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| number = ML091400522
| number = ML091400522
| issue date = 04/30/2009
| issue date = 04/30/2009
| title = Watts Bar, Unit 2 - Final Safety Analysis Report (Fsar), Amendment 93, Section 2.4 Hydrologic Engineering Through Figure 2.4-111
| title = Final Safety Analysis Report (Fsar), Amendment 93, Section 2.4 Hydrologic Engineering Through Figure 2.4-111
| author name =  
| author name =  
| author affiliation = Tennessee Valley Authority
| author affiliation = Tennessee Valley Authority
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{{#Wiki_filter:HYDROLOGIC ENGINEERING2.4-1WATTS BAR WBNP 922.4  HYDROLOGIC ENGINEERINGWatts Bar Nuclear Plant is located on the right bank of Chickamauga Lake at Tennessee River Mile (TRM) 528 with plant grade at elevation 728 MSL. The plant has been designed to have the capability for safe shutdown in floods up to the computed maximum water level, in accordance with regulatory position 2 of Regulatory Guide 1.59, Revision 2, August 1977.Determination of the maximum flood level included consideration of postulated dam failures from seismic and hydrologic causes. The maximum flood Elevation 734.9 would result from an occurrence of the probable maximum storm. Allowances for concurrent wind waves could raise lake levels to Elevation 736.2 with run up on the 4:1 slopes approaching the plant reaching about Elevation 736.9.The nearest surface water user located downstream from Watts Bar Nuclear Plant is Dayton, Tennessee, at TRM 503.8, 24.2 miles downstream. All surface water supplies withdrawn from the 58.9 mile reach of the mainstream of the Tennessee River between Watts Bar Dam (TRM 529.9) and Chickamauga Dam (TRM 471.0) are listed in Table 2.4-4.The probable minimum flow past the site is estimated to be 2000 cfs, which is more than adequate for plant water requirements.
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====2.4.1 Hydrological====
Description 2.4.1.1  Sites and FacilitiesThe location of key plant structures and their relationship to the original site topography is shown on Figure 2.1-5. The structures which have safety-related equipment and systems are indicated on this figure and are tabulated below along with the elevation of exterior accesses.StructureAccessAccessesElev.Intake Pumping(1) Access Hatches3728.0 Structure(2) Stairwell Entrances2741.0(3) Access Hatches6741.0Auxiliary and(1) Door to Turbine Bldg.1708.0Control Bldgs.(2) Door to Service Bldg.2713.0(3) Railroad Access Opening1729.0 (4) Door to Turbine Bldg.2729.0 (5) Emergency Exit1730.0 (6) Door to Turbine Bldg.2755.0
 
2.4-2 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83Exterior accesses are also provided to each of the Class 1E electrical systems manholes and handholes at elevations varying from 714.5 feet MSL to 728.5 feet MSL, depending upon the location of each structure.The relationship of the plant site to the surrounding area can be seen in Figures 2.1-4a and 2.1-5. It can be seen from these figures that significant natural drainage features of the site have not been altered. Local surface runoff drains into the Tennessee River.
2.4.1.2  HydrosphereThe Watts Bar Nuclear Plant site, along with the Watts Bar Dam Reservation, comprises approximately 1770 acres on the west bank of Chickamauga Lake at TRM 528. As shown by Figure 2.1-4a, the site is on high ground with the Tennessee River being the major potential source of flooding.The Tennessee River above the Watts Bar plant site drains 17,319 square miles. Watts Bar Dam, 1.9 miles upstream, has a drainage area of 17,310 square miles. Chickamauga Dam, the next dam downstream, has a drainage area of 20,790 square miles. Two major tributaries, Little Tennessee and French Broad Rivers, rise to the east in the rugged Southern Appalachian Highlands. They flow northwestward through the Appalachian Divide which is essentially defined by the North Carolina-Tennessee border to join the Tennessee River which flows southwestward. The Tennessee River and its Clinch and Holston River tributaries flow southwest through the Valley and Ridge physiographic province which, while not as rugged as the Southern Highlands, Shield Building(1) Personnel Lock1714.0 (2) Equipment Hatch1753.0 (3) Personnel Lock1755.0Diesel Generator(1) Equipment Access Doors4742.0 Building(2) Emergency Exits742.0(3) Personnel Access Door1742.0 (4) Emergency Exit1760.5Additional(1) Equipment Access Door2742.0  Diesel(2) Personnel Access Door1742.0 Generator(3) Emergency Exit1742.0 Building(4) Emergency Exit1760.5StructureAccessAccessesElev.
 
HYDROLOGIC ENGINEERING2.4-3WATTS BARWBNP-92features a number of mountains including the Clinch and Powell Mountain chains. The drainage pattern is shown on Figure 2.1-1. About 20% of the watershed rises above elevation 3,000 with a maximum elevation of 6684 at Mt. Mitchell, North Carolina. The watershed is about 70% forested with much of the mountainous area being 100%
forested.The climate of the watershed is humid temperate. Mean annual precipitation for the Tennessee Valley is shown in Figure 2.4-1. Above Watts Bar Dam annual rainfall averages 50 inches and varies from a low of 40 inches at sheltered locations within the mountains to high spots of 90 inches on the southern and eastern divide. Rainfall occurs fairly evenly throughout the year. The lowest monthly average is 2.8 inches in October. The highest monthly average is 5.4 inches in July, with March a close second with an average of 5.1 inches.Major flood-producing storms are of two general types:  the cool-season, winter type, and the warm-season, hurricane type. Most floods at Watts Bar Nuclear Plant, however, have been produced by winter-ty pe storms in the flood-season months of January through early April.Watershed snowfall is relatively light, averaging about 14 inches annually above the plant. Snowfall above the 3,000-foot elevation averages 22 inches annually. The highest average annual snowfall in the basin is 63 inches at Mt. Mitchell, the highest point east of the Mississippi River. Individual snowfalls are normally light, with an average of 13 snowfalls per year. Snowmelt is not a factor in maximum flood determinations.The Tennessee River, particularly above Chattanooga, Tennessee, is one of the most highly regulated rivers in the United States. The TVA reservoir system is operated for flood control, navigation, and power generation with flood control a prime purpose with particular emphasis on protection for Chattanooga, 64 miles downstream from Watts Bar Nuclear Plant.Chickamauga Dam, 57 miles downstream, affects water surface elevations at Watts Bar Nuclear Plant. Normal full pool elevation is 682.5 feet. At this elevation the reservoir is 58.9 miles long on the Tennessee River and 32 miles long on the Hiwassee River, covering an area of 35,400 acres, with a volume of 628,000 acre-feet. The reservoir has an average width of nearly 1 mile, ranging from 700 feet to 1.7 miles. At the Watts Bar site the reservoir is about 1100 feet wide with depths ranging between 18 feet and 26 feet at normal pool elevation.There are 12 major reservoirs in the T VA system upstream Watts Bar Nuclear Plant, ten of which have substantial reserved flood detention capacity during the flood season. Table 2.4-1 lists pertinent data for TVA's major dams prior to modifications made by the Dam Safety Program (See Table 2.4-16). Figures 2.4-2 through 2.4-14 show general plans, elevations, and sections for these dams and Chickamauga Dam downstream. In addition, there are six major dams owned by the Aluminum Company of America (ALCOA). The ALCOA reservoirs often contribute to flood reduction, but they do not have dependable reserved flood detention capacity. Table 2.4-2 lists 2.4-4 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92pertinent data for the ALCOA dams and Walters Dam (Waterville Lake). The locations of these dams are shown on Figure 2.1-1. Flood control above the plant is provided largely by eight tributary reservoirs. Tellico Dam is counted as a tributary reservoir because it is located on the Little Tennessee River although, because of canal connection with Fort Loudoun Dam, it also functions as a main river dam. On March 15, near the end of the flood season, these provide a minimum of 4,069,200 acre-feet of detention capacity equivalent to 6.1 inches on the 12,452-square-mile area they control. This is 89% of the total available above the plant. The two main river reservoirs, Fort Loudoun and Watts Bar, provide 490,000 acre-feet equivalent to 1.9 inches on the remaining 4,858-square-mile area above Watts Bar Dam.The flood detention capacity reserved in the TVA system varies seasonally, with the greatest amounts during the January through March flood season. Figures 2.4-15 through 2.4-24 show the reservoir seasonal operating guides for reservoirs above the plant site. Table 2.4-3 shows the flood control reservations at the multiple-purpose projects above Watts Bar Nuclear Plant at the beginning and end of the winter flood season and in the summer. Total assured system detention capacity above Watts Bar Dam varies from 6.2 inches on January 1 to 4.9 inches on March 15 and decreasing to 1.2 inches during the summer and fall. Actual detention capacity may exceed these amounts, depending upon inflows and power demands.Chickamauga Dam, the headwater elevation of which affects flood elevations at the plant, has a drainage area of 20,790 square miles, 3,480 square miles more than Watts Bar Dam. There are eight major tributary dams in the 3,480-square-mile intervening watershed, of which three have substantial reserved capacity. On March 15, near the end of the flood season, these provide a minimum of 366,700 acre-feet equivalent to 7.1 inches on the 968-square-mile controlled area. Chickamauga Dam contains 347,000 acre-feet of detention capacity on March 15 equivalent to 2.6 inches on the remaining 2,512 square miles. Figure 2.4-26 shows the seasonal operating guide for Chickamauga. Elevation-storage relationships for the 12 reservoirs above the site and Chickamauga, downstream, are shown in Figures 2.4-25 and 2.4-27 through 2.4-38. Curves determined at selected years as part of TVA's program of monitoring changes due to sedimentation are shown. These show that sedimentation is not significant in these reservoirs.The original hydrologic design of the dams was based upon a combination of design flood and freeboard which in some cases did not meet probable maximum flood (PMF) criteria imposed by Regulatory Guide 1.70.17, January 1975. The potential consequences of overtopping of those dams not meeting current criteria were evaluated where failure would significantly influence plant site flood levels and were described in Section 2.4.3.4 per the original analysis.
