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Pilgrim - Entergy'S Required Response of the Near-Term Task Force Recommendation 2.1: Flooding-Hazard Reevaluation Report
	ML15075A082
Person / Time
Site:	Pilgrim
Issue date:	03/12/2015
From:	Dent J A; Entergy Nuclear Operations
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	2.15.016
	Download: ML15075A082 (156)
	v • d • e

m EntergyEntergy Nuclear Operations, Inc.Pilgrim Nuclear Power Station600 Rocky Hill RoadPlymouth, MA 02360John A Dent, Jr.Site Vice President March 12, 2015U.S. Nuclear Regulatory Commission ATTN: Document Control Desk11555 Rockville PikeRockville, MD 20852

SUBJECT:

Entergy's Required Response of the Near-Term Task ForceRecommendation 2.1: Flooding-Hazard Reevaluation ReportPilgrim Nuclear Power StationDocket No. 50-293License No. DPR-35

REFERENCE:

NRC Letter, "Request for Information Pursuant to Title 10 of the Code ofFederal Regulations 50.54(f)

Regarding Recommendations 2.1, 2.3, and9.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident",

dated March 12, 2012 (ADAMS Accession No.ML12073A348)

LETTER NUMBER 2.15.016

Dear Sir or Madam:

On March 12, 2012, the NRC issued the referenced letter requesting information to supportthe evaluation of the NRC staff recommendations for the Near-Term Task Force (NTTF)review of the accident at the Fukushima Dai-ichi nuclear facility.

Enclosure 2 of thereferenced letter contains specific requested

actions, requested information, and requiredresponses associated with Recommendation 2.1: Flooding.

Pursuant to Required Response 2 of Enclosure 2, Entergy is providing the HazardReevaluation Report for Pilgrim Nuclear Power Station in Attachment 1.This letter contains no new regulatory commitments.

Should you have any questions concerning the content of this letter, please contact Mr.Everett (Chip) Perkins Jr. at (508) 830-8323.

AJ6(C)

PNPS Letter 2.15.016Page 2 of 3I declare under penalty of perjury that the foregoing is true and correct; executed onMarch 12, 2015.Sincerely, he .Denth'r.

Site Vice President JAD/rmb

Attachment:

Pilgrim Nuclear Power Station Flooding Hazard Reevaluation Reportcc: Mr. Daniel H. DormanRegional Administrator, Region 1U.S. Nuclear Regulatory Commission 2100 Renaissance Boulevard, Suite 100King of Prussia, PA 19406-1415 U. S. Nuclear Regulatory Commission ATTN: Director, Office of Nuclear Reactor Regulation One White Flint North11555 Rockville PikeRockville, MD 20852NRC Senior Resident Inspector Pilgrim Nuclear Power StationMs. Nadiyah Morgan, Project ManagerOffice of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop O-8C2AWashington, DC 20555Mr. John Giarrusso Jr.Planning, Preparedness

& Nuclear Section ChiefMass. Emergency Management Agency400 Worcester RoadFramingham, MA 01702U. S. Nuclear Regulatory Commission ATTN: Robert J. Fretz Jr.Mail Stop OWFN/4A15A 11555 Rockville PikeRockville, MD 20852-2378 PNPS Letter 2.15.016Page 3 of 3U. S. Nuclear Regulatory Commission ATTN: Robert L. DennigMail Stop OWFN/1iE1 11555 Rockville PikeRockville, MD 20852-2378 U. S. Nuclear Regulatory Commission ATTN: G. Edward MillerMail Stop OWFN/8B1A 11555 Rockville PikeRockville, MD 20852-2378 ATTACHMENT ToPNPS Letter 2.15.016PILGRIM NUCLEAR POWER STATIONFLOODING HAZARD REEVALUATION REPORT A20004-021 (01/30/2014)

AREVAAREVA Inc.Engineering Information RecordDocument No.:51 -9226940 -000Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportPage 1 of 152 AARIEVA20004-021 (01/3012014)

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Page 2 of 162 AAREVA20004-021 (01/30/2014)

Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportRecord of RevisionRevision Pages/Sections/

No. Paragraphs Changed Brief Description I Change Authorization 000 All Initial release.i it -ii ii iPage 3 of 152 A 20004-021 (01/30/2014)

AR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportExecutive SummaryFollowing the Fukushima Dai-ichi accident on March 11, 2011, which resulted from an earthquake andsubsequent

tsunami, the U.S. Nuclear Regulatory Commission (NRC) established the Near-Term Task Force(NTTF) to review the accident.

The NTTF subsequently prepared a report with a comprehensive set ofrecommendations.

Recommendation 2.1 Flooding Enclosure 2 of Title 10 Code of Federal Regulations (CFR)Section 50.54(f) contains a "Requested Information" section which requires a "Hazard Reevaluation Report".This report provides the requested information pursuant to flooding hazards for the Pilgrim Nuclear Power Station(PNPS).The following flood-causing mechanisms were considered in the flood hazard re-evaluation for PNPS:1. Local Intense Precipitation;

2. Flooding in Streams and Rivers;3. Dam Breaches and Failures;

4. Storm Surge;5. Seiche;6. Tsunami;7. Ice Induced Flooding, and;8. Channel Migration or Diversion.

In addition, a combined effect flood (i.e., a combination of storm surge and wave effects) was also evaluated.

Flooding due to local intense precipitation and the combined effect flood are the only flood mechanisms thatresult in inundation at PNPS; however, plant walkdowns have confirmed that inundation associated with thesetwo flood events will not impact systems, structures or components important to safety.Page 4 of 152 A 20004-021 (01/30/2014)

AR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportOverviewThis report describes the approach,

methods, and results from the re-evaluation of flood hazards at the PilgrimNuclear Power Station (PNPS). It provides the information, in part, requested by the U.S. Nuclear Regulatory Commission (NRC) to support the evaluation of the NRC staff recommendations for the Near-Term Task Force(NTTF) review of the accident at the Fukushima Dai-ichi nuclear facility.

Section 1.0 provides introductory infonnation related to the flood hazard. The section includes background regulatory information, scope, general method used for the re-evaluation, assumptions, and the elevation dataused in this report.Section 2.0 describes detailed PNPS site information, including present-day site layout, topography, and currentlicensing basis flood protection and mitigation features.

The section also identifies relevant changes since licenseissuance to the local area and watershed as well as flood protections.

Section 3.0 presents the results of the flood hazard re-evaluation.

It addresses each of the eight flood-causing mechanisms required by the NRC as well as a combined effect flood. In cases where a mechanism does not applyto the PNPS site, ajustification is included.

The section also provides a basis for inputs and assumptions,

methods, and models used.Section 4.0 compares the current and re-evaluated flood-causing mechanisms.

It provides an assessment of thecurrent licensing and design basis flood elevation to the re-evaluated flood elevation for each applicable flood-causing mechanism evaluated in Section 3.0.Section 5.0 presents an interim evaluation and actions taken or planned to address those higher flooding hazardsidentified in Section 4.0 relative to the current licensing and design basis.Section 6.0 describes the additional actions taken to support the interim actions described in Section 5.0. Notethat no additional flood mitigating actions are planned.The report also contains one appendix.

Appendix A provides large scale drawings of the local intenseprecipitation model setup and results, as well as relevant input/output files for review of the simulation.

Page 5 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable of ContentsPageSIG NATURE BLO CK .........................................................................................

...................................

2RECO RD O F REVISIO N .......................................................................................................................

3EXECUTIVE SUM M ARY .......................................................................................................................

4OVERVIEW

...........................................................................................................................................

5LIST O F TABLES ..................................................................................................................................

9LIST O F FIG URES ..............................................................................................................................

10ACRO NYM S AND ABBREVIATIO NS ...............................................................................................

121.0 INTRO DUCTIO N ......................................................................................................................

161.1 Purpose ........................................................................................................................

161.2 Scope ...........................................................................................................................

161.3 M ethod .........................................................................................................................

161.4 Assum ptions .................................................................................................................

171.5 Elevation Values ......................................................................................................

171.6 References

...................................................................................................................

172.0 INFORMATION RELATED TO THE FLOOD HAZARD .......................................................

192.1 Site Inform ation .......................................................................................................

192.1.1 Site Layout ..............................................................................................

192.1.2 Site Topography

.....................................................................................

192.2 Current Design Basis Flood Inform ation and Elevations

...........................................

192.2.1 Elevations of Safety Structures, Systems and Components

.....................

202.3 Current Flood Protection

..........................................................................................

202.3.1 Current Flood Causing M echanism s .......................................................

202.3.2 Current Flood Protection and M itigation Features

....................................

202.4 Licensing Basis Flood-Related and Flood Protection Changes .................................

212.5 W atershed and Local Area Changes .......................................................................

212.5.1 General PNPS Site Hydrological Description

...........................................

212.5.2 W atershed Changes .................................................................................

212.5.3 Local Area Changes .................................................................................

212.6 Additional Site Details -W alkdow n Results ..............................................................

212.7 References

...................................................................................................................

223.0 FLO O D HAZARD RE-EVALUATIO N ...................................................................................

253.1 Local Intense Precipitation

........................................................................................

253.1.1 M ethodology

............................................................................................

25Page 6 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable of Contents(continued)

Page3.1.2 Results ...................................................................................................

253.1.3 Conclusions

.............................................................................................

293.1.4 References

...............................................................................................

293.2 Flooding in Rivers and Streams .................................................................................

403.2.1 Methodology

............................................................................................

403.2.2 Results ...................................................................................................

403.2.3 Conclusions

.............................................................................................

413.2.4 References

................................................................................................

413.3 Dam Breaches and Failures

.....................................................................................

443.3.1 Methodology

.............................................................................................

443.3.2 Results ...................................................................................................

443.3.3 Conclusions

.............................................................................................

443.3.4 References

...............................................................................................

453.4 Storm Surge .................................................................................................................

473.4.1 Methodology

.............................................................................................

473.4.2 Results ...................................................................................................

493.4.3 Conclusions

.............................................................................................

563.4.4 References

...............................................................................................

563 .5 S e ic h e ..........................................................................................................................

8 23.5.1 Methodology

.............................................................................................

823.5.2 Results ...................................................................................................

823.5.3 Conclusions

.............................................................................................

843.5.4 References

...............................................................................................

843 .6 T s u n a m i ........................................................................................................................

8 83.6.1 Methodology

.............................................................................................

883.6.2 Results ...................................................................................................

883.6.3 Conclusions

.............................................................................................

893.6.4 References

...............................................................................................

893.7 Ice-Induced Flooding

.................................................................................................

933.7.1 Methodology

.............................................................................................

933.7.2 Results ...................................................................................................

933.7.3 Conclusions

.............................................................................................

943.7.4 References

...............................................................................................

953.8 Channel Migration or Diversion

.................................................................................

963.8.1 Methodology

.............................................................................................

96Page 7 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable of Contents(continued)

Page3.8.2 Results .................................................................................................

963.8.3 Conclusions

...........................................................................................

973.8.4 Findings

..................................................................................................

973.9 Com bined Effect Flood .............................................................................................

1003.9.1 M ethodology

............................................................................................

1003.9.2 Results ....................................................................................................

1013.9.3 Conclusions

.............................................................................................

1043.9.4 References

................................................................................................

1044.0 FLOOD PARAMETERS AND COMPARISON WITH CURRENT LICENSING BASIS ............

1274.1 Summary of Current Licensing Basis and Flood Re-Evaluation Results .....................

1294.1.1 Local Intense Precipitation

.........................................................................

1294.1.2 Flooding in Streams and Rivers .................................................................

1294.1.3 Dam Breaches and Failures

......................................................................

1294.1.4 Storm Surge ..............................................................................................

1304.1.5 Seiche .......................................................................................................

1304.1.6 Tsunam i .....................................................................................................

1304.1.7 Ice Induced Flooding

.................................................................................

1304.1.8 Channel M igration or Diversion

..................................................................

1304.1.9 Com bined Effect ........................................................................................

1304.2 References

.................................................................................................................

1365.0 INTERIM EVALUATION AND ACTIONS TAKEN OR PLANNED ...........................................

1375.1 Im pacts of Re-Evaluated Flood Elevations

.................................................................

1375.1.1 LIP Affected Locations

...............................................................................

1375.1.2 Com bined Effect Flood Affected Locations

................................................

1395.2 Conclusions

................................................................................................................

1395.3 References

.................................................................................................................

1396.0 ADDITIO NAL ACTIONS .........................................................................................................

142APPENDIX A : LOCAL INTENSE PRECIPITATIO N .....................................................

A-1Page 8 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportList of TablesPageTA BLE 3-1: LIP M O D EL R ESULTS ...............................................................................................

31TABLE 3-2: MANNING'S N VALUES FOR SELECTED LAND COVER CATEGORIES

..................

32TABLE 3-3: CURVE NUMBER (CN) VALUES FOR SELECTED LAND COVER CATEGORIES

........

32TABLE 3-4: PMH PARAMETERS AND PARAMETER RANGES PER NWS 23 FOR PNPS ....... 58TABLE 3-5: RECOMMENDED PMH PARAMETERS FOR PNPS VICINITY BASED ON SITE-SPECIFIC M ETEOROLOGY STUDY ..............................................................................

59TABLE 3-6: FORWARD (I.E., TRANSLATIONAL)

SPEEDS FOR EIGHT OF THE TOP TEN EXTRA-TROPICAL STORMS IN THE PNPS VICINITY

.............................................................

60TABLE 3-7: PMH CONFIGURATIONS USED IN REFINEMENT SIMULATIONS WITH ADCIRC ANDA D C IR C + S W A N .................................................................................................................

6 1TABLE 3-8: SIMULATED MAXIMUM STILL WATER AND TOTAL WATER SURFACE ELEVATIONS FO R ST O R M ID 3397 ...................................................................................................

6 1TABLE 3-9: RANGES OF EVALUATED PMWS BEARING AND FORWARD SPEED ....................

62TABLE 3-10: SIMULATED MAXIMUM STILL WATER AND TOTAL WATER SURFACE ELEVATIONS FOR STORM IDS ET_1, ET_2 AND ET_3 ...................................................................

62TABLE 3-11: SUMMARY OF EXTREME WAVE CONDITIONS AT WIS STATIONS NEAR PNPS... 106TABLE 3-12: COUPLED ADCIRC+SWAN SIMULATION RESULTS -PMH ....................................

106TABLE 3-13: COUPLED ADCIRC+SWAN SIMULATION RESULTS-PMWS ..................................

107TABLE 3-14: NEARSHORE/SHALLOW WATER SWAN SIMULATION RESULTS-PMH ...............

108TABLE 3-15: NEARSHORE/SHALLOW WATER SWAN SIMULATION RESULTS -PMWS ............

109TABLE 3-16: PNPS INTAKE W AVE EFFECTS ................................................................................

110TA B LE 3-17: P N PS P M H R U N U P ....................................................................................................

110TABLE 4-1: FLOOD ELEVATION COM PARISON ............................................................................

131TABLE 4-2: LOCAL INTENSE PRECIPITATION

..............................................................................

132TABLE 4-3: LIP FLOOD DEPTHS AND DURATIONS AT SELECT LOCATIONS

.............................

134TABLE 4-4: CO M BINED EFFECT FLOO D .......................................................................................

135Page 9 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportList of FiguresPageFIG U RE 2-1: SITE LO CATIO N M A P ..............................................................................................

23FIGURE 2-2: SITE TOPOGRAPHY AND LAYOUT ........................................................................

24FIGURE 3-1: PNPS IMPORTANT LOCATIONS

..............................................................................

33FIGURE 3-2: FLO-2D COMPUTATIONAL BOUNDARY

.................................................................

34FIGURE 3-3: FLO-2D MANNING'S COEFFICIENT ASSIGNMENT

................................................

35FIGURE 3-4: FLO-2D CURVE NUMBER SELECTIONS

.................................................................

36F IG U R E 3-5: LIP H Y ET O G RA P H .......................................................................................................

37FIGURE 3-6: PNPS MAXIMUM WATER SURFACE ELEVATIONS (FEET, NAVD88) ....................

38FIGURE 3-7: SUPERCRITICAL FLOW REGIME ............................................................................

39FIGURE 3-8: PLYMOUTH COUNTY MASSACHUSETTS TOPOGRAPHIC MAP ...........................

42FIGURE 3-9: HYDROLOGIC UNITS NEAR PNPS .........................................................................

43FIGURE 3-10: DAMS WITHIN THE SOUTH COASTAL AND CAPE COD WATERSHED BASINS .... 46F IG U R E 3-11: S IT E S ETT IN G ............................................................................................................

63FIGURE 3-12: NWS 23 LOCATOR MAP WITH PNPS MILE POST IDENTIFIED

...........................

64FIGURE 3-13: HURDAT2 STORM TRACKS AND SIX-HOUR POSITIONS

...................

65FIGURE 3-14: PEAK-OVER-THRESHOLD AND GENERALIZED PARETO DISTRIBUTION FUNCTIONAL FIT TO WRT MAXIMUM WIND SPEED DATA WITHIN THE PNPSS U B R E G IO N ......................................................................................................................

6 6FIGURE 3-15: DISTRIBUTION OF MAXIMUM WIND SPEED (VM) FROM THE WRT DATA WITHINT H E P N PS S U BR EG IO N ...............................................................................................

67FIGURE 3-16: COMPARISON OF MAXIMUM WIND SPEED FROM THE WRT DATA TO THERESULTING DISTRIBUTION DERIVED VIA THE KERNEL METHOD ...........................

68FIGURE 3-17: DISTRIBUTION OF STORM BEARING (FDIR) FROM THE WRT DATA WITHIN THEP N P S S U B R E G IO N ...........................................................................................................

6 9FIGURE 3-18: DISTRIBUTION OF FORWARD SPEED (FSPD) FROM THE WRT DATA WITHIN THEP N P S S U B R E G IO N ...........................................................................................................

70FIGURE 3-19: MAXIMUM WIND SPEED AS A FUNCTION OF STORM BEARING AT FIXEDRETURN PERIODS OF 100, 1,000, 10,000, 100,000 AND 1,000,000 YEARS ...............

71FIGURE 3-20: STORM TRACKS ASSOCIATED WITH HISTORICALLY-SIGNIFICANT EXTRA-TROPICAL EVENTS IN THE VICINITY OF PNPS ........................................................

72FIGURE 3-21: PMW S RADIAL SELECTION

..................................................................................

73FIGURE 3-22: PMW S W IND AND PRESSURE FIELDS ...............................................................

74FIGURE 3-23: SLOSH MODEL BASIN -OUTPUT CELL LOCATION

............................................

75FIGURE 3-24: SENSITIVITY OF SLOSH-SIMULATED STORM SURGE TO PMH RADIUS TOMAXIMUM W INDS AND STORM BEARING .................................................................

76FIGURE 3-25: SENSITIVITY OF SLOSH-SIMULATED STORM SURGE TO PMH LANDFALLLOCATIO N AND STORM BEARING ..............................................................................

77Page 10 of 152 AAR EVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFIGURE 3-26: SENSITIVITY OF SLOSH-SIMULATED STORM SURGE TO PMH FORWARD SPEEDA N D STO R M B EA R IN G .................................................................................................

78FIGURE 3-27: PMH STORM TRACKS EVALUATED DURING SENSITIVITY ASSESSMENT WITHS L O S H ...............................................................................................................................

7 9FIGURE 3-28:FIGURE 3-29:FIGURE 3-30:FIGURE 3-31:FIGURE 3-32:FIGURE 3-33:FIGURE 3-34:FIGURE 3-35:FIGURE 3-36:FIGURE 3-37:FIGURE 3-38:FIGURE 3-39:FIGURE 3-40:FIGURE 3-41:FIGURE 3-42:ADCIRC/ADCIRC+SWAN FINITE ELEMENT MESH FOR PNPS -PNPS VICINITY..

80PM W S STO R M TRA CKS ........................................................................................

81C A P E C O D BA Y ......................................................................................................

86PNPS INTAKE AND DISCHARGE CHANNELS

......................................................

87TSUNAMIGENIC SOURCE LOCATIONS

..............................................................

91GULF OF MAINE BATHYM ETRY ...........................................................................

92PN PS SH O R ELIN E IN 1977 .....................................................................................

98PN PS SH O R ELIN E IN 2012 .....................................................................................

99W IS W AVE GAG E LO CATIO NS ...............................................................................

111COUPLED ADCIRC+SW AN COMPUTATION

...........................................................

112ADCIRC MODEL M ESH ELEVATIONS

.....................................................................

113COUPLED ADCIRC+SWAN SIMULATION OUTPUT LOCATIONS

-PMH ...............

114COUPLED ADCIRC+SWAN SIMULATION OUTPUT LOCATIONS

-PMWS ...........

115NEARSHORE/SHALLOW WATER SWAN SIMULATION MODEL ELEVATIONS

..... 116NEARSHORE/SHALLOW-WATER SWAN SIMULATION INPUT WATER LEVEL -P M H .................................................................................................................................

1 1 7FIGURE 3-43: NEARSHORE/SHALLOW-WATER SWAN INPUT WIND SPEED AND WINDD IR E C T IO N -P M H ...........................................................................................................

118FIGURE 3-44: NEARSHORE/SHALLOW-WATER SWAN SIMULATION INPUT WATER LEVEL -P M W S ..............................................................................................................................

1 1 9FIGURE 3-45: NEARSHORE/SHALLOW-WATER SWAN INPUT WIND SPEED AND WAVED IR E C T IO N -P M W S ........................................................................................................

120FIGURE 3-46: PEAK SIGNIFICANT WAVE HEIGHT- PMH ............................................................

121FIGURE 3-47: PEAK SIGNIFICANT WAVE HEIGHT- PMWS .........................................................

122FIGURE 3-48: NEARSHORE/SHALLOW-WATER SWAN SIMULATION OUTPUT LOCATIONS

-PMH& P M W S ...........................................................................................................................

1 2 3FIG URE 3-49: TRANSECT LO CATIO NS ..........................................................................................

124FIGURE 3-50: NEARSHORE/SHALLOW-WATER SWAN SIMULATION WAVE BREAKING ZONE -P M H .................................................................................................................................

1 2 5FIGURE 3-51: NEARSHORE/SHALLOW-WATER SWAN SIMULATION WAVE BREAKING ZONE -P M W S ...............................................................................................................................

1 2 6FIGURE 5-1: LIP SELECT LOCATIONS ON SOUTH SIDE OF PLANT ............................................

140FIG URE 5-2: TURBINE BUILDING FLOW PATH .............................................................................

141Page 11 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportAcronyms and Abbreviations Acronym/Abbreviation Description ADCIRC Advanced Circulation ADCIRC+SWAN Advanced Circulation plus Simulating Waves Nearshore AGMTHAG Atlantic and Gulf of Mexico Tsunami Hazard Assessment GroupANSI American National Standards Institute ARC Antecedent Rainfall Condition ASCE American Society of Civil Engineers ASCII American Standard Code for Information Interchange ASPRS American Society for Photogrammetry and Remote SensingAWL Antecedent Water LevelCAP Corrective Action ProgramCEM Coastal Engineering ManualCFR Code of Federal Regulations CLB Current License BasisCN Curve NumberCO-OPS Center for Operational Oceanographic Products and ServicesDEM Digital Elevation ModelDTM Digital Terrain ModelDUT Delft University of Technology EDG Emergency Diesel Generator EVA Extreme Value AnalysisFEMA Federal Emergency Management AgencyFSAR Final Safety Analysis ReportGIS Geographic Information SystemsPage 12 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportAcronym/Abbreviation Description GPD Generalized Pareto Distribution HEC Hydrologic Engineering CenterHELB High Energy Line BreakHHA Hierarchical Hazard Assessment HMR Hydrometeorological ReportHUC Hydrologic Unit CodeHURDAT Hurricane DatabaseIJC International Joint Commission IPEEE Individual Plant Examination of External EventsISFSI Independent Spent Fuel Storage Installation ISG Interim Staff Guidance (NRC)LiDAR Light Detection and RangingLIP Local Intense Precipitation MA Massachusetts MSL Mean Sea LevelMLW Mean Low WaterNAD83 North American Datum of 1983NAVD88 North American Vertical Datum of 1988NCDC National Climatic Data CenterNEH National Engineering HandbookNGDC National Geophysical Data CenterNGS National Geodetic SurveyNGVD29 National Geodetic Vertical Datum of 1929NHC National Hurricane CenterPage 13 of 152 AAR EVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportAcronym/Abbreviation Description NHD National Hydrography DatabaseNID National Inventory of DamsNOAA National Oceanic and Atmospheric Administration NRC U.S. Nuclear Regulatory Commission NRCS Natural Resources Conservation ServiceNTTF Near-Term Task ForceNWS National Weather ServicePDF Probable Density FunctionPDH Probable Density Histogram PMF Probable Maximum FloodPMH Probable Maximum Hurricane PMP Probable Maximum Precipitation PMSS Probable Maximum Storm SurgePMT Probable Maximum TsunamiPMWS Probable Maximum Wind StormPNPS Pilgrim Nuclear Power StationPOT Peak over Threshold RMSE Root Mean Square ErrorSCS Soil Conservation ServiceSLOSH Sea, Lakes and Overland SurgesSLR Sea Level RiseSMF Submarine Mass FailureSSCs Structures, Systems and Components SWAN Simulating Waves Nearshore Page 14 of 152 AAR EVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportAcronym/Abbreviation Description USACE U.S. Army Corps of Engineers USGS U.S. Geological SurveyUTC Coordinated Universal TimeWIS Wave Information StudiesWSEL Water Surface Elevation WRT Wind Risk Tech1-min, 10-m I-minute, 10-meterfdir forward direction fspd forward speedfps feet per secondHg Mercurykm kilometer kt knotsmb millibars mi2 square milemph miles per hourmxw average wind speednm nautical milespsf pounds per square footpsi pounds per square inchPage 15 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report

1.0 INTRODUCTION

Following the Fukushima Dai-ichi accident on March 11, 2011, which resulted from an earthquake andsubsequent

tsunami, the U.S. Nuclear Regulatory Commission (NRC) established the Near-Term Task Force(NTTF) to review the accident.

The NTTF subsequently prepared a report with a comprehensive set ofrecommendations.

