6, REV. 1 2-196EE 14-E16, REV. 12-196 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-1: MPS2 Intake Structure Layout(Figure from Dominion, 2014b)EE 14-El 6, REV. 1 2-197EE 14-El 6, REV. 12-197 9ACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-2: MPS3 Intake Structure Layout+43.0 FEET MSL-+41.2 FEET MSLLS+39.0 FEET MSL4 14.5 FEET MSL+ "11.5 FEET MSL-7.0 FEET MSLFEET MSL-30 FEET MSLINCIDENT WAVE-WAVE HEIGHT: 16.2 FEETWAVE PERIOD: 9.0 SECONDS0 5 10 15 20 25I I I I ! ISCALE-FEET(Figure from Dominion, 2014a)EE 14-E16, REV. 1 2-198EE 14-El 6, REV. 12-198 ZACHry ule E IYcDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-3: Wave load schematicDOW -uo WillTmb* fi c*"w #A014 owE(Figure from FEMA, 2011)EE 14-El 6, REV. 1 2-199EE 14-El 6, REV. 12-199 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-4: Stage Hydrograph (Surge +Wave Setup) for Deterministic PMSSWater Surface Elevation at MPS Intake~104..'Uciwa,U(USt1~a'NOW.-/15 15.25 15.5 15.7516 16.25 16.5 16.75Day (Simulated Date)17 17.25 17.5 17.75 18EE 14-E16, REV. 1 2-200EE 14-E16, REV. 12-200 Z'ACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-5: Wind Speed vs Time for the Deterministic PMSSWind Speed at MPS Intake656055504540E-35(/ 30C3: 252015105015 15.25 15.5 15.7516 16.25 16.5 16.75 17 17.25 17.5 17.75 18Days in May, 2003EE 14-E16, REV. 1 2-201EE 14-E16, REV. 12-201 ZAC lear Ee Inc.DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachiy Nuclear Engineering, Inc.Negative values indicate topographic contours.Negative values indicate topographic contours.EE 14-E16, REV. 12-202 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.lnur 2-9 Mavimujm Ainnlfirant Wava Hpinht anti f'nrrmqnnndiinn WavA flirmifinn- notorminiatir, PMQ-EE 14-E16, REV. 1 2-203EE 14-E16, REV. 12-203 ZAChrHulerEgnernIYcDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-8: Maximum Significant Wave Height and Corresponding Wave Direction- Probabilistic Storm Surge + 4.2Cgad* Irsifial I ,aEE 14-El 6, REV. 1 2-204EE 14-E16, REV. 12-204 ZAyNa iDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zschry Nuclear Engineering, Inc.EE 14-.E16, REv. 1 2-205EE 14-E16, REV. 12-205 Z'ACHRiYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Figure 2.9-10: Stage Hydrographs (Surge +Wave Setup) for Probabilistic Storm + 4.2 Feet Initial Water LevelWater Surface Elevation at MPS near Intake Structures0-wLU2221201918171615141312111098765432100.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00Time (days)EE 14-E16, REV. 1 2-206EE 14-E16, REV. 12-206 Z M" DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.3.0 COMPARISON OF CURRENT AND REEVALUATED FLOOD CAUSINGMECHANISMSThis section provides a comparison of current and reevaluated flood causing mechanisms atMPS identified in Enclosure 2 of the NRC RFI letter pursuant to Title 10 CFR 50.54(f) datedMarch 12, 2012.An assessment of the current design basis flood elevation is provided relative to the beyonddesign basis, reevaluated flood elevation. A conclusion of whether or not the current designbasis flood bounds the reevaluated flood hazard is provided for each flood mechanism at eachof MPS2 and MPS3. The FSAR for MPS3 (Dominion 2014a) is used as a source of currentdesign basis information for flooding. MPS2, constructed before MPS3, also providesinformation on current design basis information for flooding (Dominion 2014b). The MPSFlooding Walkdown report, which was reviewed and approved by the NRC, also containsinformation describing the current design basis (Dominion Nuclear Connecticut, 2012).Summary tables are provided in Table 3.0-1 and Table 3.0-2 for MPS2 and MPS3, respectively.A detailed LIP comparison at MPS3 is provided in Table 3.0-3.As discussed below, the following reevaluated external flood mechanisms exceed the currentdesign basis flood elevation at one or more areas of MPS2 and/or MPS3:* Local Intense Precipitation (see Section 3.1);* Storm Surge (see Section 3.4);* Tsunami (see Section 3.5);* Combined Effect Flooding (see Section 3.9).Interim flood protection measures for the safety-related and important-to-safety SSCs aredescribed in Section 4 of this report.EE 14-El 6, REV. 1 3-1EE 14-E16, REV. 13-1 OWIACLIRY DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.3.1. Local Intense PrecipitationCurrent Design BasisThe FSAR for MPS2 summarizes flooding due to LIP. Runoff was calculated using the RationalMethod, based on a rainfall intensity of 9.4 inches per hour (Dominion, 2014b). A total runoffflow of 60 cubic feet per second (cfs) was calculated and compared to the capacity of the stormdrain (i.e., catch basin number 9 outfall to Niantic Bay) of 8.8 cfs. Excess runoff was toaccumulate in the yard area until it reaches Elevation 14.5 feet MSL and overtop a site accessroadway, into Jordan Cove and Niantic Bay. Site grade at MPS2 is 14.0 feet MSL; therefore,the flood depth is 0.5 feet. The FSAR also notes that the MPS2 rainfall event would notproduce a more significant flood than the flood associated with the storm surge (see Section3.4).MPS3 uses HMR-51 and 52 to calculate the flooding due to LIP (Dominion, 2014a). The one-hour PMP was calculated as 17.4 inches and the six-hour PMP was calculated to be 26.0inches. The LIP analysis was performed using one-dimensional methods: a rainfall-runoffanalysis was performed using the USACE HEC-1 computer program (predecessor to HEC-HMS) and water surface elevations were calculated using HEC-2 (predecessor to HEC-RAS).The calculation assumed no credit for the storm drain system and zero infiltration. The plantarea was divided into individual drainage basins and the resulting computed runoff values wererouted through "channels" based on site topography and project features such as buildings,roadways, and railroad tracks. Computed maximum water surface elevations (in feet, MSL) foreach structure are summarized below (reprinted from Table 2.4-11 of Dominion 2014a):Auxiliary Building 24.85Control Building 24.27Emergency Generator Enclosure 24.27Main Steam Valve Building 24.85Hydrogen Recombiner Building 24.85Auxiliary Building 24.85Engineered Safety Features Building 24.85Fuel Building 24.85RWST/SIL Valve Enclosure 24.85Demineralized Water Storage Tank Block House 24.85Although some of the above water surface elevations exceed the typical door sill elevation atMPS3 of 24.50 feet MSL, no affects upon safety-related equipment were anticipated due toinsignificant leakage rates through doors.EE 14-E16, REV. 13-2 MW AM 1HIRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Reevaluation ResultsThe reevaluation used a two-dimensional hydrodynamic computer program to develop floodlevels due to the LIP. A site-specific meteorology study was performed to develop the localProbable Maximum Precipitation (PMP) as an input to the LIP analysis. The site-specific PMPvalues are more refined than generic Hydrometeorological Report Nos. 51 and 52 and are usedconsistent with the Hierarchical Hazard Assessment (HHA) approach. Resulting maximumflood depths and maximum LIP flood elevations vary by location.Maximum LIP elevations at MPS3 are below the current licensing basis values. Maximum LIPelevations at the MPS3 Control Building and the Emergency Generator Enclosure are 24.2 feetMSL and 24.0 feet MSL, respectively (compared to the current design basis value of 24.27 feetMSL at both locations). The maximum LIP elevations for the remainder of MPS3 locationsidentified above are 24.8 feet MSL or less, which is at least 0.05 feet below the current designbasis maximum LIP elevation.Maximum LIP elevations at MPS2 locally exceed the current licensing basis values. MaximumLIP elevations at MPS2 range from El. 14.3 feet MSL at Flood Gate No. 20 (Item 218) situatedat the intake structure to El. 17.5 feet MSL at Flood Gate No. 13 (Item 211) at the northernperimeter of the Containment Enclosure building. The LIP maximum flood elevations in theimmediate vicinity of MPS3 range from EI.1 4.0 feet MSL at Door WP-1 4-7A (Item. 302) to locallyas high as El. 24.8 feet MSL at Door A-24-6 (Item 357) in the alleyway south of the ServiceBuilding (Building No. 317). Table 2.1-7 presents the maximum LIP flood depths and elevationsat many door locations throughout MPS.Please refer to Section 4.0 for a discussion of interim actions that have been developed torespond to LIP flooding.3.2. Probable Maximum Flood in Streams and RiversCurrent Design BasisThe MPS3 FSAR (Dominion, 2014a) states that: "There are no major rivers or streams in thevicinity of Millstone Point, nor are there any watercourses on the site." The MPS3 FSARacknowledges the number of small brooks which flow into Jordan Cove, east of MPS, butconcludes that: "In each area, local topography precludes flooding of any portion of the sitefrom the landward side." Detailed analyses or calculations were not performed. The MPS2FSAR similarly concludes that, due to the limited drainage area of the Niantic River, riverineflooding would not result in flooding of MPS. (Dominion, 2014b).Reevaluation ResultsThe reevaluation addresses the potential for flooding at MPS due to the Probable MaximumFlood (PMF) on the small unnamed coastal stream near MPS. Riverine flooding in the NianticRiver was not analyzed because flooding from the Niantic River is expected to dissipate intoNiantic Bay and have a negligible effect on MPS.As described in Section 2.2, the PMF peak flow rate in the small coastal stream near MPS wascalculated to be 1,100 cfs. The peak PMF water surface elevation at MPS is 11.2 feet MSL,which is below MPS site grade at MPS2 of 14 feet MSL (Dominion, 2014b) and MPS3 siteEE 14-El 6, REV. 13-3 OIA C H IRY DOMINION FLOODING HAZARD REEVALUATION REPORT FORZAC H KYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.grade of 24 feet MSL (Dominion, 2014a). Therefore, the current design basis flood evaluation isconsidered to be consistent with the conclusions of the reevaluated flood hazard evaluation andfurther action is not necessary.3.3. Dam FailuresCurrent Design BasisThe FSARs for MPS2 and MPS3 do not include calculation of flood elevations due to damfailure because there are no dams on the Niantic River and no major rivers or streams in thevicinity of MPS (Dominion 2014b, Dominion 2014a).Reevaluation ResultsThe local drainage area of MPS and the 87-acre watershed contributing to a small coastalstream located approximately 200 feet east of the ISFSI were evaluated for potential damfailures as part of the flood hazard re-evaluation. The review of the databases did not identifyany dams within the local drainage basins near MPS. Additionally, any upstream dam failureflows that reach Niantic Bay will dissipate quickly in Niantic Bay (i.e., Long Island Sound) and nosignificant increase in water surface elevation in Niantic Bay is expected.Therefore, the current design basis flood evaluation is considered to be consistent with theconclusions of the reevaluated flood hazard evaluation and further action is not necessary.3.4. Probable Maximum Storm SurgeCurrent Design BasisMPS2:The MPS2 FSAR describes potential flooding due to the PMH (Dominion 2014b). The PMHwas developed using NOAA technical report HUR 7-97 which has been superseded by NWS-23. The PMH parameters are as follows:* Central pressure index = 27.26 inches (Peripheral pressure 30.56 inches)Radius of maximum winds = 48 nautical milesForward speed of translation = 15 knotsMaximum gradient wind = 123 miles per hourMaximum (overwater) wind speed = 124 miles per hour (108 knots)The track of the PMH was generally northwestward across Long Island and Long Island Sound,with landfall occurring east of New Haven, Connecticut. Other combinations of storm size andforward speed were evaluated but did not result in higher surges than the PMH presentedabove. The calculated surge components were:Wind setup = 12.41 feet;EE 14-El 6, REV. 13-4 ZA C H IRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.