HYDROLOGIC ENGINEERING2.4-5WATTS BARWBNP-92In 1982, TVA officially began a safety review of all its dams. The TVA Dam Safety Program was designed to be consistent with the Federal Emergency Management Agency's (FEMA) Federal Guidelines for Dam Safety and similar efforts by other Federal agencies. Technical studies and engineering analyses were conducted and physical modifications implemented to ensure the hydrologic and seismic integrity of the TVA dams and demonstrate that TVA's dams can be operated in accordance with FEMA guidelines. Table 2.4-16 provides the status of TVA Dam Safety hydrologic modifications as of early 1998. These modifications enable these projects to safely pass the probable maximum flood. The remaining hydrologic modifications planned for Bear Creek Dam and Chickamauga dam will not affect Watts Bar in any manner which might invalidate the reanalysis described below.In 1997-98, TVA reanalyzed the nuclear plant design basis flood events. The purpose of the reanalysis was to evaluate the effects of the hydrologic dam safety modifications on the flood elevations and response times in the WBN FSAR and to confirm the adequacy of the plant flood plans. The following methods and assumptions were applied to the reanalysis:
(1)The computer programs and modeling methods were the same as previosly used and documented in the plant FSAR.
(2)Probable maximum precipitation, time distribution of precipitation, precipitation losses and reservoir operating procedures were unchanged from the original analysis.
(3)All of the original stability analyses and postulated seismic dam failure assumptions were conservatively assumed to occur in the same manner and in combination with the same previously postulated rainfall events. No credit was taken for the 1988 post-tensioning of Fontana and Melton Hill Dams to prevent seismic failure. Nor was any credit taken for Dam Safety seismic evaluations of Norris, Cherokee, Douglas, Fort Loudon, Tellico, Hiwassee, Apalachia, and Blue Ridge Dams which demonstrated their structural integrity for a seismic event with a return period of approximately 10,000 years.(4)The planned modification of Chickamauga Dam (armoring the embankment to permit overtopping) was conservatively assumed to have been implemented for the purpose of calculating flood effects. However, the condition of Chickamauga Dam, 57 miles downstream, has negligible impact on flood levels at the plant.
(5)Bear Creek Dam is downstream of the nuclear plant and its planned modification has no relevance to this reassessment.Daily flow volumes at the plant, for all practical purposes, are represented by discharges from Watts Bar Dam with a drainage area of 17,310 square miles, only 9 square miles less than at the plant. Momentary flows at the nuclear plant site may vary considerably from daily averages, depending upon turbine operations at Watts Bar and Chickamauga Dams. There may be periods of several hours when no releases from 2.4-6 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92either or both Watts Bar and Chickamauga Dams occur. Rapid turbine shutdown at Chickamauga may sometimes cause periods of upstream flow in Chickamauga Reservoir.Based upon Watts Bar Dam discharge records since dam closure in 1942, the average daily streamflow at the plant is 27,800 cfs. The maximum daily discharge was 187,000 cfs on December 30, 1941 prior to present regulation. Daily average releases of zero have been recorded on seven occasions during the past 28 years. Flow data for water years 1960-1987 with regulation essentially equivalent to present conditions indicate an average rate of about 23,700 cfs during the summer months (May-October) and about 31,900 cfs during the winter months (November-April). Flow durations based upon Watts Bar Dam discharge records for the period 1960-1987 are tabulated below:Channel velocities at the Watts Bar site average about 2.3 fps under normal winter conditions. Because of lower flows and higher reservoir elevations in the summer months, channel velocities average about 1.0 fps.The Watts Bar plant site is underlain by geologic formations belonging to the lower Conasauga Formation of Middle Cambrian age. The formation consists of interbedded shales and limestones overlain by alluvial material averaging 40 feet in thickness. Ground water yields from this formation are low.All surface water supplies withdrawn from the 58.9 mile reach of the mainstream of the Tennessee River between Watts Bar Dam (TRM 529.9) and Chickamauga Dam (TRM 471.0) are listed in Table 2.4-4. See Section 2.4.13.2 for description of the ground water users in the vicinity of the Watts Bar site.2.4.2  Floods 2.4.2.1  Flood HistoryThe nearest location with extensive formal flood records is 64 miles downstream at Chattanooga, Tennessee, where continuous records are available since 1874. Knowledge about significant floods extends back to 1826 based upon newspaper and Average Daily Discharge, cfs  Percent of TimeEqualled or Exceeded5,00098.910,00093.2 15,00083.5 20,00069.3 25,00050.6 30,00032.9 35,00020.1 HYDROLOGIC ENGINEERING2.4-7WATTS BARWBNP-83historical reports. Flood flows and stages at Chattanooga have been altered by TVA's reservoir system beginning with closure of Norris Dam in 1936 and reaching essentially the present level of control in 1952 with closure of Boone Dam, the last major dam with reserved flood detention capacity constructed above Chattanooga prior to construction of Tellico Dam. Tellico Dam provides additional reserved flood detention capacity; however, the percentage increase in the total retention capacity above the Watts Bar site is small. Therefore, flood records for the period 1952 to date can be considered representative of prevailing conditions. Figure 2.4-40 shows the known flood experience at Chattanooga in diagram form. The maximum known flood under natural conditions occurred in 1867. This flood reached elevation 716.3 at Watts Bar Nuclear Plant site with a discharge of 440,000 cfs. The maximum flood under present-day regulation reached Elevation 696.18 at the site on March 17, 1973.The following tabulation lists the highest floods at the Watts Bar Nuclear Plant site under present-day regulation:There are no records of flooding from seic hes, dam failures, or ice jams. Historic information about icing is provided in Section 2.4.7.