In response to the NTTF recommendations, and pursuant to Title 10 of the Code of Federal Regulations (CFR),Section 50.54(0, the NRC has requested information from all operating power licensees (NRC 2012). Thepurpose of the request is to gather information to re-evaluate seismic and flooding hazards at U.S. operating reactor sites.The Pilgrim Nuclear Power Station (PNPS), located on the western shore of Cape Cod Bay in the Town ofPlymouth, Plymouth County Massachusetts, is one of the sites required to submit information.

The NRC information request to flooding hazards requires licensees to re-evaluate their sites using updatedflooding hazard information and present-day regulatory guidance and methodologies and then compare the resultsagainst the site's current licensing basis (CLB) for protection and mitigation from external flood events.1.1 PurposeThis report satisfies the "Hazard Reevaluation Report" Request for Information pursuant to 10 CFR 50.54(f) bythe NRC dated November 12, 2012, NTTF Recommendation 2.1 Flooding Enclosure 2.The report describes the approach, methods and results from the re-evaluation of flood hazards at PNPS.1.2 ScopeThis report addresses the eight flood-causing mechanisms and a combined effect flood, identified in Attachment Ito Enclosure 2 of the NRC information request (NRC 2012). No additional flood causing mechanisms wereidentified for PNPS.Each of the re-evaluated flood causing mechanisms and the potential effects on the PNPS site are described inSections 3.0 and 4.0 of this report.1.3 MethodThis report follows the Hierarchical Hazard Assessment (HHA) approach, as described in NUREG/CR-7046, "Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States ofAmerica" (NRC 2011), NRC Interim Staff Guidance (ISG), as appropriate, and their supporting reference documents.

A HIHA consists of a series of stepwise, progressively more refined analyses to evaluate the hazard resulting fromphenomena at a given nuclear power plant site to structures, systems and components (SSCs) important to safetywith the most conservative plausible assumptions consistent with the available data. The HHA starts with themost conservative, simplifying assumptions that maximize the hazards from the maximum probable event. If theassessed hazards result in an adverse effect or exposure to any SSCs important to safety, a more site-specific hazard assessment is performed for the probable maximum event.The HHA approach was carried out for each flood-causing mechanism, with the controlling flood being the eventthat resulted in the most severe hazard to the SSCs important to safety at PNPS. The steps involved to estimatethe design-basis flood typically included the following:

Page 16 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportI. Identify flood-causing phenomena or mechanisms by reviewing historical data and assessing thegeohydrological and structural failure phenomena in the vicinity of the site and region.2. For each flood-causing phenomena, develop a conservative estimate of the flood from the corresponding probable maximum event using conservative simplifying assumptions.

3. If any SSCs important to safety are adversely affected by flood hazards, use site-specific data and/or morerefined analyses to provide more realistic conditions and flood analysis, while ensuring that theseconditions are consistent with those used by Federal agencies in similar design considerations.

4. Repeat Step 2 until all SSCs important to safety are unaffected by the estimated flood, or if all site-specific data and model refinement options have been used.Section 3.0 of this report provides additional IHA detail for each of the flood-causing mechanisms evaluated.

Due to use of the HHA approach, the results (water elevation) for any given flood hazard mechanism may besignificantly higher than results that could be obtained using more refined approaches.

Where initial, overlyconservative assumptions and inputs result in water elevations bounded by the CLB, no subsequent refinedanalyses are required to develop flood elevations that are more realistic or reflect a certain level of probability.

1.4 Assumptions

Assumptions used to support the flood re-evaluation are described in Section 3.0 and its subsections, and dependon the mechanism being evaluated.

Details relating to assumption justifications are discussed further inreferenced, supporting documentation.

None of the assumptions require verification, i.e., need to be confirmed prior to use of the results.1.5 Elevation ValuesElevations listed as mean sea level (MSL) or mean low water (MLW) in this report refer to elevations provided inplant documentation such as the FSAR. The datum relationship at PNPS is as follows:MSL + 4.78 feet = MLW (PNPS 2013, Section 2.4.4.2).

Pursuant to United States Army Corps of Engineers (USACE) document EM 1110-1-1005 Appendix C (USACE2007), National Geodetic Vertical Datum of 1929 (NGVD29) was originally named the Mean Sea Level Datumof 1929. Therefore, elevations in NGVD29 in this report are equivalent to elevations in MSL (AREVA 2015).Updated topographic data for the site was developed using aerial light detection and ranging (LiDAR) andsupporting ground control surveying performed in 2014 (AREVA 2014). This topographic survey providedresults in NAD83 Massachusetts State Plane (horizontal) datum and elevations are in North American VerticalDatum of 1988 (NAVD88)

(vertical) datum. The unit of the survey is U.S. feet (AREVA 2014 and AREVA2015). In order to compare plant document elevations against the 2014 topographic survey results, a conversion factor of 0.827 feet was added to the NAVD88 elevations to obtain the NGVD29 (and MSL) elevations (AREVA2015). The conversion factor between NAVD88 to NGVD29 was determined through the National GeodeticSurvey (NGS) VertCon tool (NGS 2014).1.6 References AREVA 2014. AREVA Document No. 38-9226913-000, PNPS Topographic Survey Deliverables, 2014.AREVA 2015. AREVA Document No. 32-9226914-000, Pilgrim Nuclear Power Station Flooding Hazard Re-Evaluation

-Local Intense Precipitation, 2015.Page 17 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportNGS 2014. VERTCON -North American Vertical Datum Conversion, National Geodetic Survey,http://www.ngs.noaa.gov/TOOLS/Vertcon/vertcon.html, Date accessed:

August 2, 2014, Date modified:

January24, 2013. (See AREVA Document No. 32-9226914-000)

NRC 2011. NUREG/CR-7046, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plantsin the United States of America -NUREG/CR-7046, U.S. Nuclear Regulatory Commission, November 2011.(ADAMS Accession No. ML1 1321A 195)NRC 2012. Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f)

Regarding Recommendations 2.1, 2.3 and 9.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-lchiAccident, U.S. Nuclear Regulatory Commission, March 2012. (ADAMS Accession No. ML12053A340)

PNPS 2013. Pilgrim Nuclear Power Station Final Safety Analysis Report (FSAR), Revision 29, October 2013.(AREVA Doc. No. 38-9226908-000)

USACE 2007. Development and Implementation of NAVD88, EM 110-1-1005 Appendix C, U.S. Army Corpsof Engineers, January 1, 2007. (See AREVA Document No. 32-9226914-000)

Page 18 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report2.0 INFORMATION RELATED TO THE FLOOD HAZARD2.1 Site Information PNPS is situated on the western shore of Cape Cod Bay in the Town of Plymouth, Plymouth County,Massachusetts, and encompasses approximately 517 acres (PNPS 2013, Section 2.2.1). See Figure 2-1, SiteLocation Map. The PNPS site is surrounded by hills to the north, south and west, and is situated on the northeast side of Pine Hills, a north-south trending glacial ridge approximately four miles long with a maximum elevation of 395 feet (PNPS 2012, Section 2.0 and PNPS 2013, Sections 2.4.1.2 and 2.5.2.4.1).

2.1.1 Site LayoutFigure 2-2, Site Topography and Layout, shows the PNPS site layout and topography, including important features related to flood modeling.

2.1.2 Site Topography The PNPS site varies from 14 to 32 feet above MSL. Station grade is at 20 feet MSL. The elevation in thevicinity of the power block is at 22 feet MSL and the building floor elevation at grade level is 23 feet MSL. The40 foot MSL ground surface contour crosses Rocky Hill Road, a public road, and closes within the site boundaries and is open only to the bay. The 24 foot MSL contour closes on the bay side of Rocky Hill Road. (PNPS 2012,Section 2.0 and PNPS 2013, Sections 2.4.1.2, 2.5.2.1 and 2.5.2.4.1).

It is unlikely that the PNPS shoreline will experience changes due to shoreline erosion since the PNPS shoreline isstabilized against erosion from wind, currents, water fluctuations and storm conditions by a series of breakwaters and discharge channel jetties constructed of heavy rock (AREVA 2014). For further discussion, refer to Section3.8.The groundwater table generally follows the site surface topography, resulting in moderately steep groundwater gradients present beneath the PNPS site with flow towards Cape Cod Bay (PNPS 2013, Sections 1.6.1.1.6 and2.4.1.3.2).

The Reactor, Turbine and Radwaste Buildings have a waterproofing membrane designed to prevent orminimize groundwater in leakage (PNPS 2013, Section 12.2.4.4.3).

2.2 Current Design Basis Flood Information and Elevations The current design basis flood is described in the PNPS FSAR (PNPS 2013, Section 2.4.4) and in the PilgrimNuclear Power Station Flooding Walkdown Submittal Report for resolution of Fukushima NTTFRecommendation 2.3 (PNPS 2012) required as part of the response to the 10 CFR 50.54(f) letter.The PNPS design basis flood is the extreme design storm tide level of 13.5 feet MSL (18.3 feet MLW).To assist in the design of PNPS waterfront structures (i.e., dredged channels, breakwaters, jetties and onshorerevetments),

a series of wave action model studies were performed in which the waterfront was subjected to threestill water elevations:

1) 11 feet MSL (15.8 feet MLW), the level of the 100 year storm; 2) 13.5 feet MSL (18.3feet MLW), the design maximum storm level, and; 3) 14.7 feet MSL (19.5 feet MLW), an arbitrary elevation which exceeds any postulated design condition and is the highest elevation at which the model could be operatedsatisfactorily (PNPS 2013, Section 2.4.4.3).

The top elevation of the breakwaters and the nominal elevation forthe discharge channel jetties are at 11.2 feet MSL (16 feet MLW) (PNPS 2013, Section 2.4.4.1).

The top of theshorefront revetment is at elevation 20.2 feet MSL (25 feet MLW) (PNPS 2012 Section 2.0).The probable maximum precipitation (PMP) event at PNPS was evaluated as part of the Individual PlantExamination of External Events (IPEEE).

The PMP event results in flood depths of 24.5 feet MSL along thePage 19 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Reportsouth side of plant buildings, 22.5 feet MSL along the north side of plant buildings, and ponding on building roofsof about 0.5 feet (PNPS 2012).2.2.1 Elevations of Safety Structures, Systems and Components The minimum entrance elevation for areas housing SSCs important to safety is 23 feet MSL (see Section 3.1).2.3 Current Flood Protection The CLB for flooding protection at PNPS is described in the FSAR (PNPS 2013, Section 2.4.4). Flood protection features for the PMP, evaluated as part of the IPEEE, are described in the 2012 walkdown report (PNPS 2012).2.3.1 Current Flood Causing Mechanisms The following is a summary of current flood causing mechanisms for PNPS.2.3.1.1 Extreme Storm Tide LevelThe extreme storm tide event is the only CLB flood hazard. The maximum storm tide level of 13.5 feet MSL(18.3 feet MLW) may result from a tropical or an extra-tropical event (i.e., a nor'easter or a hurricane).

For astandard project nor'easter for New England, established by the hydrometeorological section of the U.S. WeatherBureau, the extreme design storm tide level is based on a peak storm surge of 6.6 feet coincident with a high tideof 6.9 feet MSL. Similarly, for the most severe hurricane parameters from Hydrometeorological BranchMemorandum HUR 7-97, including a spring high tide of 6.9 feet MSL., the maximum hurricane produced stormsurge results in a still water level of 13.5 feet MSL (18.3 feet MLW). (PNPS 2012 Section 2.0 and PNPS 2013,Section 2.4.4)2.3.1.2 Probable Maximum Precipitation Although not part of the CLB, the PMP event was evaluated as part of the IPEEE and exceeds the CLB extremestorm tide level. PMP water depths along the power block buildings are based on one hour precipitation rateshaving a probability of occurrence of I x 10.6 per year. The rainfall rates were developed from the NationalWeather Service HYDRO-35 report, and the U.S. Army Corp of Engineers (USACE) Flood Hydrograph PackageHEC-1 was used to develop the runoff flowrate.

The duration of the PMP event is one hour, during which timethe flood level starts at zero height, increases to PMP levels, and then recedes back to zero height. The PMPresults in water depths slightly (i.e., up to 1.5 feet) above power block building door sill elevations, and in roofponding (PNPS 2012).2.3.2 Current Flood Protection and Mitigation FeaturesReferring to Figure 2-2, the breakwaters protect the Intake Structure and revetment from excessive wave actionand overtopping due to wave runup; they also minimize on-site flooding from storms. The rev'etments on eitherside of the Intake Structure provide shore stabilization and prevent the Reactor Building from being floodedduring severe storms. Although open ocean wave heights up to 31 feet were generated during the model wavestudies noted in Section 2.2 above, the test results demonstrated that the generated waves at the Intake Structure would be adequately reduced and that there would be no adverse impact to the service water pumps for still waterelevations up to 14.7 feet MSL (19.5 feet MLW); in addition, the Reactor Building would not be subjected toflooding (PNPS 2013, Section 2.4.4.3).

Flooding protection against the PMP event includes exterior doors on power block buildings, roof drains andinternal seals for conduits originating in manholes (PNPS 2012, Section 3.3). Although door sills on the southside of the plant would be 1.5 feet below the maximum predicted PMP flood depth, an evaluation determined thatPage 20 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Reportthe doors could withstand the corresponding hydrostatic load. Potential water intrusion through door perimeters was also evaluated and found to be bounded by the plant's internal flooding analysis.

Additionally, it wasdetermined that roof ponding during a PMP event would not exceed roof design capacity if the roof drains werefully functioning.

It was also determined that water ingress via manholes would be prevented by cable to conduitseals, or mitigated by tortuous conduit pathways.

(PNPS 2012, Section 3.1).Although no actions or procedures are credited for flooding protection, the plant's procedure for operation duringsevere weather (i.e., PNPS Procedure 2.1.42, Operation During Severe Weather) includes measures that can beused for mitigating external flood conditions (e.g., ensuring that exterior doors are closed, installing sandbags atdoor bottoms and drain scuppers)

(PNPS 2012, Sections 3.1 and 5.2.2).2.4 Licensing Basis Flood-Related and Flood Protection ChangesFollowing damage to the breakwaters during the winters of 1977-1978 and 1978-1979, the breakwaters wererepaired both times to their original configuration.

Resolution to NRC concerns included a commitment tomonitoring of the breakwaters to ensure their integrity (PNPS 2013, Section 2.4.4.1).

2.5 Watershed and Local Area Changes2.5.1 General PNPS Site Hydrological Description There are no perennial or intermittent streams in the vicinity of PNPS. The closest hydrologic

feature, BartlettPond, is approximately one and three-quarter miles southeast of the PNPS site (USGS 2012). Due to localtopography, the PNPS drainage basin is isolated from other area watershed basins. All site surface drainage flowsinto Cape Cod Bay (PNPS 2013, Section 2.4.1.2).

2.5.2 Watershed ChangesConsidering that there are no perennial streams on or adjacent to the PNPS site, no significant changes to thePNPS watershed were identified (USGS 1977 and USGS 2012).2.5.3 Local Area ChangesThe 2012 walkdown report indicates that plant changes since the time that the PMP analysis was performed, include the installation of security fences along the bay, and construction of the Engineering and Plant SupportBuilding on the east side of the plant. However, despite these changes, the 2012 walkdown report found that theoverland drainage path for the PMP analysis (i.e., rain water flowing around the east and west sides of plantstructures and then northward over the shore revetment),

still remained.

Therefore, the 2012 walkdown reportconcluded that any changes in the overland drainage path due to plant changes, would be offset by conservatisms in the PMP analysis (PNPS 2012, Section 5.2).Since the addition and relocation of PNPS vehicle security barriers may also impact localized surface waterdrainage, refer to the local intense precipitation evaluation in Section 3.1 for further discussion.

2.6 Additional Site Details -Walkdown ResultsA total of 33 walkdown flood protection

features, including 138 attributes, were reviewed during the 2012walkdown.

Of the total flood protection

features, 28 were defined as passive -incorporated, none as passive -temporary, five as active -incorporated and none as active -temporary.

The walkdown scope included a visualinspection of shorefront

features, doors and conduit seals. The 2012 walkdown report indicates that the roofdrains were not inspected at that time, since it was determined that the roof drains are periodically inspected andPage 21 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Reportcleaned by plant maintenance personnel.

Observations that did not meet the walkdown acceptance criteria wereentered into the plant's corrective action program and subsequently rectified.

(PNPS 2012, Section 7.0)2.7 References AREVA 2014. Channel Diversion AREVA Document No. 51-9226930-000, Pilgrim Nuclear Power StationFlooding Hazard Re-Evaluation

-Screening for Channel Diversion, October 2014.PNPS 2012. Engineering Report No. PNPS-CS-12-00002, Pilgrim Station Flooding Walkdown Submittal Reportfor Resolution of Fukushima Near-Term Task Force Recommendation 2.3: Flooding, Rev. 1. (see AREVA Doc.No. 38-9226908-000)

PNPS 2013. Pilgrim Nuclear Power Station Final Safety Analysis Report (FSAR), Revision 29, October 2013.(see AREVA Doc. No. 38-9226908-000)

USGS 1977. Manomet Topographic Quadrangle Map 1977, Massachusetts-Plymouth County, 7.5 Minute Series,Scale 1: 25 000, U.S. Geological Survey. (See AREVA Document No. 51-9226922-000)

USGS 2012. Manomet Topographic Quadrangle Map 2012, Massachusetts-Plymouth County, 7.5 Minute Series,Scale 1: 24 000, U.S. Geological Survey. (See AREVA Document No. 51-9226922-000)

Page 22 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 2-1: Site Location MapM--- In _Z In AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 2-2: Site Topography and Layout750 1,000 Le.ed AM- --ý I _Z A 1^

AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.0 FLOOD HAZARD RE-EVALUATION This section details the evaluation of the eight flood causing mechanisms and combined effects for PNPS asdescribed in Attachment I to Enclosure 2 of the NRC information request.

No additional flood causingmechanisms were identified for PNPS.3.1 Local Intense Precipitation This section addresses the potential for flooding at PNPS due to the local intense precipitation (LIP) event. TheLIP event is a distinct flooding mechanism that consists of a short-duration, locally heavy rainfall centered uponthe plant site itself.This section summarizes the LIP evaluation performed in AREVA Document No. 32-9226914-000, PilgrimNuclear Power Station Flooding Hazard Re-Evaluation

-Local Intense Precipitation (AREVA, 2014a).3.1.1 Methodology The hierarchical hazard assessment (HHA) approach described in NUREG/CR-7046 (NRC 2011, Section 2) wasused for the evaluation of the LIP and resultant water surface elevations at PNPS.With respect to LIP, the HHA used the following steps:I. Develop LIP/PMP inputs.2. Develop a FLO-2D hydrodynamic computer model with site features.

3. Perform flood simulations in FLO-2D and estimate maximum water surface elevations throughout thePNPS site.3.1.2 ResultsRecent survey data has confirmed that the minimum entrance elevation for all areas housing structures important to safety is 23.0 feet MSL (IPEEE 1994, Section 5.2.1). Maximum LIP flood elevations calculated by FLO-2D(Table 3-1) for selected important locations indicate flooding above elevation 23.0 feet MSL at several areas, witha maximum water surface elevation of 25.2 feet MSL. The highest LIP water surface elevations occur on thesouth side of the plant structures.

Important locations examined in the LIP flood model are shown on Figure 3-1.3.1.2.1 FLO-2D Model Limits for LIP AnalysisDue to anticipated unconfined flow characteristics, a two-dimensional hydrodynamic computer model, FLO-2D,was used for the LIP analysis.

FLO-2D (AREVA 2014b) is a physical process model that routes floodhydrographs and rainfall-runoff over unconfined flow surfaces or in channels using the dynamic waveapproximation to the momentum equation (FLO-2D 2013). See Appendix A. The FLO-2D model computational boundary is shown in Figure 3-2. The computational domain of the FLO-2D model encompasses the PNPS plantand its peripheral site features/structures.

The model computational boundary also includes the PNPS sitedrainage basin; therefore, the LIP analysis bounds a PMF evaluation that considers only the PNPS drainage area,which is less than the LIP model boundary.

The computational domain of the FLO-2D model is bounded by CapeCod Bay and topographic ridges to the north, south and west. The total FLO-2D model extent is approximately 600 acres (0.94 square miles), while the PNPS drainage area is approximately 337 acres (BEC 1993).The FLO-2D model includes topography, site location and building structures.

Grid elements along the modelcomputational boundary were selected as outflow grid elements.

Page 25 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.1.2.2 FLO-2D Computer Model with Site FeaturesSite Topography and Buildings Alignment:

Current site topography (digital terrain model (DTM)) and buildings alignment at PNPS were extracted from the site topographic survey provided in AutoCADTM format (AREVA2014c). Additional elevation data was used based on the topographic site plan (AREVA 2014c) produced alongwith the DTM. Topographic data for PNPS was developed based on a site-specific aerial survey usingmethodology consistent with the need for first-order level of accuracy (i.e. +/- 0.1 feet). The topographic surveyperformed in 2014 at PNPS was required to meet the American Society for Photogrammetry and Remote Sensing(ASPRS) Class 1 Accuracy Standard for I" = 100' planimetrics and 1-foot contour intervals, with +/- 1 feethorizontal

accuracy,

+/- 0.33 feet Root Mean Square Error (RMSE) vertical accuracy for 1 foot contours and +/-0.17 feet RMSE vertical accuracy for spot elevations and DTM points, at well-defined points. Additional designated important structures and locations with respect to site flooding impacts were identified and surveyedwith a vertical accuracy of +/- 0.1 feet. The methodology of the topographic survey was aerial LIDAR mappingof the site with sufficient control points for calibration meeting the mapping standard, and conventional groundsurvey loops for the important structures and locations (AREVA 2014d).FLO-2D grid element elevation data was interpolated based on imported digital terrain (DTM) points from thetopographic survey of the site that were added to the working region. The interpolation method used in the FLO-2D model was an inverse distance weighting formula exponent to assign elevations to the grid element from theDTM points.Model grid elevations cannot be more accurate than the survey they are based upon. Therefore model gridelevations have a minimum level of uncertainty of +/- 0.1 feet. A minimum of two closest DTM points withinthe vicinity of a grid element was used in computing grid elevations.

The density of spot elevations on the DTMprovided for adequate coverage for each grid element.Uncertainty regarding onsite flood elevations is generally limited to the level of accuracy of the site survey. Thenature of the two dimensional flow model is such that the impact of potential inaccuracy in the elevation of anysingle grid element is generally mitigated by the surrounding grid elements.

LIP results were computed asmaximum water surface depths, which were then compared to the known height of flood protection at important

elements, thus reducing uncertainty related to potential issues with elevation datum normalization.

Levee Elements:

The concrete shoreline

barriers, which impede flow away from the site, were modeled as leveestructures using the levee component within FLO-2D (FLO-2D 2013). The top elevation of the concrete shoreline barriers was interpolated between surveyed points from the additional topographic survey (AREVA 2014c).Simulation of the LIP with the concrete shoreline barriers results in a more conservative water surface elevation than without the concrete shoreline barriers as the barriers would prevent water from flowing freely into CapeCod Bay. Vehicle barrier systems were conservatively not included in the model as they would only impede flowand are not considered flood protection elements.

Water Surface Elevation at Cape Cod Bay: With the general site grade at 20 feet MSL and the disparity betweenthe highest still water surface elevation of 14.8 feet MSL, as listed in the PNPS FSAR (PNPS 2013), the originaldigital elevation model (DEM) water surface elevations (approximately 0.0 feet NAVD88) were unchanged formodeling simplicity.

Calculate Manning's Roughness Coefficients:

Manning's n-values used in FLO-2D are composite values thatrepresent flow resistance.

An "apparent land cover" Geographic Information Systems (GIS) shape file wascreated based on visual assessment of high resolution orthoimagery (AREVA 2014d). Grid element Manning's n-values were conservatively assigned based on the land cover at the site, and the recommended upper end of therange of Manning's roughness coefficients contained in Table I of the FLO-2D Reference Manual (FLO-2D2013). Table 3-2 shows the relationship between Manning's n values and selected land cover categories.

ThePage 26 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportManning's roughness coefficient values for the grid elements generally range from 0.02 for concrete or pavedareas to 0.4 for wooded areas. Figure 3-3 shows the Manning's coefficients selection for each land cover.Calculate Curve Number to Model Infiltration:

The Curve Number (CN) Method developed by the SoilConservation Service (SCS, now known as Natural Resources Conservation Service or NRCS) was used to modelinfiltration for the LIP analysis.

The SCS infiltration method in FLO-2D is computed by subtracting thecalculated infiltration loss based on the CN from the total precipitation before the flood routing starts at each gridelement, which is similar to using a lower precipitation.

CN used in FLO-2D are composite values that represent potential infiltration.

A land cover GIS shapefile was used for the CN calculation.

The SCS hydrologic soilgroup classification (A, B, C or D from lowest runoff potential to highest runoff potential) was determined fromthe Web Soil Survey by NRCS (NRCS 2013).A GIS shape file was created with CN values assigned by correlating land cover types with soil types based ontables provided in Chapter 9 of the NRCS National Engineering Handbook (NEH) Part 630 Hydrology (NRCS2004a) that assume normal Antecedent Rainfall Conditions (ARC 1I). The selected CNs were then conservatively replaced to assume ARC III (i.e., wet conditions) based on NRCS guidance (Table 10-1 in Chapter 10, Estimation of Direct Runoff from Storm Rainfall of NEH Part 630 Hydrology; NRCS 2004b). ARC 1, II, and Ill represent dry, normal and wet conditions, respectively.

The GIS shape file with the ARC III CN values was used tocompute the grid elements CN in the FLO-2D model. Note that for a land cover category with multiplehydrologic conditions (good, fair and poor), the ground cover was assessed using aerial photography to determine the appropriate hydrologic condition.

Table 3-3 shows the relationship between CN values and selected land cover categories.

The CN values for thegrid elements generally range from 43 for wooded and brush areas to 99 for concrete or paved areas. Note thatthe CN values for the wooded areas were conservatively selected as the same as the "brush-brush-forbs-grass" areas (Table 9-1 of NRCS 2004a). Figure 3-4 shows graphically and the FLO-2D output file "INFIL.DAT" liststhe grid element CN values used by the model. According to the FLO-2D output file "SUMMARY.OUT,"

approximately 4.4 inches or 18-percent of the total precipitation (25.5 inches) was infiltrated or decreased fromthe total precipitation before flood routing started.Buildings and RoofTops:

Buildings at PNPS were incorporated into the FLO-2D model based on the highresolution orthoimagery and the site survey (AREVA 2014a) by changing the grid elevations to incorporate building height into the terrain.