* Water level rise due to pressure drop = 2.20 feet;Astronomical tide = 2.50 feet;Initial rise (forerunner) = 1.00 feet;Total surge stillwater level increase = 18.11 feet.The initial rise value was based on several discussions with the Atomic Energy Commission(AEC), predecessor to the NRC. The FSAR notes that the AEC accepted a PMH total stillwatersurge elevation of 18.2 feet MSL. Wave action was also calculated and combined with stormsurge, as described in Section 3.9.MPS2 is generally protected by gates and walls to an elevation of 22.0 feet MSL. The MPS2intake structure has service water pump motors and associated equipment that are alsoprotected to an elevation of 22.0 feet MSL. The MPS2 walkdown report notes that one servicewater pump motor is protected to Elevation 26.5 feet MSL (Dominion Nuclear Connecticut,2012).MPS3:The MPS3 FSAR also uses NOAA technical report HUR 7-97 to develop the PMH (Dominion2014a). Nine different PMH candidate combinations were evaluated. The surge analysis useda computerized bathystrophic storm surge model. The highest surge resulted from thefollowing PMH parameters:Central pressure index = 27.26 inches (Peripheral pressure 30.56 inches)Radius of maximum winds = 48 nautical milesForward speed of translation = 15 knotsMaximum gradient wind = 124 to 131 miles per hour (108 to 114 knots)In addition, the surge was combined with an astronomical tide (10 percent exceedance hightide) of 2.4 feet above MSL and an initial rise of 1.0 foot. The hurricane track followed a similarpath as the MPS2 PMH. The resulting maximum surge stillwater elevation was calculated to be19.7 feet MSL. Wave action was also evaluated, as described in Section 3.9.The safety-related structures and equipment at MPS3 are protected from flooding by the sitegrade elevation of 24 feet MSL, with the exception of the circulating and service water pumphouse (i.e., intake structure). The seaward wall of the intake structure is constructed towithstand the forces of a standing wave, or clapotis, with a maximum crest elevation of 41.2 feetMSL.Reevaluation ResultsThe reevaluation performed detailed analyses of the PMH and storm surge consistent with theHHA approach. First, the PMH was developed deterministically and the resulting PMSS wascalculated using a two-dimensional hydrodynamic program, ADCIRC. As a second step,EE 14-El 6, REV. 13-5 EIW DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.refinement of the analysis was performed by completing a probabilistic storm surge calculation,supported by a site-specific hurricane meteorology and climatology study. Several additionalADCIRC simulations were performed to support a Joint Probability Method-Optimum Samplingcalculation of very low probability storm surge. At an annual exceedance probability ofapproximately 1 E-6 (i.e., return period of 1,000,000 years), the storm surge stillwater elevationat MPS was calculated to be 21.0 ft MSL. The stillwater elevation was then used as an input tothe combined effect analysis to develop final maximum flood levels at MPS-see Section 3.9.3.5. SeicheCurrent Design BasisThe FSARs for MPS2 and MPS3 do not include calculation of flood elevations due to seiche(Dominion 2014b, Dominion 2014a). The MPS2 FSAR does not discuss seiche. The MPS3FSAR sections on surge and seiche focus on storm surge.Reevaluation ResultsSeiche within two surface water bodies at MPS were analyzed for reevaluation, including: 1)the Long Island Sound and 2) the discharge basin (former quarry). Seiche was found to poseno flood risk to MPS based on the screening analysis performed using Merian's formula andliterature review. Indications of resonance that could lead to significant seiche developmentwere not found. Therefore, the current design basis flood evaluation is considered to beconsistent with the conclusions of the reevaluated flood hazard evaluation and further action isnot necessary.3.6. TsunamiCurrent Design BasisThe MPS3 FSAR notes that the North Atlantic coastline has an extremely low probability oftsunamis (Dominion 2014a). Thus, analyses of flooding and drawdown were not discussed inthe MPS3 FSAR. The MPS2 FSAR does not discuss tsunami potential (Dominion 2014b).Reevaluation ResultsThe tsunami flooding reevaluation analysis concluded that there is a regional tsunami hazardpotential at MPS. Numerical modeling was then performed to account for the complexgeography in and around Long Island Sound (see Section 2.6).Several tsunamigenic sources were assessed. The analysis indicated the highest predictedrunup elevations in the vicinity of MPS result from the subaerial landslide (extreme flank failure)of the CVV. Other tsunamigenic sources, such as the near-field submarine mass failure, do notresult in flooding at MPS.Propagation of the initial CVV surface waves across the Atlantic Ocean and into Long IslandSound results in maximum water levels of approximately 14.7 feet MSL near MPS as shownbelow:EE 14-El 6, REV. 13-6 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Maximum Water Maximum Water Maximum Depth Depth of Water Time fromSurface Surface of Water Above Above MPS3 TsunamigenicElevation at MPS Elevation on the MPS2 Average Average Site Source Event toMPS2 and MPS3 Eastern Side of Site Grade (14 ft Grade (24 ft Tsunami(feet MSL) the Site (feet MSL) MSL) Reaching MPSMSL) (hr)14.7 12.0 0.7 0.0 8.7As shown on Figure 2.6-19, inundation areas are highest in areas west of MPS2 and MPS3, inthe vicinity of the parking areas, storage buildings, and wooded areas north and west of theintake structures. MPS is protected from flooding due to high water in these areas primarily bytopography, but also by buildings not important to safety and security barriers.However, maximum flood elevations of 14.7 feet MSL are predicted at the intake structures andat MPS2. In these areas, shallow flooding above average MPS2 site grade of 14 feet ispossible (up to 0.7 feet).A warning time of at least 8 hours from the initiating tsunamigenic event is predicted.Additionally, the NOAA National Tsunami Warning Center (NTWC) provides tsunami detection,forecasts, and warnings for the U.S. including the Atlantic coast. NTWC operates 24 hours perday, with a goal of issuing tsunami warnings within five minutes of an earthquake (NTWC,2014).MPS3 is not impacted by flooding due to tsunami, owing to the higher average site grade atMPS3 of 24 ft MSL.See Section 4.0 for a discussion of interim actions planned or taken in response to tsunamihazard.3.7. Ice-Induced FloodingThe criteria for ice-induced flooding is provided in NUREG/CR-7046, Appendix D (NRC 2011).Two ice-induced events may lead to flooding at MPS and are recommended and discussed inNUREG/CR-7046, Appendix D including:1. Ice jams or dams that form upstream of a site that collapse, causing a floodwave; and2. Ice jams or dams that form downstream of a site that result in backwater flooding.The MPS3 FSAR (Dominion, 2014a) does not specifically discuss the potential for flooding dueto upstream or downstream ice jams. It does note that there is no history of ice in Niantic Bay orin the area of the circulating and service water pumphouse. The MPS3 FSAR describespreventive measures to recirculate water to prevent icing near the circulating and service waterpumphouse, as well as features of the pumphouse that prohibit ice from entering thepumphouse. The MPS2 FSAR (Dominion, 2014b) notes that the formation of ice in front of theintake structure is highly unlikely and also discusses a recirculation procedure that can be usedto limit icing.EE 14-E16, REV. 13-7 ZI CW DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Reevaluation ResultsThe re-evaluation concluded that the MPS's location at the downstream-most end of the NianticBay creates conditions which are unlikely to sustain a downstream ice dam due to both watersalinity and channel morphology. Therefore, the potential for flooding to occur at MPS as aresult of a downstream ice jam is not significant.The failure of a conservatively-estimated hypothetical upstream ice jam would not exceed theprotected elevation at MPS. The resulting rise in water level at Millstone was conservativelyestimated to be 2.9 feet (see Section 2.7).Safety-related structures at MPS3 are flood-protected up to a minimum elevation 24.0 feetexcept for the service water pumps and pump motors located in the intake structure, which areflood protected to elevation 25.5 feet (Dominion, 2014a). MPS2 is passively (i.e., does notrequire manual actions) flood protected up to the average site grade elevation of 14 feetNGVD29, except for the service water pump motors and associated electrical and controlequipment located in the intake structure, which are flood protected to elevation 22 feetNGVD29 (Dominion 2014b). The estimated freeboard to the protected elevation in the MPS2intake structure is:MPS2 Intake Structure El. 22 feet -2.9 feet = 19.1 feetand the estimated freeboard to the protected elevation in the MPS3 intake structure is:MPS3 Intake Structure El. 25.5 feet -2.9 feet = 22.6 feetThe lowest protected elevation at MPS2 is:MPS2 average site grade El. 14 feet -2.9 feet = 11.1 feetTherefore, the current design basis flood evaluation is considered to be consistent with theconclusions of the reevaluated flood hazard evaluation and further action is not necessary.3.8. Channel Migration or DiversionThe MPS3 FSAR (Dominion, 2014a) states that: "There are no channel diversions to the coolingwater supply which would have any effect on safety related equipment." Detailed analyses orcalculations were not performed. The MPS2 FSAR does not discuss channel migration ordiversion (Dominion, 2014b).Reevaluation ResultsThe reevaluation concluded that the Niantic River has not exhibited a tendency to meander.Long Island Sound also serves to dissipate high flows in the river. The geology and foundationmaterials at the site are resistant to erosion. The shoreline near MPS is protected with riprap.Given these conditions, channel migration or diversion is not considered to be a potentialcontributor to flooding at MPS. Therefore, the current design basis flood evaluation isconsidered to be consistent with the conclusions of the reevaluated flood hazard evaluation andfurther action is not necessary.EE 14-E16, REV. 13-8 DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.3.9. Combined Effect FloodingCurrent Desiqn BasisMPS2:The MPS2 