2.4.2.2  Flood Design ConsiderationsTVA has planned the Watts Bar project to conform with regulatory position 2 of Regulatory Guide 1.59.The types of events evaluated to determine the worst potential flood included  (1) Probable Maximum Precipitation (PMP) on the total watershed and critical sub-water sheds including seasonal variations and potential consequent dam failures and (2) dam failures in a postulated SSE or OBE with guide specified concurrent flood conditions.Specific analysis of Tennessee River flood levels resulting from ocean front surges and tsunamis is not required because of the inland location of the plant. Snow melt and ice jam considerations are also unnecessary because of the temperate zone location of the plant. Flood waves from landslides into upstream reservoirs required no specific analysis, in part because of the absence of major elevation relief in nearby upstream reservoirs and because the prevailing thin soils offer small slide volume potential compared to the available detention space in reservoirs. Seiches pose no flood threats because of the size and configuration of the lake and the elevation difference between normal lake level and plant grade. Date Elevation, Feet Discharge, cfs February 2, 1957692.08157,600 November 19, 1957693.17151,600 March 13, 1963693.85167,700 January 1, 1970692.27167,300 March 17, 1973696.18184, 800 2.4-8 HYDROLOGIC ENGINEERINGWATTS BARWBNP-93The maximum plant site flood level from any cause is Elevation 734.9. This elevation would result from the PMP critically centered on the watershed as described in Section 2.4.3. The maximum flood level is 3.2 feet lower than originally determined in the FSAR as a result of dam safety modifications.Wind waves from a March wind with velocity of 21 miles per hour was assumed to occur coincident with the flood peak. This would create waves 2.0 feet high (trough to crest) and produce maximum lake levels to Elevation 736.2.All safety-related facilities, systems, and equipment are housed in structures which provide protection from flooding for all flood conditions up to plant grade at Elevation 728. See Section 2.4.10 for more specific information.Other rainfall floods will also exceed plant grade Elevation 728 and require plant shutdown. Flood warning criteria and forecasting techniques have been developed to assure that there will always be adequate time to shut the plant down and be ready for floodwaters above plant grade. Section 2.4.14 describes emergency protective measures to be taken in flood events exceeding plant grade.Seismic and flood events could cause dam failure surges approaching plant grade Elevation 728. In all such events there is time for safe plant shutdown after the seismic event before plant grade would be crossed. Section 2.4.14 describes emergency protective measures to be taken in seismic events exceeding plant grade.For the condition where flooding exceeds plant grade, as described in Sections 2.4.3 and 2.4.4, those safety-related facilities, systems, and equipment located in the containment structure are protected from flooding by the Shield Building structure with those accesses and penetrations below the maximum flood level designed and constructed as watertight elements. The Diesel Generator Building and Essential Raw Cooling Water (ERCW) pumps are located above this flood level, thereby providing protection from flooding.Wind wave run up during the PMF at the Diesel Generator Building reaches Elevation 736.9 which is 5.1 feet below the operating floor. Consequently, wind wave run up will not impair the safety functions of the Diesel Generator Building.Those Class 1E electrical system conduit banks located below the PMF plus wind run up flood level are designed to function submerged with either continuous cable runs or qualified, type tested splices. The ERCW pumps are structurally protected from wind waves. Therefore, the safety function of the ERCW pumps will not be affected by floods or flood-related conditions.The Turbine, Control, and Auxiliary Buildings will be allowed to flood. All equipment required to maintain the plant safely during the flood, and for 100 days after the beginning of the flood, is either designed to operate submerged, is located above the maximum flood level, or is otherwise protected.The electrical equipment room of the intake pumping structure will flood at HYDROLOGIC ENGINEERING2.4-9WATTS BARWBNP-83Elevation 728. However, the design basis water level for the remaining structure is Elevation 740.1. The Auxiliary and Control Buildings will flood with the water level at Elevation 729. The design basis water level for the Shield Building is Elevation 740.1. The Diesel Generator Building is located above the design basis water level (Elevation 740.1).2.4.2.3  Effects of Lo cal Intense PrecipitationAll streams in the vicinity of the plant shown on Figure 2.1-4a were investigated, including Yellow Creek, with probable maximum flows from a local storm and from breaching of the Watts Bar Dam west saddle dike and were found not to create potential flood problems at the plant. Local drainage which required detailed design is from the plant area itself and from a 150-acre area north of the plant.The underground storm drainage system is designed for a maximum 1-hour rainfall of 4 inches. The 1-hour rainfall with 1% exceedance frequency is 3.3 inches. Structures housing safety-related facilities, systems, and equipment are protected from flooding during a local PMF by the slope of the plant yard. The yard is graded so that the surface runoff will be carried to Chickamauga Reservoir without exceeding the elevation of the accesses given in Section 2.4.1.1. The exterior accesses that are below the grade elevation for that specific structure exit from that structure into another structure and are not exterior in the sense that they exit or are exposed to the environment. For any access exposed to the environment and located at grade elevation, sufficient drainage is provided to prevent water from entering the opening. This is accomplished by sloping away from the opening.PMP for the plant drainage systems has been defined for TVA by the Hydrometeorological Branch of the National Weather Service and is described in Hydrometeorological Report No. 56.Ice accumulation would occur only at infrequent intervals because of the temperate climate. Maximum winter precipitation concurrent with ice accumulation would impose less severe conditions on the drainage system than would the PMF.Figure 2.4-40a (sheet 1) shows the Watts Bar site grading and drainage system and building outlines for the main plant area. Direction of flow for runoff has been indicated by arrows. Figures 2.4-40a (sheets 2 & 3) show paved and unpaved areas. Figure 2.4-40b shows the Watts Bar general plan; Figure 2.4-40c shows the site grading and drainage system for the area north and northwest of the plant along with the outline of the low-level radwaste storage facility. The 150-acre drainage area north of the site has been outlined on Figure 2.4-40b with direction of flow for runoff indicated by arrows.Figure 2.4-40d (three sheets) shows the plans and profiles for the perimeter roads; Figure 2.4-40e (two sheets) shows the plan and profile for the access highway. Figure 2.4-40f (three sheets) shows the plan, sections, and profiles for the main plant railroad tracks. Figure 2.4-40g (three sheets) shows the yard grading, drainage, and surfacing for the switchyard.
2.4-10 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83In testing the adequacy of the site drainage system, all underground drains were assumed clogged. Peak discharges were evaluated using storm intensities for the maximum 1-hour rainfall obtained from the PMP mass curve shown on Figure 2.4-40h. Runoff was assumed equal to rainfall. Each watershed was analyzed using the more appropriate of two methods:  (1) when flow conditions controlled, standard-step backwater from the control section using peak discharges estimated from rainfall intensities corresponding to the time of concentration of the area above the control or (2) when ponding or reservoir-type conditions controlled, storage routing the inflow hydrograph equivalent to the PMP hydrograph using 2-minute time intervals. Computed maximum water surface elevations are below critical floor Elevation 729. The separate watershed areas are numbered for identification on Figure 2.4-40a.Runoff from the employee parking lot and the areas south of the office building and west of the Turbine Building (area 1) will flow along the perimeter road west of the switchyard and drain into the area surrounding the chemical holdup ponds. The control is the drainage ditch and road which acts as a channel between the west end of the switchyard and the embankment to the west. To be conservative it was assumed water would not flow into the switchyard. Maximum water surface elevations at the office and Turbine Buildings computed using method (1) were less than 729.Flow from the area west of the Service, Auxiliary, Reactor, and Diesel Generator Buildings and north of the office building and gatehouse (area 2) will drain along and then across the perimeter road, flow west through a swale and across the low point in the access road. The swale and the roads have sufficient capacity to keep water surface elevations below 729 at all buildings. Method (1) was used in this analysis.The area east of the Turbine, Reactor, and Diesel Generator Buildings (area 3) forms a pool bounded by the main and transformer yard railroad tracks with top of rail elevations at 728.00 and 728.25 respectively. Method (2) was used to route the inflow hydrograph through this pool from an initial elevation of 728.00 with outflow over the railroads. Maximum water surface elevations at the Turbine and Reactor Buildings were less than Elevation 729. Use of method (1) starting just downstream of the railroad confirmed this result.The flow from area 3 over the railroad north of the east-west baseline drains north along a channel between the main railroad and the ERCW maintenance road and east between the ERCW maintenance road and the north cooling tower. Flow from area 3 over the railroad south of the east-west baseline drains south along a channel between the storage yard road and the switchyard past the storage yard to the river. Analysis using method (1) shows that flow over the Diesel Generator Building road controls the elevations at the Turbine and Reactor Buildings. Maximum water surface elevations were computed to be less than Elevation 729.Flow from the switchyard and transformer yard (area 4) will drain to the east, west, and south. Maximum water surface elevations at the Turbine Building obtained using method (2) were less than Elevation 729.
HYDROLOGIC ENGINEERING2.4-11WATTS BARWBNP-92Table 2.4-14 provides the weir length description and coefficient of discharge used in the analysis for areas 3 and 4. Flow from the 150-acre drainage area north of the site drains two ways:  (1) 50 acres drain east through the double 96-inch culvert under the access railroad shown on Figure 2.4-40c and (2) drainage from the remaining 100 acres is diverted to the west through an 81- by 59-inch pipe arch and, when flows exceed the pipe capacity, south over a swale in the construction access road. The flow over the construction access road drains to the west across the access highway. The following information provides details of our analysis.The discharge hydrograph for the 100-acre area north of the plant and upstream from the construction access road was determined using a dimensionless unit graph based upon SCS procedures and PMP defined by the National Weather Service.