Buildings were modeled as elevated grid elements (i.e., higher than surrounding areas) in the FLO-2D model to ensure that rainfall runs off the building rooftops to the surrounding areas and toensure overland flow around the buildings (i.e., not through the buildings).

Building roof top elevations wereassigned to represent the approximate runoff pattern (i.e., runoff flows from higher elevation roof top to lowerelevation rooftop),

based on rooftop elevation points within the "DTM-Buildings" layer of the surveyed DTM(AREVA 2014a). Area Reduction Factors and Width Reduction Factors were not used. This methodology accounts for the contribution of roof drainage on the ground surface runoff in accordance with Section 11.4 ofANSI/ANS 2.8 -1992 (ANS 1992). Elevating building cells allows for FLO-2D to recognize those grid elementsare obstructions relative to much lower ground grid elements.

To evaluate the worst case for site surface drainage(ANS 1992), roof drains connected to subsurface drainage systems are assumed to be blocked and potential storage resulting from roof parapet walls was conservatively not incorporated.

3.1.2.3 LIP/PMP InputsThe LIP parameters were defined using Hydrometeorological Report (HMR)-51 and HMR-52; (NOAA 1977 andNOAA 1982, respectively) as prescribed in NUREG/CR-7046 (NRC 2011, Section 3.2). The total rainfall depthfor the 1-hour, 1-mi2probable maximum precipitation (PMP) is 17.1 inches. The total rainfall depth for the 6-Page 27 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Reporthour PMP is 25.5 inches. The rainfall hyetograph distribution used as input into the model for the LIP simulation is based on Figure B-5 of NUREG/CR-7046 (NRC 2011). The 6-hour PMP hyetograph was constructed usingthe 1-hour PMP for the first hour and equal rainfall increments for the next five hours (Figure 3-5).3.1.2.4 LIP Simulation ResultsThe results of the LIP simulation are summarized in Table 3-1 and shown in Figure 3-6. Large plots showing theLIP grid element numbers, interpolated ground surface elevations, water surface elevations, depths, velocity anddirection are provided in Appendix A.The maximum LIP flood elevations near important locations range from 22.5 feet NAVD88 (23.3 feet MSL) nearthe Water Treatment Area ground level door on the west side of the buildings to 24.4 feet NAVD88 (25.2 feetMSL) near the O&M Building ground level door on the south side of the buildings.

Calculated maximum flooddepths near important locations range from 0.6 feet near the Emergency Diesel Generator Building door on thenorth side of the buildings to 2.6 feet near the O&M Building ground level door on the south side of the buildings.

Maximum flow velocities within the computational area are up to 12.6 feet per second (fps) in the entrance of thedischarge channel.

This is reasonable given the difference in elevation between the channel water surfaceelevation and the ground surface elevation at the head of the channel.

The channel is stone lined (BEC 1969)while the majority of the power block area is concrete.

According to Table 2 of Fischenich 2001, the maximumpermissible mean velocity threshold for large diameter stone is greater than 14 fps; while for concrete areas it isgreater than 18 fps. Therefore, scour and erosion in the power block and channel is not expected.

Appendix A contains the stage hydrographs near important locations.

Peak flood levels occur well after the peakrainfall intensity, which can be attributed to the contribution of off-site drainage (i.e., lag). Additionally, there is asmaller peak at the beginning of the stage hydrographs approximately coincident with the peak rainfall intensity.

Generally, the maximum flood depths occur within the first two hours of the simulation.

In some instances, theseflood depths can take over ten hours to recede, specifically on the south side of the powerblock area.The FLO-2D reference manual (FLO-2D.

2013) provides three keys to a successful project application.

Theseinclude volume conservation, area of inundation, and maximum velocities and numerical surging.* Volume Conservation:

Reviews of the "SUMMARY.OUT" files (included in Appendix A) indicatevolume conservation errors of 0.000004 percent for the FLO-2D runs. This value is well below thethreshold of 0.001 percent specified in the FLO-2D Data Input manual (FLO-2D 2013) for a successful project application.

Area of Inundation:

Reviews of the "SUMMARY.OUT" files (included in Appendix A) indicatemaximum inundated areas of 601.1 acres. The FLO-2D model is made up of 65,499 grid elements each20 feet by 20 feet in dimension.

The LIP was simulated within the entire computational domain of themodel. The maximum inundation area should therefore be equal to the area of the computational domainof 601.5 acres ((20 x 20 x 65,499) x (1 acre /43,560 feet)). The FLO-2D calculated maximum inundation area virtually matches the computational area. Visual inspection of flood depth results also is consistent with expected results; areas of high flood depth were noted and discussed above. This information indicates a successful project application.

" Maximum Velocities and Numerical Surging:

Numerical

surging, if it exists, would be evident inunreasonably high velocities in the "VELTIMEFP" (floodplain) file or "VELTIMEC" (channel) file(FLO-2D 2013). A review of the "VELTIMEFP.OUT" file (included in Appendix A) does not indicateunreasonably high velocities in the model runs and indicates a successful project application.

Themaximum velocity is up to 10. 1 fps reported in the "VELTIMEFP.OUT" file and occurred at the interface between the floodplain and discharge channel.

A similar review of the "VELTIMEC.OUT" file does notindicate unreasonably high velocities in the model runs. The maximum velocity is up to 12.6 fps, whichPage 28 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Reportoccurs at the drop off between the site grade and the channel.

This indicates a successful projectapplication.

3.1.2.5 Review Areas of Supercritical FlowFLO-2D does not simulate supercritical flow conditions (FLO-2D 2013). No Froude number limitations wereused; therefore, FLO-2D does not adjust the Manning's roughness'n' coefficient.

Grid elements are determined to be supercritical if the calculated Froude number is greater than 1.0 (FLO-2D 2013). The SUPER.OUT filereports grid elements that are supercritical.

Review of the SUPER.OUT file indicated that supercritical flow isoccurring generally at the intersection of building grid elements and grid elements representing the adjacent grade(see Figure 3-7) possibly due to the artificially high hydraulic gradient created by elevating grid elements torepresent buildings.

The FLO-2D model results in conservative estimates for flow depth, because supercritical flow is shallower, and the program limits supercritical flow by reducing the velocity which increases the flowdepth.3.1.3 Conclusions The maximum water surface elevations at the site due to the LIP at PNPS result from a PMP depth of 17.1 inchesin I hour and 25.5 inches within six hours. The maximum flood depths range from 0.6 feet to locally as high asapproximately 2.6 feet above grade near the important locations as shown in Table 3-1. The maximum LIP floodelevation at an important location examined in the LIP analysis is 24.4 feet NAVD88 (25.2 feet MSL).3.1.4 References ANS 1992. American National Standard for Determining Design Basis Flooding at Power Reactor Sites(ANSI/ANS 2.8- 1992).AREVA 2014a. AREVA Document No. 32-9226914-000, Pilgrim Nuclear Power Station Flooding Hazard Re-Evaluation

-Local Intense Precipitation, 2014.AREVA 2014b. Computer Software Certification

-FLO-2D Professional

Version, Build No. 14.03.07, GZAGeoEnvironmental, Inc., 2014. (See AREVA Document No. 38-9225054-000)

AREVA 2014c. PNPS Mapping Deliveries, June 17, 2014. (See AREVA Document No. 38-9226913-000)

AREVA 2014d. PNPS (Pilgrim)

Critical Structures CAD Files, August 28, 2014. (See AREVA Document No.38-9226913-000)

BEC 1969. Waterfront Development Detail Plan Intake and Discharge Area", Drawing No. C-416, Revision El,Boston Edison Company, 1969. (See AREVA Document No. 32-9226914-000)

BEC 1993. IPEEE -External Flooding Analysis (Local Intense Precipitation),

BEC-039, Boston EdisonCompany, 1993. (See AREVA Document No. 38-9226908-000)

Fischenich 2001. C. Fischenich, Stability Thresholds for Stream Restoration Materials, EMRRP, Publication No.ERDC TN-EMRRP-SR-29, May 2001.FLO-2D 2013. FLO-2D Pro Reference Manual, FLO-2D Software, Inc., Nutrioso, Arizona (www.flo-2d.com),

2013. (See AREVA No. 32-9226914-000)

IPEEE 1994. Pilgrim Nuclear Power Station -Individual Plant Examination for External Events (GL 88-20),Rev. 0, July 1994. (See AREVA Document No. 38-9226908-000)

Page 29 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportNOAA 1977. Probable Maximum Precipitation Estimates

-United States East of the 105th Meridian, Hydrometeorological Report No. 51 (HMR-5 1) by US Department of Commerce

& USACE, August 1977.NOAA 1982. Application of Probable Maximum Precipitation Estimates

-United States East of the 105thMeridian, NOAA Hydrometeorological Report No.52 (HMR-52) by US Department of Commerce

& USACE,August 1982.NRC 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United Statesof America -NUREG/CR-7046, U.S. Nuclear Regulatory Commission, November 2011.NRCS 2004a. Chapter 9 Hydrologic Soil-Cover Complexes, Part 630 Hydrology, National Engineering

Handbook, U.S. Department of Agriculture Natural Resource Conservation

Service, July 2004. (See AREVADocument No. 32-9226914-000, Appendix E.2)NRCS 2004b. Chapter 10 Estimation of Direct Runoff from Storm Rainfall, Part 630 Hydrology, NationalEngineering

Handbook, U.S. Department of Agriculture Natural Resource Conservation

Service, July 2004. (SeeAREVA Document No. 32-9226914-000.,

Appendix E.3)NRCS 2013. Web Soil Survey, U.S. Department of Agriculture Natural Resource Conservation Service(http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm),

revised December 06., 2013, accessed September 26,2014. (See AREVA Document No. 32-9226914-000, Appendix E.1)PNPS 2013. Pilgrim Nuclear Power Station Final Safety Analysis Report, Revision 29, October 2013. (SeeAREVA Document No. 38-9226908-000)

Page 30 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-1: LIP Model ResultsIdentification Description Representative Grid Element Maximum Maximum Maximum Time to MaximumNumber Grid Element Ground Flood Flood Flood Maximum Velocity (feetSurface Elevation Elevation Depth Flood Elevation per second)Elevation (feet, (feet, MSL) (feet) (hours)(feet, NAVD88)NAVD88)8 Emergency Diesel Generator 7467 22.1 22.7 23.5 0.6 0.1 2.7Building Door -North Side9 ReactorBuildingTruckLock 7169 21.8 22.5 23.3 0.7 1.5 1.7Door -West Side10 Water Treatment Area Ground 7606 21.7 22.5 23.3 0.8 1.5 0.7Level Door -West Side11 Turbine Building Truck Rollup 10264 21.9 24.4 25.2 2.5 1.4 0.8Door -South Side12 O&M Building Ground Level 10085 21.8 24.4 25.2 2.6 1.4 2.0Door -South Side13 Hatch A- Turbine Building-10077 23.3 24.4 25.2 1.1 1.4 0.5South Side14 Hatch B -Turbine Building

-9897 23.2 24.4 25.2 1.1 1.4 1.0South Side15 Air Vent -Redline Building

-9728 22.1 24.4 25.2 2.2 1.4 1.1South Side INote: Due to rounding, maximum flood depths added to ground surface elevations may not be exactly equal to the maximum flood elevations (NAVD88)indicated above. The variance is within 0.1 feet.M___ ýA _Z All AAREVADocument No.: 5.1-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-2: Manning's n Values for Selected Land Cover Categories Land Cover Category Manning's nPaved / Concrete 0.02Building Roofs 0.02Water 0.025Sandy Areas with No Cover 0.10Grass 0.20Trees 0.40Notes: 1) The Manning's n value for "Open Ground, no Debris" was used for the "Sandy Area" (e.g., dunes) asthe reference used for Manning's n (FLO-2D 2013) does not include a land use category related to sand.Table 3-3: Curve Number (CN) Values for Selected Land Cover Categories ARC III CN2 for HSGLand Cover Category NRCS Cover Type' A B C DCranberry Bog Water 99 99 99Forest Woods 43 74 85 89Forested Wetland Water 99 99 99 99High Density Residential 1/4 Acre Lot 78 88 93 -Industrial Impervious 99 99 99 99Multi-Family Residential 1/8 Acre Lot --91 -Non-Forested Wetland Water 99 99 99 99Open Land Impervious 96Powerline/Utility Brush 50 68 -87Saltwater Sandy Beach Impervious 99 99 99 99Very Low Density Residential 2 Acre Lot 92Notes: 1) All NRCS cover types were assumed to be in fair condition.

2) The CN values in the table above forARC III were taken from Table 10-1 of NRCS 2004b.Page 32 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-1: PNPS Important Locations Basemap Source: High resolution orthoimagery (AREVA 2014c). Note that a larger version of this figure is available in Appendix A.Page 33 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-2: FLO-2D Computational BoundaryBasemap Source: High resolution orthoimagery (AREVA 2014c)M- --n A _Z A rý AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-3: FLO-2D Manning's Coefficient Assignment I0400360320270230190150 10006<-= U.2Page 35 of 152 AAREVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-4: FLO-2D Curve Number Selections Page 36 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-5: LIP Hyetograph 300300 U1000.00rime (hours)Page 37 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-6: PNPS Maximum Water Surface Elevations (feet, NAVD88)Basemap Source: High resolution orthoimagery (AREVA 2014c). Note that a larger version of this figure is available in Appendix A.Page 38 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-7: Supercritical Flow RegimePage 39 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.2 Flooding in Rivers and StreamsThis section addresses potential flooding at PNPS due to the probable maximum flood (PMF) in rivers andstreams.

For further details of the assessment, refer to AREVA Document No. 51-9226922-000 (AREVA 2014).3.2.1 Methodology The method used to address the PMF in rivers and streams followed the HHA approach as described in Section3.3 of NUREG/CR-7046 (NRC 2011), which states that the following series of steps should be considered, asapplicable:

1. Identify the plant's drainage basin and locate nearby surface water sources (i.e., rivers, streams, channels) with the potential to impact flooding at the PNPS site due to precipitation runoff.2. Perform PMF maximum evaluations to assess the flooding hazard impacts for surface water sourcesidentified in Step 1.For the PNPS site, based on the findings for Step 1, it was not necessary to perform Step 2. Refer to thediscussion below.3.2.2 ResultsThe PNPS site is located at the Atlantic Ocean shoreline with hills to the north, south and west, and Cape CodBay to the east. The site varies from 14 to 32 feet above MSL. Station grade is at 20 feet MSL. The 40 footMSL ground surface contour crosses Rocky Hill Road, a public road, and closes within the site boundaries and isopen only to the bay. The 24 foot MSL contour closes on the bay side of Rocky Hill Road. There are no rivers orstreams on or adjacent to the site. As such, PNPS is located within an isolated drainage area on the northeast sideof Pine Hills which is a north-south trending glacial ridge with a maximum elevation of 395 feet. All site surfacedrainage flows into the bay (PNPS 2013, Sections 2.4.1.2, 2.5.2.1 and 2.5.2.4.1).

The nearest, prominent inland bodies of water are Bartlett Pond which is approximately one and three-quarter miles southeast of PNPS at a topographic low point near the shore, and the Eel River which is approximately twoand one-quarter miles west of PNPS and about three-quarters of a mile west of Pine Hills (Figure 3-8). The 1977and 2012 topographic maps indicate that Bartlett Pond flows into Cape Cod Bay and that the Eel River flows intoPlymouth Bay which is located in the northwestern portion of Cape Cod Bay. The topographic maps also depict asmall body of water, essentially a wetland, at a topographic low point, about one and a quarter miles west ofPNPS along the shoreline (USGS 1977 and USGS 2012). Refer to Figure 3-8. Several wetlands and a cranberry bog are also depicted on the 1977 topographic map in the site vicinity.

Similarly, although the United States Geologic Survey (USGS)'s National Hydrography Database (NHD) shows afew, small ponds near PNPS, there are no rivers or perennial or intermittent streams in the site vicinity (USGS2014). Referring to Figure 3-9, the closest hydrologic feature is Beaver Dam Brook (USGS 1977) which flowsinto Bartlett Pond about one and three-quarter miles southeast of PNPS, at White Horse Beach. Figure 3-9 alsoindicates that the next closest hydrologic feature (the Eel River) is approximately two and one-quarter miles westof PNPS.Since there are no rivers, streams or channels in the vicinity of the PNPS site, a PMF study in rivers and streamswas not performed.

Page 40 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.2.3 Conclusions No surface water channels, streams or rivers are present within or adjacent to the PNPS drainage basin and nosurface hydrologic features were identified by the USGS as a perennial or intermittent stream in the vicinity ofPNPS. Due to local topography, the PNPS drainage basin is isolated from other area watershed basins.3.2.4 References AREVA 2014. AREVA Document No. 51-9226922-000, Pilgrim Nuclear Power Station Flooding Hazard Re-Evaluation

-Screening for Probable Maximum Flood, October 2014.NRC 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United Statesof America, NUREG/CR-7046, U.S. Nuclear Regulatory Commission, November 2011.PNPS 2013. Pilgrim Nuclear Power Station Final Safety Analysis Report (FSAR), Revision 29, October 2013.(AREVA Doc. No. 38-9226908-000)

USGS 1977. Manomet Topographic Quadrangle Map 1977, Massachusetts-Plymouth County, 7.5 Minute Series,Scale 1:25 000, U.S. Geological Survey. (See AREVA Document No. 51-9226922-000)

USGS 2012. Manomet Topographic Quadrangle Map 2012, Massachusetts-Plymouth County, 7.5 Minute Series,Scale 1: 24 000, U.S. Geological Survey. (See AREVA Document No. 51-9226922-000)

USGS 2014. "The National Map -National Hydrography Database",

United States Geologic Survey NationalMap Viewer, http://viewer.nationalmap.gov/viewer/nhd.html?p-nhd, date accessed 9/3/2014, date modified N/A.(See AREVA Document No. 51-9226922-000)

Page 41 of 152 AAR EVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-8: Plymouth County Massachusetts Topographic Map[Source:

USGS 2012]~? -JMLUS2K 3X M 7D M Su~ ~ UMm0Page 42 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-9: Hydrologic Units Near PNPS[Source for hydrology:

USGS 2014]Page 43 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.3 Dam Breaches and FailuresThis section summarizes the assessment performed for flooding at PNPS due to potential dam breaches andfailures.

For further details of the assessment, refer to AREVA Document No. 5 1-9226924-000 (AREVA 2014).3.3.1 Methodology As part of the HHA approach described in NUREG/CR-7046 (NRC 2011), assessments for potential dam-breach induced floods should consider the following steps, as applicable:

1. Investigate the failure of a subset of all upstream dams, while assuming that peak discharges ofindividual dam-failure induced floods reach the site at the same time.2. Investigate the most severe cascading failure combination.

For the PNPS site, Step 1 was performed.

Based on the findings for Step 1, it was not necessary to perform Step2 as discussed below.3.3.2 ResultsThe State of Massachusetts is hydrologically divided into 27 major watersheds.

Each watershed has unique landand water features, history of water use, and development patterns influencing its water resources.

PNPS issituated within the South Coastal Watershed Basin (see Figure 3-10). The South Coastal Watershed Basindischarges directly into the ocean and consists of 14 coastal river watersheds with a total drainage area ofapproximately 240.7 square miles. The basin spans over all of or part of 19 municipalities (MassGIS 2003 andMEEA 2014a). There are 61 dams within the South Coastal Watershed Basin with a total maximum storagecapacity of 15,506.5 acre-feet (USACE 2013).Referring to Figure 3-10, the Cape Cod Watershed Basin is situated south of the South Coastal Watershed Basin.It encompasses approximately 440 square miles and extends 70 miles into the ocean. It is surrounded byBuzzards Bay, Cape Cod Bay, the Atlantic Ocean and Nantucket Sound (MEEA 2014b). There are seven damson tributaries to Cape Cod Bay within the Cape Cod Watershed Basin with a total maximum storage capacity of656.9 acre-feet (USACE 2013).Cape Cod Bay constitutes the southernmost part of the Gulf of Maine. The bay is bordered by land to the west,south and east and it is open to Massachusetts Bay and the Gulf of Maine to the north. The surface area of CapeCod Bay is approximately 795 square kilometers (307 square miles) and it has a water volume of about 4.5 x 1010cubic meters (1.6 x 1012 cubic feet) (Davis 1992). If the total volume of all 61 South Coastal Basin dams and theseven dams on bay tributaries were to simultaneously fail and be instantly added to Cape Cod Bay, the water levelincrease within the bay would be less than one inch. Thus, the postulated failure of dams would have a negligible flooding effect at the PNPS site.3.3.3 Conclusions Based on conservative assumptions, potential breaches of dams within the South Coastal Watershed Basin and ontributaries to Cape Cod Bay within the Cape Cod Watershed Basin, would not impact SSCs important to safety atPNPS considering the following:

The failure of dams on watersheds that discharge to Cape Cod Bay or to Massachusetts Bay, just north ofCape Cod Bay, would have an insignificant impact on the water level within Cape Cod Bay.Page 44 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report* Once the flood waves from dam breaks reach Cape Cod Bay, water levels would be attenuated by thesize and storage volume available in Cape Cod Bay as well as in Massachusetts Bay and the Gulf ofMaine.3.3.4 References AREVA 2014. AREVA Document No. 51-9226924-000, Pilgrim Nuclear Power Station Flooding Hazard Re-Evaluation

-Screening for Dam Failures, October 2014.Davis 1992. Western Cape Cod Bay: Hydrographic, Geological, Ecological, and Meteorological Backgrounds for Environmental Studies by J. D. Davis, American Geophysical Union -Transferred from Springer-Verlag inJune 1992. (See AREVA Document No. 51-9226924-000)

MassGIS 2003. Massachusetts Office of Geographic Information, date modified March 2003; Available at:http://www.mass.gov/anf/research-and-tech/it-serv-and-support/application-serv/office-of-geographic-information-massgis/datalayers/majbas.html, date accessed August 15 and 19, 2014. (See AREVA DocumentNo. 51-9226924-000)

MEEA 2014a. The Massachusetts Executive Office of Energy and Environmental

Affairs, South CoastalWatersheds; Available at: http://www.mass.gov/eea/waste-mgnt-recycling/water-resources/preserving-water-resources/mass-watersheds/south-coastal-watersheds.html, date accessed August 19, 2014. (See AREVADocument No. 51-9226924-000)

MEEA 2014b. The Massachusetts Executive Office of Energy and Environmental

Affairs, Cape Cod Watershed; Available at: http://www.mass.gov/eea/waste-mgnt-recycling/water-resources/preserving-water-resources/mass-watersheds/cape-cod-watershed.html, date accessed August 19, 2014. (See AREVA Document No. 51-9226924-000)NRC 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United Statesof America, NUREG/CR-7046, U.S. Nuclear Regulatory Commission, November 2011.USACE 2013. U.S. Army Corps of Engineers National Inventory of Dams, date modified February 2013;Available at: http://geo.usace.army.mil/pgis/fp=397:

1:10956392017256, date accessed August 15 and 19, 2014.(See AREVA Document No. 51-9226924-000)

Page 45 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-10: Dams within the South Coastal and Cape Cod Watershed Basins[Source:

MassGIS 2003 and USACE 2013]Page 46 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.4 Storm SurgeStorm surges are defined as rises in offshore water elevations caused principally by the shear force ofwinds acting on water surfaces (NRC 2011, Section 3.5). Storm surges can be caused by a variety ofmeteorological events, including tropical cyclones and extra-tropical storms.An evaluation of the Probable Maximum Storm Surge (PMSS) flood hazard at PNPS was performed in amanner consistent with the HHA approach described in NUREG/CR-7046 (NRC 2011, Section 2). Thisevaluation was performed in two calculations.

The AREVA Calculation "Pilgrim Nuclear Power StationFlooding Hazard Re-Evaluation

-Probable Maximum Hurricane

/ Probable Maximum Wind Storm"(AREVA 2015a) assessed the Probable Maximum Hurricane (PMH) and the Probable Maximum WindStorm (PMWS) at PNPS. Parameters defining the PMH and PMWS, which were ultimately determined based on a site-specific meteorology study, were used as input to the storm surge analysis presented inAREVA Document No. 32-9226919-001, Pilgrim Nuclear Power Station Flooding Hazard Re-Evaluation

-Probable Maximum Storm Surge (AREVA 2015b), which developed the maximum still water surfaceelevation representative of the PMSS at PNPS.The methodology, results and conclusions associated with these calculations are presented below.3.4.1 Methodology The following sections summarize the methodology used to evaluate the PMH, PMWS and the PMSSelevation at PNPS..3.4.1.1 Probable Maximum Hurricane and Probable Maximum Wind StormA step-wise approach consistent with the HHA approach described in NUREG/CR-7046 (NRC 2011,Section 2) was used to deterministically evaluate the PMH and PMWS at PNPS, as both hurricanes andextra-tropical storms are of concern in the vicinity of PNPS as surge-generating meteorological events.The PNMH and PMWS were evaluated independently using the methods summarized below.The evaluation of the PMH included analyses of National Hurricane Center (NHC) historical, "Best-Track" hurricane data (i.e., HURDAT2) and, to supplement the extremely limited historical data,synthetic hurricane data representative of a large set of synthetic tropical cyclone tracks. The synthetic data were developed for the PNPS region by Dr. Kerry Emanuel of WindRiskTech, LLC (i.e., referred toherein as WRT) using coupled intensity and atmospheric models (refer to AREVA 2015a). Themethodology used to develop the synthetic tropical cyclone tracks and storm parameters includes:

1)storm generation;

2) storm track generation; and 3) deterministic modeling of hurricane intensity.

Usingthis methodology, a large number (i.e., 10,013) of synthetic storm tracks (i.e., referred to herein as theWRT storm set) was generated and filtered within a radius of 200 kilometers (kin) of Plymouth, Massachusetts (MA) to support the evaluation of the PMH at PNPS.The WRT storm set was compared to storm characteristics described by the HURDAT2 data set and,where present, variance from the historical hurricane data was identified.

Comparisons were performed for parameters reflecting storm intensity, direction, size and speed. Based on these comparisons, thesignificantly larger WRT data set was ultimately demonstrated to be a conservative reflection of stormcharacteristics within the PNPS vicinity.