FSAR describes coincident wave action combined with the PMSS elevation of 18.1feet (Dominion, 2014b). The FSAR reports the wind would be from the southeast during thepeak of the surge and MPS1 would "shield" MPS2 (other than the intake structure) from directwave attack. The maximum PMSS stillwater depth of 4.1 feet was calculated from the MPS2 Iaverage ground elevation near plant buildings of 14.0 feet MSL. A maximum, depth-limitedwave of 3.2 feet could be generated anywhere around MPS2 buildings, producing a maximumrunup elevation of 25.1 feet MSL. While this is 3.1 feet above the top of the flood gates andflood walls protecting MPS2, the minimum elevation of the exterior concrete walls of thecontainment building, auxiliary building, and warehouse building is up to elevation 54.5 feetMSL. The turbine building and the enclosure building are protected by metal siding which iscontinuous over the exterior flood walls and sealed at the interface between the flood wall andsiding with waterproof caulked connections. Therefore, the FSAR concluded that the waverunup elevation of 25.1 feet MSL does not result in adverse effects on any safety-relatedequipment.A maximum wave level of 42.5 feet MSL was calculated at the vertical wall of the intakestructure, which is open to the coast. The maximum water level inside the intake structurecaused by the standing wave condition was calculated to be 26.5 feet MSL. The analysisconsidered the profile of the incident wave, in-leakage through the louvers and system headloss. The service water system is the only safety-related system in the intake structure. Theservice water pump motors and electrical equipment are protected to elevation 22 feet MSL,with one exception: The MPS2 walkdown report notes that one service water pump is protectedthrough installation of protection for the service water motor to elevation 26.5 feet MSL(Dominion Nuclear Connecticut, 2012).The FSAR notes the intake structure and vicinity is designed to be stable against all forces fromwave action, including buoyancy and scour. The shores are protected by post-tensionedreinforced concrete walls founded upon bedrock. Areas immediately back of the walls areprotected by riprap designed for the PMH condition. The maximum pressure at the foot of theintake structure was calculated to be 3,960 pounds per square foot and the stability of thestructure was found to be stable under such conditions. The louvers in the front of the intakestructure are capable of withstanding a maximum pressure of 1,120 pounds per square foot dueto pressure from a nonbreaking wave.MPS3:The MPS3 FSAR (Dominion, 2014a) discusses the calculation of deep water waves, shallowwater waves, wave shoaling, refraction, and resulting runup. The FSAR notes that thetopography and configuration of Millstone Point protects the MPS3 area from open ocean wavesand breaking waves during the period of peak tidal flooding when the winds are from thesoutheast. The FSAR indicates very large deepwater maximum waves approaching orexceeding 100 feet are reduced to 10 to 16 feet in maximum height by the time waves near theMillstone Point shoreline.EE 14-El 6, REV. 13-9 MZWA IJRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRI~YFoo.ozoMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Three transects were used to calculate runup: two at the west side of MPS3, including theintake structure, and one at the east side of the structure. The calculation used Saville'smethod of composite slopes using wave steepness, structure type, and depth at the structuretoe as input values. The maximum calculated runup value was 23.8 feet MSL. The maximumwater level on the intake structure was calculated to be 41.2 feet MSL, based on a maximumwave height of 16.2 feet.MPS3 safety-related structures are protected by the site grade elevation of 24 feet MSL. Waveaction only effects the intake structure, which is designed to withstand the PMH, includingresultant loading. Service water pumps and pump motors inside the intake structurepumphouse are housed in individual watertight cubicles. The cubicles are watertight up toelevation 25.5 feet MSL. Access openings below 23.8 feet MSL are fitted with watertight doorscapable of withstanding the maximum hydrostatic loading. The seaward wall of the intakestructure is reinforced concrete designed to withstand the standing wave or clapotis up to 41.2feet MSL. Maximum wave loading was calculated to be 3,642 pounds per square foot.Maximum uplift pressure on the pumphouse floor was calculated to be 863 pounds per squarefoot.Reevaluation ResultsThe reevaluation evaluated combined effect flooding based on the combination of floodsprovided in NUREG/CR-7046, Appendix H. These combined effect floods were considered tobe appropriate for MPS. Riverine hazards were screened-out.The stillwater level resulting from the combination of the storm surge corresponding to the 1 E-6annual exceedance probability (i.e., 1,000,000-year-return period) and mean high tide with sealevel rise was calculated to be 21.0 feet, MSL. This elevation is the combination of the modeledstillwater (i.e., including wave setup) elevation of 16.8 feet MSL and the uncertainty effects of4.249 feet., which include consideration of applicable sea level rise. Thus, the stillwater levelincludes wind setup, aleatory variability and epistemic uncertainty and 50-year sea level riseprojections. MPS3 is not exposed to flooding as the site grade of 24 feet, MSL is above thestillwater elevation of 21 feet, MSL. Due to the dissipation of wave energy by the MPS1buildings and lack of inundation on the eastern portion of the site, the wave effects areconsidered negligible on the eastern side of the MPS2. The reflected wave crest at the westside of MPS2 is 3.4 feet, with a maximum elevation of 24.4 feet, MSL. This elevation is about2.4 feet above the flood wall elevation of 22 feet, MSL at MPS2.MPS2 and MPS3 each have intake structures west of the main building complex that are ocean-front structures. Wave heights are approximately 6.3 feet at the MPS2 intake. At the MPS3intake, wave heights are approximately 7.0 feet. Reflected wave crest heights are 7.8 feet atMPS2 intake and 7.7 feet at MPS3 intake, respectively. Maximum elevations associated withreflected wave crests are 28.8 feet, MSL outside the MPS2 intake, and 28.7 feet, MSL outsidethe MPS3 intake which will not result in overtopping of the intake structures. While there maybe a portion of waves breaking against the intakes, this would result in splash and spray on thestructures, and not result in any significant overtopping. The effect of wave action on outside ofthe intake structures on components inside the Intake Structures will be further evaluated -seeSection 4.0 for more information.Hydrostatic, hydrodynamic, and debris loading forces were conservatively developed for theProbabilistic combined effect flooding scenario, which bounds the tsunami scenario. TheseEE 14-El 6, REV. 13-10 ZI Cw DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.forces are anticipated to be localized to the area around the MPS2 and MPS3 Intake Structures,as well as the west side of MPS2. Hydrostatic forces at the Intakes are estimated to beapproximately 83,232 pounds per foot, acting at an elevation of -13 feet MSL. The pressure atthe bottom of the intakes was estimated to be 3,264 pounds per square foot.The hydrodynamic loading varies from 1,962 pounds per linear foot to 2,747 pounds per linearfoot near MPS2 for the controlling probabilistic combined effect flood. The hydrodynamicloading near MPS2 act at elevation 17.5 feet, MSL. The hydrodynamic loading was calculatedto be 51,760 pounds per linear foot at the MPS2 intake structure and 54,774 pounds per linearfoot at the MPS3 intake structure. The hydrodynamic loading at the intake structures acts atelevation -4.5 feet, MSL. The maximum breaking wave load on vertical walls was calculated as19,600 pounds per foot near MPS2 and 1,040,400 pounds per foot for the intake structures,based on a conservative upper bound water velocity up to 34.5 feet per second. Debris impactloads on exterior portions of structures were calculated as 31,200 pounds for the west side ofMPS2, 70,720 pounds at the MPS2 intake structure, and 71,760 pounds at the MPS3 intakestructure. Debris impact loads act at the water surface elevation.Impact forces for flood loading conditions are not discussed in detail for the current licensingbasis and differing methodologies used for the reevaluation make it difficult to provide specificcomparisons to the current design basis for loading. Please refer to Section 4 for moreinformation.3.10. References3.10-1 Dominion, 2014a. Millstone Power Station Final Safety Analysis Report (MPS-3 FSAR),Rev. 25.2.3.10-2 Dominion, 2014b. Millstone Power Station Final Safety Analysis Report (MPS-2 FSAR),Rev. 30.2.3.10-3 Dominion Nuclear Connecticut, 2012. Millstone Power Station Units 2 and 3, FloodingWalkdowns Results Report for Resolution of Fukushima Near-Term Task ForceRecommendation 2.3: Flooding, November, 20123.10-4 NRC, 2011. "Design Basis Flood Estimation for Site Characterization at Nuclear PowerPlants -NUREG/CR-7046", U.S. Nuclear Regulatory Commission, November 2011.3.10-5 NTWC, 2014. National Oceanic and Atmospheric Administration, National WeatherService, National Tsunami Warning Center, "User's Guide for the Tsunami WarningSystem in the U.S. National Tsunami Warning Center Area-of-Responsibility," UpdatedJuly, 2014.EE 14-El 6, REV. 1 3-11EE 14-E16, REV. 13-11 ZACIH-RYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 3.0-1: Summary of the Comparison of Current and Reevaluated Flood CausingMechanisms for MPS2Flooding Flood Critical Current Current Flood ReevaluatedMechanism Structure (Per FSAR) Design Basis Protection Flood LevelFlood Level Elevation (MSL) (MSL)(MSL) [2]Combined MPS2, except Intake 21 .3 ft 22 ft 21.0 ft at east sideEffects Structure (Stillwater plus of MPS2;wave crest) 24.4 ft at west side25.1 ft of MPS2(Wave runup)MPS2 Intake Structure 26.5 ft 22 ft Wave runup up to(standing wave except 26.5 ft (at 28.8 ft at theinside Intake exept Intake structureone serviceStructure) water pumpmotor)Storm Surge Diesel Generator & 18.2 ft 22 ft 21 .0 ft(Stillwater Intake Structure [3]Elevation)Local Containment & 14.5 ft 14.5 ft 14.3 ft to 17.5 ftIntense Enclosure Building, (22 ft if the Flood [1]Precipitation Aux Building, EDG Gates areBuildings, Control closed)Building, TurbineBuilding, IntakeStructure, Fire PumpHouse, and RSSTTsunami Intake Structures No Flooding 14.5 ft 14.7 ft(including Expected (22 ft if the Floodwave runup) Gates areclosed)Flooding in No Flooding Expected No Flooding No Flooding 11.2 ftStreams Expected Expected (No Floodingand Rivers Expected -BelowSite Grade)Upstream No Flooding Expected No Flooding No Flooding No FloodingDam Expected Expected ExpectedFailuresNotes are located on the next pageEE 14-El 6, REV. 13-12 Z'ACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 3.0-1 (Continued): Summary of the Comparison of Current and Reevaluated FloodCausing Mechanisms for MPS2Flooding Flood Critical Current Current