[1] The PMP mass curve used in the determination is shown on Figure 2.4-40h. Runoff was assumed equal to rainfall. The construction access road will act as a dam with the 81- by 59-inch pipe arch acting as a low-level outlet. Flow is prevented from draining to the east above the construction access road by a dike with top elevation at 736.5 (dike location and cross section shown on Figure 2.4-40c). The profile of the construction access road and the location of the pipe arch are shown on Figure 2.4-40c. The discharge hydrograph was routed using 2-minute time intervals through the pipe arch and over the construction access road using standard storage routing techniques. The rating curve for flow over the construction access road was developed from critical flow relationships with losses assumed equal to 0.5 V 2/2g. The maximum elevation reached at the construction access road was 735.28. The pipe arch is designed for AASHTO H-20 loading which we judg e is adequate for the loading expected. In the unlikely event of pipe arch failure and flow blockage, the maximum flood level at the construction access road would increase only 0.12 foot, from Elevation 735.28 to 735.4. The peak flow over the construction road was used in computations.Flow over the construction access road discharges into the 67-acre area west of the Service, Auxiliary, Reactor, and Diesel Generator Buildings and north of the office building and gatehouse (area 2 of Figure 2.4-40a) before flowing west across the access highway (Figure 2.4-40e). Flow from 60 additional acres to the northwest of the site is also added to this area just upstream of the main access road. Elevations for area 2 were examined to include these additional flows. Backwater was computed from downstream of the access highway, crossing the perimeter road, to the Reactor, Diesel Generator, and Waste Evaporation System Buildings. The elevation at the access highway control was computed conservatively assuming that the peak flows from area 2 and over the construction road added directly. The maximum flood elevation reached in the main plant area was less than Elevation 729.The discharge hydrograph for the 50-acre area north of the plant was conservatively assumed equivalent to the PMP hydrograph using 2 minute time intervals. This hydrograph was routed using 2-minute time intervals through the double 96-inch culvert using standard storage routing techniques.
2.4-12 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92The maximum elevation reached at the culvert was 725.67. Flow is prevented from entering the main plant area by site grading as shown on Figure 2.4-40c. The double 96-inch culvert is designed to carry a Cooper E-80 loading as recommended by the American Railway Engineering Association (AREA). The culvert has already been exposed to the maximum loading (the generator stator with a total load of 792 tons on 22 axles) with no damage to the pipes or tracks. This maximum loading is less than the design load. Loading conditions will not be a problem.The site will be well maintained and any debris generated from it will be minimal; therefore, debris blockage of the double 96-inch culvert or the 81- by 59-inch pipe arch will not be a problem.Table 2.4-15 provides a description of drainage area, estimated peak discharge, and computed maximum water surface elevation for each subwatershed investigated in the site drainage analysis.A local PMF on the holding pond does not pose a threat with respect to flooding of safety-related structures. The top of the holding pond dikes is set at Elevation 714.0, whereas water level must exceed the plant grade at Elevation 728.0 before safety- related structures can be flooded. A wide emergency spillway is cut in original ground at an elevation 2 feet below the top of the dikes. During a local PMF the water trapped by the pond rise will be considerably less than the 14-foot difference between the top of the dikes and plant grade.
 
====2.4.3 Probable====
Maximum Flood (PMF) on Streams and RiversThe guidance of Appendix A of Regulatory Guide 1.59 was followed in determining the PMF.The PMF was determined from PMP for the total watershed above the plant with consideration given to seasonal and areal variations. The original PMF determination also considered a PMF at upstream tributary dams whose failure has the potential to cause maximum plant site flood levels. Dam safety modifications have eliminated the potential of a PMF at upstrean tributary dams to cause maximum plant site flood levels.Two basic storm situations were found to have the potential to produce a maximum flood at Watts Bar Nuclear Plant. These are (1) a sequence of March storms producing maximum rainfall on the 21,400-square-mile watershed above Chattanooga and (2) a sequence of March storms centered and producing maximum rains in the basin to the west of the Appalachian Divide and above Chattanooga, hereafter called the 7,980-square-mile storm. The maximum flood level at the plant would be caused by the PMP on the  7,980-square-mile storm. The flood level for the 21,400 square mile storm would be slightly less.In both storms the West Saddle Dike at Watts Bar Dam would be overtopped and breached. No other failure would occur. Maximum discharge at the plant 1,288,000 cfs for the  7,980-square-mile storm. The resulting probable maximum elevation at the plant would be 734.9 for both floods excluding wind wave effects.
HYDROLOGIC ENGINEERING2.4-13WATTS BARWBNP-922.4.3.1  Probable Maximum Precipitation (PMP)Probable maximum precipitation (PMP) for the watershed above Chickamauga and Watts Bar Dams has been defined for TVA by the Hydrometeorological Report No.41[4]. Hydrometeorological Report No.45
[1] defines PMP for watersheds above tributary dams. These reports define depth-area-duration characteristics and antecedent storm potentials. Snowmelt is not a factor in generating maximum floods at the site.Two basic total watershed storm positions have the potential to produce a maximum flood at the Watts Bar plant site. One would produce maximum rainfall over the 21,400-square-mile watershed above Chattanooga. The other would produce maximum rains on the part of the basin downstream from major TVA tributary reservoirs, hereafter referred to as the 7,980-square-mile storm. These storms would occur in March. Depths for other months would be less.Two possible isohyetal patterns producing the 21,400-square-mile area depths are presented in Report No. 41
[4]. The pattern critical to this study is the 'downstream pattern' shown in Figure 2.4-41 along with the maximum 6-hour storm depths. The isohyetal pattern for the 7,980-square-mile storm is shown in Figure 2.4-42 along with the maximum 6-hour storm depths. The pattern is not orographically fixed and can be moved parallel to the long axis northeast and southwest along the valley.Potential storm amounts differing by seasons were analyzed in sufficient number to make certain that the March storms would be controlling. Enough centerings were investigated to assure that a most critical position was used.A 3-day storm, 3 days antecedent to the 3-day main storm, was assumed to occur in all total basin PMP situations. Depths equivalent to 40% of the main storm were used for the antecedent storms with uniform areal distribution as recommended in Report
 
No. 41[4].In the original analysis, storms producing PMP above upstream tributary dams were also evaluated. Storm depths and isohyetal patterns for tributary watersheds with drainage areas less than 3000 square miles are defined in Hydrometeorological Report No. 45
[1]. For Douglas Dam, drainage area 4541 square miles, a 72-hour PMP storm depth of 22.3 inches was determined using Hydrometeorological Report No.
45[1] data. Nonorographic PMP was determined from Figure 3-11 from Report No.45
[1] and increased slightly for orgraphic effects by the ratio of mean annual precipitation above Douglas to mean annual nonorographic precipitation for the area (Figure 3-16 from Report No. 45
[1]). Areal distribution of PMP rainfall was patterned after mean annual precipitation isohyets and isohyets of Hydrometeorological Report No. 45
[1] PMP estimates for subbasins above Douglas Dam. Residual rainfall on the area below Douglas and above Watts Bar was such that the total above Watts Bar was 80% of the PMP. These storms would occur in the June to October warm season months. For conservatism, a July date was postulated because reservoirs would be at maximum summer levels.
2.4-14 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92A 3-day storm, 3 days antecedent to the 3-day main storm, was applied in these small area PMP situations. Depths equal to 30% of the main storm were used for the antecedent storms with uniform areal distribution as recommended in Report No. 45[1].A standard time distribution pattern was adopted for all storms based upon major observed storms transposable to the Tennessee Valley and in conformance with the usual practice of Federal agencies. The adopted distribution is shown on Figure 2.4-43.Both the 21,400 square mile total basin storm with downstream orographically fixed pattern (Figure 2.4-41) and the 7,980 square mile storm centered at Bulls Gap, Tennessee (50 miles northeast of Knoxville) produce essentially the same peak stage. These storms would follow an antecedent storm commencing on March 15. For the purpose of this report all subsequent rainfall statistics are for the 21,400-square-mile storm because of equivalent flood levels larger total storm volumes involved and the fact that it produces the controlling storm for the Sequoyah Nuclear Plant downstream.
Translation of the PMP from Report No. 41
[4] to the basin above Watts Bar results in an antecedent storm producing an average precipitation of 6.44 inches in 3 days, followed by a 3-day dry period, and then by the main storm producing an average precipitation of 16.34 inches in 3 days. Figure 2.4-44 is an isohyetal map of the maximum 3-day PMP. Basin rainfall depths are given in Table 2.4-5.
2.4.3.2  Precipitation LossesA multi-variable relationship, used in the day-to-day operation of the TVA system, has been applied to determine precipitation excess P e directly. The relationships were developed from observed data. They relate precipitation excess to the rainfall, week of the year, geographic location, and antecedent precipitation index (API). In their application P e becomes an increasing fraction of rainfall as the storm progresses in time and becomes equal to rainfall when from 6 to 16 inches have fallen.For this study, a median API as determined from past records was used at the start of the antecedent storm. The antecedent storm is so large, however, that the main storm is not sensitive to variations in adopted API.For review purposes, precipitation losses have been determined by subtracting P e from rainfall. In the critical probable maximum storm losses are 2.24 inches, amounting to 35% of rainfall, for the 3-day antecedent storm, and 1.78 inches, 11% of rainfall, for the 3-day main storm above Watts Bar Dam. Table 2.4-5 displays the API, rain, and precipitation excess for each of the 45 subwatersheds of the hydrologic model for the Watts Bar probable maximum flood.