The following steps were then used to evaluate the historical and synthetic data and characterize the PMHat PNPS:Page 47 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report1. Determination of National Weather Service (NWS)-23 PMH parameters:

Consistent withguidance presented in NUREG/CR-7046 (NRC 2011), ranges of potential PMH meteorological parameters were initially determined using NWS 23 (NOAA 1979). These parameters includedthe following:

1) peripheral

pressure,

2) central pressure,

3) permissible range for radius ofmaximum winds, 4) permissible range of forward speeds, 5) permissible range of track direction, and 6) estimated maximum I 0-meter, 10-minute over-water wind speed.2. Site-Specific Meteorology Study: The site-specific meteorology study included a statistical analysis of the HURDAT2 database and the synthetically-developed hurricane parameter data set.The analysis focused on data reflecting storm intensity, direction and physical dimensions in theregion of PNPS. Parameter selection was based on data availability within the HURDAT2database and relevance with respect to comparison to parameter estimates derived from NWS 23.Probability Density Functions (PDFs) were constructed for these parameters from Probability Density Histograms (PDHs) using a non-parametric kernel method. To further refine the analysisof the low probability portion of the 1-minute, 10-meter altitude (1-min, 10-m) average windspeed (mxw) distribution, Extreme Value Analysis (EVA) was used based on the Peak OverThreshold (POT) method and the Generalized Pareto Distribution (GPD). A detailed statistical analysis of the WRT storm data was then performed using techniques determined to beappropriate by expert meteorologist judgment.

These techniques included a univariate stormparameter probability

analysis, an analysis of storm parameter covariance, and development of alarge synthetic storm set extension (i.e., the 3,000,000 or 3M data set). Based on this analysis, adimensionless scaling function was developed to conservatively reflect the deterministic upper-limit of storm intensity (i.e., maximum wind speed) in the PNPS vicinity in consideration of co-variability with storm direction (i.e., storm bearing reflecting direction of storm travel measuredpositive in a clockwise direction from north).The site-specific meteorology study also included an evaluation of the PMWS. As part of this study, areview of available surface weather maps reflecting conditions during historically-significant extra-tropical storms in the PNPS vicinity was performed.

Following this review, an up-scaled wind fieldrepresentative of the PMWS at PNPS was developed in accordance with applicable guidance (e.g., ANS1992).The above-described methodology provided input to the storm surge analyses described below.3.4.1.2 Probable Maximum Storm SurgeThe HHA approach described in NUREG/CR-7046 (NRC 2011, Section 2) was also applied incalculating the PMSS at PNPS. Again, the PMH and PMWS were evaluated independently for surgegenerating potential using the methods summarized below.In evaluating the PMSS caused by the PMH, a screening-level assessment was first performed using thetwo-dimensional Sea, Lakes and Overland Surges from Hurricanes (SLOSH) computer model (NOAA2012a and NOAA 2012b). SLOSH is computationally efficient, allowing many simulations to beperformed over a relatively short period of time; however, the SLOSH model has limitations, including itsrelatively coarse, structured model grid. Therefore, SLOSH was applied in a relative manner to evaluateparameter sensitivity, and in a second phase of modeling, additional simulations were performed using theADvanced CIRCulation (ADCIRC) model (Luettich et al., 1992). Simulations were also performed usingADCIRC+SWAN (i.e., also known as ADCSWAN),

which is a form of ADCIRC that is tightly-coupled with the Simulating Waves Nearshore (SWAN) model (Booij et al., 1999). While ADCIRC andPage 48 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportADCIRC+SWAN are not hindered by many of the limitations associated with SLOSH, the high-resolution, finite-element mesh and related high computational demand prevent broad applications (i.e.,only a limited number of storm simulations is practicable in the context of a given analysis).

Therefore, ADCIRC was applied in a targeted fashion to further evaluate and refine surge predictions associated withthe storms identified based on the SLOSH sensitivity analysis.

More specifically, the PMSS methodology associated with the PMH included the following steps:I. Calculation of the Antecedent Water Level: An Antecedent Water Level (AWL) was calculated using data obtained from the Boston, MA National Oceanic and Atmospheric Administration (NOAA) tidal gaging station per applicable regulatory guidelines (ANS 1992 and NRC 2011). Inaccordance with these guidelines, observed monthly maximum tide data obtained over acontinuous 21-year period (i.e., January 1, 1993 through December 31, 2013) were used tocalculate the 10 percent exceedance high tide. Cumulative Sea Level Rise (SLR) based onobserved rates at the Boston station projected over a 50 year period was then added to obtain theAWL.2. PMH Parameter Sensitivity Assessment (SLOSH):

Simulations were performed using theSLOSH model, the Initial Storm Set, and the AWL to identify:

1) the sensitivity of storm surge atPNPS to different storm parameters (i.e., storm track, radius of maximum winds, etc.) asconstrained by the PMH calculation; and 2) the specific combinations of storm parameters andstorm tracks that result in the largest predicted storm surges at PNPS, also constrained by thePMH calculation.

The simulations assumed steady-state conditions (i.e., storm parameters werenot varied from the initial specifications).

A set of storms was selected for ADCIRC andADCIRC+SWAN simulations after processing the results of the SLOSH sensitivity analysis.

3. Refinement-Level Assessment of the PMH (ADCIRC and ADCIRC+SWAN):

Refined stormsurge simulations were performed using ADCIRC to evaluate the maximum storm surgeassociated with the PMH. Simulations were performed assuming steady conditions similar to thescreening-level assessment for the purpose of comparing ADCIRC to SLOSH. ADCIRCsimulations focused on predicting the maximum still water elevation associated with the PMSS;whereas, ADCIRC+SWAN simulations qualitatively evaluated wave setup and generated inputrequired for a combined effects analysis.

4. Assessment of the PMWS (ADCIRC and ADCIRC+SWAN):

To evaluate the maximum stormsurge caused by the PMWS, ADCIRC and ADCIRC+SWAN were directly applied based on theresults of the PMWS evaluation in a manner consistent with guidance presented in ANSI/ANS-2.8-1992, American National Standard for Determining Design Basis Flooding at NuclearReactor Sites (ANS 1992) and the HHA approach.

This evaluation included utilization of thepreviously-calculated AWL and the up-scaled PMWS wind and pressure field. Sensitivity ofsurge to stonn path (i.e., track direction) and storm forward speed was evaluated.

Note that the PMSS was determined as the greater of the maximum water surface elevations resulting from either the PMH or the PMWS.3.4.2 ResultsThe following sections describe the results of the PMIH, PMWS and PMSS evaluations at PNPS.Page 49 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.4.2.1 Probable Maximum Hlurricane

/ Probable Maximum Wind Storm3.4.2.1.1 Determination of NWS 23 PMH Parameters The location of PNPS is shown in Figure 3-11. Figure 3-12 also shows the location of PNPS in relation tocoastal distance intervals (i.e., mile posts) presented in NWS 23 (NOAA 1979). As indicated on Figure3-12, PNPS is located in the vicinity of NWS mile post 2800, where coastal distance is measured innautical miles from the Gulf of Mexico. Based on the location of PNPS, the PMH parameters shown inTable 3-4 were extracted from NWS 23.The methods of parameter development presented in NWS 23 are generally not consistent with thecurrent state of knowledge for characterizing the PMH affecting the PNPS vicinity.

In specific reference to PMH intensity reflected by maximum wind speed, NWS 23 values are recognized as lacking areflection of the relationship between storm direction and storm magnitude (i.e., co-variability),

which islikely to result in overly conservative intensity recommendations for west-of-north tracking (i.e.,westerly) storms. Thus, a detailed site-specific meteorology study was performed to develop thehurricane meteorological parameters for analysis of flooding due to combined storm surge and wind-generated waves. The results of this study, which also included an analysis of the PMWS at PNPS, aresummarized below.3.4.2.1.2 Site-Specific Meteorology Study -PMHRecorded track positions of tropical storms and hurricanes are maintained by the NHC in the annuallyupdated HURDAT database.

The official HURDAT database, referred to as HURDAT2, containsinformation on actual cyclones dating from 1851 through 2013 (NOAA 2014a). This American StandardCode for Information Interchange (ASCII)-formatted database contains six-hourly (00, 06, 12, 18Coordinated Universal Time, UTC) cyclone center locations (i.e., with differences in locations beingrepresentative of storm direction and translational speed) and intensities, with intensity being measured bythe maximum, 1-min sustained wind speed. Beginning with the 2012 hurricane season, the HURDAT2database contains additional storm information including some position and intensity data at nonstandard times and estimates of the radial distances of several wind speed thresholds.

The wind data at radialdistances are insufficient for estimating the radius of maximum winds, a parameter useful for storm surgemodeling but unavailable from the HURDAT2 dataset.

The HURDAT2 maximum sustained wind dataalso have limited precision.

Prior to 1885, storm intensity was recorded to the nearest ten knots and to thenearest five knots thereafter.

This becomes important in estimating the long return periods of stronghurricanes using extreme value statistics.

Statistical analyses were performed using data extracted from the HURDAT2 database over severalsampling domains depicted in Figure 3-13. The statistical analyses of these historical storm data werelimited with respect to characterizing the PMH due to the small sample size of hurricanes affecting thePNPS vicinity, particularly with respect to the representation of storms with high intensities.

For thisreason, synthetic hurricane data, which greatly increase the sample size of intense hurricanes in thevicinity of PNPS, were used to perform a more detailed statistical analysis of storm characteristics withinthe study area. This analysis, which included qualitative comparisons to the limited historical data, isdescribed below.The synthetic storm set, referred to herein as the WRT storm set, contains over 10,000 tropical storms andhurricanes characterized by track positions and various storm parameters.

These storms are generated byocean-coupled atmospheric and hurricane intensity models. The storm parameters are available at two-Page 50 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Reporthour intervals, and are pre-screened to impact the Cape Cod Bay (i.e., the source of surge impacts toPNPS).First, an EVA was performed using maximum wind speed data from the WRT storm set, the results werecompared to a similar analysis of the HURDAT2 data. The data, along with functional fits to the data, areshown in Figure 3-14. Based on visual inspection of this figure, the function derived from least-squares fitting appears to be non-conservative for maximum wind speeds exceeding approximately 105 knots (i.e.,due to probability-space weighting);

whereas, the fit derived from manual parameter selection demonstrates potential bias introduced through fitting to unrealistic data. In recognition of theunsatisfactory results produced by these fitting methods, a kernel method was used to generate aunivariate distribution (i.e., CDF) representative of maximum wind speed data in the PNPS subregion (refer to Figure 3-15). The results, shown in CDF form in Figure 3-15 and in terms of log return period inFigure 3-16, are less influenced by the unrealistic maximum wind speed data identified above (i.e.,probability determinations derived via the kernel method are not significantly biased by the previously-discussed unrealistic storms).

However, as the unrealistic data are not excluded from the analysis, aninfluence of these data on the kernel method predictions is evident (i.e., rather than plateauing near 120knots, as suggested by the behavior of the functional fit based on least squares fitting, the kernel methodpredictions continue to increase as return periods approach 100,000 years).Figure 3-15 and Figure 3-16 can also be used to evaluate probability determinations derived via the kernelmethod for the HURDAT2 data within the PNPS subregion (i.e., shown as dashed lines in each figure).The results indicate that the WRT maximum wind speeds produce conservative exceedance probability predictions at higher intensity levels (i.e., above approximately 95 knots) relative to analyses performed using HURDAT2 data, which are very limited with respect to sample size within the PNPS subregion.

For these reasons, the kernel method is carried forward to the extended analyses described below.The univariate distribution of storm bearing within the PNPS subregion, generated by the kernel method,is shown in Figure 3-17 based on WRT data. Tabulated cumulative frequencies and annualized cumulative frequencies are included over the same intervals as reported for the HURDAT2 analysis.

Forcomparison, the CDF curve from the HURDAT2 data is included as a dashed line. The distribution functions for the WRT and HURDAT2 data coincide

overall, but the comparison is particularly favorable for west-of-north bearings.

The annual cumulative frequencies associated with the WRT data are higherthan comparable HURDAT2 values for bearings west of -40* and lower for bearings in the range -30* to+10%; differences which are attributable to the small HURDAT2 sample size and the smoothing effect ofthe kernel method at the tail of the distribution.

In general, the WRT analysis produces more conservative return period estimates for most west-of-north storms.The distribution of storm forward speed from the WRT dataset is shown in Figure 3-18. HURDAT2 dataare shown as a dashed line for comparison.

Although the two distributions generally reflect agreement, the WRT dataset produces more frequent storms moving slower than 25 knots and less frequent stormsmoving at greater speeds compared to the HURDAT2 dataset.

As with the storm bearing distribution, differences are likely attributable to the small HURDAT2 sample size and smoothing effect introduced bythe kernel method at distribution tails.The results indicate that use of the WRT representation of the empirical storm data for estimating independent and joint variability of hurricane parameters will contain a conservative bias. While stormintensity is well-represented by the WRT data for major storms, the WRT's bias toward more frequentwesterly storms and lower forward speeds is expected, given the sensitivity to storm surge within CapePage 51 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportCod Bay relative to westerly storm tracks, to conservatively predict more frequent and larger storm surgesnear PNPS.Based on the analyses described above, parameters and parameter ranges representative of the PMH atPNPS were developed in recognition of parameter co-variability (refer to Table 3-5). The considered bearing range includes storms with bearings between -80' and 400 to provide a bounding parameter set(i.e., relative to the anticipated PMH) inclusive of more intense, northerly-bound storms. Maximumstorm intensities (i.e., maximum wind speeds) were determined by identifying a dimensionless scalingfunction that recovered variability of maximum wind speed as a function of storm bearing (Figure 3-19).While the process of identifying this scaling function involved probability calculations for parameter combinations (i.e., storm bearing and maximum wind speed), the resulting parameter combinations represent deterministic PMI-l limits, as the NWS 23 PMH maximum wind speed is used to establish theprobability threshold.

Ranges of the radius to maximum winds and forward speed parameters were also developed inconsideration of parameter covariability and a comparison to the NWS 23 recommended PMH parameter ranges. In the case of the radius to maximum winds parameter.,

an analysis of the synthetic data supported the NWS 23 recommended range; therefore, no change was warranted.

For the forward speed parameter, an evaluation of the synthetic data suggested an expanded range (i.e., decrease in the lower bound from40 to 20 knots) relative to the NWS 23 recommendation was supported and demonstrably conservative.

3.4.2.1.3 Site-Specific Meteorology Study -PMWSIn accordance with the procedures outlined in ANSIIANS-2.8-1992 (ANS 1992), the February 7, 1978storm was selected as a representative extra-tropical storm event for use in developing the properties ofthe PMWS. Surface weather maps for the storm were obtained from the National Climatic Data Center(NCDC) (NOAA 2014b) and used as input into the PMWS model. These maps were used to calculate isobars.,

distances between isobars, and wind angles affecting the PNPS region and to establish arelationship between the pressure maps and a geographic coordinate system in order to determine stormspeed.The February 7, 1978 extra-tropical storm approached Cape Cod from the south and travelled along theUS East Coast in an approximately southwest-to-northeast direction.

This path is similar to the tracksassociated with many of the historically-significant storms that have affected this region, as shown inFigure 3-20. The translation speed calculated for the February 7, 1978 extra-tropical storm in the PNPSvicinity ranged from 10 to 15 miles per hour (mph) with an average speed of 13 mph. As shown in Table3-6, the average translation speed ranged from 11 to 37 mph for eight of the top ten surge events atBoston, MA.To evaluate other potential PMWS paths, the tracks associated with storms responsible for the top 20storm surges at Boston, MA were digitized from the United States Daily Weather Maps from the NOAACentral Library (NOAA 2014c) and, where available, three-hour surface weather maps from NOAA(NOAA 2014d). The digitized storm tracks are shown in Figure 3-20.A spatially varying pressure and wind field was developed by dividing the PMWS into twelve radials(refer to Figure 3-21). Additional radials in the western half of the storm were added to more accurately spatially resolve the winds that cause the surge at PNPS. The PMWS isobar pattern was used to calculate the pressure, wind speed, and wind direction at points between each isobar for each radial.Page 52 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportThe PMWS pressure, wind speed, and wind direction at points between each isobar for each radial wascalculated using the methods presented in the USACE Coastal Engineering Manual (CEM) (Resio et al,2008). Wind direction for each point was estimated from the orientation of the isobars.

Wind directions were calculated to be at an angle of 10 degrees convergent across the isobars, as specified by ANSI/ANS-2.8-1992 (ANS 1992).In order for the maximum wind speed to reach 100 mph, the wind field speeds were scaled up by a factorequal to the ratio of 100 to the maximum wind speed of the entire storm (ANS 1992). In order for theminimum pressure to reach 950 millibars (mb), the minimum pressure of the storm, 991.4 mb, was scaleddown to 950 mb using a reduction of 41.4 mb for each pressure value. The resulting PMWS wind andpressure fields are shown in Figure 3-22.3.4.2.2 Probable Maximum Storm Surge3.4.2.2.1 Development of the Antecedent Water LevelIn accordance with NUREG/CR-7046 (NRC 2011), the PMSS is required to be evaluated coincidentally with an AWL equal to the 10 percent exceedance high tide plus long term changes in sea level. The 10percent exceedance high tide is defined as the high tide level that is equaled or exceeded by 10 percent ofthe maximum monthly tides over a continuous 21 year period. In accordance with ANSI/ANS-2.8-1992 (ANS 1992), this tide can be determined from recorded tide data or from predicted astronomical tidetables.In this calculation, the 10 percent exceedance high tide was calculated using recorded monthly maximumtide elevations from the Boston, MA tidal gaging station.

Using this approach, a value of 7.34 feetNAVD88 (8.17 feet MSL) was obtained.

In consideration of SLR, which was projected over 50 yearsusing the annual rate at the Boston, MA station, the AWL was determined to be 7.80 feet NAVD88 (8.63feet MSL).3.4.2.2.2 PMH Parameter Sensitivity Assessment (SLOSH)In performing the PMH parameter sensitivity analysis using the NOAA SLOSH model, results from5,005 simulations (i.e., tracks shown in the form of simulated surge elevation time series for eachsimulation) were extracted at locations including the model cell representing the PNPS shoreline (Figure3-23). The time series were reduced to peak surge elevations at this location for each simulated storm.Figure 3-24, Figure 3-25 and Figure 3-26 summarize the results of the PMH sensitivity assessment atPNPS. As indicated by Figure 3-24, SLOSH-simulated maximum still water elevations were found to bepositively correlated with radius to maximum winds. The upper limit of the radius to maximum windsrange (i.e., based on input derived from the PMH/PMWS calculation, AREVA 2015a) was found toconsistently result in the maximum still water elevation for all potential values of potential PMH bearing.As indicated by Figure 3-25, SLOSH-simulated maximum still water elevations were also found to havedirectionally-dependent (i.e., functionally related to storm bearing) sensitivities to landfall location.

Ingeneral, maximum still water elevations produced by PMH configurations moving west-of-north wereless sensitive to landfall location;

whereas, PMH configurations moving east-of-north producedmaximum still water elevations that were highly sensitive to landfall location.

However, in all cases,Page 53 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Reportsensitivity profiles (i.e., evaluated on a bearing-specific basis) indicated maximum still water elevations were well represented by PMiH configurations passing through landfall location 5 (refer to Figure 3-27).Finally, as indicated by Figure 3-26, SLOSH-simulated maximum still water elevations were found tohave directionally-dependent (i.e., functionally related to storm bearing) sensitivities to forward speed. Ingeneral, maximum still water elevations produced by PMH configurations moving west-of-north occurredfor forward speeds between 30 and 35 knots; PMH configurations moving south-to-north and east-of-north produced maximum still water elevations for forward speeds between 20 and 25 knots.The above-described process identified 13 PMH configurations to be simulated using ADCIRC and/orADCIRC+SWAN to produce maximum water surface elevation (WSEL) values at PNPS (i.e.,representative of storm-induced surge and wind-driven wave setup). The parameter combinations associated with these PMH configurations, which attempt to maximize surge response for each potential storm bearing within the considered range, are summarized in Table 3-7.3.4.2.2.3 Refinement Level Assessment of the PMH (ADCIRC and ADCIRC+SWAN)

ADCIRC+SWAN simulations were performed for PMH parameter combinations judged to berepresentative of conditions responsible for maximizing surge responses at PNPS for each considered storm bearing value based on the results of the sensitivity analysis described above. Results wereevaluated at a location within the model mesh representative of the PNPS shoreline (Figure 3-28).Simulations were again performed assuming steady-state storm forcing conditions occurring coincidentally with the AWL. Based on these simulations, the following combination of stormparameters was identified as being responsible for the maximum WSEL caused by a PMH configuration at PNPS:STORM ID = 3397 (refer to Figure 3-27)* Track Direction (0) = 10 degrees (0);* Landfall Location

= 5 (Latitude 41.7390, Longitude

-69.934');

Radius of Maximum Winds (Rmax) = 35 nautical miles (nm);* Forward Speed (Vf) = 20 knots* Maximum Wind Speed (Vm) = 128 knots; and* Central Pressure Deficit (CPD) = 112 mb.After identifying the controlling PMH configuration (i.e., STORM ID responsible for the highest WSELat PNPS), an additional ADCIRC-only simulation was performed to assess the amount of wave setupcontributing to the maximum WSEL at PNPS. The results of this simulation, which are tabulated inTable 3-8, indicate wave setup is a relatively small contributor (i.e., only 0. 1 feet) to the total maximumWSEL resulting from STORM ID 3397. This value is likely to be conservative, as breaking wave actionand near-shore wave reformation as a result of the influence of the breakwaters is likely to reduce near-shore wave setup. Additional evaluations of flooding potential and wave runup effects relative to plantgrade and flood protection elevations for equipment important to safety were performed using high-resolution, near-shore wave modeling as part of the combined flooding effects evaluation (see Section3.9).Page 54 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.4.2.2.4 Assessment of the PMWS (ADCIRC and ADCIRC+SWAN)

As a first step in evaluating the maximum surge caused by the PMWS, a set of base storm tracks wascreated using three values of potential storm bearing (Figure 3-29). The base track value of 76.50 reflectsthe generalized track direction associated with the "Blizzard of '78", or the extra-tropical storm that formsthe basis for the PMWS wind and pressure fields in the vicinity of PNPS. The two additional values (i.e.,61.50 and 91.50) represent 150 rotations of the base track. These rotations are used to evaluate alignment of maximum PMWS winds with the primary axis of the water body, in accordance with applicable guidance (ANS 1992).Each track was then assigned three values of forward speed (i.e., 9, 12 and 15 knots) based on the rangeof potential PMWS forward speeds identified during the PMWS evaluation.

The three tested valuesrepresent bounding conditions based on an assessment of the range of forward speeds associated withhistorically-significant extra-tropical events at the Boston, MA NOAA Center for Operational Oceanographic Products and Services (CO-OPS) station (AREVA 201 5a).Finally, the tracks were paired with the PMWS wind and pressure field developed from the PMWSevaluation to create the PMWS Storm Set. The PMWS Storm Set consists of the following nineparameter combinations:

3 (bearing) x 3 (forward speed) = 9 PMWS Parameter Combinations Each resulting PMWS configuration was assigned a unique storm identification (STORM ID) numberranging from ET_1 to ET_9. Table 3-9 shows the parameters associated with each PMWS simulation.

ADCIRC-only simulations were first performed for each of the PMWS Storm Set parameter combinations, with the results being representative of maximum still water elevations withoutcontributions from wind-driven wave setup. After assessing the results of the ADCIRC simulations, ADCIRC+SWAN simulations were performed for a subset of the PMWS Storm Set (i.e., bearing = 61.5',or the bearing associated with the highest maximum still water elevations) to calculate maximum WSELsin consideration of wind-driven wave setup.ADCIRC-simulated maximum still water elevations and ADCIRC+SWAN-simulated maximum WSELsat the PNPS shoreline location are provided in Table 3-10 for STORM IDs ET_I, ET_2 and ET 3. Asindicated by this table, the controlling parameter combination (i.e., STORM ID ET_2) produced thehighest maximum WSEL at PNPS of the three PMWS configurations simulated with ADCIRC+SWAN (i.e., bearing = 61.50). The parameters defining PMWS STORMID ET_2 are provided below:PMWS STORMID = ET_2* Track Direction (0) = 61.5'* Forward Speed (Vf) = 12 knots* Maximum wind speed and central pressure defined by PMWS wind and pressure fieldTable 3-10 also indicates that wave setup is, again, a relatively small contributor (i.e., only 0.5 feet) to thetotal maximum WSEL resulting from STORM ID ET_2. As previously noted, this value is likely to beconservative, as breaking wave action and near-shore wave reformation as a result of the influence of thebreakwaters is likely to reduce near-shore wave setup. Refer to Section 3.9 for additional evaluations offlooding potential and wave effects relative to plant grade and flood protection elevations for equipment Page 55 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Reportimportant to safety in which high-resolution, near-shore wave modeling was used to specifically evaluatethe effects of these features under combined flooding effect scenarios.

3.4.3 Conclusions

Based on the analyses described above, the following conclusions are reached:* Per ANSI/ANS-2.8-1992 (ANS 1992) and JLD-ISG-2012-06 (NRC 2013), the antecedent waterlevel inclusive of 50 years of projected SLR is 7.8 feet NAVD88.* The maximum still water elevation generated by a PMH configuration is 14.9 feet NAVD88 (15.7feet MSL). This elevation is caused by a PMH configuration landfalling along the eastern shoreof Cape Cod and traveling slightly east-of-north (i.e., bearing of 100)." The maximum still water elevationgenerated by a PMWS configuration is 14.0 feet NAVD88(14.8 feet MSL). This elevation is caused by a PMWS configuration passing to the south of CapeCod and traveling in an east-northeast direction (i.e., bearing of 61.50).* In both cases (i.e., the PMH and PMWS), wave setup contributions to total WSELs aredetermined to be relatively small and generally consistent between the two storm types (i.e., 0.1feet for the PMH versus 0.5 feet for the PMWS).* The PMSS at PNPS (i.e., assessed in terms of maximum still water elevation and wave setup) isthus determined to be 15.0 feet NAVD88 (15.8 feet MSL) resulting from a PMH.Uncertainty and conservatism were considered in the calculation as per Section 5.4 of NUREG/CR-7046 (NRC 2011), as follows.