Flood ReevaluatedMechanism Structure (Per FSAR) Design Basis Protection Flood LevelFlood Level Elevation (MSL) (MSL)(MSL) [2]Seiche No Flooding Expected No Flooding No Flooding No FloodingExpected Expected ExpectedIce Induced No Flooding Expected No Flooding No Flooding No FloodingFlooding Expected Expected ExpectedChannel No Flooding Expected No Flooding No Flooding No FloodingMigration or Expected Expected ExpectedDiversionNotes:[1] Flood level is location dependent;[2] Flood Protection Elevation 22 ft. assumes that there is sufficient warning time to closeall MPS2 flood gates;[3] Current Design Basis Flood Level considers stillwater level plus wave runup. Waveaction in conjunction with wave runup is projected to cause higher levels in somelocations and was independently calculated.EE 14-El 6, REV. 1 3-13EE 14-El 6, REV. 13-13 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 3.0-2: Summary of the Comparison of Current and Reevaluated Flood CausingMechanisms for MPS3Flooding Flood Critical Current Current Flood ReevaluatedMechanism Structure (Per FSAR) Design Protection Flood LevelBasis Flood Elevation (MSL) (MSL)Level (MSL)Combined Intake Structure 23.8 ft (near 24 ft (25.5 ft for 21.0 ft (stillwaterEffects MPS3 except SW Pumps) elevation -siteat front of grade protectsIntake against waveStructure) runup except at41.2 ft (at Intake)seaward wall 28.7 ft at Intakeof IntakeStructure)[2]Storm Surge Intake Structure 19.7 ft 24 ft (25.5 ft for 21.0 ft(Stillwater [2] SW Pumps)Elevation)Local Aux Building, Control 24.85 ft Typical door sill Up to 24.8 ft;Intense Building, DWST Block except elevation is 24.5 24.2 ft at ControlPrecipitation House, Emergency 24.27 ft at ft -No affects Building; 24.0 ft atGenerator Enclosure, Control upon safety- EmergencyESF Building, Fuel Building and related GeneratorBuilding, Hydrogen Emergency equipment EnclosureRecombiner Building, Generator anticipated forMSV Building, and Enclosure. water levels up (See Table 3.0-3)RWST/SIL Valve to El. 24.85 ft.Enclosure (See Table [1]3.0-3)Tsunami Intake Structure No flooding 24 ft (25.5 ft for 14.7 ft(including Expected SW Pumps) (No floodingwave runup) expected)Flooding in No Flooding Expected No Flooding No Flooding 11.2 ftStreams Expected Expected (No Floodingand Rivers Expected -BelowSite Grade)Upstream No Flooding Expected No Flooding No Flooding No FloodingDam Expected Expected ExpectedFailuresSeiche No Flooding Expected No Flooding No Flooding No FloodingExpected Expected ExpectedNotes are located on next pageEE 14-El 6, REV. 13-14 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 3.0-2 (Continued): Summary of the Comparison of Current and Reevaluated FloodCausing Mechanisms for MPS3Flooding Flood Critical Current Current Flood ReevaluatedMechanism Structure (Per FSAR) Design Basis Protection Flood LevelFlood Level Elevation (MSL) (MSL)(MSL)Ice Induced No Flooding Expected No Flooding No Flooding No FloodingFlooding Expected Expected ExpectedChannel No Flooding Expected No Flooding No Flooding No FloodingMigration or Expected Expected ExpectedDiversionNotes:[1] Flood level is location dependent;[2] Current Design Basis Flood Level considers stillwater level plus wave runup. Waveaction in conjunction with wave runup is projected to cause higher levels in somelocations and was independently calculated.EE 14-El 6, REV. 1 3-15EE 14-El 6, REV. 13-15 ZACHIRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.Table 3.0-3: Summary of the Comparison of Current and Reevaluated LIP for MPS3Building Current Design Reevaluated Representative RepresentativeBasis Maximum Flood FLO-2D Grid LocationMaximum Flood Elevation ElementElevation(feet, MSL) (feet, MSL)Auxiliary 24.85 24.57 43655 Aux Building DoorBuilding A-24-1Control, 24.27 24.24 45449 Control BuildingBuilding Door -C-24-1Emergency 24.27 24.08 43336 EDG BuildingGenerator Door -EG-24-1EnclosureMain Steam 24.85 24.50 50744 Steam ValveValve Building Building Door -SV-24-3Hydrogen 24.85 24.19 51892 HydrogenRecombiner Recombiner DoorBuilding HR-24-5Auxiliary 24.85 24.78 48433 Aux Building DoorBuilding A-24-6Engineered 24.85 24.20 49907 ESF BuildingSafety Door -SF-24-2FeaturesBuildingFuel Building 24.85 24.50 44888 Fuel BuildingDoor -F-24-4RWST/SIL 24.85 24.26 49042 North Side ofValve StructureEnclosureDemineralized 24.85 24.23 48170 South Side ofWater Storage StructureTank BlockHouseEE 14-El 6, REV. 1 3-16EE 14-El 6, REV. 13-16 EW DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACH-RYMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.4.0 INTERIM EVALUATION AND ACTIONSThis section identifies the interim evaluation and actions taken or planned prior to thecompletion of the integrated assessment to address any greater flooding hazards relative to theCLB. Identification of interim actions was requested in Enclosure 2 of the NRC RFI letterpursuant to Title 10 CFR 50.54(f) dated March 12, 2012.Combined Effects Flooding due to storm surge is the bounding event that exceeds the CurrentLicensing Basis Flood Level. The proposed interim evaluations and actions to address thisflooding concern are discussed in Section 4.1. Additionally, unique flooding concerns associatedwith Local Intense Precipitation resulting from the Site Specific Probable Maximum Precipitation,and a Tsunami resulting from the subaerial landslide (extreme flank failure) of the Cumbre ViejaVolcano will be discussed in Sections 4.2 and 4.3, respectively.4.1. Combined Effects FloodingThe Combined Effects Flooding considers two different approaches to storm surge (probabilisticand deterministic analysis), and investigates structural loading due to flooding. The basis for thissection of the Flood Hazard Reevaluation Report will rely on the probabilistic analysis approachonly. The Combined Effects Flooding analysis produced stillwater elevations of 21.0 ft MSL,which are above the CLB stillwater elevations for both MPS2 and MPS3, however, this level isbelow current flood protection levels.The combined effects flooding results due to wave action vary across the site. Due to thedissipation of wave energy acting on MPS1 and the lack of inundation on the east side of thesite, no significant wave activity is expected in these areas. Therefore, MPS2 is bounded undercurrent flood protection levels on the east side of the plant. MPS3 (with the exception of theIntake Structure) is unaffected by wave activity based on the general site grade of 24.0 ft MSL.The west side of the MPS2 Turbine Building and both MPS2 and MPS3 Intake structures maybe subjected to flooding levels higher than the current license basis. The reflected wave crest,imposed on top of the stillwater level, creates a periodic wave that reaches an elevation of 24.4ft MSL on the west side of the MPS2 Turbine Building and causes a BDB flooding elevation of28.6 ft MSL and 28.7 ft MSL on the MPS2 and MPS3 Intake Structures (external floodingelevations), respectively. Additionally there are loads on the west side of the MPS2 TurbineBuilding from hydrostatic loading, hydrodynamic loading, debris impact, and wave impact thatneed further evaluation. The same types of loadings are seen on the Intake structures, exceptthe loadings at the Intake Structures are of a larger magnitude and there is an additionalcombined effect loading introduced from the tsunami. Based on these results, in the event thateither one or both Intake Structures become inoperable due to Combined Effects Flooding, theplanned interim action is to invoke Millstone's FLEX strategies to respond to a loss of ultimateheat sink (UHS) event.In addition to flood gates, the west side of the MPS2 Turbine Building has a concrete wall up to22 ft MSL. On the exterior of the building, metal siding overlaps this wall and extends up to theparapet of the Turbine Building. The probabilistic storm surge is created by the ProbableMaximum Hurricane (PMH), which has wind characteristics of a Category 4/5 hurricane on theSaffir-Simpson Hurricane Wind Scale. Based on the different hurricane parameters (such asEE 14-El 6, REV. 14-1 EWA C DOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.wind, wind generated debris, etc.), in addition to flooding, relying on the siding to keep floodwaters out of the Turbine Building will be further evaluated in the Integrated Assessment.The Combined Effects hazard (caused by the PMH) would be identified in advance bymeteorological forecasting. There are current measures (procedure driven) that would beinvoked by the site to prepare for these events. Some of the existing features includeadjustments to staffing, power levels, various tank levels, and the installation of flood protectionbarriers in preparation for hurricane surge and loss of power on site.Potential flooding inside the MPS2 Turbine Building has been considered and abnormaloperations procedures have been updated to prepare for such an event. To mitigate flooding inthe Turbine Building (due to flood water bypassing floodgates) the following preparatory actionswill be taken in advance of an approaching storm in accordance with existing stationprocedures.The following equipment will be staged in the Turbine Building condenser pit:* Self-powered pumps* Electric pumps with generators" Air-driven diaphragm pumps* Hoses to direct water outsideAdditionally a BDB AFW pump will be staged at the Turbine Building Railway Access.Operations will request that sandbag walls (at least 2 feet high) be established at the followinglocations:* Outside the 125VDC Swithgear room door" Inside the Machine Shop to West Service Corridor door* Inside Service Building Hallway door between the men's locker room and the ServiceBuilding elevator area* Inside the Control Building northwest door* Outside East entrance to TDAFW Pump Room door" Outside TDAFW Pump Room to Outside double doorsTherefore, an integrated assessment will be performed in response to the results of theCombined Effects flood hazards for MPS2 and MPS3. The assessment will validateexisting and/or develop new mitigating strategies in response to combined effects floodingwhich may compromise existing flood protection and challenge SSCs in the MPS2 TurbineBuilding. Additionally, the MPS2 and MPS3 Intake Structures will be evaluated based onincreased flood levels and new/increased structural loading.4.2. Local Intense PrecipitationThe LIP calculation, following Hydrometeorological Report (HMR) No. 52 methodologyendorsed by the 10 CFR 50.54(f) letter, produced results which were above the current floodEE 14-El 6, REV. 14-2 Z 9w DOMINION FLOODING HAZARD REEVALUATION REPORT FORZACHRY oorR+-,MILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.protection levels on site for an extended period of time. As an immediate action, a site specificLIP calculation was performed, relying on modern day technology and methodology (instead ofthe HMR No. 52 methodology). The results indicated that the flood levels at MPS3 are belowthose for the current LIP model considered in the MPS3 FSAR. Based on this no further actionis required for MPS3. The results for MPS2 are above the CLB, but are bounded by flood levelsfor the CLB storm surge.The interim action will