2.4.3.3  Runoff and St ream Course ModelThe runoff model used to determine Tennessee River flood hydrographs at Watts Bar Nuclear Plant is divided into 45 unit areas and includes the total watershed above Chickamauga Dam downstream. Unit hydrographs are used to compute flows from the unit areas. The unit area flows are combined with appropriate time sequencing or HYDROLOGIC ENGINEERING2.4-15WATTS BARWBNP-83channel routing procedures to compute inflows into the most upstream reservoirs which in turn are routed through the reservoirs using standard techniques. Resulting outflows are combined with additional local inflows and carried downstream using appropriate time sequencing or routing procedures including unsteady flow routing. Figure 2.4-45 shows unit areas of the watershed upstream from Chickamauga Dam.The runoff model differs from that used in the PSAR because of refinements made in some elements of the model during PMF studies for other nuclear plants and those made from information gained from the 1973 flood, the largest that has occurred for present reservoir conditions. Changes are identified when appropriate in the text. They include both additional and revised unit hydrographs and additional and revised unsteady flow stream course models.Unit hydrographs were developed for each unit area from maximum flood hydrographs either recorded at stream gaging stations or estimated from reservoir headwater elevation, inflow, and discharge data using the procedures described by Newton and Vineyard, Reference [5]. The number of unit areas has been increased from 34 to 45.
The differences include:
(1)Combining the two unit areas for Watauga River (Sugar Grove and Watauga local) into one unit area and dividing the Cherokee to Gate City area into two unit areas (Surgoinsville local and Cherokee local below Surgoinsville);
(2)Increasing the unit areas on the Clinch River from 1 to 11 and the Watts Bar local from 1 to 2; (3)Changes to add an unsteady flow model for the Fort Loudoun-Tellico Dam complex which included dividing the lower Little Tennessee River into two unit areas (Fontana to Chilhowee and Chilhowee to Tellico), and the Fort Loudoun local unit area into three unit areas (French Broad River local, Holston River local and Fort Loudoun local);
(4)Combining the two unit areas above Fontana (Tuckasegee River at Bryson City and Oconaluftee River at Birdtown) into one unit area (Tuckasegee River at Bryson City) and; (5)Combining the two unit areas above Ocoee No. 1 (Ocoee No. 1 and Ocoee No. 3) into one unit area (Ocoee No. 1 to Blue Ridge) and dividing the Chickamauga local unit area into two unit areas (Chickamauga local and lower Hiwassee).In addition, 12 of the unit graphs have been revised. Figure 2.4-46, which contains 11 sheets, shows the unit hydrographs. Table 2.4-6 contains essential dimension data for each unit hydrograph and identification of those hydrographs which are new or revised.
Tributary reservoir routings, except for Tellico, were made using the Goodrich semigraphical method and flat pool storage conditions. Main river reservoir and Tellico routings were made using unsteady flow te chniques. This differs from the PSAR in that:
2.4-16 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83 (1)An unsteady flow model has been added for Fort Loudoun Tellico complex, and (2)The Chickamauga unsteady flow model has been revised using the 1973 flood data and the HEC-2 backwater computer program.Unsteady flow routings were computer solved with a mathematical model based on the equations of unsteady flow, Reference [6]. Boundary conditions prescribed were inflow hydrographs at the upstream boundary, local inflows, and headwater discharge relationships at the downstream boundary based upon normal operating rules, or based upon rated curves when geometry controlled.The unsteady flow mathematical model for the 49.9-mile long Fort Loudoun Reservoir was divided into 24, 2.08-mile reaches. The model was verified at 3 gaged points in Fort Loudoun Reservoir using 1963 and 1973 flood data. The unsteady flow model was extended upstream on the French Broad and Holston Rivers to Douglas and Cherokee Dams, respectively. The French Broad and Holston River unsteady flow models were verified at one gaged point each (mile 7.4 and 5.5, respectively) using 1963 and 1973 flood data.The Little Tennessee River was modeled from Tellico Dam, mile 0.3, through Tellico Reservoir to Chilhowee Dam at mile 33.6 and upstream to Fontana Dam at mile 61.0.
The model for Tellico Reservoir to Chilhowee Dam was tested for adequacy by comparing its results with steady-state profiles at 1,000,000 and 2,000,000 cfs computed by the standard-step method. Minor decreases in conveyance in the unsteady flow model yielded good agreement. The average conveyance correction found necessary in the reach below Chilhowee Dam to make the unsteady flow model agree with the standard-step method was also used in the river reach from Chilhowee to Fontana Dam.The Fort Loudoun and Tellico unsteady flow models were joined by a canal unsteady flow model. The canal was modeled with five equally-spaced cross-sections at 525-feet intervals for the 2100-foot long canal.The unsteady flow routing model for the 72.4-mile-long Watts Bar Reservoir was divided into 34, 2.13-mile reaches. The Watts Bar model was verified at two gaged points within the reservoir using 1963 flood data.The unsteady flow routing model for the total 58.9-mile-long Chickamauga Reservoir was divided into 28, 2.1-mile reaches. The Chickamauga Reservoir unsteady flow model was verified at four gaged points within the reservoir using 1973 flood data. This differs from the PSAR in that the 1973 flood was added for verification replacing the 1963 flood. The 1973 flood is the largest which has occurred since closure of South Holston Dam in 1950. Comparisons between observed and computed stages in Chickamauga Reservoir are shown in Figure 2.4-50.It is impossible to verify the model with actual data approaching the magnitude of the PMF. The best remaining alternative was to compare the model elevations in a state of steady flow with elevations computed by the standard-step method. This was done HYDROLOGIC ENGINEERING2.4-17WATTS BARWBNP-92for steady flows ranging up to 1,500,000 cfs. An example shown by the rating curve of Figure 2.4-51 shows the good agreement.The runoff model was verified by using it to reproduce the March 1963 and March 1973 floods. This differs from the PSAR in th at the 1973 flood was added for verification replacing the 1957 flood. The 1973 flood is the largest which has occurred since closure of South Holston Dam in 1950. Observed volumes of precipitation excess were used in the verification. Comparisons between observed and computed outflows from Watts Bar and Chickamauga Dams for the 1963 and 1973 floods are shown in Figures 2.4-48 and 2.4-49, respectively.From a study of the basic units of the predicting system and the systems response to alterations in various basic elements, it is concluded that the runoff model serves adequately and conservatively to determine maximum flood levels. This conclusion is based in part upon studies by others
[7,8,9] and unpublished work of TVA which indicate the assumption of linearity in unit hydrographs, an important element of the system, is valid when they are developed from large, out-of-bank floods produced by major, basin-wide storms or will duplicate such floods.Reservoir routings started at median observed elevations for the appropriate season, mid-March for the large area PMP storms. Median levels were reevaluated using operating experience for:
(1)The total project period, or (2)The 5-year period, 1972-1976, for those projects whose operating guides were changed in 1971.Because of the wet years of 1972-1975 and the operating guide changes, median elevations were higher for 7 of the 13 tributary reservoirs where routing is involved.Normal reservoir operating procedures were used in the antecedent storm. These used turbine and sluice discharge in the tributary reservoirs. Turbine discharges are not used in the main river reservoirs after large flood flows develop because head differentials are too small. Normal operating procedures were used in the principal storm except that turbine discharge was not used in either the tributary or main river dams. All gates were determined to be operable without failures during the flood.
Gates on main river dams would be fully raised, thus requiring no additional operations, by the last day of the storm which is before the structures and access roads would be inundated. Median initial reservoir elevations were used at the start of the storm sequence used to define the PMF to be consistent with statistical experience and to avoid unreasonable combinations of extreme events. As a result 55% of the total reserved system flood detention capacity above the plant was occupied at the start of the main flood. This is considered to he amply conservative. Neither the initial reservoir levels nor the operating rules would have significant effect on maximum flood discharges and elevations at the plant site because spillway capacities, and hence uncontrolled conditions, were reached early in the flood.