The PMH and PMWS parameters, which are the basis for the ADCIRC modelused to calculate the PMSS, were adjusted to provide the most adverse conditions.

The adjustments included:

" Conservatism was promoted through the use of synthetic data, which show bias toward morefrequent, higher intensity tropical cyclones;

Conservatism introduced through the assumptions used in developing the antecedent water level,including the use of a 50-year projection window for defining applicable SLR;" Conservatism introduced by the generally positive bias demonstrated by theADCIRC/ADCIRC+SWAN model mesh verification with respect to simulated high water levelsrelative to observed data in the vicinity of PNPS (i.e., Boston, MA);* The predicted peak wind speed for the PMWS was increased to reflect a maximum over-water wind speed of 100 mph (as defined in ANSI/ANS-2.8-1992);

and" Storm tracks were simulated as straight lines, and forward speeds were set and constant (i.e.,steady) rates to increase the effect of the pressure gradients and resulting wind speeds.Thus, the results of this calculation represent a conservative deterministic assessment of the PMSS atPNPS.3.4.4 References ANS 1992. American National Standard for Determining Design Basis Flooding at Power Reactor Sites(ANSI/ANS 2.8 -1992).Page 56 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportAREVA 2015a. AREVA Document No. 32-9226726-000, Pilgrim Nuclear Power Station FloodingHazard Re-Evaluation

-Probable Maximum Hurricane

/ Probable Maximum Wind Storm, 2014.AREVA 2015b. AREVA Document No. 32-9226919-001, Pilgrim Nuclear Power Station FloodingHazard Re-Evaluation

-Probable Maximum Storm Surge, 2014.Booij et al., 1999. A third-generation wave model for coastal regions:

1. Model description andvalidation, J. Geophys.

Res., 104, 7649-7666, Booij, N., R. C. Ris, and L. H. Holthuijsen, 1999. (SeeAREVA Document No. 32-9226919-001)

Luettich et al., 1992. ADCIRC: An Advanced Three-Dimensional Circulation Model for Shelves Coastsand Estuaries:

Report I Theory and Methodology of ADCIRC-2DDI and ADCIRC-3DL, DredgingResearch Program Technical Report, DRP-92-6, R.A. Luettich Jr., J.J. Westerink and N.W. Scheffner, U.S., Army Engineers Waterways Experiment

Station, November 1992.NOAA 1979. Meteorological Criteria for Standard Project Hurricane and Probable Maximum Hurricane Wind Fields, Gulf and East Coast of the United States, National Oceanic and Atmospheric Administration Technical Report NWS 23, September 1979. (See AREVA Document No. 32-9226726-000)

NOAA 2012a. SLOSH Model v3.97 National Oceanic and Atmospheric Administration, Evaluation Branch, Meteorological Development Lab, National Weather Service, January 2012. (See AREVADocument No. 32-9226919-00 1 )NOAA 2012b. SLOSH Display Program (1.65b),

National Oceanic and Atmospheric Administration, Evaluation Branch, Meteorological Development Lab, National Weather Service, January 2012. (SeeAREVA Document No. 32-9226919-001)

NOAA 2014a. Revised Atlantic Hurricane Database (HURDAT2),

Atlantic Oceanographic andMeteorological Laboratory, National Oceanic Atmospheric Administration, Date accessed:

September and October, 2014. Date updated:

May 17, 2014. (See AREVA Document No. 32-9226726-000)

NOAA 2014b. National Oceanic and Atmospheric Administration, National Center for Environmental Prediction

/ National Center for Atmospheric Research (NCEP/NCAR)

Reanalysis Project.

NCEPReanalysis data provided by the NOAA/OAR/ESRL PSD, Boulder,

Colorado, USA, from their website athttp://www.esrl.noaa.gov/psd/

(See AREVA Document No. 32-9226726-000)

NOAA 2014c. U.S. Daily Weather Maps", National Oceanic and Atmospheric Administration, NationalWeather Service, various dates,http://www.lib.noaa.gov/collections/imgdocmaps/dailyweather-maps.html, date accessed:

October,2014. (See AREVA Document No. 32-9226726-000)

NOAA 2014d. SRRS Analysis and Forecast Charts, National Oceanic and Atmospheric Administration, various dates, date accessed:

November, 2014. (See AREVA Document No. 32-9226726-000)

NRC 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in theUnited States of America-NUREG/CR-7046, U.S. Nuclear Regulatory Commission, November 2011.NRC 2013. JLD-ISG-2012-06:

Guidance for Performing a Tsunami, Surge, or Seiche HazardAssessment, U.S. Nuclear Regulatory Commission, Revision 0, January 2013.Resio et al., 2008. Coastal Engineering Manual, Part II, Hydrodynamics, Chapter 11-2 Meteorology andWave Climate, Engineering Manual 1110-2-1100, U.S. Army Corps of Engineers, D. Resio, S. Bratosand E. Vincent, 2008. (See AREVA Document No. 32-9226726-000)

Page 57 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-4: PMH Parameters and Parameter Ranges per NWS 23 for PNPSParameter Peripheral

Pressure, P,Central Pressure, PoPressure

Deficit, APRadius to Max. Winds, RmaxForward Speed, TTrack Direction, 0Storm Bearing, FdirMaximum I-minute wind speed, VmaxUnitin Hg (mb)in Hg (rub)in Hg (mb)(rum)(kt)(0)(0)(kt)Lower Bound Upper Bound30.12 (1020)27.23 (922)2.89 (98)17 3440 50100 155-80 -25132.8 138.8Note: mb = millibars; kt = knots; nm = nautical miles; ' = degrees.Page 58 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-5: Recommended PMH Parameters for PNPS Vicinity Based on Site-Specific Meteorology StudyStorm Maximum Radius of MaximumBearing Wind Speed, Forward Speed, Vf0 Vm Winds, IIax.800 .88 k-t-700 91_kt 1-600 95 k-t-500 101 kit-400 108 k-t-300 114 kt20 to 50 kt 17 to 34 nm-200 119 kt..... .... ..(applies to all bearings)

(applies to all bearings)

-100 123 kt00 125 kt100 128 kt200 129 kt300 130 kt-400 128 kt INote: Maximum wind speed reflected as I-minute average.,

0-meter altitude value.Page 59 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-6: Forward (i.e., translational)

Speeds for Eight of the Top Ten Extra-Tropical Storms inthe PNPS VicinityStorm Event Forward Speed (mph) Forward Speed (kt)Blizzard of'78 13.0 11.3January 1987 16.4 14.3Perfect Storm 20.0 17.4January 1979 19.6 17.0December 1992 10.6 9.2December 1959 36.9 32.0December 1972 21.3 18.5December 2010 15.0 13.0Page 60 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-7: PMH Configurations Used in Refinement Simulations with ADCIRC andADCIRC+SWAN STORM ID2737295731773397361838384058427944994719493951605380CPD(mb)11211511311210098928072615345430(deg from N)Vf(kt)Rmax(nm)LandfallLocationVm(kt)403020100-10-20-30-40-50-60-70-8020202020252525303030303535353535353535353535353535355555555555555128130129128124123119114108101959188Note: Maximum wind speed (Vm) reflected as 1-minute

average, 10-meter altitude valueTable 3-8: Simulated Maximum Still Water and Total Water Surface Elevations forSTORM ID 3397ADCIRCSTORM ID (feetNAVD88)ADCIRC ADCIRC+SWAN ADCIRC+SWAN (feet MSL) (feet NAVD88) (feet MSL)WaveSetup(feet)3397 14.9 15.7 15.0 15.8 0.1Note: Tabulated values reflect rounding to one tenth of a foot precision.

Page 61 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-9: Ranges of Evaluated PMWS Bearing and Forward SpeedSTORM ID Storm Bearing Forward Speed(degrees from north) (kt)ET_1 61.5 9ET_2 61.5 12ET_3 61.5 15ET_4 76.5 9ET_5 76.5 12ET_6 76.5 15ET 7 91.5 9ET_8 91.5 12ET_9 91.5 15Table 3-10: Simulated Maximum Still Water and Total Water Surface Elevations for STORM IlDsET_I, ET_2 and ET_3STORM IDETI ET2 ET_3Without Wave Setup (feet NAVD88) 14.0 14.0 13.7With Wave Setup (feet NAVD88) 14.4 14.5 14.1Without Wave Setup (feet MSL) 14.8 14.8 14.5With Wave Setup (feet MSL) 15.2 15.3 14.9Wave Setup (feet) 0.5 0.5 0.4Page 62 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-11: Site SettingIPage 63 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-12: NWS 23 Locator Map with PNPS Mile Post Identified

[Source:

NOAA 1979]Note: Any illegible text or features in this figure are not pertinent to the technical purposes of this document.

Page 64 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-13: HURDAT2 Storm Tracks and Six-Hour Positions HURDAT2 Storm Tracks and 6-hourly positions (1851-2013)

Page 65 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-14: Peak-Over-Threshold and Generalized Pareto Distribution Functional Fit toWRT Maximum Wind Speed Data within the PNPS Subregion Return Periods:

GPO fit fut Cat>= 1 PNPS12'0A9It100I~Data: Filtered WRT (PNPS)leaslSq:

4 =-0.14: tr= 11.4Manual: k=-O.I;r=13.A anProb >=Cat 1: 0.024HURDAT2GPD function

, 4Manual Fit/---0* ~-~-I,AALeast Squares Fit7041LogliRetum Period (yrs)l(b)Note: "Stacks" indicate empty bins (i.e., no data) below the top circle.Page 66 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-15: Distribution of Maximum Wind Speed (vm) from the WRT Data within thePNPS Subregion WRT: COF(vm):

PNPS01.106S0.402000IHURDAT2CDFn= 273420 40 60 80 ICMaxvnum Sustained WOWds (Mi)Tabulated Wind Speed Exceedance Frequencies:

WRT PNPS region70 T s 100 110 10 13D 40Prvm) 0,452371 0214223 0061133 0.027149 01 62 0002014 j 000689 0.0006 -0000016An FrMq(Nm 0028373 00143 00050 0001703 0000499 0000126 0000043 0000014 O.OOOODIPage 67 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-16: Comparison of Maximum Wind Speed from the WRT Data to the Resulting Distribution Derived via the Kernel MethodReturn Periods:

GPD fit for Cat>= 1. PNPS140"130120.N 1101oo20Data: Filtered WRT (PNPS)leastSq:

4=-0.14:

t=11.4manual: 4=-0.1; a=131an Prob >=Cat 1: 0024HURDAT2 ,GPD function-IWRT (PNPS)Kernel Method)$807020I34Log[Retum Period (yrs)]Note: "Stacks" indicate empty bins (i.e., no data) below the top circle.Page 68 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-17: Distribution of Storm Bearing (fdir) from the WRT Data within the PNPSSubregion WRT: CDF(fdir):

PNPS1008 HUj 04020 2 :J~tn=-150 -100 -50 0 50o1Bowing (dogXNosU=O; Eestpo=vo)

HRDAT2CDF27340ooISOTabulated Track Bearing Frequencies:

WRT PNPS region-80 -70 40 40 20 -10 0 0 20 30 '40Pv~fdir) 0.0`101 0 0126100162 00225{00341 00552 0.0912 01486 0,2300=1 3510495660.6495 07855An Froqfdir) 0000 00008 0.001 0.0014 0.0021 0.0035 00067 0.0093 0,0147 0,0221 00311 00407 0.0493... ....0 0 .. ... ...0 ..........6. ..... .. ..... .......Page 69 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-18: Distribution of Forward Speed (fspd) from the WRT Data within the PNPSSubregion WRT: CDF(Is.pd):

PNPS0.4)HURIDAT2CDFn= 273410 D 10 ~I , 4-^aid Spccd (k(4~Tabulated Storm Forward Speed Frequencies:

WRT P.NPS regon20 14 45 '.0 0)1rlIsNIJ 0 544)7 0436" 0 21.011 40'"2A 104144 (11)111 11014)2M o01417 -(4Au " I w4ItpJ f4) I, hs 04)2q I412 I )04) I Zt 4)3N (22 t 0 M)" o) IA4~o0Page 70 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-19: Maximum Wind Speed as a Function of Storm Bearing at Fixed Return Periods of 100, 1,000, 10,000, 100,000 and1,000,000 years.WRT (3M; 3Mi): vmjbearing at RP=100.1000,10000,100000 yrs>.C--80 40 -20 0Bearing (0=N, >0=East)Note: Joint parameter variability is reflected in blue and independent parameter variability is reflected in red.-----9 A -

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-20: Storm Tracks Associated with Historically-Significant Extra-Tropical Events in theVicinity of PNPSNote: Any illegible text or features in this figure are not pertinent to the technical purposes of this document.

Page 72 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-21: PMWS Radial Selection Note: Any illegible text or features in this figure are not pertinent to the technical purposes of this document.

Page 73 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-22: PMWS Wind and Pressure FieldsLegend0 PNPSFebruary 7th, 1978Historical Storm TrackIsobarsRadial WindslOmr-Wind (mph)0.0 -15.015.0- 30.030.0-50.0 50.0-70.0

-70.0- 100.0Note: Any illegible text or features in this figure are not pertinent to the technical purposes of this document.

Page 74 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-23: SLOSH Model Basin -Output Cell LocationSLOSH cell(71 162)Note: Any illegible text or features in this figure are not pertinent to the technical purposes of this document.

Page 75 of 152 AARE VADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-24: Sensitivity of SLOSH-simulated Storm Surge to PMH Radius to Maximum Winds and Storm BearingME17 T1615 j1413 4-11 -* 16-17* 15-16w 14-15w 13-14E 12-13* 11-12-35 _E5 xE099S- -ZU -10 0Storm Bearing (deg. from north)203040__ --11 -ý -

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-25: Sensitivity of SLOSH-simulated Storm Surge to PMH Landfall Location and Storm Bearing17qr 16Co~ 15~14E13Eu~1211.............................

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..... .....-,---80 -60 i *--20 -_+0 ---20 -4011 10 9 8 7 6 5 441.444 41.505 41.551 4L611 41.635 4L666 41.739 41.863Landfall ID / Landfall Latitude (dec. degrees)341.9812 142.069 42.168M___ .1-AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-26: Sensitivity of SLOSH-simulated Storm Surge to PMH Forward Speed and Storm Bearing1716i15a,b..2 14E 13ES2i121120 25 30 35 40 45 50Forward Speed (kt)__ ----Z .I-AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-27: PMH Storm Tracks Evaluated During Sensitivity Assessment with SLOSHNote: Any illegible text or features in this figure are not pertinent to the technical purposes of this document.

Page 79 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-28: ADCIRC/ADCIRC+SWAN Finite Element Mesh for PNPS -PNPS Vicinityý_ _nf _Z III AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-29: PMWS Storm TracksPage 81 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.5 SeicheThis section addresses the potential for flooding at PNPS due to a seiche. Seiches are standing waves oroscillations of the free surface of a water body in an enclosed or semi-enclosed basin (Scheffner 2008). Seichesare initiated by external forcing mechanisms.

This section summarizes the seiche hazard assessment performed for the PNPS site. For further details, refer toAREVA Document No. 51-9226926-000 (AREVA, 2015).3.5.1 Methodology The HHA approach described in NUREG/CR-7046 (NRC 2011) was used to determine whether a seiche in CapeCod Bay can result in significant flooding at PNPS. This approach initially involves the determination of thenatural period of the bay, evaluation of the natural oscillation periods of the external forces and comparison of theperiods to determine if resonance is possible.

The intake and discharge channels were also evaluated for a seichehazard.3.5.2 Results3.5.2.1 Natural Periods of Cape Cod BayCape Cod Bay, at the southernmost end of the Gulf of Maine, is a generally rectangular embayment (Davis 1992).The mouth of the bay is 17.5 miles in width, extending from Race Point (located on the bay's east side) westwardto Bartlet Rock off the entrance to Green Harbor (located on the bay's west side) in the Town of Marshfield, Massachusetts, north of the Town of Plymouth.

At its widest point near its south end, the bay is 24 nautical mileswide (east-west direction).

In the north-south direction, the bay is approximately 20 nautical miles. The averagedepth of the bay is 82 feet. (PNPS 2013, Section 2.4.3.1.1 and Davis 1992)Referring to Figure 3-30, Cape Cod Bay is an open mouthed water body (PNPS 2013, Section 2.4.3.1.1),

with itsnorth end open and its south end closed. As such, the bay was evaluated as an open-ended/semi-enclosed basin inthe north-south direction, and as an enclosed basin in the east-west direction.

Using Merian's modified formula for a semi-enclosed basin (see Equation I below) which is based on the quarterwavelength theory, the bay's natural period in the north-south direction was estimated to be approximately 2.6hours. Using Merian's formula for an enclosed basin (see Equation 2 below), the bay's natural period in the east-west direction was estimated to range between 1.1 hours1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months (i.e., at the mouth of the bay) and 1.6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months (i.e., at thesouth end of the bay).T = 4L / (1 + 2n)(gh)°5 [Equation 1] (Scheffner 2008)Where:T is the periodL is the length of the basing is the acceleration due to gravityh is the average depth of the basin(gh)°5 is the shallow water wave speedn = the number of nodes along the axis of the basin (i.e., '0' is the primary mode for a semi-enclosed basin)Page 82 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportT = 2L / n(gh)05 [Equation 2] (Scheffner 2008)Where:T is the periodL is the length of the basing is the acceleration due to gravityh is the average depth of the basin(gh)°5 is the shallow water wave speedn = the number of nodes along the axis of the basin (i.e., 'I' is the primary mode in an enclosedbasin)3.5.2.2 External Forcing Mechanisms in Cape Cod BayReferring to Section 3.5.2.1 above, external

forcing, generally

seismic, astronomical and meteorological in nature,must have a period of approximately one to three hours to cause resonance within Cape Cod Bay. Therefore, theperiods of external forcing mechanisms were evaluated to determine if resonance with the periods of the bay islikely.Based on the PNPS operating basis earthquake and safe shutdown earthquake response spectrums, peak seismicforcing would not exceed 10 seconds (PNPS 2013, Figures 2.5-5 and 2.5-6); therefore, resonance within CapeCod Bay will not occur due to the large difference between the primary seiche modes of the bay and the period ofseismic motions.

Similarly, considering that astronomical tides are the primary forcing mechanism for flowwithin the bay and are dominated by semidiurnal tides (USGS 1992), the bay is not resonant near the semidiurnal frequency of 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months for astronomical forcing.

Meteorological forcing also does not have sufficient energy todrive a seiche in Cape Cod Bay. Wind generated waves in the bay have periods ranging from eight to eighteenseconds (PNPS 2013, Section 2.4.4.2),

which are too short to force a seiche in the bay. Additionally, localconvection drives wind gusts with a period of about one minute, and diurnal heating and cooling also drive weakperiodic motions.

For periods longer than a day, wind energy typically reaches a maximum fluctuation at a periodof a few days (i.e., three to seven days) due to the large synoptic scale variability of the atmosphere (Wells 1997).3.5.2.3 Natural Periods of the Intake and Discharge ChannelsReferring to Figure 3-3 1, the PNPS intake channel is situated between the main breakwater (i.e., the northwest breakwater) and the east breakwater (i.e., the breakwater on the southeast side). The east breakwater isapproximately 700 feet long, and the widest distance between the main and east breakwaters is approximately 2,000 feet (PNPS 2013, Section 2.4.4.1 and PNPS 2008). Based on bathymetric data for the northwestern portionof the intake channel, the channel has an average depth of about 12.5 feet (PNPS 2013a, Attachment G). UsingMerian's

formula, the intake channel's natural periods as a semi-enclosed basin and enclosed basin are estimated to be 2.3 minutes (in the northeast-southwest direction) and 3.3 minutes (in the northwest-southeast direction),

respectively.

The PNPS discharge channel is located north/northwest of the intake structure (see Figure 3-31) and is protected by rock-fill jetties (PNPS 2013, Section 2.4.4.1).

It is about 870 feet long (PNPS 2013, Section 2.4.4.1) and about100 feet wide (PNPS 1970, Figure 6). Based on the mean spring tidal range depth of 10.6 feet (PNPS 2013,Section 2.4.4.2),

the discharge channel's natural periods are estimated to be 3.1 minutes in the longitudinal direction and 1 seconds in the transverse direction.

3.5.2.4 External Forcing Mechanisms in the Intake and Discharge ChannelsReferring to Section 3.5.2.2 above, the periods for peak earthquake frequency and wind generated waves are lessthan the natural periods of the intake channel, whereas the tidal flow period is several orders of magnitude larger.Page 83 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportHowever, the period of one minute for wind gusts is close to the intake channel's natural periods.

If a seiche wereto occur in the intake channel, the height of the seiche in the northeast-southwest direction and in the northwest-southeast direction would be limited to the elevation of the breakwaters at 11.2 feet MSL. As such, it would notovertop the land side of the intake channel which has a minimum elevation of 20 feet MSL (PNPS 2013, Sections2.4.1.2 and 2.4.4.1).

The period of the primary mode of the discharge channel in the transverse direction is near the range ofearthquake frequency.

However, the height of a seiche in the transverse direction would be limited by theelevation of the jetties at 16 feet mean low water (MLW). Considering that station grade is at 20 feet MSL, whichis equivalent to 24.78 feet MLW (PNPS 2013, Section 2.4.4.2),

the seiche would not overtop the landward end ofthe channel.

For similar reasons, although the period of one minute for wind gusts is close to that of thedischarge channel in the longitudinal direction, it would not result in flooding.

Although astronomical tides inCape Cod Bay have periods that are several orders of magnitude larger than the longitudinal period of thedischarge channel and will not cause resonance within the channel, wind generated waves could occur withperiods in the range of the discharge channel's transverse period; however, the channel's geometry does not allowwaves to enter in the transverse direction.

3.5.3 Conclusions

Cape Cod Bay was identified as being susceptible to seiches.

However, the large difference between the naturalperiods of the bay and the periods of seismic motions and semidiurnal tides precludes seismic-induced orastronomical-induced seiches.

Additionally, although meteorological forcing has a broad energy spectrum, ittypically does not have sufficient energy to drive a seiche in Cape Cod Bay at the estimated seiche modes. ThePNPS intake and discharge channels were also identified as susceptible to seiches;

however, potential seiches inthe channels would not result in flooding.

Therefore, no further analysis or modeling is required for the seicheflooding hazard.3.5.4 References AREVA 2015. AREVA Document No. 51-9226926-000, Pilgrim Nuclear Power Station Flooding Hazard Re-Evaluation

-Screening for Seiche, January 2015.Davis 1992. Western Cape Cod Bay: Hydrographic, Geological, Ecological, and Meteorological Backgrounds for Environmental Studies by J. D. Davis, American Geophysical Union -Transferred from Springer-Verlag inJune 1992. (AREVA Document No. 51-9226926-000)

NRC 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United Statesof America -NUREG/CR-7046, U.S. Nuclear Regulatory Commission, November 2011.PNIPS 1970. Pilgrim Nuclear Power Station Model Wave Study, Prepared by Alden Research Laboratories, datedFebruary 1970. (AREVA Doc. No. 38-9226908-000)

PNPS 2008. Pilgrim Nuclear Power Station Site Plan, EC #5000072228, dated September 22, 2008. (AREVADoc. No. 38-9226908-000)

PNPS 2013. Pilgrim Nuclear Power Station Final Safety Analysis Report (FSAR), Revision 29, October 2013.(AREVA Doc. No. 38-9226908-000)

PNPS 2013a. Pilgrim Nuclear Power Station Document CR-PNP-2013-5246, HT -Apparent Cause Evaluation, Technical Specification Limit Exceeded for UHS Temperature, Rev. 1, dated September 3, 2013. (AREVA Doc.No. 38-9226908-000)

Page 84 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportScheffner 2008. Water Levels and Long Waves, In: Demirbilek, Z., Coastal Engineering Manual, Part II,Coastal Hydrodynamics.,

Chapter 5, Engineering Manual 1110-2-1100, U.S. Army corps of Engineers, Washington, D.C. (See AREVA Document No. 51-9226926-000)

USGS 1992. Woods Hole Branch of the U.S. Geological Survey, WHOI-92-35, Technical Report Tides ofMassachusetts and Cape Cod Bays by J.D. Irish and R.P. Signell, September 1992; Available at:http://www.dtic.-nil/dtic/tr/fulltext/u2/a264790.pdf, Accessed August 12, 2014. Abstract available at:http://www.researchgate.net/publication/33547852_Tides of Massachusetts andCapeCodBays, AccessedAugust 1, 2014. (See AREVA Document No. 51-9226926-000)

Wells 1997. The Atmosphere and Ocean, A Physical Introduction, by N. Wells, 2nd Edition, John Wiley & SonsLtd., 1997. (See AREVA Document No. 51-9226926-000)

Page 85 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-30: Cape Cod Bay[Source:

Davis 1992]GoF0*C)20CC)2.0mgFigure 1. Cape Cod Bay, Cape Cod, Buzzards Bay, and adjacent land and waters. Locations of PilgrimNuclear Power Station and Canal Power Station Indicated.

o<Page 86 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-31: PNPS Intake and Discharge Channels[Source:

PNPS 1970]Page 87 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.6 TsunamiThis section addresses the potential for flooding at PNPS due to the Probable Maximum Tsunami (PMT). PNPSis considered a "coastal" nuclear power plant site; therefore, an evaluation of the potential impact of oceanictsunamis was required.

Tsunami or tsunamis are waves generated by a vertical displacement of a water column.The waves propagate radially from a subsurface point of origin, which is commonly referred to as thetsunamigenic source (NRC 2009). According to Grilli et al. 2011, examples of potential tsunamigenic sourcesinclude seismic activity (e.g., tectonic displacement) and indirect or secondary effects of seismic (i.e., co-seismic tsunamis) or volcanic activity (e.g., submarine mass failure (SMF) or volcanic flank collapse stemming from asubmarine eruption).