be to review, revise, and include necessary steps to enhance theapplicable station abnormal weather procedures for mitigation of a BDB potential flooding eventdue to a local intense precipitation (LIP) event. The procedure update will implement existingstation flood protection features (for example closing flood gates) based on a notification of animminent LIP event and include an entry condition (trigger event) to initiate required actions.4.3. TsunamiThe controlling tsunami wave (generated from the subaerial landslide (extreme flank failure) ofthe Cumbre Vieja Volcano) impacts the south side of the plant at an elevation of 14.7 ft MSL,which is above the current site grade of MPS2 (14.0 ft MSL). Other potential tsunami sourcesinvestigated produced results which are below the current site grade. The flood levels producedfrom the tsunami are bounded by storm surge; however the warning time on the tsunami is lessthan that of a storm surge. The tsunami is predicted to take an estimated 8.7 hours to reachMPS from the initiation of the event.The interim action will be to review, revise, and include necessary steps to enhance theapplicable station abnormal weather procedures for prevention and mitigation of a potentialflooding event due to a tsunami. The procedure updates will implement existing station floodprotection features (for example closing flood gates) based on a notification of an imminenttsunami and include an entry condition (based on a tsunami warning from NOAA's/NWSNational Tsunami Warning Center) to initiate required actions.4.4. All other Flood Causing MechanismsProbable Maximum Flood in Streams and Rivers, Dam Failure, Seiche, Ice Induced Flooding,and Channel Migration/Diversion evaluations produced results that are either below currentdesign basis, do not challenge existing flood protection features, or are not a threat to generatea new flooding condition for Millstone Power Station. Therefore, no further evaluation or interimactions are required for these flood-causing mechanisms.4.5. ConclusionBased on the scenarios discussed in Section 4.1, an Integrated Assessment will be performedthat addresses any concerns from the Combined Effects event. Sections 4.2 and 4.3 will beresolved as an interim action with improvements to station procedures currently in place. Thisand other identified interim actions will provide flood protection until the Integrated Assessmentcan be performed. All interim actions will be entered into the Dominion corrective actionprogram.EE 14-El 6, REV. 1 4-3EE 14-E16, REV. 14-3 ZACHRYDOMINION FLOODING HAZARD REEVALUATION REPORT FORMILLSTONE POWER STATION UNITS 2 AND 3Zachry Nuclear Engineering, Inc.5.0 ADDITIONAL ACTIONSThere are no additional actions beyond those discussed in Section 4.0. During the developmentof the Integrated Assessment, additional actions may be required, which will be developed andaddressed in the Integrated Assessment, or will be identified in a Condition Report andaddressed appropriately.EE 14-E16, REv. 1 5-1EE 14-El 6, REV. 15-1 Appendix AFLO-2D Technical DescriptionZachry EE 14-E16, Rev. 1Page Al of A7 FLO-2D TECHNICAL DESCRIPTION1. Model DescriptionThe FLO-2D Pro Model, Build No. 14.03.07 (FLO-2D) computer program was developed byFLO-2D Software, Inc., Nutrioso, Arizona. FLO-2D is a combined two-dimensional hydrologicand hydraulic model that is designed to simulate river and overbank flows as well as unconfinedflows over complex topography and variable roughness, split channel flows, mud/debris flowsand urban flooding. FLO-2D is a physical process model that routes rainfall-runoff and floodhydrographs over unconfined flow surfaces using the dynamic wave approximation to themomentum equation. FLO-2D moves flood volume on a series of tiles (grid) for overland flow orthrough stream segments for channel routing.Application of the model requires knowledge of the site, the watershed (and coastal, asappropriate) setting, goals of the study, and engineering judgment.2. Model ComponentsFLO-2D has components to simulate overland flow, channel/riverine flow including flow throughculverts, flow exchange between a channel and the floodplain, buildings and obstructions,rainfall-runoff and levees. The model also has components to simulate street flow, spatiallyvariable rainfall and infiltration, evaporation, sediment transport, and levee and dam breachfailures.Overland Flow SimulationThis FLO-2D component simulates overland flow and computes flow depth, velocities, impactforces, static pressure and specific energy for each grid. Predicted flow depth and velocitybetween grid elements represent average hydraulic flow conditions computed for a small timestep. For unconfined overland flow, FLO-2D applies the equations of motion to compute theaverage flow velocity across a grid element (cell) boundary. Each cell is defined by 8 sidesrepresenting the eight potential flow directions (the four compass directions and the fourdiagonal directions). The discharge sharing between cells is based on sides or boundaries inthe eight directions. At runtime, the model sets up an array of side connections that are onlyaccessed once during a time step. The surface storage area or flow path can be modified forobstructions including buildings and levees. Rainfall and infiltration losses can add or subtractfrom the flow volume on the floodplain surface.Channel Flow SimulationThis component simulates channel flow in one-dimension. The channel is represented bynatural, rectangular or trapezoidal cross sections. Discharge between channel grid elementsare defined by average flow hydraulics of velocity and depth. Flow transition betweensubcritical and supercritical flow is based on the average conditions between two channelelements. River channel flow is routed with the dynamic wave approximation to the momentumequation. Channel connections can be simulated by assigning channel confluence elements.Channel -floodplain InterfaceThis FLO-2D component exchanges channel flow with the floodplain grid elements in aseparate routine after the channel, street and floodplain flow subroutines have beenZachry EE 14-E16, Rev. 1Page A2 of A7 completed. An overbank discharge is computed when the channel conveyance capacity isexceeded. The channel-floodplain flow exchange is limited by the available exchange volumein the channel or by the available storage volume on the floodplain. Flow exchange betweenstreets and floodplain are also computed during this subroutine. The diffusive wave equation isused to compute the velocity of either the outflow from the channel or the return flow to thechannel.Floodplain Surface Storage Area Modification and Flow ObstructionThis FLO-2D component enhances detail by enabling the simulation of flow problemsassociated with flow obstructions or loss of flood storage. This is achieved by the application ofcoefficients (Area reduction factors (ARFs) and width reduction factors (WRFs)) that modify theindividual grid element surface area storage and flow width. ARFs can be used to reduce theflood volume storage on grid elements due to buildings or topography and WRFs can beassigned to any of the eight flow directions in a grid element to partially or completely obstructflow paths in all eight directions simulating floodwalls, buildings or berms. Floodplainmodifications due to buildings and/or storage basins can also be achieved by manuallymodifying grid element elevations.Rainfall -Runoff SimulationRainfall can be simulated in FLO-2D. The storm rainfall is discretized as a cumulative percent ofthe total. This discretization of the storm hyetograph is established through local rainfall data orthrough regional drainage criteria that defines storm duration, intensity and distribution. Rain isadded in the model using an S-curve to define the percent depth over time. The rainfall isuniformly distributed over the grid system and once a certain depth requirement (0.01-0.05 ft) ismet, the model begins to route flow.Hydraulic Structures and Storm DrainsHydraulic structures including bridges and culverts and storm drains may be simulated in FLO-2D using the hydraulic structures component. Discharge through round and rectangular culvertswith potential for inlet and outlet control can be computed using equations based onexperimental and theoretical results from the U.S. Department of Transportation procedures(Hydraulic Design of Highway Culverts; Publication Number FHWA-NHI-01-020 revised May,2005). The equations include options for box and pipe culverts and take into account differententrance types for box culverts (wingwall flare 30 to 70 degrees, wingwall flare 90 or 15 degreesand wingwall flare 0 degrees) and three entrance types for pipe culverts (square headwall,socket end with headwall and socket end projecting).Storm drains are modeled using the EPA SWMM Model. FLO-2D is linked to the EPA SWMMModel at runtime to exchange surface water and storm drain conveyance. FLO-2D computesthe surface water depth at grid elements prescribed with storm drains and computes thedischarge inflow to the storm drain based on input storm drain geometry. The EPA SWMMmodel then computes the pipe network flow distribution and potential return flow to the surfacewater.LeveesThis FLO-2D component confines flow on the floodplain surface by blocking one of the eightflow directions. A levee crest elevation can be assigned for each of the eight flow directions in agiven grid element. The model predicts levee overtopping. When the flow depth exceeds theZachry EE 14-E16, Rev. 1Page A3 of A7 levee height, the discharge over the levee is computed using the broad-crested weir flowequation with a 3.1 coefficient. Weir flow occurs until the tailwater depth is 85% if the headwaterdepth. At higher flows, the water is exchanged across the levees using the difference in watersurface elevations.3. Governing EquationsThe general constitutive fluid equations include the continuity equation, and the equation ofmotion (dynamic wave momentum equation):c h V-h+ a =1at e.x8bt v 8V I 8vSr = Soex gc- gatwhere h is the flow depth and V is the depth-averaged velocity in one of the eight flow directionsx. The excess rainfall intensity (i) may be nonzero on the flow surface. The friction slopecomponent Sf is based on Manning's equation. The other terms include the bed slope (S,),pressure gradient and convective and local acceleration terms.The equations of motion in FLO-2D are applied by computing the average flow velocity across agrid element boundary one direction at time. There are eight potential flow directions, the fourcompass directions (north, east, south and west) and the four diagonal directions (northeast,southeast, southwest and northwest). Each velocity computation is essentially one-dimensionalin nature and is solved independently of the other seven directions. The stability of this explicitnumerical scheme is based on strict criteria to control the magnitude of the variablecomputational timestep.4. Model Implementation4.1 AssumptionsThe inherent assumptions in a FLO-2D simulation are as follows:o Grid element is represented by a single elevation, n-value, flow deptho