2.4-18 HYDROLOGIC ENGINEERINGWATTS BARWBNP-922.4.3.4  Probable Maximum Flood FlowThe analysis to determine the probable maximum flood (PMF) flow included evaluation of PMP over the total watershed with consideration of critical seasonal and areal variations. A comparison of candidate events is provided by Table 2.4-7.The PMF discharge was determined to be 1,288,000 cfs resulting from the 7,980-square-mile storm centered at Bulls Gap. The peak discharge of 1,230,000 cfs resulting from the total basin, downstream centered, orographically fixed storm produced an equivalent peak stage. The dam safety modifications to Fort Loudon - Tellico and Watts Bar enable these projects to safely pass the PMF. The West Saddle Dike at Watts Bar Dam would be overtopped and breached. Chickamauga Dam would be overtopped but was assumed not to fail (failure would reduce the flood level at the site). In the original analysis, Fort Loudoun-Tellico and Watts Bar upstream and Chickamauga Dam downstream would be overtopped and the earth embankments breached. The PMF hydrograph is shown in Figure 2.4-52. Rainfall and precipitation shown in Figure 2.4-52 are for the total basin storm.Following is a more complete description of candidate situations examined.The storm producing the PMF discharge is the 7,980-square-mile storm centered at Bulls Gap, Tennessee, 50 miles northeast of Knoxville, shown in Figure 2.4-42. The flood from this storm would overtop and breach the West Saddle Dike at Watts Bar Dam (Figure 2.4-53).The storm producing the next highest discharge and the equivalent level as the PMF was the March storm producing the PMP on the 21,400-square-mile watershed above Chattanooga with downstream centered and orographically fixed isohyetal pattern shown in Figure 2.4-44, and is more completely described in Section 2.4.3.1. The flood would overtop and breach the earth West saddle dike at Watts Bar Dam upstream.
Chickamauga Dam, downstream,would be over topped but was conservatively assumed not to fail. The previous PMF evaluations also considered candidate situations involving upstream tributary dams, Douglas and Watauga. These two dams were overtopped and breached in their respective PMFs. These two situations were shown at that time to be non-governing. Dam safety modifications have since eliminated the potential failures of these dams; therefore, these two candidate situations have been eliminated.Following is a more complete description of dam stability and earth embankment breaching analysis made to define PMF conditions.Concrete Section AnalysisFor concrete dam sections, comparisons were made between the original design headwater and tailwater levels and those that would prevail in the PMF. If the overturning moments and horizontal forces were not increased by more than about 20%, the structures were considered safe against failure. All upstream dams passed HYDROLOGIC ENGINEERING2.4-19WATTS BARWBNP-83this test except Douglas, Fort Loudoun, and Watts Bar. Original designs showed the spillway sections of these dams to be most vulnerable. These spillway sections were examined in further detail and judged to be stable.
Spillway GatesDuring peak PMF conditions the radial spillway gates of Fort Loudoun and Watts Bar Dams will be wide open with flow over the gates and under the gates. For this condition both the static and dynamic load stresses in the main structural members of the gate will be less than the yield stress by a factor of 3. The stress in the trunnion pin is less than the allowable design stress by a factor of greater than 10. The trunnion pin is prevented from dislodgement by a key into the gate anchorage assembly and fitting into a slot in the pin.The gates were also investigated for the condition when rising headwater level first begins to exceed the bottom of the gates in the wide-open position. This condition produces the largest forces, tending to rotate the radial gates upward. In the wideopen position the gates are dogged against steel gate stops anchored to the concrete piers.
The stresses in the gate stop members are less than the yield stress of the material by a factor of 2.It is concluded that the above-listed margins are sufficient to provide assurance also that the gates will not fail as a result of additional stresses which may result from possible vibrations of the gates acting as orifices.Waterborne ObjectsConsideration has been given to the effect of waterborne objects striking the spillway gates and bents supporting the bridge across Watts Bar Dam at peak water level at the dam. The most severe potential for damage would be by a barge which has been torn loose from its moorings and floats into the dam.Should the barge approach the spillway portion of the dam end on, one bridge bent could be failed by the barge and two spillway gates could be damaged and possibly swept away. The loss of one bridge bent will not collapse the bridge because the bridge girders are continuous members and the stress in the girders will be less than the ultimate stress for this condition of one support being lost. Should two gates be swept away, the nappe of the water surface over the spillway weir would be such that the barge would be grounded on the tops of the concrete spillway piers and provide a partial obstruction to flow comparable to unfailed spillway gates. Hence the loss of two gates from this cause will have little effect on the peak flow and elevation.Should the barge approach the spillway portion broadside, two and possibly three bridge bents could be failed. For this condition the bridge would collapse on the barge and the barge would be grounded on the tops of the spillway piers. This would be probable because the approach velocity of the barge would be from 4 to 7 miles per hour and the bottom of the barge would be about 6 inches above the tops of the piers. For this condition the barge would be grounded before striking the spillway gates 2.4-20 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92because the gates are about 20 feet downstream from the leg of the upstream bridge bents.Lock GatesThe lock gates at Fort Loudoun, Watts Bar, and Chickamauga were examined for possible failure with the conclusion that no potential for failure exists because the gates are designed for a differential hydrostatic head greater than that which exists during the probable maximum flood.Embankment BreachingThe potential for embankment breaching was examined for all PMF candidate situations. In the 1998 reanalysis the only embankment failure would be the West Saddle Dike at Watts Bar Dam. Chickamauga Dam, 57 miles downstream of the plant, would be overtopped but was assumed not to fail. This is conservative as failure would slightly lower flood elevations at the plant.Figure 2.4-47b shows the headwater and tailwater discharge relationships for Fort Loudon Dam as modified. Figures 2.4-47c and 2.4-55 show these relationships for Tellico and Watts Bar Dams, respectively.The adopted relationship to compute the rate of erosion in an earth dam failure is that developed and used by the Bureau of Reclamation in connection with its safety of dams program
[11]. The expression below relates the volume of eroded fill material to the volume of water flowing through the breach. The equation is:
whereQ soil  = Volume of soil eroded in each time period Q water = Volume of water discharged each time period K = Constant of proportionality, 1 for the soil and discharge relationships in this studye = Base of natural logarithm systemQsoil Qwater--------------------
-Ke x-=X b H---- d tan=
HYDROLOGIC ENGINEERING2.4-21WATTS BARWBNP-92 whereb  = Base length of overflow channel at any given time H  = Hydraulic head at any given time d = Developed angle of friction of soil material. A conservative value of 13 degrees was adopted for materials in the dams investigated.Solving the equation, which was computerized, involves a trial-and-error procedure over short depth and time increments. In the program depth changes of 0.1 foot or less are used to keep time increments to less than one second during rapid failure and up to about 350 seconds prior to breaching.The solution of an earth embankment breach begins by solving the erosion equation using a headwater elevation hydrograph, assuming no failure. Erosion is postulated to occur across the entire earth section and to start at the downstream edge when headwater elevations reached a selected depth above the dam top elevation.
Subsequently, when erosion reaches the upstream edge of the embankment, breaching and rapid lowering of the embankment begins. Thereafter, computations include headwater adjustments for increased reservoir outflow resulting from the breach.Watts Bar West Saddle Dike FailureThe west saddle dike was examined and found subject to failure from overtopping. This failure would be a complete washout and would add to the discharge from Watts Bar Dam.Given the hour of failure, the peak discharge was determined based upon the headwater and tailwater depths at that time. Unsteady flow routing techniques were used to define the rest of the outflow hydrograph. This was accomplished using headwater discharge relationships at the dam treated as the downstream boundary to the Watts Bar Reservoir routing reach. Some verification for the breaching computational procedures illustrated above was obtained by comparison and actual failures reported in the literature and in informal discussion with hydrologic engineers. These reports show that overtopped earth embankments do not necessarily fail. Earth embankments have sustained overtopping of several feet for several hours before failure occurred. An extreme example is Oros earth dam in Brazil
[12] which was overtopped to a depth of approximately 2.6 feet along a 2,000-foot length for 12 hours before breaching began.
Once an earth embankment is breached, failure tends to progress rapidly, however. How rapidly depends upon the material and headwater depths during failure. Complete failures computed in this and other studies have varied from about one half to 6 hours after initial breaching. This is consistent with actual failures.