The PMT is defined as that tsunami for which the impact at the site is derived from the useof the best available scientific information to arrive at the set of scenarios reasonably expected to affect thenuclear power plant site, taking into account:

1) appropriate consideration of the most severe of the naturalphenomena that have been historically reported for the site and surrounding area, with sufficient margin for thelimited accuracy, quantity and period of time in which the historical data have been accumulated;

2) appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena; and 3)the importance of safety functions to be performed (NRC 2009).This section summarizes the PMT assessment performed in AREVA Document No. 51-9226934-000, PilgrimNuclear Power Station Flooding Hazard Re-Evaluation

-Screening for Tsunami (AREVA 2014).3.6.1 Methodology The 1HA screening approach described in NUREG/CR-6966, Tsunami Hazard Assessment at Nuclear PowerPlant Sites in the United States of America (NRC 2009) and Interim Staff Guidance (ISG) JLD-ISG-2012-06, Guidance for Performing a Tsunamni, Surge, or Seiche Hazard Assessment (NRC 2013) was used to determine iftsunami-induced inundation represents the controlling flooding mechanism at PNPS. Consistent with thisapproach, regional and site screening tests were performed.

The regional screening test assessed near-field and far-field tsunamigenic sources based on a review of industry-standard technical literature and available scientific data on tsunami hazards in the Atlantic Ocean. The reviewedinformation included:

1) the NOAA NGDC tsunami and earthquake databases (NGDC 2014); 2) a comprehensive study of the tsunami hazard in the Atlantic Ocean published by the Atlantic and Gulf of Mexico Tsunami HazardAssessment Group (AGMTHAG 2008); and 3)a detailed literature review performed by leading researchers focusing on tsunamigenic sources associated with tsunami hazards along the Atlantic Coast (Grilli et al., 2011).The review of this literature was used identify potential tsunamigenic sources and determine the source posing thegreatest potential threat to PNPS (i.e., the source associated with the PMT).The site screening test compared the location and elevation of PNPS relative to areas affected by tsunamis in theregion. Consideration was given to local characteristics, including plant grade relative to the water surfaceelevation and distance to the shoreline.

This test was used to assess the risk of site flooding from the PMTrelative to other potential flood-causing mechanisms (e.g., the Probable Maximum Storm Surge) as defined inNUREG/CR-7046 (NRC 2011).Per the screening protocols defined by NUREG/CR-6966 (NRC 2009), more detailed

analyses, which mayinclude detailed numerical modeling of tsunami genesis and propagation, are required if projected PMT runupeffects suggest risk relative to flood-protected elevations and site SSCs important to safety.3.6.2 ResultsBased on a review of available information, the regional screening test identified a near-field tsumanigenic source(e.g., an SMF along the continental shelf potentially triggered by seismic activity) as being the source responsible for the PMT (Figure 3-32). Three historic tsunamis have been observed resulting from either earthquakes orPage 88 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrm Nuclear Power StationFlood Hazard Re-Evaluation Reportsubmarine landslides caused by earthquakes along the Nova Scotia Margin and in the Labrador Sea off the coastof Newfoundland (NGDC 2014). However, several physical characteristics that would mitigate the tsunami riskin the vicinity of PNPS were identified.

These characteristics include:

1) the shallow, generally-continuous bank/shelf of Georges Bank, the Scotian Shelf, and Nova Scotia, which enclose and protect the Gulf of Maine; 2)the southern and eastern outer banks of Cape Cod, which protect Cape Cod Bay to the south and east; 3) theshallow banks (e.g., Stellwagen Bank), which extend from the northern tip of Cape Cod toward Cape Ann to thenorth; 4) the significant distance (i.e., over 200 miles) between the outer edge of the continental shelf (i.e.,primary potential SMF tsunami source) and PNPS; and 5) the orientation of the continental shelf and slope (i.e.,and potential SMFs along the slope) relative to PNPS (Figure 3-33).The site-screening test identified shielding resulting from the location of PNPS relative to the hooked peninsula ofCape Cod and northwest-trending

shallows, which include Stellwagen Bank. Due to this shielding and inrecognition of the orientation of the continental shelf, flooding effects at PNPS due to tsunami events weredetermined to be bounded by other potential flood-causing mechanisms, specifically the PMSS.3.6.3 Conclusions While tsunamis may be generated from far-field and near-field

sources, the regional screening test suggested thata near-field source, such as an SMF along the continental shelf, represents the most significant tsunami hazardrisk in the vicinity of PNPS. However, review of the NOAA NGDC tsunami database (NGDC 2014) did notidentify any documented, historic tsunami events along the U.S. East Coast that resulted in significant historical tsunami impacts (i.e., runup heights greater than two to three feet). Furthermore, local and regional physicalcharacteristics, such as the protection provided by the orientation of Cape Cod, Georges Bank, the Scotian Shelf,and Nova Scotia, greatly reduce the potential impact of a tsunami generated by a near-field source in the PNPSvicinity.

The results of the site screening test suggested that a tsunami would not be a significant contributor to floodingpotential at PNPS in consideration of 1) the site's location relative to Cape Cod Bay; 2) the relatively low level ofexposure to the open ocean; and 3) the complex geography and bathymetry of the region (i.e., Cape Cod andGeorges Bank). Therefore, a tsunami was not considered to be the controlling flood hazard at PNPS.No further analysis or modeling is required due to the results of the screening

analysis, as potential tsunami eventswill not cause the controlling flooding event at PNPS and will not impact SSCs important to safety.3.6.4 References AGMTHAG 2008. Atlantic and Gulf of Mexico Tsunami Hazard Assessment Group, Evaluation of TsunamiSources with the Potential to Impact the U.S. Atlantic and Gulf Coasts -An Updated Report to the NuclearRegulatory Commission, U.S. Geological Survey, 2008. (See AREVA Document No. 51-9226934-000)

AREVA 2014. AREVA Document No. 51-9226934-000, Pilgrim Nuclear Power Station Flooding Hazard Re-evaluation

-Screening for Tsunami, 2014.Grilli et al., 2011. Grilli, S. T., Harris, J. C., & Tajalli Bakhsh, T., Literature Review of Tsunami SourcesAffecting Tsunami Hazard Along the U. S. East Coast, Center for Applied Coastal Research, University ofDelaware/University of Rhode Island, 2011. (See AREVA Document No. 51-9226934-000)

NGDC 2014. National Geophysical Data Center / World Data Service:

Global Historical Tsunami Database.

National Geophysical Data Center, NOAA, doi: 10.7289/V5PN93H7; Accessed:

July 28, 2014. (See AREVADocument 51-9226934-000)

NRC 2009. Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America-FinalReport.,

NUREG/CR-6966, March 2009.Page 89 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportNRC 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the UnitedStates of America, NUREG/CR-7046, U.S. Nuclear Regulatory Commission, November 2011.NRC 2013. JLD-ISG-2012-06, Guidance for Performing a Tsunami, Surge, or Seiche Hazard Assessment, Interim Staff Guidance, Revision 0, January 2013.Page 90 of 152 AAR EVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-32: Tsunamigenic Source Locations

[Source:

Grilli et al., 2011]____ ýA -Z ý I, AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-33: Gulf of Maine Bathymetry M_ ---_Z A 1^

AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.7 Ice-Induced FloodingIce jams and ice dams can form in rivers and streams adjacent to a site and may lead to flooding by twomechanisms (NRC 2011):* Collapse of an ice jam or a dam upstream of the site can result in a dam breach-like flood wave thatmay propagate to the site, and;* An ice jam or a dam downstream of a site may impound water upstream of itself, thus causing a floodvia backwater effects.In addition, although frazil ice is not related directly to flooding, NUREG/CR-7046 (NRC 2011) recommends thatair temperature data for meteorological stations located near the site be collected since frazil ice can be aprecursor to the formation of ice jams or ice dams. Frazil ice forms in supercooled, turbulent water that is free ofice and snow cover. For supercooling to occur, the air temperature usually must be 18 OF or lower (NRC 2011,Appendix G).The following summarizes the ice induced flooding assessment performed for the PNPS site.3.7.1 Methodology The HHA approach described in NUREG/CR-7046 (NRC 2011) was used for ice induced flooding.

As such,historical data was reviewed to assess if the site vicinity is subject to ice induced flooding and a site assessment was performed using conservative, simplifying assumptions to develop a conservative estimate of the effects atthe site from the corresponding, historically observed event (AREVA 2014).3.7.2 Results3.7.2.1 Regional FindingsA search of the U.S. Army Corps of Engineers (USACE) Ice Jams Database was performed and revealed thatthere have been no ice jams on or near Cape Cod Bay (USACE 2014). Air temperature data summaries for thenearest National Climatic Data Center (NCDC) meteorological stations to PNPS, Plymouth-Kingston andPlymouth Municipal Airport stations, were also reviewed and indicated that for the years of 1981 to 2010, theannual/seasonal normal, winter minimum temperature for both stations was near 18 °F. In addition, the normalminimum temperature for the month of January for the Plymouth-Kingston Station was 17.9 °F and that for thePlymouth Municipal Airport was 18.6 °F (NCDC 2014). Therefore, although temperatures along the Cape CodBay shoreline are typically tempered due to relatively warm water in the winter compared to temperatures forinland locations (PNPS 2013, Section 2.3.1), since conditions can potentially exist along the bay's shoreline forfrazil ice to form, a site assessment was subsequently performed.

3.7.2.2 Site FindingsAs noted in the PNPS FSAR, ice glaze formation typically develops a few times each winter during favorable weather and past storms have deposited ice glaze of 0.25 inches or more in thickness in the site area, although thecoastal location of the PNPS site makes it less susceptible to ice glaze formation than nearby inland locations (PNPS 2013, Section 2.3.6). Additionally, although the mean temperature of bay water is about 35 °F in thewinter, the water temperature can dip below 30 "F (PNPS 2013, Figure 2.4-2). However, it is likely that thewarmer water associated with service water and circulating water discharges back to the bay via the discharge channel (PNPS 2013, Sections 10.7.5 and 11.6.3) aid in suppressing the development of frazil ice.Page 93 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportThere are no rivers adjacent to the PNPS site. Discharge for Bartlett Pond/Beaver Dam Brook and the mouth ofthe Eel River are approximately one and three-quarter, and two and one-quarter miles from PNPS, respectively.

Similarly, there are no streams adjacent to the PNPS site. PNPS is located in a small, isolated drainage area onthe northeast side of Pine Hill. Since flooding at PNPS due to ice jams or ice dams on rivers or streams is notlikely, a hypothetical ice jam within the intake and discharge channels was postulated.

To estimate the maximumsurface ice thickness that could form, accumulated freezing degree-day (AFDD) data was obtained.

Freezingdegree-days accumulated at a specific location are defined as the differences between mean daily air temperatures and the freezing point of water (32 OF). For the Plymouth Municipal

Airport, the winter of 2013-2014 wasparticularly cold and resulted in a maximum AFDD value of about 410 for March 2014 (CRREL 2014). Usingthe modified Stefan equation presented by the U.S Army Corps of Engineers, surface ice thickness was estimated as a function of AFDD as follows:Ice Thickness (in), t = C(AFDD)°5 (USACE 2004)Where: t = Ice thickness, in inchesC = Coefficient for water body size, wind conditions and snow cover. The 'C' value ranges from 0.12 to0.8 with a usual range between 0.3 and 0.6.AFDD = Accumulated Freezing Degree-Days, in OFUsing a conservative

'C' value of 0.8, representing a windy lake with no snow, and the maximum AFDD of 410,gives an estimated ice thickness of 16 inches. This estimate is considered conservative in regards to seawater icethickness because it assumes a freshwater freezing point of 32 OF. The freezing point of water in Cape Cod Baywill be depressed due to its salinity

content, which will mitigate the formation of surface ice. Assuming that theestimated ice thickness of 16 inches melts and becomes impounded within the intake and discharge channelswhen the tide is at its historical high elevation of 10.5 feet MSL (i.e., which occurred at Boston in February 1723and is the highest still water tide level ever recorded in the site area (PNPS 2013, Section 2.4.4.2)),

water withinthe channels would rise to elevation 11.83 feet MSL; however, the rise in water level would be below PNPSstation grade at 20 feet MSL (PNPS 2013, Section 2.4.1.2).

In the event that the estimated ice thickness of 16inches was to develop in the service water pump bays when the tide is at the predicted minimum low water levelelevation of (-)10.1 feet MSL (PNPS 2013, Section 2.4.4.2),

the available water level would be at (-) 11.43 feetMSL. Considering that the Salt Service Water System, which provides a heat sink for the Reactor BuildingClosed Cooling Water System, is not anticipated to be adversely impacted unless the seawater level is 13.75 feetMSL (PNPS 2013, Sections 2.4.4.2 and 10.7.1),

a margin of 2.32 feet would remain for flow passage.3.7.3 Conclusions Based on historical records and a hypothetical ice jam, ice induced flooding at PNPS is not likely to impactsafety-related SSCs considering the following:

There are no ice jams on record for Cape Cod Bay or on waterways in the site vicinity.

There are no streams adjacent to PNPS in which ice jams or ice dams could form and impact PNPS. Sitedrainage is independent of other area drainage basins.* Although PNPS is potentially susceptible to frazil ice formation, frazil ice would not directly result inflooding.

" A potential rise in water level within the intake and discharge channels would be below station grade forconservatively assumed ice melt conditions.

Ice formation within the service water pump bays would still allow for sufficient service water flow.Page 94 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportIce formation on Cape Cod Bay is not likely to result in flooding at PNPS.3.7.4 References AREVA 2014. AREVA Document No. 51-9226932-000, Pilgrim Nuclear Power Station Flooding Hazard Re-Evaluation

-Screening for Ice Induced, October 2014.CRREL 2014. USA Cold Regions Research

& Engineering Laboratory, Accumulated Freezing Degree-Days forMassachusetts, Available at: https:/Hwebcam.crrel.usace.army.ml/AFDD/

andhttps://webcam.crrel.usace.army.rniI/AFDD/maplymouth_muni.gif, dated accessed August 21 and 22, 2014.(See AREVA Document No. 51-9226932-000)

NCDC 2014. National Climatic Data Center, Data Tools: 1981-2010

Normals, Available at:http://www.ncdc.noaa.gov/cdo-web/datatools/normals, date accessed August 25, 2014. (See AREVA DocumentNo. 51-9226932-000)

NRC 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the UnitedStates of America, NUREG/CR-7046, U.S. Nuclear Regulatory Commission.,

November 2011.PNPS 2013. Pilgrim Nuclear Power Station Final Safety Analysis Report (FSAR), Revision 29, October 2013.(AREVA Doc. No. 38-9226908-000)

USACE 2014. U.S. Army Corps of Engineers, Ice Jams Database, Ice Engineering Research Group, ColdRegions Research and Engineering Laboratory; Available at: http://icejams.crrel.usace.army.mil/;

date accessedAugust 21. 2014. (See AREVA Document No. 51-9226932-000)

Page 95 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.8 Channel Migration or Diversion Natural channels may migrate or divert either away from or toward the site. The relevant event for flooding is thediversion of water towards the site. There are no well-established predictive models for channel diversions.

Therefore, it is not possible to postulate a probable maximum channel diversion event. Instead, historical recordsand hydro-geomorphological data should be used to determine whether an adjacent

channel, stream, or river hasexhibited the tendency to meander towards the site (NRC 2011, Section 3.8).This section summarizes the Channel Diversion evaluation performed in AREVA Document No. 51-9226930-000 (AREVA 2014).3.8.1 Methodology The channel diversion flooding evaluation followed the H-A approach described in NUREG/CR-7046, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America (NRC2011).With respect to channel diversion, the following two steps were used for the H]A:1. Channel diversion phenomena or mechanisms were identified by reviewing historical and hydro-geomorphological data and assessing the effects of the phenomena in the site region.2. A conservative estimate of the effects at the site from historical and hydro-geomorphological data usingconservative simplifying assumptions was developed.

3.8.2 ResultsSince there are no channels, rivers or streams adjacent to the PNPS site or nearby (i.e., Bartlett Pond and BeaverDam Brook, which flows into Bartlett Pond, are about one and three-quarter miles to the southeast and the EelRiver is about two and one-quarter miles to the west (USGS 1977 and USGS 2012)), channel diversion/shoreline erosion of Cape Cod Bay was evaluated.

3.8.2.1 Regional FindingsThe shoreline of Cape Cod Bay is at risk of erosion due to high winds, waves and storm surge flooding as a resultof tropical and extratropical storms (hurricanes and nor'easters).

As such, Plymouth County on Cape Cod Baywas selected for the Federal Emergency Management Agency (FEMA) erosion hazard mapping study (O'Connell 1999) since its shoreline ranges from low-lying beaches to high, unconsolidated sedimentary cliffs, which isrepresentative of the coastal environments in Massachusetts.

Based on 147 years of available data, FEMA's studyfound that although there are areas with recession rates as high as four feet per year, Plymouth County has a fairlylow rate of erosion.

Approximately, one third of the county was determined to have a relatively stable coastline and about 40 percent of the shoreline erosion rate was found to be less than 1.5 feet per year, with an averageannual erosion rate of about 0.5 feet per year (O'Connell 1999). Based on the 1977 and 2012 topographic maps,there are no readily apparent signs of shoreline erosion on Cape Cod Bay in the vicinity of the PNPS site (USGS1977 and USGS 2012). Referring to Figure 3-34 and Figure 3-35, the absence of significant shoreline erosion isshown on the 1:25,000 (1977) and 1:24,000 (2012) scale topographic maps by the close similarity of shoreline configuration maintained during the intervening 35 years. However, since the Cape Cod Bay shoreline is prone toerosion which may divert bay water inland, a site assessment was subsequently performed.

3.8.2.2 Site FindingsThe PNPS shoreline is stabilized against erosion from wind, currents, water fluctuations and storm conditions bya series of breakwaters and discharge channel jetties constructed of heavy rock (PNPS 2013, Section 2.4.4. 1).Page 96 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportThe main breakwater is 1,400 feet long and parallel to the shoreline; it separates the intake channel from CapeCod Bay. The east breakwater is 700 feet long and perpendicular to the shoreline at the southeast shorefront.

Thetop of both breakwaters is at elevation 11.2 feet MSL (BEC 1993, PNPS 2013, Section 2.4.4.1 and PNPS 2014).In addition to preventing rapid siltation of the dredged intake channel, the breakwaters protect the intake structure and revetments from excessive wave action and overtopping so that storm flooding at PNPS is limited.

The on-shore, stone revetments on either side of the intake structure also provide shoreline stabilization and preventflooding during severe storms (PNPS 2013, Sections 1.6.1.1.8 and 2.4.4.1).

Similarly, the 870 foot long discharge channel jetties, with a nominal elevation of 11.2 feet MSL., protect thedischarge and intake structures from wave action (PNPS 2013, Section 2.4.4.1).

The breakwaters were damaged during the winters of 1977-1978 and 1978-1979 and were subsequently repairedto their original configuration.

In addition to repairing the breakwaters, resolution also included a commitment tothe NRC by PNPS to monitor the breakwaters on an annual basis and after major storms to ensure their integrity.

(BEC 1993, Attachments 6, 9 and 10, and PNPS 2013, Section 2.4.4.1).

Hence, it is unlikely that the shoreline atPNPS will experience changes due to shoreline erosion processes that would divert bay water towards the PNPSsite and impact safety-related components.

3.8.3 Conclusions

The historical, topographic and geologic data in the region indicate that there is limited potential fordiversion/erosion of the Cape Cod Bay shoreline at the PNPS site. Although the bay's shore in Plymouth Countyis prone to erosion, there is no apparent evidence of such for the plant's shoreline.

The shoreline protection system at the plant, consisting of breakwaters, jetties and revetments, has been effective in stabilizing the site'sshorefront since construction of the breakwaters in 1970 (PNPS 2013, Section 2.4.4.2).

3.8.4 FindingsAREVA 2014. AREVA Document No. 51-9226930-000, Pilgrim Nuclear Power Station Flooding Hazard Re-Evaluation

-Screening for Channel Diversion, October 2014.BEC 1993. IPEEE -External Flooding Analysis (Local Intense Precipitation),

BEC-039, Boston EdisonCompany, 1993. (See AREVA Document No. 38-9226908-000)

NRC 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United Statesof America, NUREG/CR-7046, U.S. Nuclear Regulatory Commission, November 2011.O'Connell 1999. Coastal Erosion Hazards and Mapping Along the Massachusetts Shore by O'Connell, J.F. andLeatherman, S.P., Journal of Coastal Research, SI(28), 27-33, Royal Palm Beach (Florida),

Spring 1999. (SeeAREVA Document No. 51-9226930-000)

PNPS 2013. Pilgrim Nuclear Power Station Final Safety Analysis Report (FSAR), Revision 29, October 2013.(AREVA Doc. No. 38-9226908-000)

PNIPS 2014. Pilgrim Drawing C2, Rev. 10, "Site Plan". (AREVA Doc. No. 38-9226908-000)

USGS 1977. Manomet Topographic Quadrangle Map 1977, Massachusetts-Plymouth County, 7.5 Minute Series,Scale 1: 25 000, U.S. Geological Survey. (See AREVA Document No. 51-9226930-000)

USGS 2012. Manomet Topographic Quadrangle Map 2012, Massachusetts-Plymouth County, 7.5 Minute Series,Scale 1: 24 000, U.S. Geological Survey. (See AREVA Document No. 51-9226930-000)

Page 97 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-34: PNPS Shoreline in 1977[Source:

USGS 1977]SCALE 1:25 000AU~ikA ~i )---~1 17.A -t ;LLTPage 98 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-35: PNPS Shoreline in 2012[Source:

USGS 2012]SCALE 1:24 0001050 KILOMETERS 2low0METERS0long20001asIas 0PILESI0= 0 1000 2000 3O 400 500 000 7000 8000 9O0 10000FEETPage 99 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.9 Combined Effect FloodThis section addresses combined events flooding at PNPS. This evaluation includes consideration of the impactsof 1) the Probable Maximum Storm Surge (PMSS) on Cape Cod Bay, which includes the design antecedent waterlevel; and 2) wave effects associated with the Probable Maximum Hurricane (PMH) and Probable MaximumWind Storm (PMWS). These wave effects include wave runup. Other combined events flood scenarios wereassessed and screened out as not applicable at PNPS.This section summarizes the evaluation of combined flooding events performed in the AREVA Calculation, Pilgrim Nuclear Power Station Flooding Hazard Re-Evaluation

-Combined Events (AREVA 2015).3.9.1 Methodology The criteria for assessing combined events are provided in NUREG/CR-7046, Appendix H (NRC 201 1). Of thefive scenarios presented, one applies to PNPS: floods along shores of semi-enclosed water bodies (Scenario H.3).Other combined effect flood scenarios described in NUREG/CR-7046 were screened out as not being applicable to PNPS. The flooding impact of the Scenario H.3 combined events flood mechanism was assessed, as described below.Scenario H.3: In consideration of the site location on the western shore of Cape Cod Bay, the H.3 combined floodevent sub-scenario that is applicable to the site is:Shore Location:

Probable maximum surge and seiche with wind-wave activity.

Antecedent 10 percent exceedance high tide.The "streamside location" sub-scenario of H.3 does not apply because there are no significant rivers or streamsthat would contribute to a combined effects flooding event.The methodology used to evaluate the H.3 -Shoreside combined flood event at PNPS consisted of the following steps:1. Review of the USACE Wave Information Studies (WIS) for comparison to the simulated

offshore, deep-water wave heights and periods.

Historic wave data from three WIS stations near PNPS, Station 63057,Station 63060, and Station 63061 were compiled to provide a comparison to simulated deep wave heightsand periods (see Figure 3-36).2. Development of the deep-water waves resulting during the PMSS using the ADvanced CIRCulation (ADCIRC) model coupled with the Delft University of Technology's (DUT) Simulating WAvesNearshore (SWAN) model Version 41.01 of Cape Cod Bay developed in the PMSS Calculation (refer toSection 3.4). The coupling of ADCIRC and SWAN involves an integrated modeling process that isillustrated in Figure 3-37. ADCIRC passes the wind velocities, water levels, and currents to SWAN,which uses those values as forcing to its calculations (Dietrich et al., 2012). The coupled ADCIRC +SWAN model (i.e., also referred to as ADCSWAN) outputs water level that includes wave setup becausethe coupled ADCIRC model takes into account wave radiation stress output by SWAN. The combinedstorm surge and wave setup hydrograph was used as input to the nearshore/shallow water SWAN model(described below) as it accounts for wave setup. Deep-water wave spectra outputted at the nearshore model boundary at four points were also used as the incoming parametric spectra for the nearshore model.The ADCIRC model mesh elevations are shown in Figure 3-38.Page 100 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3. Development of the nearshore and shallow-water waves near PNPS resulting from the PMH or PMWSusing the SWAN Version 41.01 model. A local SWAN grid was used to provide greater resolution in thevicinity of PNPS, including nearshore features such as the breakwaters.

4. Wind-wave

effects, including runup, were calculated using SWAN output reflecting wave characteristics for the PMH and PMSS and by FEMA (FEMA 2007) and ASCE-7 (ASCE 2010) methodology.

The methodology was applied to the PMH and PMWS in parallel until it was determined which forcing eventwould produce the controlling combined events flooding.

3.9.2 Results3.9.2.1 Potential Shoreside Location on Semi-Enclosed Waterbody Combined Event3.9.2.1.1 Review of Historical Wave DataHindcasts of deep-water significant wave heights resulting from historical storms range from 23.7 to 29.1 feet andthe range of peak periods is 12.6 to 17.1 seconds for the top ten wave events reported at the WIS stations (USACE2010), see Table 3-1l. The WIS stations provide a good indication of deep-water wave conditions offshore ofPNPS. Because they are in deeper water than the SWAN output points discussed below, the wave heightprovided by WIS would become depth limited as they approach shore. However, because period is invariant, itcan be compared to the shallow water wave periods predicted by SWAN.3.9.2.1.2 Offshore Wave ResultsDeep-water waves offshore of PNPS were simulated using the coupled ADCIRC and SWAN model under bothPMH and PMWS conditions.

PMHPeak significant wave heights and periods for the coupled ADCIRC+SWAN model output locations (see Figure3-39 for output locations) are shown in Table 3-12. At the peak of the PMH, the significant deep-water waveheight varies from 18.4 to 29.7 feet across the seven boundary output locations.

The peak spectral wave periodassociated with the significant wave height range from 9.9 to 15.7 seconds at the boundary output points.Simulated maximum significant wave heights and wave periods were compared to published data to determine theconservativeness of the model. The 100-year significant wave height at WIS station 63061 was 34.8 feet(USACE 2010). The coupled ADCIRC+SWAN output at that location (longitude

-69.92, latitude 42.17) was 62.0feet, which is 27.2 feet higher than the maximum WIS hindcast data. The large difference is the result of theextreme intensity associated with the PMH and PMWS; therefore, the coupled ADCIRC+SWAN results areconsidered consistent and conservative.