Steady flow for the duration of the timestepo Hydrostatic pressure distributiono 1-dimensional channel flow (no secondary currents, no vertical velocity distributions)o Rapidly varying flow such as hydraulic jumps or shock waves are smoothed out inmodel calculations. Subcritical and supercritical flow transitions are assimilated intothe average hydraulic conditions between two grid elements.4.2 Spatial and Temporal Discretization SchemesThe solution domain in the FLO-2D model is discretized into uniform, square gridelements. The differential form of the continuity and momentum equations in the FLO-Zachry EE 14-E16, Rev. 1Page A4 of A7 2D model is solved with a central, finite difference numerical scheme. This explicitalgorithm solves the momentum equation for the flow velocity across the grid elementboundary one element at a time.4.3 Interpolation MethodsGrid element elevation data is based on imported digital terrain (DTM) points orelevation points that are added to the working region. Interpolation methods available inFLO-2D include:o Using a user specified minimum number of closest DTM points within the vicinityof a grid element to compute the grid elevation;o Using a user specified radius of interpolation which defines a circle around eachgrid element node to select DTM points for use in computing the grid elementelevation; ando Using an inverse distance weighting formula exponent to assign elevations to thegrid element from the DTM points4.4 Solution Procedures and Convergence CriteriaThe solution algorithm incorporates the following steps:1. The average flow geometry, roughness and slope between two grid elements arecomputed.2. The flow depth dx for computing the velocity across a grid boundary for the nexttimestep (i+1) is estimated from the previous timestep i using a linear estimate (theaverage depth between two elements).&#xf7;X d x+33. The first estimate of the velocity is computed using the diffusive wave equation. Theonly unknown variable in the diffusive wave equation is the velocity for overland, channelor street flow.4. The predicted diffusive wave velocity for the current timestep is used as a seed in theNewton-Raphson solution to solve the full dynamic wave equation for the solutionvelocity. It should be noted that for hyperconcentrated sediment flows such as mud anddebris flows, the velocity calculations include the additional viscous and yield stressterms.5. The discharge Q across the boundary is computed by multiplying the velocity by thecross sectional flow area. For overland flow, the flow width is adjusted by the widthreduction factors (WRFs).Zachry EE 14-E16, Rev. 1Page A5 of A7
+: 6. The incremental discharge for the timestep across the eight boundaries (or upstreamand downstream channel elements) are summed,A -Q +QQQ+/-Q-0+QQ+Q,, +QO.and the change in volume (net discharge x timestep) is distributed over the availablestorage area within the grid or channel element to determine an incremental increase inthe flow depth.A~d' = A.QO At ..-A!,,&#xfd;fwhere AQx is the net change in discharge in the eight floodplain directions for the gridelement for the timestep At between time i and i + 1.7. The numerical stability criteria are then checked for the new grid element flow depth. Ifany of the stability criteria are exceeded, the simulation time is reset to the previoussimulation time, the timestep increment is reduced, all the previous timestepcomputations are discarded and the velocity computations begin again.8. The simulation progresses with increasing timesteps until the stability criteria areexceeded.The convergence criteria for the solution in FLO-2D are +/- 0.01 ft/s for velocity and +/- 0.01 ftfor depth.4.5 Timestep SelectionFLO-2D has a variable timestep that varies depending on whether the numerical stabilitycriteria are not exceeded or not. Timesteps generally range from 0.1 second to 30seconds. The model starts with the a minimum timestep equal to 1 second andincreases it until the numerical stability criteria exceeded, then the timestep isdecreased. If the stability criteria continue to be exceeded, the timestep is decreaseduntil a minimum timestep is reached. If the minimum timestep is not small enough toconserve volume or maintain numerical stability, then the minimum timestep can bereduced, the numerical stability coefficients can be adjusted or the input data can bemodified. The timesteps are a function of the discharge flux for a given grid element andits size. Small grid elements with a steep rising hydrograph and large peak dischargerequire small timesteps. Accuracy is not compromised if small timesteps are used, butthe computational time can be long if the grid system is large.5 Input Data RequirementsThe major design inputs to the FLO-2D computer model are:o Digital terrain model of the land surface,Zachry EE 14-E16, Rev. 1Page A6 of A7 o inflow hydrograph and/or rainfall data,o Manning's roughness coefficient ando Soil hydrologic properties such as the SCS curve number.The digital terrain model of the land surface is used in creating the elevation grid systemover which flow is routed. The specific design inputs depend on the modeling purpose andthe level of detail desired.6 Output DetailsFLO-2D model outputs include:o Maximum flow depths at each grid element;o Maximum velocity at each grid element;o Maximum water surface elevation at each grid element;o Time the peak water surface elevations and velocities occur;o The discharge hydrograph overtopping a levee within a grid element;o The discharge hydrograph through a hydraulic structure; ando Maximum flow depth and water surface elevation in channel segments.References1. FLO-2D Software, Inc, 2014. FLO-2D Pro Reference Manual, Nutrioso, Arizona,www.flo-2d.com2. FLO-2D Software, Inc, 2011. FLO-2D Model Validation for Version 2009 and upprepared for FEMA, June 2011.Zachry EE 14-E16, Rev. 1Page A7 of A7 Appendix BFLO-2D Grid Elements ResultsPageB1 -Grid Element NumberB2 -Ground Elevations (feet, MSL)B3 -Maximum Flow Depth (feet)B4 -Maximum Water Surface Elevation (feet, MSL)B5 -Maximum Flow Velocity (feet per second)B6 -Maximum Flow Velocity VectorB2B3B4B5B6B7Note: Pages B2 through B7 are not numbered. In lieu of numbering, page numbers are identified above.Zachry EE 14-E16, Rev. 1Page B I of B7 BI -GRID ELEMENT NUMBERFeetI B2 -GROUND ELEVATIONS (FEET, MSL)NN ____________________________NS1) MAW0 Photo (Mourn & Creed. 20128) for referenc only asA 1h0,, bukkns aO an 01,09,. aoo" .Use but"0 0,*hw0ft0.. 11000 (paw. & Creed. 2012.) for .01.0.0 to actual2) S118tegiC b00011, (Ram0) # 344 Uses same1 FLO-2D gridak00 as fter, #34301w4 111,0#393 uses sameo FLO.2D WW1040.0001 as hem, Ar 3110. Rem # 344 and ha0m1# 393 am1 001101,040in004.. map loo loplay 00,Z =:=z~~LogondLiii ~ 00000.0110050,110.11,4--L0,~00, 000,0, 00,S0000~~000~~0 125 250 500 750 1.000Feet B3 -MAXIMUM FLOW DEPTH (FEET)N ____________Feet B4 -MAXIMUM WATER SURFACE ELEVATION (FEET, MSL)r~IFeet B5 -MAXIMUM FLOW VELOCITY (FEET PER SECOND)NosN ___________________,0Feet B6 -MAXIMUM FLOW VELOCITY VECTOR Appendix CBuilding LocationsNote: Pages C2 to CIO are not numbered due to their size.Zachry EE 14-E16, Rev. 1Page C1 of C10 r? r --~ ~ -( -- t f/j ,-~-1KI1jAIS~wa STATION DIIIOZG UNOM.0 *llEEL-=VU C -/.5-0~SCALE f.200!STHE COWECTlCUT LOT IS POM R_MILLSTONE POINT
+-- I+/-0-+-t-+ HI'llA-+/- A- + ,+ H- ++ + +-t-I.." T...H-. ... .. .+ HT H -ONCIU H-H-H--F-K + H- H-~ SCALE ~ -rn-F 'ALt~I~J -C -~ ----' -'L~L.i~~i -'A
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+T---tH-+H-i+/-d--Fa--vt-~-t-J++/-+/-+-F1--p+-F%__A. H-I FI+/- t +&#xf7;&#xf7;+/-&#xf7;-+/-+/-+&#xf7;&#xf7;&#xf7;H-++/-H-+/-&#xf7;H-H-&#xf7;-H-1-CH- H~( WPTHE ='C- (S3A ~ ~ PMTP'--I --B I I
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+* 1- v -B', so' H- H,.,r ,,,-,-, -T I r+/-&#xf7;-t+&#xf7;&#xf7;&#xf7;+/-+/-4++/-H&#xf7;H-+/-r A'+I&#xf7;-++&#xf7;-*+/-+H--f+/-7-- A C " m CAF /X p-?-ASCALE f-5d Appendix DExtended Third-Party ReviewZachry EE 14-E16, Rev. 1Page Dl of Dl11 GZAGeoEnvironmental, Inc.Engineers andScientistsDecember 15, 2014File No. 01.0171382.13Zachry Nuclear Engineering, Inc.14 Lord's Hill RdStonington, CT 06378Attention: Mr. Michael KerstProject ManagerRe:Transmittal and Response to Third Party Review CommentsDominion Nuclear Flood Hazard Re-Evaluation Project
+==Dear Mr. Kerst,==
+Vanderbilt AvenueNorwood, Massachusetts02062781-278-3700FAX 781-278-5701www.gza.comThe purpose of this letter is to transmit and provide responses to the independent peer review ofthe External Flood Hazard Re-Evaluation hurricane and surge calculation methodology by Dr.Donald T. Resio (Attachment 2). It is GZA's opinion that Dr. Resio's review of External FloodHazard Re-Evaluation hurricane and surge calculation methodology used at Surry Power Station(SPS) is valid for hurricane and surge calculations for Millstone Power Station (MPS) because theanalyses were performed by GZA in parallel using nearly identical methodological approaches. Itis important to note that extension of this review to the MPS calculations is limited tomethodology only, as Dr. Resio has not specifically reviewed the MPS calculations or theassociated results. A summary of Dr. Resio's experience and qualifications is provided inAttachment 1.Dr. Resio performed a focused review of the following calculations, which represent elements ofa step-wise assessment of the coastal flooding hazard at SPS:* Calculation No. 14-028, Rev. 0 -Probable Maximum Hurricane for Surry Power Station0 Calculation No. 14-116, Rev. 0 -Deterministic Probable Maximum Storm Surge forSurry Power Station0 Calculation No. 14-117, Rev. 0 -Probabilistic Storm Surge for Surry Power StationGZA's calculations for MPS follow the identical process:0 Calculation No. 14-034, Rev. 0 -Probable Maximum Hurricane for Millstone PowerStation0 Calculation No. 14-162, Rev. 0 -Deterministic Probable Maximum Storm Surge forMillstone Power Station* Calculation No. 14-161, Rev. 0 -Probabilistic Storm Surge for Millstone Power StationIn addition the calculation documentation, Dr. Resio's review was informed by discussions withGZA during a series of teleconferences between May of 2014 and December of 2014. Thisreview culminated in the opinion summary provided as Attachment 2. In general, Dr. Resio'scomments and recommendations were considered by GZA prior to finalizing each calculationabove. A summary of Dr. Resio's comments for each calculation and GZA discussion follows:Zachry EE 14-E16, Rev. 1Page D2 of D1 1 December 15, 2014Page 2File No. 01.0171382.13CL~Calculation No. 14-028, Rev. 0 -"Probable Maximum Hurricane for Surry Power Station"Overall, Dr. Resio concurred with the employed methodology and results associated with thiscalculation. Items highlighted by Dr. Resio's review judged by GZA to require additionaldiscussion are as follows." On Page 2 of Attachment 2, Dr. Resio notes that it is difficult to validate the WRTsynthetic data as being representative of extreme conditions. GZA agrees with thisposition, and points to the fact that available historical data do not characterize theseextremes due to a paucity of data relative to the range