2.4-22 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92Chickamauga Embankment FailureIn the original analysis the failure of earth embankments at Chickamauga Dam, 57 miles downstream from Watts Bar Nuclear Plant  reduced flood levels at the plant by 0.2 foot. Future embankment improvements are planned for Chickamauga Dam which might eventually invalidate assumption of failure. Therefore, the dam was assumed not to fail in determining flood elevations for the plant. This assumption is conservative.Wave Front From Watts Bar BreachingThis subsection describes analysis of the wave from resulting from the embankment failure of Watts Bar Dam. Embankment improvements made by the Dam Safety Program ensure that failure in the PMF will not occur. This subsection is retained for historical purposes.Because Watts Bar Nuclear Plant is located only 1.9 miles downstream from Watts Bar Dam, the magnitude and shape of the wave front resulting from the sudden failure of the Watts Bar embankment during the PMF was examined in detail. The analysis consisted of determining the magnitude of the wave resulting from the embankment failure (1) immediately after failure, (2) after  traveling downstream 8500 feet and striking a ridge on the left bank, and (3) reflected from the ridge directed toward the plant on the right bank.The water levels upstream and downstream from the earth embankment for the conditions which exist just prior to and immediately following embankment failure are shown schematically on Figure 2.4-61. Immediately after failure of the 750-foot wide portion of the embankment a bore will develop. The relative height of the bore has been defined by Stoker
[31] by the following functional relationship, which is shown graphically on Figure 2.4-62.In which, h 0 , h 1, and h 2, are defined in Figure 2.4-61.For the initial conditions shown schematically on Figure 2.4-61.Entering Figure 2.4-62 with h 0/h 1, = 0.435 h 2 h 0-h 1------------------h 1 h 0=h 0 h 1------727700-762700--------------------------
-27 62------0.435===h 2 h 0-h 1------------------0.250=
HYDROLOGIC ENGINEERING2.4-23WATTS BARWBNP-83Solving this equation for the bore height above tailwater, (h 2-h 0) gives:Solving for the depth behind the bore, h 2, gives:The initial bore velocity per Reference [31], can be computed from:In which,Therefore, immediately after the failure of the embankment, the height of the bore, will be 15.5 feet above the initial tailwater depth, its width will be 750 feet at the dam and it will move toward Blalock Ridge with an initial velocity of 54 feet per second.The bore is conservatively estimated to spread laterally at 10° as it moves out from the dam, as shown on Figure 2.4-63. The height of the bore would be reduced by the 10° expansion from 15.5 feet at the dam to 3.1 feet at Blalock Ridge. The ridge is sloped and heavily wooded and would absorb a large percentage of the incident bore energy. Since wave energy is proportional to the square of the wave amplitude A,[32] the following expression can be written:in which subscripts i, r, and a, refer to incident, reflected and absorbed components, respectively. This equation may be written as:
h 2 h 0-0.250h 10.250x6215.5feet===h 20.250h 1 h 0+0.250x6227
+42.5feet==='V 0=gh 2 h 0---------h 0 h 2+2------------------+'12.032.242.5 27-----------2742.5+2------------------------12.042.0+54.0fps==+=V 0Qbefore failureTailwater area---------------------------------------
-971000300027-------------------------
-12fps===A i 2 A r 2 A a 2+=1 A r2 A i-------------
A a2 A i--------------
+=
2.4-24 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83Using  and  where C r is the reflection coefficient and C a is the absorption coefficient, the expression becomes:The following table was computed using this expression.Where:*C a 2 is the fraction of wave energy absorbed
*C r 2 is the fraction of wave energy reflectedValues of C ranging from about 0.16 up to 0.72 have been reported in the literature for tree-like materials, with most values being nearer the 0.16 value
[33]. Assuming 50% of the bore energy would be absorbed by the ridge and 50% reflected, gives from the preceding tablewith A i = 3.1 feet, the reflected bore height would be:
*C a 2*C r 2 C a=A a/A i C r=A r/A i01010.10.90.320.95 0.20.80.450.89 0.30.70.550.84 0.40.60.630.77 0.5O.50.710.71 0.60.40.770.63 0.70.30.840.55 0.80.20.890.45 0.90.10.950.32 1.0010 C r A r A i=C a A a A i=C r 1C a 2-=C r A r A i-----0.71==A r2.2 feet=
HYDROLOGIC ENGINEERING2.4-25WATTS BARWBNP-92In addition to the conservative assumption regarding the absorption of bore energy, the following additional factors which would further reduce the reflected wave height have been neglected. These factors are:
(1)The shape of the ridge is such that it does not parallel the wave front, therefore only a portion of the wave front would be directed toward the plant site. Considerable dispersion of the wave front would result from the curved shape of Blalock ridge.
(2)The ridge is sloped, therefore run-off would further reduce the reflected wave height.(3)After striking Blalock Ridge no further wave expansion has been considered in this analysis.Thus, a wave height of about 2.2 feet is conservatively estimated to be reflected from Blalock Ridge and directed toward the plant site. This compares with the computed wave height in the PSAR of 2.0 feet. This wave would travel at about 30 feet per second on the flood plain as it approaches the plant site.The reflected wave would arrive at the plant site in about 5 to 10 minutes following embankment failure (embankment failure was postulated to occur at 11:30 on March 24). At the time the wave arrives at the plant site, the water level is about elevation 728 as shown in FSAR Figure 2.4-64 producing a water level at the plant site of El 730.2. The maximum PMF level occurs some one and one-half days later. Forces resulting from the 2.2-foot bore were evaluated for each of the safety-related structures required to remain functional and maintain their structural integrity during the probable maximum flood. The design criteria for the structures described in Section 3.8 were not exceeded.2.4.3.5  Water Level DeterminationsThe maximum plant site flood elevation 734.9 is produced by the 7980 square mile storm. The less critical 21,400 square mile storm would produce elevation 734.7 at the plant site. The flood elevation hydrographis shown in Figure 2.4-57. Elevations were computed concurrently with discharges for the site using the unsteady flow reservoir model. Figure 2.4-65 shows the PMF profile together with the regulated maximum known flood and thalweg profiles along a 16-mile reach of the Chickamauga Reservoir which encompasses the plant location.The third candidate situation considered, failure of Douglas Dam during its PMF, was shown in the original analysis to produce a flood crest at the plant site approximately 4.4 feet below the controlling PMF event. Dam safety modifications to Douglas Dam involved raising the height of the dam to prevent overtopping in the PMF and this eliminates failure of Douglas as a candidate situation.The elevations from the potential controlling PMF events are compared in Table 2.4-7.
2.4-26 HYDROLOGIC ENGINEERINGWATTS BARWBNP-922.4.3.6  Coincident Wind Wave ActivitySome wind waves are likely when the probable maximum flood crests at Watts Bar Nuclear Plant. The flood would be near its crest for a day beginning about 2 days after cessation of the probable maximum storm (Figure 2.4-57). The day of occurrence would be in the month of March or possibly the first week in April. Figure 2.4-98 shows the main plant general grading plan. The diesel generator buildings to the north and the pumping station to the east of the main building complex must be protected from flooding to assure plant safety. The diesel generator buildings operating floors are at elevation 742 which are well above the maximum computed elevation including wind wave runup. The pumping station is shielded from direct wave action on all sides except to the south by either buildings, earth embankments, or the cooling towers. The maximum effective fetch of 1.3 miles occurs from both the southwest and northeast directions (Figure 2.4-67). This allows for the sheltering effect of several hills on the south riverbank which become islands at maximum flood levels.For the Watts Bar FSAR, the two-year extreme wind for the season in which the PMF could occur was adopted to associate with the PMF crest as specified in Regulatory Guide 1.59. The storm studies on which the PMF determination is based
[4] show that the season of maximum rain depth is the month of March. Wind velocity was determined from a statistical analysis of maximum March winds observed at Chattanooga, Tennessee.Records of daily maximum average hourly winds for each direction are available at the Watts Bar site for the period May 23, 1973, through April 30, 1978. This record, however, is too short to use in a statistical analysis to determine the 2-year extreme wind, as specified in ANSI Standard N170-1976, an appendix to Regulatory Guide 1.59. Further, the necessary 30-minute wind data are not available. To determine applicability of Chattanooga winds at the Watts Bar plant, a Kolmogorov-Smirnov (K-S) statistical test was applied to cumulative frequency distributions of daily maximum hourly winds for each direction at Chattanooga and Watts Bar. The winds compared were those recorded at Chattanooga during the period 1948-74 (the period when the necessary triple-register records were available for analysis) and the Watts Bar record. A concurrent record is not available; however, the K-S test showed that (except for the noncritical east direction) the record of daily maximum hourly velocities at Chattanooga were equal to or greater than that at Watts Bar. From this analysis it was concluded that use of the Chattanooga wind records to define seasonal maximum winds at the Watts Bar site is conservative.The available data at Chattanooga included 30-minute and hourly winds by seasons and direction for the 27-year period 1948 through 1974. The March 30-minute wind data which was used directly in subsequent wind wave calculations were adjusted to 30 feet by the equation:
V 30 V z30Z17=
HYDROLOGIC ENGINEERING2.4-27WATTS BARWBNP-92where: V 30 = wind speed at 30 feet V z  = wind speed at height Z above the groundThe adjusted 30-minute wind data were analyzed for both the southwest and northeast directions. The winds from the northeast are considerably less than those from the southwest; hence, the southwest direction is controlling. Figure 2.4-66 shows the plot of the Chattanooga March maximum 30-minute winds from the critical southwest direction. The 2-year, 30-minute wind speed is 21 miles per hour determined from a mathematical fit to the Gumbel distribution. This compares with 15 miles per hour determined for the March season from the noncontrolling northeast direction.Wind wave calculations call for a 28-minute sustained wind. There is, however, no significant difference between a 2-year, 30-minute wind velocity and a 2-year, 28-minute wind velocity. Thus, the 2-year, 30-minute, 21 mile per hour wind velocity was used to compute wind waves.Computation of wind waves used the procedures of the Corps Of Engineers
[14]. The critical direction for the PMF elevations is from the southwest with an effective fetch of
 
===1.3 miles===
as shown in Figure 2.4-67. For a 28-minute sustained 21-mile-per-hour wind, 99.6% of the waves approaching the plant would be less than 2.0 feet high, crest to trough, resulting in maximum water elevation of 736.2.At the diesel generator building, corresponding runup on the earth embankment with a 4:1 slope would be 2.0 feet, reaching elevation 736.9. The runup on the south wall of the pumping station would be to elevation 736.9.Wind wave setup is not a problem since the wind direction is opposite to the flow of the river. The static effect of wind waves was accounted for by taking the static water pressure from the maximum height of the runup. The dynamic effects of wind waves were accounted for as follows:The dynamic effect of nonbreaking waves on the walls of safety-related structures was investigated using the Rainflow method
[15]. Concrete and reinforcing stresses were found to be within allowable limits.The dynamic effect of breaking waves on the walls of safety-related structures was investigated using a method developed by D. D. Gaillard and D. A. Molitar
[16]. The concrete and reinforcing stresses were found to be less than the allowable stresses.The dynamic effect of broken waves on the walls of safety-related structures was investigated using the method proposed by the U.S. Army Coastal Engineering Research Center.[15] Concrete and reinforcing stresses were found to be within allowable limits.