PMWSPeak significant wave heights and periods for the coupled ADCIRC+SWAN model output locations (see Figure3-40 for output locations) are shown in Table 3-13. At the peak of the PMWS, the significant deep-water waveheight varies from 16.8 to 34.5 feet across the seventeen boundary output locations.

The peak spectral waveperiod associated with the significant wave height range from 11.5 to 16.4 seconds at the output points.Simulated maximum significant wave heights and wave periods were compared to published data at the WISstations to determine the conservativeness of the model. The 100-year significant wave height at station 63061was 34.8 feet (USACE 2010). The coupled ADCIRC+SWAN output at that location (longitude

-69.92, latitude42.17) was 56.7 feet, which is 21.9 feet higher than the maximum WIS hindcast data. The large difference is thePage 101 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Reportresult of the extreme intensity associated with the PMWS, and therefore the coupled ADCIRC+SWAN simulation is considered conservative.

3.9.2.1.3 Nearshore Wave ResultsPMHNearshore and shallow waves in the vicinity of PNPS during the PMH were simulated using the SWAN model.The nearshore/shallow-water SWAN grid extent and elevations are shown in Figure 3-41. Figure 3-42 shows thetime-varying water level that was generated by the deep-water coupled ADCIRC+SWAN model and used as inputto the nearshore/shallow-water SWAN simulation.

Figure 3-43 shows the time-varying wind speed and wavedirection results used as input to the SWAN simulation.

Output of wave characteristics was specified at nineoutput nodes representative of important locations and structures at PNPS (Figure 3-48 and Table 3-14). Peaksignificant wave heights and periods for the output locations ranged from 0.9 to 7.3 feet and 1.8 to 9.6 seconds,respectively, as shown in Table 3-14. Figure 3-46 shows the peak significant wave height and vector resultswithin the breakwaters compared to outside of the breakwaters.

The fraction of breaking waves due to depth-induced breaking generated by the nearshore SWAN model is shownin Figure 3-50 for the PMH. Large deep-water waves break along the breakwaters before reaching the site.Shoreward structures are well beyond the breakwater structure and are therefore protected from the largeroffshore waves.PMWSNearshore and shallow waves in the vicinity of PNPS during the PMWS were simulated using the SWAN model.The nearshore/shallow-water SWAN grid extent and elevations are shown in Figure 3-41. Figure 3-44 shows thetime-varying water level which was output from the deep-water coupled ADCIRC+SWAN model and was usedas input to the nearshore/shallow-water SWAN simulation.

Figure 3-45 shows the time-varying wind speed andwave direction which was used as input to the SWAN simulation.

Output of wave characteristics was specified atnine output nodes which were representative of important locations and structures at PNPS shown on Figure 3-48and Table 3-15. Peak significant wave heights and periods for the output locations ranged from 0.6 to 7.1 feet andup to 12.7 seconds, respectively, as shown in Table 3-15. Figure 3-47 shows the peak significant wave heightand vector results within the breakwaters compared to outside of the breakwaters.

The fraction of breaking waves due to depth-induced breaking was output from SWAN and is shown in Figure3-51 for the PMWS. Large deep-water waves break along the breakwater before reaching the site. Shoreward structures are well beyond the breakwater structure and are therefore protected from the larger offshore waves.3.9.2.1.4 Incident Wave Characteristics PMHPeak significant wave height, peak wave period and wave crest elevations of the peak significant waves forimportant locations are presented in Table 3-14. At the peak of the PMH, the significant wave heights at theselocations vary from 0.9 to 7.3 feet. The corresponding maximum wave heights and depth-limited heights at theselocations were calculated as per NRC guidance (NRC 2013). Maximum wave heights and depth-limited heightsare also reported in Table 3-14. Maximum wave heights ranged from 1.5 to 12.2 feet based on the significant wave heights calculated by SWAN, and depth-limited wave heights ranged from 11.5 to 30.4 feet in the site area.Wave crest elevations for maximum waves at the peak of the PMH ranged from 16.6 to 21.9 feet MSL in the sitearea. The lesser of the maximum wave or breaking wave is considered in establishing the controlling combinedevents flood elevations, as per guidance in NUREG (NRC 2013).Page 102 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportPMWSPeak significant wave height, peak wave period and wave crest elevations of the peak significant waves forimportant locations are presented in Table 3-15. At the peak of the PMWS,. the significant wave heights at thelocations vary from 0.6 to 7.1 feet. The corresponding maximum wave heights and depth-limited heights at theselocations were calculated as per NRC guidance (NRC 2013). Maximum wave heights and depth-limited heightsare also reported in Table 3-15. Maximum wave heights ranged from 1.0 to 11.9 feet based on the significant wave heights calculated by SWAN, and depth-limited heights ranged from 11.2 to 30.1 feet in the site area. Wavecrest elevations for maximum waves at the peak of the PMWS ranged from 15.8 to 21.2 feet MSL in the site area.The lesser of the maximum wave or breaking wave is considered in establishing the controlling combined eventsflood elevations, as per guidance in NUREG (NRC 2013).Because simulated wave conditions generated by the PMWS are equal to or less than those generated by thePMH, and because the maximum water surface elevation of 15.3 feet MSL resulting from the PMWS isapproximately 0.5 feet lower than the maximum water surface elevation of 15.8 feet MSL resulting from thePMH, the PMH was determined to be the controlling storm event for combined effects flooding.

Therefore, waveeffects were calculated based on the PMSS resulting from the PMH and wind-wave effect generated by the PMH.It is noted that while the wave effects generated by the PMWS are not greater than those generated by the PMH,the duration of high intensity wave action ranges from 50 to 60 hours6.944444e-4 days 0.0167 hours 9.920635e-5 weeks 2.283e-5 months for the PMWS compared to 10 to 15 hour1.736111e-4 days 0.00417 hours 2.480159e-5 weeks 5.7075e-6 months sfor the PMH.3.9.2.1.5 Standing Wave Height at Vertical Structures Wave effects at the PNPS Intake Structure headwall were calculated using the Sainflou formulas for fully head-onnon-breaking waves (USACE 2006). The maximum incident significant wave height near the intake wascalculated in SWAN to be approximately 3.0 feet with a wavelength of 30.4 feet. This wave results in a reflected wave crest height of approximately 4.0 feet (see Table 3-16) and an elevation of 19.8 feet MSL. This elevation isapproximately 1.7 feet below the top of the Intake Structure (PNPS 2005). The maximum wave height calculated at the intake headwall is approximately 5.0 feet. The maximum wave crest elevation is 20.8 feet MSL, whichmay result in infrequent runup wedge overtopping of the intake headwall (at 21.5 feet MSL). Overtopping due tothe maximum height wave will be cycled back into the intake via the grating on the deck of the Intake Structure.

The Sainflou formulas for the reflected wave crest are for fully head-on regular waves (i.e., perpendicular to theintake headwall) and the conservatism built into the reflected wave crest elevations at the PNPS intake headwallare considered appropriate.

Figure 3-46 shows the waves approaching in a general head on direction for thePMH.3.9.2.1.6 Wave Runup onto a Plateau above a Low BluffWave runup in the yard area at PNPS was determined using empirical equations for runup on a rock armoredslope (USACE 2006). Significant, two percent, and maximum runup from PMH waves was computed usingsignificant wave heights as input. Initial runup estimates were adjusted using FEMA methodology for specialconditions where runup may appreciably exceed the top elevation of a revetment.

Wave heights ranging fromapproximately 0.9 feet to 7.3 feet will occur for a duration of approximately ten to fifteen hours during the PMHcontrolling event.The maximum runup elevation at PNPS caused by the PMH was 22.1 feet MSL at Transect

3. This coincides witha significant wave height of 7.3 feet and mean period of 7.7 seconds.

Maximum runup elevation at Transect 2was calculated to be 21.9 feet MSL (see Figure 3-49 for transect locations and Table 3-17 for runup values.).

Page 103 of 152

.AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report3.9.2.1.7 Combined Events Water Elevations at PNPSThe maximum combined events water surface elevation at PNPS was determined to be 22.1 feet MSL due torunup from a fully head-on wave on the revetment slightly east of the Reactor Building portion of the plant. Thisresults in shallow flooding of the shoreline area of the site due to overtopping flow from wave action at therevetment.

3.9.2.1.8 Structure Loading and Associated EffectsFlood loading at the Intake Structure was considered.

The hydrostatic loading on the Intake Structure wasdetermined to be approximately 61,400 pounds per linear foot from the reflected wave crest elevation loading at19.8 feet MSL. This conservatively assumes a uniform structure and does not take into account the intakeopening and potential water surface elevation within the Intake Structure.

The flow velocity was determined to beapproximately 28.0 feet per second based on a reflected wave crest elevation of 19.8 feet MSL. This assumes anaverage channel invert at the reflected wave crest elevation.

The hydrodynamic load was determined to beapproximately 39,000 pounds per linear foot based on the reflected wave crest elevation of 19.8 feet MSL and thevelocity within the channel.

The debris impact load was determined to be 45,000 pounds based on a debrisweight of 2,000 pounds.A dedicated analysis of groundwater elevations was not performed as part of the combined events calculation.

Ingeneral, effects of storm surge on groundwater elevations are expected to be limited to those areas currently observing tidal influence on groundwater elevations.

Additionally, as stated in the Individual Plant Examination for External Events (IPEEE),

the minimum entry level for all safety related structures is 23 feet MSL (IPEEE1994, Section 5.2.1). NRC guidance states that the impact of scour, sediment transport and deposition should beconsidered when storm surge flood levels impinge on flood protection, safety-related SSCs and foundation materials (NRC 2013). NRC guidance states that detailed analyses should be conducted to evaluate the effects ofsediment and erosion (NRC 2013).3.9.3 Conclusions The following summarizes the results and conclusions relative to combined events flooding at PNPS:* The maximum combined events flood elevation, including wave action, near the reactor building in the siteyard area between the plant buildings and the shore revetment is 22.1 feet MSL." The maximum combined events flood elevation at the upstream face of the Intake Structure is 19.8 feet MSL." Because wind-wave activity during the PMSS impacts the Intake Structure, it will be subject to hydrostatic, hydrodynamic, and wave loads.3.9.4 References AREVA 2015. Pilgrim Nuclear Power Station Flood Hazard Re-evaluation

-Combined Events, AREVADocument No. 32-9226937-000, 2015.ASCE 2010. Minimum Design Loads for Buildings and Other Structures, ASCE/SEI 7-10, American Society ofCivil Engineers (ASCE), 2010.Dietrich et al., 2012. Performance of the Unstructured-Mesh, SWAN+ADCIRC Model in Computing Hurricane Waves and Surge, J.C. Dietrich, S. Tanaka, J.J. Westerink, C.N. Dawson, R.A. Luettich Jr., M. Zijlema, L.H.Holthuijsen, J.M. Smith, L.G. Westerink, and H.J. Westerink, Journal of Scientific Computing, Volume 52,Issue2, August 2012. (See AREVA Document No. 32-9226937-000)

Page 104 of 152 AR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFEMA 2007. Atlantic Ocean and Gulf of Mexico Coastal Guidelines Update, Federal Emergency Management Agency, February 2007.IPEEE 1994. Pilgrim Nuclear Power Station -Individual Plant Examination for External Events (GL 88-20),Rev. 0, July 1994. (See AREVA Document No. 38-9226908-000)

NRC 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United Statesof America.,

NUREG/CR-7046, U.S. Nuclear Regulatory Commission, November 2011.NRC 2013. Guidance for Performing a Tsunami, Surge, or Seiche Hazard Assessment, JLD-ISG-2012-06, Revision 0, U.S. Nuclear Regulatory Commission, January 4, 2013.PNPS 2005. Intake Structure

Sections, Drawing No. C46, Pilgrim Nuclear Power Station, Date Revised:December 2005. (See AREVA Document No. 38-9226908-000)

USACE 2006. Coastal Engineering Manual -Part VI, Chapter 5, Fundamentals of Design, EM 1110-2-1100, U.S. Army Corps of Engineers, June 2006.USACE 2010. Wave Information Studies:

Atlantic, U.S. Army Corps of Engineers, Engineer Research andDevelopment Center Coastal and Hydraulics Laboratory, December 2010.Page 105 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-11: Summary of Extreme Wave Conditions at WIS Stations near PNPSWIS Station 63057 WIS Station 63060 WIS Station 63061Rank Significant Peak Wave Significant Wave Significant Wave Peak WaveWave Height Period Sign t Wave Period Sign t Wave Period(feet) (seconds)

Height (feet) (seconds)

Height (feet) (seconds) 1 24.3 17.1 23.7 16.6 29.1 12.62 23.0 12.3 23.1 12.7 28.3 17.13 22.9 12.8 22.4 13.1 27.1 13.34 22.5 13.3 22.2 11.8 26.9 12.86 19.9 11.3 19.8 11.1 24.0 12.47 19.9 12.3 19.5 11.0 22.9 12.28 19.1 11.8 18.7 11.8 22.8 11.49 18.9 11.2 18.7 11.0 22.0 11.610 18.5 11.0 18.5 10.9 21.8 13.2Table 3-12:Coupled ADCIRC+SWAN Simulation Results -PMHOutput Location Peak Wave Height (feet) Wave Period (seconds)

BI 28.0 10.2B2 28.1 10.1B3 29.7 10.1B4 27.6 10.1B5 27.3 9.9B6 22.0 10.6B7 25.0 9.9Vi 22.6 15.7V2 18.4 10.9Page 106 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-13: Coupled ADCIRC+SWAN Simulation Results -PMWSOutput Location Peak Wave Height (feet) Wave Period (seconds)

B 1 29.5 16.4B2 29.9 15.9B3 33.3 15.7B4 33.8 15.6B5 34.5 15.7B6 22.8 16.2B7 29.1 15.6B8 34.0 15.7B9 31.0 15.7BIO 26.6 15.5BI1 16.8 15.5B12 27.2 16.3B13 24.4 16.3B114 21.2 16.0BI5 20.7 11.5B16 19.8 15.5B17 20.1 15.0VI 22.6 15.7V2 20.0 15.7Page 107 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-14: Nearshore/Shallow Water SWAN Simulation Results -PMHPeak Maximum Depth- limitePeak Significant Maximum Wave t limitedPek Wave Wave Waveitees ID Depth Significant Wave Crest Wave WaveNumb Description Longitude Latitude (feet) Wave Height Period Crest Height Elevation Wave Elevation De sp(feet) c(seconds)

Elevation (feet) (feet Height (feet,(feet) (feet, (feet)(feet MSL) MSL) MSL)12 Intake -70.57919583 41.94565794 39.0 3.0 9.5 17.3 5.0 18.3 30.4 37.113 Revetment

-70.57901323 41.94567853 28.6 3.6 9.4 17.6 6.0 18.8 22.3 31.414 Revetment

-70.5786544 41.94586094 23.0 5.1 9.6 18.4 8.5 20.1 17.9 28.415 Revetment

-70.57785935 41.94570467 24.0 6.2 9.6 18.9 10.4 21.0 18.7 28.916 Revetment

-70.57732438 41.94550411 22.4 6.8 9.5 19.2 11.4 21.5 17.5 28.017 Discharge

-70.57978726 41.94573224 20.3 0.9 1.8 16.3 1.5 16.6 15.8 26.918 Discharge

-70.57974751 41.94569664 20.2 0.9 1.8 16.3 1.5 16.6 15.8 26.819 Discharge

-70.57979678 41.9458015 20.3 0.9 1.8 16.3 1.5 16.6 15.8 26.920 Boat Ramp -70.57679734 41.9450345 14.7 7.3 9.5 19.5 12.2 21.9 11.5 23.8Note: See Figure 3-48 for locations of points.M___ I^ _ý.-

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-15: Nearshore/Shallow Water SWAN Simulation Results -PMWSPeak Peak Depth- Depth-limited ID Depth Significant Wave Significant Wave Wave Crest Welimited WeNumber Description Longitude Latitude (feet) Wave Period Wave Crest Height Elevation Wave Elevation Height (seconds)

Elevation Height(feet) (feet, MSL) (feet) (feet, MSL) (feet) (feet, MSL)12 Intake -70.57919583 41.94565794 38.6 2.5 10.6 16.6 4.2 17.4 30.1 36.413 Revetment

-70.57901323 41.94567853 28.3 3.0 10.3 16.8 5.0 17.8 22.1 30.814 Revetment

-70.5786544 41.94586094 22.6 4.5 10.7 17.6 7.5 19.1 17.6 27.615 Revetment

-70.57785935 41.94570467 17.8 5.6 10.6 18.1 9.4 20.0 13.9 25.016 Revetment

-70.57732438 41.94550411 22.0 6.4 10.5 18.5 10.7 20.6 17.2 27.317 Discharge

-70.57978726 41.94573224 19.9 0.6 N/A 15.6 1.0 15.8 15.5 26.218 Discharge

-70.57974751 41.94569664 19.9 0.6 N/A 15.6 1.0 15.8 15.5 26.219 Discharge

-70.57979678 41.9458015 19.9 0.6 N/A 15.6 1.0 15.8 15.5 26.220 Boat Ramp -70.57679734 41.9450345 14.3 7.1 12.7 18.9 11.9 21.2 11.2 23.1Note: See Figure 3-48 for locations of points.---- ý -_Z A -

AARE VADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 3-16: PNPS Intake Wave EffectsParameter Transect 1 Parameter Description h 22 Depth at intake, feetT 9.5 Peak period from SWAN, secondsL 30.4 Wavelength from SWAN, feetHs 3.02 Hs from SWAN, feetVertical Shift 0.94 feetWave Crest 3.96 feetSetup 0.10 feetInitial SWEL 15.70 PMSS still water SWEL, feet MSLTotal WSE 19.8 Combined Event Elevation, feet MSLHeight of Intake 21.5 feet MSLNote: See Figure 3-49 for locations of transect.

Table 3-17: PNPS PMH RunupRunup (Percent Exceedance)

Transect 2 (feet, MSL) Transect 3 (feet, MSL)%0.1 21.9 22.1%2.0 21.5 21.6%5.0 20.9 21.1Note: See Figure 3-49 for locations of transect.

Page 110 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-36: WIS Wave Gage Locations i4Any illegible text or features in this figure are not pertinent to the technical purposes of this document.

Page 111 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-37: Coupled ADCIRC+SWAN Computation

/NWave Radiation StressWind Velocity, Water Level andCurrentPage 112 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-38: ADCIRC Model Mesh Elevations

-___ A ý ý _X A rl AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-39: Coupled ADCIRC+SWAN Simulation Output Locations

-PMHM---AAA-ZAr^

AARE VADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-40: Coupled ADCIRC+SWAN Simulation Output Locations

-PMWSM___ A I _Z A -

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-41: NearshorelShallow Water SWAN Simulation Model Elevations M___ A, -ZAI^

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-42: Nearshore/Shallow-Water SWAN Simulation Input Water Level -PMH16151413~12.~11109876A05 1015 20 25Time (hours)30 35 404550Note: Results from coupled ADCIRC+SWAN simulation at representative output location V2: -70.5722412556 longitude, 41.9465878842 latitude; seeFigure 3-39 for location.

-___ A A- _X All AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-43: Nearshore/Shallow-Water SWAN Input Wind Speed and Wind Direction

-PMH2.C,1009080 470 -605040302010 b-Wind Speed -Wave D rection250200150 tW.210050003001020405060Time (Hours)Note: Results from coupled ADCIRC+SWAN simulation at representative output location V2: -70.5722412556 longitude, 41.9465878842 latitude; seeFigure 3-39 for location.

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-44: NearshorelShallow-Water SWAN Simulation Input Water Level -PMWS16151413-123: 109876AV0102030 Time1gours) 50 607080Note: Results from coupled ADCIRC+SWAN simulation at representative output location V2: -70.5722412556 longitude, 41.9465878842 latitude; seeFigure 3-40 for location.

-___ ý A ý -1 A -

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-45: NearshorelShallow-Water SWAN Input Wind Speed and Wave Direction

-PMWS100908070CLýECL605040302010WindýW Speed ~-ý,Walfe Direction K __ .I ...r -/ _______/________,

'___/ __! /* .... ..... ..... .. .. .........-.. .L ,.... ....... ... .. ....... ..] ....... .... ....250200a,150C010050001020304050607080Time (Hours)Note: Results from coupled ADCIRC+SWAN simulation at representative output location V2: -70.5722412556 longitude, 41.9465878842 latitude; seeFigure 3-40 for location.

M___ A^^ _X Ar^

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-46: Peak Significant Wave Height -PMHý___ A^A _X A rn AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-47: Peak Significant Wave Height -PMWSM___ -1 _Z A -

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-48: NearshorelShallow-Water SWAN Simulation Output Locations

-PMH & PMWSK F.__7 ____________________

A NGeMho GiAMu Locatlo fM --_ .. -n AAR EVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-49: Transect Locations M --- A,. _Z .1^

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-50: Nearshore/Shallow-Water SWAN Simulation Wave Breaking Zone -PMHM- --A -_X A e^

AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 3-51: NearshorelShallow-Water SWAN Simulation Wave Breaking Zone -PMWSM -ý -_Z A -

AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report4.0 FLOOD PARAMETERS AND COMPARISON WITH CURRENT LICENSING BASISPer the March 12, 2012, 50.54(f) letter (NRC 2012a), Enclosure 2, the following flood-causing mechanisms wereconsidered in the flood hazard re-evaluation for PNPS." Local Intense Precipitation;

" Flooding in Streams and Rivers;" Darn Breaches and Failures;

Storm Surge;* Seiche;* Tsunami;* Ice Induced Flooding, and;" Channel Migration or Diversion Some of these individual mechanisms are incorporated into alternative

'Combined Effect Flood' scenarios perAppendix H of NUREG/CR-7046 (NRC 2011).The March 12, 2012, 10 CFR 50.54(f) letter, Enclosure 2, requests the licensee to perform an integrated assessment of the plant's response to the re-evaluated hazard if the re-evaluated flood hazard is not bounded bythe current licensing basis (NRC 2012a). This section provides comparisons with the current licensing basis floodhazard and applicable flood scenario parameters per Section 5.2 of JLD-ISG-2012-05 (NRC 2012b), including:

1. Flood height and associated effectsa. Still water elevation;

b. Wind waves and runup effects;c. Hydrodynamic

loading, including debris;d. Effects caused by sediment deposition and erosion (e.g., flow velocities, scour);e. Concurrent site conditions, including adverse weather conditions; and,f. Groundwater ingress.2. Flood event duration parameters (per Figure 6 (below) of JLD-ISG-2012-05 (NRC 2012b))a. Warning time (may include information from relevant forecasting methods (e.g., products from local,regional or national weather forecasting centers) and ascension time of the flood hydrograph to a point(e.g., intermediate water surface elevations) triggering entry into flood procedures and actions by plantpersonnel);

b. Period of site preparation (after entry into flood procedures and before flood waters reach site grade);c. Period of inundation, and;d. Period of recession (when flood waters completely recede from site and the plant is in a safe and stablestate that can be maintained).

3. Plant mode(s) of operation during the flood event duration.

4. Other relevant plant-specific factors (e.g., waterborne projectiles).

Page 127 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report---------------

fo ood eventflood event duration,ecessionot 4Miter from site!inundaftin Conditons ae metforenty into floodp"ceduresor notificato Of floodArival of floodwaters on siteWater begins IDrecede forn siteWater cormpheAdy receded from sibeand plantin safeand stade statethatcan bemaintained indefinitely Illustration of Flood Event Duration (Figure 6 of JLD-ISG-2012-05 (NRC 2012b))Per Section 5.2 of JLD-ISG-2012-05 (NRC 2012b), flood hazards do not need to be considered individually aspart of the integrated assessment.

Instead, the integrated assessment should be performed for a set(s) of floodscenario parameters defined based on the results of the flood hazard re-evaluations.

In some cases, only onecontrolling flood hazard may exist for a site. In this case, licensees should define the flood scenario parameters based on this controlling flood hazard. However, sites that have a diversity of flood hazards to which the site maybe exposed should define multiple sets of flood scenario parameters to capture the different plant effects from thediverse flood parameters associated with applicable hazards.

In addition, sites may use different flood protection systems to protect against or mitigate different flood hazards.

In such instances, the integrated assessment shoulddefine multiple sets of flood scenario parameters.

If appropriate, it is acceptable to develop an enveloping scenario (e.g., the maximum water surface elevation and inundation duration with the minimum warning timegenerated from different hazard scenarios) instead of considering multiple sets of flood scenario parameters aspart of the integrated assessment.

For simplicity, the licensee may combine these flood parameters to generate asingle bounding set of flood scenario parameters for use in the integrated assessment.

For PNPS, the following flood-causing mechanisms were determined to result in no feasible flood hazard at thesite:* Flooding in Streams and Rivers;* Dam Breaches and Failures;

" Seiche;* Tsunami;* Ice Induced Flooding, and;* Channel Migration and Diversion PNPS was considered potentially exposed to the flood hazards listed below. In some instances, an individual flood-causing mechanism (e.g., storm surge) was also addressed in the combined effect flood scenario.

Local Intense Precipitation; Page 128 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report* Probable Maximum Storm Surge due to the Probable Maximum Hurricane or the Probable MaximumWind Storm, and;" Combined Effect Flood scenario consisting of the Probable Maximum Storm Surge and wave effects.Section 4.1 summarizes the re-evaluated flood levels for each flood mechanism and compares the flood elevations to the CLB flood parameters.

4.1 Summary of Current Licensing Basis and Flood Re-Evaluation ResultsThis section compares the current and re-evaluated flood-causing mechanisms.

It provides a comparison of theCLB flood elevation to the re-evaluated flood elevation for each applicable flood-causing mechanism.