of ammal exceedance probabilitiesbeing considered. Expert meteorologists and climatologists were retained to support thiscalculation, and their review of these data highlighted general consistency with availablehistorical data and a slight conservative bias with respect to storm intensity and generalsurge generation potential. Therefore, the synthetic WRT data are considered to be aneffective tool for characterizing extreme hurricanes affecting the SPS vicinity." On Page 3 of Attachment 2, Dr. Resio comments on sensitivity of the GPD function tothreshold selection. While GZA agrees that probability estimates derived from GPD fitscan be sensitive to the selected threshold, it is important to note that the GPD functionwas not used to develop the 3M data set; therefore, sensitivity of the GPD fits to selectedthresholds would not affect the scaling function used to calculate PMH intensities, norwould it affect maximum wind speed probabilities derived from the 3M data set itself.GPD functions were only used to evaluate error in the development of the data setextension (i.e., the 3M data set) through direct comparison to the synthetic WRT data.Calculation No. 14-116, Rev. 0 -"Deterministic Probable Maximum Storm Surge for SurryPower Station"Overall, Dr. Resio concurred with the employed methodology and results associated with thiscalculation. One item highlighted by Dr. Resio's review judged by GZA to require additionaldiscussion follows.On Page 3 of Attachment 2, Dr. Resio comments on comparing SLOSH and ADCIRC todemonstrate consistency between the models. While absolute results may differ betweenthe models due to model resolution and/or other contributing factors, similar parametersensitivities are expected. This expectation is confirmed by the results of theProbabilistic Storm Surge calculation, which shows similar parameter-specificsensitivities between SLOSH and ADCIRC despite different absolute maximumstillwater elevation estimates.Calculation No. 14-117, Rev. 0 -"Probabilistic Storm Surge for Surry Power Station"Overall, Dr. Resio concurred with the employed methodology and results associated with thiscalculation. It is noted that Dr. Resio adjusted his comments related to utilizing BayesianQuadrature to recognize the use of Response Surface methodology during a December 4, 2014telephone conversation. Items highlighted by Dr. Resio's review judged by GZA to requireadditional discussion are as follows:Zachry EE 14-E16, Rev. 1Page D3 of D1 1 December 15, 2014File No. 01.0171382.13 Page 3cz'I" On Page 4 of Attachment 2, Dr. Resio comments on demonstrating consistency inprobability mass as parameter-specific probabilities transition to the surge-frequencyresponse. GZA recognizes the desire to verify the recovery of all probability massreflective of the probability level considered in this analysis (i.e., IE-6 annual exceedanceprobability, or AEP, level). A comparison of the storm parameter definitions associatedwith this calculation and the univariate probability density functions presented in thePMH calculation shows that, while not all probability mass is directly recovered, massassociated with storm parameter responsible for extreme surge elevations has beencompletely represented. Probability mass that has not been considered is limited to morefrequent, lower-risk level characteristics (e.g., maximum wind speeds below 70 knots andstorms traveling east-of-north). Exclusion of this probability mass is analogous toexcluding contributions to the surge-frequency relationship from extra-tropical events.With respect to storm parameter combinations with probabilities smaller than 1-in-3,000,000, it is important to note that maximum wind speeds equal to or above bearing-specific PMH levels have been included in certain cases (i.e., to promote conservatism).As such, the 1-in-3,000,000 lower probability threshold is shown to be adequatelyconservative such that lower-probability storms would not contribute to the 1E-6 AEPlevel." On page 4 of Attachment 2, Dr. Resio comments on evaluating aleatory variability (i.e.,note: Figure 59, which is specifically referenced in Dr. Resio's review, has changed toFigure 60 in the final version of the calculation): This method of characterization (i.e.,via a linear functional fit, as opposed to a more complex functional fit) was necessary, asthe FEMA tool employed to distribute uncertainty requires this simplification. Asdemonstrated by Figure 60, the linear fit, which is necessitated by the uncertaintyadjustment formulations, is conservative for the majority of the wind speed range (i.e.,over-estimates the maximum wind speed difference at the 95% confidence limit between90 and approximately 138 knots).In consideration of the attached review summary and the additional discussion presented above,GZA considers the peer review of Calculation No. 14-028, 14-116 and 14-117 to be complete.As previously indicated, the methodologies used to develop these calculations are consistent withthe methodologies used to develop MPS Calculation No. 14-034, 14-162 and 14-161. Inconsideration of these consistencies, GZA also considers the peer reviews of the methodologiesused to develop MPS Calculation No. 14-034, 14-162 and 14-161 to be complete.Very truly yours,GZA GEOENVIRONMENTAL, INC.Michael A. Mobile, Ph.D.Originator/Daniel C. Stapleton, P.E.VerifierZachry EE 14-E16, Rev. 1Page D4 of D1 1 December 15, 2014Page 4File No. 01.0171382.13MAM/DCS:krAttachments1. Summary of Experience and Qualifications, Donald T. Resio2. Peer Review of Storm Surge Analysis at Surry Power Station in VirginiaOnZXZachry EE 14-E16, Rev. 1Page D5 of D1 1  . Summary of Experience and Qualifications, Donald T. ResioDr. Resio's credentials as a subject matter expert are summarized as follows:Dr. Resio is currently a Professor of Ocean Engineering at the University of North Florida (UNF) and theDirector of the Taylor Engineering Research Institute (TERI). A biographical sketch available on theNRC's website' states the following with respect to Dr. Resio's background as of 2010 (i.e., prior totaking his position at UNF): "Dr. Resio was appointed to the position of Senior Technologist (ST) inMay 1994. This position represents the highest technical rank in the DoD civil service, with less thanforty such positions authorized within the Army. Dr. Resio has been involved in performing anddirecting engineering and oceanographic research for over 30 years. He serves as the technical leader forthe Coastal Military Engineering program and is the Technical Manager (TM) for a recent successfullycompleted Advanced Technology Concept Demonstration (ACTD) for military logistics. He alsoconducts/directs research that spans a wide range of environmental and engineering areas within theCorps Civil Works Program. In this capacity he directs the MORPHOS project aimed at improving thepredictive state of the art for winds, waves, currents, surges, and coastal evolution due to storms. Mostrecently, Dr. Resio has been selected as the co-leader (with Professor Emeritus Robert Dean of theUniversity of Florida) for the IPET Task 5a (analysis of wave and surge effects, overtopping and relatedforces on levees during Katrina) and as the leader of the Risk Analysis team for the South LouisianaHurricane Protection Project, including consideration of the effects of climatic variability on hurricanecharacteristics in the Gulf of Mexico. Dr. Resio led the team that developed the new technical approachfor hurricane risk assessment along US coastlines and is now leading an effort sponsored by the NuclearRegulatory Agency to extend this approach to the estimation of hazards for Nuclear Power Plants incoastal areas. Recently, under the sponsorship of the Department of Homeland Security, Dr. Resio led ateam of researchers in the development of innovative methods for the rapid repair of levee breaches. Thiswork appears to offer new options for improved flood mitigation in many areas of the US."from information associated with the Regulatory Information Conference, 2010: http://vwww.nc.gov/public-involve/conference-symposia/ric/past/2010/bio/resiodpdfZachry EE 14-E16, Rev. 1Page D6 of D1 1 UNIVERSITYofUNFNORTH FLORIDA.Attachment 2: Peer Review of Storm Surge Analysis at Surry Power Stationin VirginiaResearch Agreement #1309-001October 30, 2014Prepared for:GZA GeoEnvironmental, Inc.249 Vanderbilt AvenueNorwood, MA 02062POC: Michael MobileI UNF Drive, Science & Engineering Building 50, Suite 3200, Jacksonville, Florida 32224An Equal OpportunitY / Equal Access /Affirmative Action InstitutionZachry EE 14-E16, Rev. 1Page D7 of D1 1 Review of Zachry Nuclear, Inc.Professor Donald T. ResioUniversity of North Florida1. IntroductionThis report presents a review of three documents pertaining to the estimation of waterlevels produced by the "controlling storm" at the Dominion/Sunry Power Station in Virginia.The first report contains material which describes the theoretical and empirical basis for thedefinition of the controlling storm and its deterministic and probabilistic attributes. The secondreport provides a deterministic analysis of the Probable Maximum Storm Surge (PMSS) resultingfrom the combination of meteorological parameters generating the PMSS at the SPS. The thirdreport provides a probabilistic analysis of storm surge for Surny Power Station (SPS) using stateof the art numerical models combined with the probabilities of meteorological parametersdeveloped in the first report. This analysis focuses on the very-low probability range of AnnualExceedance Probability (AEP) for still water at the SPS site.2. Review of Report Entitled "Probable Maximum Hurricane for Surry Power Station"This report documents the approach used in developing Probable Maximum Hurricane(PMiH) parameters for Dominion/Surry Power Station (SPS) and the approach used to developprobabilistic representations of parameters to be used in Probable Maximum Storm Surgecalculations and for probabilistic (JPM) calculations at this site.2.1 Review of PMH Parameter DevelopmentStep 1: Develop A Rationale for Selection of the Controlling Event for the PMIH.Identify the controlling meteorological event. This involved a relatively straightforward analysisof tropical and extratropical storms in this areas and it was determyned that, for the extreme rangeof low probability considered, hurricanes would be the dominant contributor to the maximumsurge at this site. This is an easy ease to make and should be readily accepted.Step 2: Develop parameters Based on NWS 23 Report. Utilize NWS 23 (1979) todevelop a set of meteorological parameters for the PMH in the area of the SPS. An initial reviewof parameters developed in the 1979 report (NWS 23) suggested that the storm characteristics forthe PMH hi this area as estimated in that study were quite intense and might not berepresentative of local conditions at the SPS, primarily due to the inclusion in NWS 23 ofheadings that do not produce maximum surges at the SPS.One factor that could use some additional discussion in this section is the treatment ofmaximum wind speed as the defining factor for storin intensity instead of the more conventional(at least in terms of storm surge generation) pressure differential. A table or graph showing therelationship between tile two (which might be a family of curves depending on latitude, stormPage 1Zachry EE 14-E16, Rev. 1Page D8 of D1 1 size and forward speed) would be extremely helpful in understanding the transition from oneparameter space to the other.Step 3: Part I Development of Deterministic PMH Parameters. Most of the stormparameters were analyzed in a fashion that produced values very consistent with the NWS 23valued. The one exception is the treatment of storm intensity. Motivated by the existence of astrong co-variation between storm heading directions and storm intensities a site-specific studywas undertaken to examine storm behavior in this area in more detail. A set of synthetic stormswas created by WindRisk Tech (WRT) using a well validated model developed by Emanuel et al.(2004). This set of storms was used to create a scaling function for storm intensity as a functionof storm heading. The maximum of this directional function was set to be equal to the NSW 23value for this area. Unfortunately, the manner in which this is written makes it sound like aprobabilistic development of a maximum wind speed rather than a dimensionless scalingfunction which is used to allow natural variability of the NWS maximum wind speed withrespect to storm heading direction. I recommend that this section be recast in terms of using theresults from the WRT simulations to scale the maximum wind speeds for hurricanes approachingfrom different directions, rather than introducing any probabilistic terms into this analysis whichmight be misunderstood. Such a misunderstanding might then necessitate a discussion ofprobability levels, sources of uncertainty and other related non-deterministic aspects of thisanalysis. The WRT methodology is robust; however, it is difficult to argue that this method forgenerating synthetic storms is correct in an absolute sense for prediction of extremes, since thedata for local comparison of such extremes is very sparse.Step 3: Part 1 Development of Probabilistic PMH Parameter Framework. This section isstraightforward in its development but the joint probability information could be displayed in aclearer fashion. An equation for p(xl,x2,x3,x4...) should be written with any jointly varyingterms written as such and graphical diagrams or equations should be presented to demonstrateclearly the final probability distributions, cumulative distributions, and complementarydistributions. Such information would really help reviewers if it were placed in the finalsummary section.Two small points that might be considered for changing are as follows:a. On Page 24, it is implied that information on central pressures is Ihnited to the1979-2012 time frame due to lack of data. Most hurricanes that passed close to the US east coasthave central pressure data back into the 1950s or so. Perhaps the intent here is to make theanalysis somewhat consistent in a climatological sense, due to changes in weather patterns, butthis is not how the comment is posed.b. The FEMA report for this area (from the USACE-Vickery study) does contain someinformation on storm sizes and should probably be referenced as a relevant source of data. Thedata there seem fairly consistent with the results presented in the WRT analyses.Step 4: Development of Joint Probabilities for Hurricane. Once the synthetic storm set isdeveloped and included within the methodology for estimating joint probabilities for the JPMapproach, a careful analysis of univariate and multivariate probabilities is performed as part ofthis report. This section is very thorough in its treatment of these different terms. One questionPage 2Zachry EE 14-E16, Rev. 1Page D9 of D11 which might be asked relative to this work is the application of tile GPD in estimating hurricanewind speeds. The GPD can be quite sensitive to the choice of the chosen threshold value. Manystudies perform analyses using at least 3 different thresholds to investigate this potential sourceof variation. Since NRC reviewers are well aware of this potential issue, it would probably be agood idea to be proactive on this issue and perform these analyses before their review. Lookingat the shape of the curve, I do not think that there will be a large sensitivity, but it should bequantified.Summary of Review of Probable Maximum Hurricane for Surry Power StationOverall, this is a very high-level analysis and is carefully performed. A few minor points asnoted should be addressed, but I do not think any of the issues raised in this review willsignificantly affect the PMH parameter or probabilistic results. Some relevant points include thefollowing:I. The upper ranges of the rmax reach relatively large sizes for all heading angles, 28.4 -41.7 nm.2. The vnax values are developed to include a storm-heading dependence which is used todeterministically scale the NWS 23 values of windspeed, which seems reasonable.3. Upper and lower bounds on forward speeds seems reasonable.4. The range of storm bearings for surge simulation seems sufficiently broad to cover theentire ranged needed.3. Review of Report 2 Entitled "Deterministic Probable Maximum Storm Surge for SurryPower Station"This report presents the deterministic analysis of the Probable Maximum Storm Surge(PMSS) for Surry Power Station, including the combined effects of storm surge, antecedentwater level, waves and river flood. It relies on report I for all estimates of all meteorologicalparameters associated with a set of hurricane parameters shown to be capable of producing thehighest storm surges reasonably expected at this site.The modeling approach seems straightforward and uses state of the art methods andmodels to perform all estimates. The SLOSH model was used as a screening tool to select asmall set of storms for detailed simulation with the ADCIRC model. There is always thepossibility of mismatched physics producing storms which are not ordered in the same sequencewhen using results from different models. The ADCIRC model is forced by a slightly differentwind field formulation than that used in the SLOSH model, however, for low values of theHolland B parameter, the net differences in winds should be relatively small. Since the valuesused here (characteristic of this region) range from 1.08 to 1.37, this should be the case here.Thus the differences in the ordering seem to relatively small. It is recommended that theADCIRC results be plotted against the SLOSH results at the sites of interest (SPS Discharge siteand SPS Intake site) to make this point graphically.Page 3Zachry EE 14-E16, Rev. 1Page D1IO of D1l1 Fifteen ADCIRC simulations were utilized to cover the range of parameter combinationsfound to produce the largest combined water levels at the Surry Power Station. Given that themaximum wind speeds are reasonably defined as a finction of storm heading, this set ofcombinations appears to cover the range needed for this purpose. A plot of the parameters in Table 4as a fiunction of the heading along with the maximum conditions defined as a function of heading inReport I would help make the point that the simulated storms constitute a set that should provide agood estimate of the maximum surges.4. Review of Report 3 Entitled "Probabilistic Storm Surges for Surry Power Station"As in Report 2, the hydrodynamic models are state of the art and are executed in astraightforward manner, so there should be no problems with the results firom these models.This report describes the effort to produce a probabilistic analysis of storm surge (JPM study)for Surry Power Station, using a Bayesian Quadrature method typical of many FEMA applicationstoday. In this approach, a joint probability of storm parameters is taken from Report 1; however,documentation of the joint probability density functions is lacking. Since the Bayesian Quadrature isused to define the probabilities of the 20 individual ADCIRC simulations, the individual probabilitymasses defined for each of the storms needs to be shown somewhere in a table hi order to enable areviewer to validate the probability estimates. These masses are determined by a Monte Carlomethod and some assumptions pertaining to the correlation lengths of different parameters. Thesecorrelation lengths should be clearly specified and hiformation on all the probability masses shouldbe included somewhere in the report, particularly since the description suggests that there might besome constraints on the event combinations. It is essential to be able to check that the complementaryprobabilities sum to one where appropriate. I tend to agree with the motivation to discretize the eventcount in defining the probabilities such that less than 1/3,000,000 is equal to zero, but it is moredefensible in a probabilistic method to let these small values (even when a number of them aresummed) actually shown to be negligible. In Section 6.2.6 (Identification of the OS Storm Set),paragraph 2 is not very clear. More information on the selection process and the application of theSurge-Stat program would be very helpfil to reviewers.The treatment of epistemic uncertainty is consistent with previous studies in this area. Thetreatment of aleatory uncertainty seems adequate and provides the magnitude of increase that seemstypical for inclusion of this type of uncertainty. The variation of surge level with vmax is clear, as isthe equation to parameterize it. However, the curve for the aleatory variation of surge elevation lookslike it is not well fit with a linear equation. Since the curve extends beyond the region of primarycontribution to the probabilities, it is recommended that Figure 59 be redone to focus on the region ofprimary contribution to the probabilities. It is verny likely that this difference in aleatory fitting is nota problem due to the range of probabilities that are affected here, but this should be checked.Donald T. Resio, Ph.D.Page 4Zachry EE 14-E16, Rev. 1Page D1 1 o D1 I Serial No. 15-106Docket Nos. 50-336/423ATTACHMENT 2MILLSTONE NTTF 2.1: FLOODING HAZARD RE-EVALUATIONINTERIM ACTIONS PLANDOMINION NUCLEAR CONNECTICUT, INC.MILLSTONE POWER STATION UNITS 2 AND 3 Serial No. 15-106Docket Nos. 50-336/423Attachment 2, Page 1 of 11Section 4.1Verify procedures are in place to initiate FLEX strategies in responseto a loss of ultimate heat sink if either one or both Millstone PowerStation (MPS) Intake Structures becomes inoperable due tocombined effects flooding.June 30, 20152 Section 4.2 Review/revise, the applicable station abnormal weather andoperational procedures for mitigation of a Beyond Design Basis June30 2015(BDB) potential flooding event due to a local intense precipitation(LIP) event for MPS Unit 2 (MPS2).3 Section 4.3 Revise applicable abnormal weather and operational procedures formitigation of a BDB potential flooding event due to a tsunami for June 30, 2015MPS2.4 Section 4.5 Perform Integrated Assessment of the flood hazards for MPS2 and March 12, 2017MPS3. (may changebased onguidance fromthe NRC)'A}}

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