Acomparison of the CLB elevations and the re-evaluated flood elevations is provided in Table 4-1.Screened mechanisms have been evaluated at a high level and determined not to be applicable to the floodinghazard for PNPS.Flooding due to LIP or the combined effect flood are the only flood mechanisms that could result in inundation inthe vicinity of plant SSCs important to safety. Potential impacts of inundation due to these two flood mechanisms are addressed in Section 5.0.4.1.1 Local Intense Precipitation Precipitation induced flooding is not currently addressed in the CLB; however, the PMP event was evaluated aspart of the IPEEE. The PMP produces water depths of 24.5 feet MSL at buildings on the south side of the plantand 22.5 feet MSL at buildings on the north side of the plant. It also results in ponding on building roofs of about0.5 feet.As part of the flood hazard re-evaluation, the maximum water surface elevations due to the LIP flood mechanism result from a PMP depth of 17.1 inches in one hour and 25.5 inches in six hours. The maximum flood depthsrange from 0.6 feet to locally as high as 2.6 feet above grade near important plant locations, with the highest LIPwater surface elevations occurring on the south side of the plant. The maximum LIP flood elevation at animportant location examined is 25.2 feet MSL.Inundation durations at the important plant locations are shown in time-series plots in Appendix A.A comparison of the re-evaluated LIP flood hazard to the CLB is provided in Table 4-2. Flood elevations, depthsand durations to maximum flood elevations at important plant locations are summarized in Table 4-3.Impacts of LIP flood elevations at important plant locations are discussed in Section 5.0.4.1.2 Flooding in Streams and RiversThe flood hazard due to flooding in streams and rivers was not specifically addressed as part of the CLB andscreened out as not impacting the site in the Flood Hazard Re-Evaluation Report for PNPS.4.1.3 Dam Breaches and FailuresThe flood hazard due to dam failures was not specifically addressed as part of the CLB and screened out as notimpacting the site in the Flood Hazard Re-Evaluation Report for PNPS.Page 129 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report4.1.4 Storm SurgeThe only flood hazard addressed in the CLB is an extreme storm tide level of 13.5 feet MSL resulting from eitherthe peak storm surge from a nor'easter and an astronomical high tide, or from a maximum hurricane producedstorm surge.Based on the evaluation summarized in Section 3.4, the maximum still water elevation for the PMSS resulting from a PMH was determined to be 15.7 feet MSL, and the maximum water surface elevation, which includeswave setup, was determined to be 15.8 feet MSL. As noted in Section 2.0, station grade is at 20 feet MSL and asnoted in Section 3.9, the minimum entry level for all safety related structures is 23 feet MSL.4.1.5 SeicheThe flood hazard due to seiche was not specifically addressed as part of the CLB and screened out as notimpacting the site in the Flood Hazard Re-Evaluation Report for PNPS.4.1.6 TsunamiThe flood hazard due to tsunami was not specifically addressed as part of the CLB and screened out as notimpacting the site in the Flood Hazard Re-Evaluation at PNPS.4.1.7 Ice Induced FloodingThe flood hazard due to ice was not specifically addressed as part of the CLB and screened out as not impacting the site in the Flood Hazard Re-Evaluation Report for PNPS.4.1.8 Channel Migration or Diversion The flood hazard due to channel migration or diversion was not specifically addressed as part of the CLB andscreened out as not impacting the site in the Flood Hazard Re-Evaluation Report for PNPS.4.1.9 Combined EffectThe flood hazard due to combined effect was not specifically addressed as part of the CLB. However, as noted inSection 2.0, a series of wave action model studies were performed to assist in the design of PNPS waterfront structures.

The combined effect flooding mechanism from the flood hazard re-evaluation is the combination of the PMSSwhich includes the design antecedent water level, and wave effects which include wave runup. The maximumcombined effect flood elevation is 22.1 feet MSL which occurs near the Reactor Building in the yard areabetween plant buildings and the shore revetment.

The maximum combined effect flood elevation at the upstreamface of the Intake Structure is 19.8 feet MSL and the Intake Structure will be subject to hydrostatic, hydrodynamic and wave loads due to impact from wind-wave activity during the PMSS. As noted in Section 2.0, station grade isat 20 feet MSL.A comparison of the re-evaluated combined effect flood hazard to the CLB is provided in Table 4-4.Impacts due to the combined effect flood are discussed in Section 5.0.Page 130 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 4-1: Flood Elevation Comparison Mechanism CLB Flood Height Re-Evaluated Flood Height Difference 22.5 feet MSL along north 23.3 to 23.5 feet MSL +0.8 to +1.0 feet MSLside of plant buildings (at important locations on northand west sides of plant)24.5 feet MSL along south 25.2 feet MSLside ofelant MSLaldngso (at important locations on south +0.7 feet MSLLocal Intense side of plant)Precipitation Roof ponding of approx. 0.5 Not Applicable feet based on all roof drains Not Applicable being 100% effective.

[Note: PMP was evaluated as part of the IPEEE.]PMF in Rivers and Streams Not Evaluated Screened Not Applicable Dam Breaches and Failures Not Evaluated Screened Not Applicable 15.8 feet MSL[max. water surface elevation Storm Surge 13.5 feet MSL (i.e., still water plus wave +2.3 feetsetup)][Note: Station grade is at 20feet MSL.]Seiche Not Evaluated Screened Not Applicable Tsunami Not Evaluated Screened Not Applicable Ice Induced Flooding Not Evaluated Screened Not Applicable Channel Migration or Not Evaluated Screened Not Applicable Diversion 22.1 feet MSL(near Reactor Building in siteyard between buildings andshore revetment)

Combined Effect Not Evaluated Not Applicable 19.8 feet MSL(upstream face of IntakeStructure)

[Note: Station gradeis at 20 feet MSL.]Note: "Not Evaluated" indicates that this flood mechanism was not defined or addressed in CLB documents.

As a result, nocomparison can be made to re-evaluated results.Page 131 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 4-2: Local Intense Precipitation BoundedRe-Evaluated Flood (B) or NotFlood Scenario Parameter CLB Flood Hazard Hazar odBouNdeHazard Bounded(NB)Max. Still Water Elevation Not identified in the CLB.24.5 feet MSL per the IPEEEPMP event.25.2 feet MSLNB(see Section5.0)MCu000il-Max. Wave Runup Elevation Still water elevation of 14.7 Wind/wave interaction was Bfeet MSL based on wave not evaluated coincident withmodel studies (see Section the LIP event.2.2)Max. Hydrodynamic/Debris Not identified in the CLB. Hydrodynamic loading was BLoading not evaluated.

Debris loadingwas not considered a crediblehazard due to limited debrissources within the protected area.Effects of Sediment Not identified in the CLB. No unreasonably high NBDeposition/Erosion velocities were indicated; the (see Sectionmaximum flow velocity 5.0)occurs at the drop off betweensite grade and the discharge channel and is reasonable given the difference betweenthe channel's surface waterelevation and ground surfaceelevation at the head of thechannel.

No erosion isexpected within the powerblock or discharge channel.Concurrent Site Conditions Not identified in the CLB. No antecedent storm was Bconsidered with the LIPevent.Effects on Groundwater The CLB indicates that theReactor, Turbine and RadwasteBuildings have a waterproofing membrane designed to preventor minimize groundwater inleakage.Effect on groundwater wasnot evaluated.

BPage 132 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportBoundedRe-Evaluated Flood (B) or NotFlood Scenario Parameter CLB Flood Hazard Hazar odBouNdeHazard Bounded(NB)Warning Time Not identified in the CLB. Not evaluated.

BPeriod of Site Preparation No preparation is indicated in Not evaluated.

Bthe CLB.Period of Inundation Not identified in the CLB. For 0.1 to 1.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months at important NBthe IPEEE PMP event, locations.

(see Sectionflooding starts at zero height, 5.0)increases to PMP levels andthen recedes back to zero0 height for the one hourC duration of maximumd o> precipitation.

w_V Period of Recession Not identified in the CLB. For Over ten hours at some NB0O the IPEEE PMP event, important locations, (see SectionL. flooding starts at zero height, specifically on the south side 5.0)increases to PMP levels and of the plant.then recedes back to zeroheight for the one hourduration of maximumprecipitation.

Other Plant Mode of Operations Not identified in the CLB. No operational modes Bassumed or evaluated.

Note: B/NB indicates if the re-evaluation parameters or results are bound/not bound by the CLB evaluation parameters orresults.Page 133 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 4-3: LIP Flood Depths and Durations at Select Locations Time toMaximumdMaximum MaximumIDFloNumber Location Description Flood Depth FloodNubrElevation FloDetFod (feet, MSL) (feet) Elevation (hours)8 Emergency Diesel Generator Building Door -23.5 0.6 0.1North Side9 Reactor Building Truck Lock Door -West 23.3 0.7 1.5Side10 Water Treatment Area Ground Level Door -West Side 23.3 0.8 1.5I I Turbine Building Truck Rollup Door -South 15.2 2.5 1.4Side12 O&M Building Ground Level Door -South 25.2 2.6 1.4Side13 Hatch A -Turbine Building-South Side 25.2 1.1 1.414 Hatch B -Turbine Building

-South Side 25.2 1.1 1.415 Air Vent -Redline Building

-South Side 25.2 2.2 1.4Page 134 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTable 4-4: Combined Effect FloodBoundedCLB Flood Hazard Re-Evaluated Flood (B) or NotFlood Scenario Parameter HazardooBounded Hazard Bounded(NB)Max. Still Water Elevation Not identified in the CLB.22.1 feet MSL(near Reactor Building in siteyard between buildings andshore revetment) 19.8 feet MSL(upstream face of IntakeStructure)

[Note: Station grade is at 20feet MSL.]NB(see Section5.0)000Max. Wave Runup Elevation Still water elevation of 14.7 22.1 feet MSL due to runup NBfeet MSL based on wave from a fully head-on wave on (see Sectionmodel studies (see Section the revetment slightly east of 5.0)2.2) the Reactor Building portionof the plant.Max. Hydrodynamic/Debris Not identified in the CLB. Hydrostatic, hydrodynamic NBLoading and debris impact loads were (see Sectiondetermined at the Intake 5.0)Structure.

Effects of Sediment Not identified in the CLB. Not evaluated.

BDeposition/Erosion Concurrent Site Conditions Not identified in the CLB. The PMSS includes the NBdesign antecedent water level. (see Section5.0)Effects on Groundwater The CLB indicates that theReactor, Turbine and RadwasteBuildings have a waterproofing membrane designed to preventor minimize groundwater inleakage.Not evaluated; effects ofstorm surge on groundwater elevations are expected to belimited to those areascurrently observing tidalinfluence on groundwater elevations.

B~4. hPage 135 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportBoundedRe-Evaluated Flood (B) or NotFlood Scenario Parameter CLB Flood Hazard Hazar odBouNdeHazard Bounded(NB)Warning Time Not identified in the CLB. Not evaluated.

B>0 Period of Site Preparation No preparation is indicated in Not evaluated.

Bthe CLB.o 3 Period of Inundation Not identified in the CLB. Not evaluated.

BU. Period of Recession Not'identified in the CLB. Not evaluated.

BOther Plant Mode of Operations Not identified in the CLB. No operational modes Bassumed or evaluated.

Note: B/NB indicates if the re-evaluation parameters or results are bound/not bound by the CLB evaluation parameters orresults.4.2 References NRC 2011. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United Statesof America.,

NUREG/CR-7046, U.S. Nuclear Regulatory Commission, November 2011.NRC 2012a. Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f)

Regarding Recommendations 2.1, 2.3 and 9.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-IchiAccident, U.S. Nuclear Regulatory Commission, March 2012.NRC 2012b. JLD-ISG-2012-05, Guidance for Performing the Integrated Assessment for External

Flooding, Interim Staff Guidance, Revision 0, 2012.Page 136 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report5.0 INTERIM EVALUATION AND ACTIONS TAKEN OR PLANNEDFlooding due to LIP or the combined effect flood are the only flood mechanisms which could cause inundation ofthe PNPS site in the vicinity of SSCs important to safety.5.1 Impacts of Re-Evaluated Flood Elevations In response to the re-evaluated flood elevations resulting from the LIP and the combined effect flood whichconsists of wind-generated waves in conjunction with the PMSS, an assessment was performed to determine theimpact of inundation at the affected locations identified in Section 3.1 due to the LIP and in Section 3.9 due to thecombined effect flood. The results of this evaluation indicate that there are no impacts to equipment important tosafety as a result of the re-evaluated flood elevations, as discussed further below.5.1.1 LIP Affected Locations Referring to Table 4-I, the re-evaluated LIP maximum flood elevation of 23.5 feet MSL exceeds the CLB/IPEEE flood elevation of 22.5 feet MSL on the north side of the plant at the following three locations:

the Emergency Diesel Generator (EDG) Building, the Reactor Building Truck Lock Door and the Water Treatment Area GroundLevel Door. Referring to Table 4-3, the maximum flood depths at these doors varies between 0.6 and 0.8 feet.All three doors were included in the PNPS 2012 Fukushima walkdowns.

In addition, per a PNPS 1993 InternalMemo, these doors are currently credited not to fail for a flood height of up to 1.5 feet. Therefore, potential flooding due to the LIP at these three doors is not of concern.

(PNPS 2015b)Referring to Table 4-1 and Table 4-3, the re-evaluated LIP maximum flood elevation of 25.2 feet MSL exceedsthe CLB/IPEEE flood elevation of 24.5 feet MSL in one area on the south side of the plant at five important locations as follows:

the Turbine Building Truck Rollup Door (Door 102), the O&M Building Ground LevelDoor, Turbine Building Hatch A, Turbine Building Hatch B, and the air vent(s) associated with the RedlineBuilding.

Turbine Building Hatches A and B lead into the Retube Building.

The Retube building does notcontain any operating, energized equipment.

Based on a walkdown of the Retube Building, all piping, wiring andconduits were observed to be sealed at penetrations in the building's north wall adjacent to the Condenser Bay. Ifthe Retube Building were to flood from water leakage through Hatches A and B, the Retube Building would holdmore than 100,000 gallons of water prior to leakage, and subsequent leakage would be removed by the TurbineBuilding's sumps. As such, SSCs important to safety would not be adversely impacted by LIP flood levels atHatches A and B. (PNPS 2015a and PNPS 2015b)Referring to Figure 5-1, potential water ingress at the Turbine Building Truck Rollup Door (Door 102), the O&MBuilding Ground Level Door and the air vent(s) associated with the Redline Building is discussed in the following subsections.

5.1.1.1 Turbine Building Truck Rollup Door -South Side of PlantThe Turbine Building Truck Rollup Door (Door 102) is not sealed from external flooding.

Although water couldpotentially penetrate into the Turbine Building at this location, there are no SSCs important to safety within thevicinity of this door. However, the flow of water over the removable oil/water barriers near interior Doors 103,105 and 311 could result in a flow path to the Lower Switch Gear Room which houses SSCs important to safety.Additionally, referring to Figure 5-2, it is not credible to assume that the leakage of water into the building areasnear Door 102, due to the maximum flood depth of 2.5 feet at Door 102, would exceed the oil/water barriers andfail Doors 103, 105 and 311. Considering that the three interior doors will not fail, the building areas adjacent toDoor 102 are judged to have adequate volume for protecting elevated switch gear within the Lower Switch GearRoom. (PNPS 2015a)Page 137 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportPer PNPS Procedure 8.C.42, Subcompartment Barrier Matrix, Door 102 has been analyzed for tornado and highenergy line break (HELB) loads for its open and closed positions.

Door 102 is also normally in its closed positionwith procedural steps in place to ensure that the door is in its closed position during storm preparations (PNPS2015a).While Door 102 is currently credited not to fail for a flood height of up to 1.5 feet, a PNPS 1993 Internal Memonotes that rolling steel doors for large openings, i.e., Door 102, could possibly experience noticeable deflections and approach the upper limit of their structural capacity due to 1.5 feet of water pressure.

However, Door 102,which is approximately 20 feet wide by 21 feet high, is designed for a wind load of 25 pounds per square foot(psf) (0.17 pounds per square inch (psi)) over its entire surface.

The average load on Door 102 from the LIPwater depth of 2.5 feet is 0.325 psi. Considering that the entire door can withstand the stated wind load, it isjudged that the door's bottom 2.5 feet can also withstand the higher water load of 0.325 psi since the wind loadover the entire door would produce a stress much greater than the stress produced by the water load on a smallersection of the door. Additionally, there is a steel angle along the bottom of Door 102 which provides additional strength to withstand deflection.

(PNPS 2015a)A visual inspection of the interior side of Door 102 was performed.

During the walkdown, it was observed thatthe door panels are bowed toward the inside of the Turbine Building up to a height of approximately five feetfrom the floor. All door panels are intact and no fractures were observed.

The inside track on both sides of thedoor is intact and bolted to an adjacent angle that spans the height of the door. No damage to the track wasobserved.

Therefore, the slightly bowed door will not fail under the LIP event and it will meet its designrequirement.

(PNPS 2015a)If water leaks into the Turbine Building through Door 102, the water would be restrained to the truck lock areaand adjacent area as shown on Figure 5-2. As previously noted, there are no SSCs important to safety in theseareas. Interior Doors 103 and 311 lead to the Lower Switch Gear Room and interior Door 105 leads to stairsaccessing the radwaste corridor.

Door 103 is similar to other doors that have previously been tested and evaluated for a loading capacity of 1.48 psi with the swing of the door uniformly

applied, or for a head of 6.82 feet withoutfailure.

Door 311 is a set of double doors and would have less head capacity than Door 103. However, based onprevious testing and evaluations performed for PNPS doors, Door 311 is judged to be able to withstand up to 2.5feet of head. For Door 105, applying a water load of 2.5 feet in depth against the swing of the door results in1.92 psi or a uniform head of 8.86 feet prior to failure.

Therefore, it is unlikely that interior Doors 103, 105 and311 would fail; however, if water were to seep through these interior doors, since the switch gear is elevated, equipment important to safety would not be adversely impacted.

(PNPS 2015a)5.1.1.2 O&M Building Ground Level Door -South Side of PlantPotential water leakage through the O&M Building Ground Level Door would be via a torturous path into theReactor Building and into the Lower Switch Gear Room. Flood water would need to enter the corridor for theO&M Building, seep through two double doors that lead into the Redline Building and then flow into theRadwaste Building via the failure of one of four other doors. The structural failure of personnel doors constructed of steel due to water acting on door exteriors is not addressed in the PNPS 1993 Internal Memo. However, doorsof the same type and of similar configuration to the O&M Building Ground Level Door and those leading into theRadwaste Building from the Redline Building have previously been evaluated for internal flooding.

Based on theprior internal flooding evaluation, the O&M Building Ground Level Door and doors between the Radwaste andRedline Buildings will not fail due to the LIP maximum flood depth of 2.6 feet at the O&M Building GroundLevel Door, which would result in a uniformly distributed water load on building doors of less than 1.48 psi.(PNPS 2015a)Page 138 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report5.1.1.3 Air Vent(s) -Redline Building

-South Side of PlantPotential water leakage at the air vent(s) -Redline Building location would be via a torturous path into theReactor Building and into the Lower Switch Gear Room. Flood water would need to enter the Redline Buildingand flow into the Radwaste Building through the failure of one of four doors and then through two double doorsthat open between the Redline Building and into an adjacent

hallway, which would allow the height of water todecrease.

The structural failure of personnel doors constructed of steel due to water acting on door exteriors is notaddressed in the PNPS 1993 Internal Memo. However, doors of the same type and of similar configuration to thedoors leading into the Radwaste Building from the Redline Building have previously been evaluated for internalflooding.

Based on the prior internal flooding evaluation, the Redline and Radwaste Building doors will not faildue to the LIP maximum flood depth of 2.2 feet at the air vent(s) -Redline Building, which would result in auniformly distributed water load on building doors of less than 1.48 psi. (PNPS 2015a)5.1.2 Combined Effect Flood Affected Locations Referring to Table 4-1 and Table 4-4, the re-evaluated combined effect flood elevation of 22.1 feet MSL,associated with a maximum water surface elevation (i.e., still water plus wave setup) of 15.8 feet MSL, exceedsthe CLB extreme storm tide level elevation of 13.5 feet MSL. As noted in Section 2.0, the wave action modelstudies performed to assist in the design of PNPS waterfront structures did not subject the Reactor Building toflooding.

Therefore, SSCs important to safety that may be adversely impacted by the combined effect flood aresituated within the EDG Building and the Intake Structure.

However, penetrations, including doors into the EDGBuilding, are at a minimum elevation of 23 feet MSL; therefore, SSCs important to safety within the EDGBuilding would not be adversely impacted.

The Intake Structure contains a Class I structure inside a Class II structure.

The entrance into the Intake Structure is at an elevation of 21.5 feet MSL. The entrance into the safety related (Class I) portion of the Intake Structure from the non-safety related (Class II) portion is at an elevation of 25.5 feet MSL. The salt service water pumpsand their motors comprise the SSCs important to safety within the Intake Structure and are at an elevation of 25.6feet MSL, situated above grating at an elevation of 25.5 feet MSL. Although water from the combined effectflood at an elevation of 22.1 feet MSL may enter into the Class II portion of the Intake Structure, it would notenter into the Class I portion.

Furthermore, although the area below the concrete floor at elevation 21.5 feet MSLis open to the salt service water bay, the concrete floor would protect the salt service water pumps from waveeffects.

(PNPS 2015a)As noted in Section 4.0, the maximum combined effect flood elevation at the upstream face of the IntakeStructure is 19.8 feet MSL and the Intake Structure will be subject to hydrostatic, hydrodynamic and wave loadsdue to impact from wind-wave activity during the PMSS. Considering that station grade is at 20 feet MSL, noadverse impact to the Intake Structure is anticipated.

5.2 Conclusions

Plant walkdowns have confirmed that inundation associated with the LIP or the combined effect flood will notimpact SSCs important to safety. As a result, no interim flood mitigating measures are planned.

(PNPS 2015a)5.3 References PNPS 2015a. PNPS Response to AREVA Request for Information RFI #2015-003, Dated February, 2015.(AREVA Document No. 38-9236113-000).

PNPS 2015b. PNPS Response to AREVA Request for Information RFI #2015-004, Dated February, 2015.(AREVA Document No. 38-9236474-000)

Page 139 of 152 AAR EVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 5-1: LIP Select Locations on South Side of Plant[Source:

PNPS 2015a]TurbineBuilding TruckLock Door-Air VentsO&M BuildingDoorPage 140 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportFigure 5-2: Turbine Building Flow Path[Source:

PNPS 2015a]Notes:1. Should water from the LIP seep through Door 102, potential flooding within Turbine Building areas is shownby the blue highlighting.

It is anticipated that flood water would be contained within the walls and doorsoutlined in green highlighting.

2. Illegible text or features in this figure are not pertinent to the technical purposes of this document.

Page 141 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation Report6.0 ADDITIONAL ACTIONSAs noted in Section 5.0, plant walkdowns have confirmed that inundation associated with the LIP or the combinedeffect flood will not impact SSCs important to safety. Therefore, no additional flood mitigating actions areplanned.Page 142 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportAPPENDIX A: LOCAL INTENSE PRECIPITATION A.1 LIP Time Series Hydrographs at Reporting Locations See the following Appendix A pages.A.2 LIP FLO-2D Input/Output FilesDue to the large size and formatting of the FLO-2D input/output files, this data is provided as an electronic attachment.

The information has been archived in the AREVA file management system, ColdStor.

The path to thefile is: \cold\General-Access\5 I \51-9226940-000\official.

This information is also provided electronically with this report as 51-9226940-000_AppendixA2.zip.

A.3 LIP Results -Large Format FiguresDue to the large file size of the large format figures, they are provided as an electronic attachment.

The information has been archived in the AREVA file management system, ColdStor.

The path to the file is: \cold\General-Access\5 I \51-9226940-000\official.

This information is also provided electronically with this report as 51-9226940-000_AppendixA3.zip.

Page A-1 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportLIP FLO-2 CRITICAL GRID ELEMENT TIME SERIES HYDROGRAPHS Page A-2 of 152 AAR EVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportEmergency Diesel Generator Building Door -North SideGrid Element 7467 -Emergency Diesel Generator Building22.822.722.6-22.522422.222.122023 4 5 6rnime From Beginning of Simulation (hours)-WSEL -Ground Elevation

-Critical Elevation 78910Page A-3 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportReactor Building Truck Lock Door -West SideGrid Element 7169 -Reactor Building Truck Lock Door22.6 __ _ _ _ _ _ _ _ ___ _ _ _22.5 ----- ----2 2 .4 .... .....22.3(22.2Z.22.1- --__2 1 .9 .... ........ .. ..... .. ... ... ... ... ... ........ ........ ........_ _21.52 1 .7 -............

.... .........................

........

... .0 1 2 3 4 5 6 7 a 9 10Time From Beginning of Simulation (hours)_WSEL -Ground Elevation

-Critical Elevation Page A-4 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportWater Treatment Area Ground Level Door -West SideGrid Element 7606 -Water Treatment Area Door2 2 .7 -- ----------

-22.622.522.422.121.821.70 1 2 3 4 5 6 7 8 9 10Time From Beginning of Simulation (hours)_WSEL -Ground Elevation

-Critical Elevation Page A-5 of 152 AAR EVA Document No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportTurbine Building Truck Rollup Door -South SideGrid Element 10264 -Turbine Building Truck Rollup Door24.5 -T-_2423.5Z220 1 2 3 4 5 6 7 8 9 10Time from Beginning of Simulation (hours)-WSEL -Ground Elevation

-Critical Elevation Page A-6 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportO&M Building Ground Level Door -South SideGrid Element 10085 -O&M Building Door (South Side)2524.52423.5S2322.52221,50 1 234 5 6Time From begisdmg~

of nubfiao (hams)-VWSEL -Ground Ekirtaion

-C'ibca ELmvabon, 7ag A0Page A-7 of 152 AARE VADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportHatch A -Turbine Building

-South SideGrid Element 10077 -Hatch A24.624.424.224z' 23.823.623.423.20I3 4 5 6Time From Beginning of Simulation (hours)_WSEt -Ground Elevation

-Critical Elevation 7810Page A-8 of 152 AARE VADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportHatch B -Turbine Building

-South SideGrid Element 9897 -Hatch B24 .6 -----------2 4 .4 ....... ...............

24.224Zz23.8' 23.623.423.2013 4 5 6Time From Beginning of Simulation (hours)-WSEL -Ground Elevation Critical Elevation 7810Page A-9 of 152 AAREVADocument No.: 51-9226940-000 Pilgrim Nuclear Power StationFlood Hazard Re-Evaluation ReportAir Vent -Redline Building

-South SideGrid Element 9728 -Air Vent24.52423.5z0ii2322.52221.51023 4 5 6 7Time From Beginning of Simulation (hours)IWSEL -Ground Elevation

Critical Elevation 8910Page A-1 of 152

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