2.4-28 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83 2.4.4  Potential Dam Fail ures, Seismically InducedThe procedures described in Appendix A of Regulatory Guide 1.59 were followed when evaluating potential flood levels from seismically induced dam failures.The plant site and upstream reservoirs are located in the Southern Appalachian Tectonic Province and, therefore, subject to moderate earthquake forces with possible attendant failure. All upstream dams whose failure has the potential to cause flood problems at the plant were investigated to determine if failure from seismic events would endanger plant safety.It should be clearly understood that these studies have been made solely to ensure the safety of Watts Bar Nuclear Plant against failure by floods caused by the assumed failure of dams due to seismic forces. To assure that safe shutdown of the Watts Bar Nuclear Plant is not impaired by flood waters, TVA has in these studies added conservative assumptions to be able to show that  the plant can be safety controlled even in the event that all these unlikely events occur in just the proper sequence. TVA is of the strong opinion that the chances of the assumed events occurring approach zero probability.By furnishing this information TVA does not infer or concede that its dams are inadequate to withstand earthquakes that may be reasonably expected to occur in the TVA region under consideration. TVA has a program of inspection and maintenance carried out on a regular schedule to keep its dams safe. Instrumentation of the dams to help keep check on their behavior was installed in many of the dams during original construction. Other instrumentation has been added since and is still being added as the need may appear or as new techniques become available. In short, TVA has confidence that its dams are safe against catastrophic destruction by any natural forces that could be expected to occur.2.4.4.1  Dam Failure PermutationsThere are 12 major dams above Watts Bar Nuclear Plant whose failure could influence plant site flood levels. These are Watts Bar and Fort Loudoun Dams on the Tennessee River; Watauga, South Holston, Boone, Fort Patrick Henry, Cherokee, and Douglas Dams above Fort Loudoun; and Norris, Melton Hill, Fontana, and Tellico Dams between Fort Loudoun and Watts Bar. Dam locations with respect to the plant site are shown in Figure 2.1-1.Analyses to determine dam integrity in seismic events were made for two basic conditions.
HYDROLOGIC ENGINEERING2.4-29WATTS BARWBNP-92 (1)Determination of the water level at the plant during one-half the PMF with full reservoirs if its crest were augmented by flood waves from the postulated failure of upstream dams during an operating basis earthquake (OBE).
(2)Determination of the water level at the plant during a 25-year flood with full reservoirs if its crest were augmented by flood waves from the postulated
 
failure of upstream dams during a safe shutdown earthquake (SSE).The OBE and SSE are defined in Sections 2.5.2.4 and 2.5.2.7 as having maximum horizontal rock acceleration levels of 0.09 g and 0.18 g respectively. As described in Section 2.5.2.4, TVA agreed to use 0.18 g as the maximum bedrock acceleration level for the SSE.Prior to the 1998 reanalysis, the flood levels from postulated seismic failure of tributary dams given in this report we re higher than those in the PSAR. These higher levels resulted from:
(1)Use of unsteady flow models for the Clinch and Little Tennessee Rivers for the routing of Norris and Fontana seismic dam failure surges which replaced approximate routing procedures used in the PSAR analysis.
(2)Use of improved Watts Bar Reservoir unsteady flow models which extended up the Clinch River embayment to Melton Hill Dam.
(3)Use of a discharge rating for Norris failed dam section developed by TVA Engineering Laboratory model studies.In the 1998 reanalysis all potentially critical seismic events involving dam failures above the plant were reevaluated. These events included the postulated OBE failure of Fontana, the postulated OBE failure of Norris, the postulated OBE failure of Cherokee and Douglas, the postulated SSE failure of Norris, Cherokee and Douglas, and the postulated SSE failure of Norris, Douglas, Fort Loudon and Tellico.The highest flood level at Watts Bar from different seismic dam failure and flood combinations would be elevation 727.5 from failure of Norris, Cherokee and Douglas Dams during the SSE earthquake coincident with the twenty-five year flood. Wind wave could raise the level to elevation 728.2. Runup could reach elevation 729.0 on a 3:1 slope.Plant safety would be assured by shutdown prior to this flood crossing plant grade, elevation 728, using the warning system described in Section 2.4.14.This is the only combination of seismic dam failures with coincident flood which could result in a flood at Watts Bar exceeding plant grade. All other combinations would produce flood levels well below plant grade.
2.4-30 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83The effect of postulated seismic bridge failure and resulting failure of spillway gate anchors at Watts Bar and Fort Loudoun Dams would not create a safety hazard at the Watts Bar plant.Concrete StructuresThe standard method of computing stability is used. The maximum base compressive stress, average base shear stress, the factor of safety against overturning, and the shear strength required for a shear-friction factor of safety of 1 are determined. To find the shear strength required to provide a safety factor of 1, a coefficient of friction of 0.65 is assigned at the elevation of the base under consideration.The analyses for earthquake are based on the pseudo-static analysis method as given by Hinds[17] with increased hydrodynamic pressures determined by the method developed by Bustamante and Flores
[18]. These analyses include applying masonry inertia forces and increased water pressure to the structure resulting from the acceleration of the structure horizontally in the upstream direction and simultaneously in a downward direction. The masonry inertia forces are det ermined by a dynamic analysis of the structure which takes into account amplification of the accelerations above the foundation rock.No reduction of hydrostatic or hydrodynamic forces due to the decrease of the unit weight of water from the downward acceleration of the reservoir bottom is included in the analysis.Waves created at the free surface of the reservoir by an earthquake are considered of no importance. Based upon studies by Chopra[19] and Zienkiewicz
[20] it is TVA's judgment that before waves of any significant height have time to develop, the earthquake will be over. The duration of earthquake used in this analysis is in the range of 20 to 30 seconds.Although accumulated silt on the reservoir bottom would dampen vertically traveling waves, the effect of silt on structures is not considered. There is only a small amount of silt now present, and the accumulation rate is slow, as measured by TVA for many years[21].EmbankmentEmbankment analysis was made using the standard slip circle method. The effect of the earthquake is taken into account by applying the appropriate static inertia force to the dam mass within the assumed slip circle (pseudo-static method).In the analysis the embankment design constants used, including the shear strength of the materials in the dam and the foundation, are the same as those used in the original stability analysis.Although detailed dynamic soil properties are not available, a value for seismic amplification through the soil has been assumed based on previous studies pertaining to TVA nuclear plants. These studies have indicated maximum amplification values slightly in excess of two for a rather wide range of shear wave velocity to soil height HYDROLOGIC ENGINEERING2.4-31WATTS BARWBNP-92ratios. For these analyses, a straight-line variation is used with an acceleration at the top of the embankment being two times the top of rock acceleration.Flood RoutingThe runoff model of Section 2.4.3.3 was used to reevaluate potentially critical events involving dam failures above the plant. The remaining events (the postulated OBE failure of Watts Bar, the postulated OBE failure of Fort Loudon, the postulated SSE failure of Fontana and Douglas, the postulated SSE failure of Norris, and the postulated SSE failure of Fontana, Fort Loudon, and Tellico) produced plant site flood levels sufficiently lower than the controlling events and were not re-evaluated.Reservoir operating procedures used were those applicable to the season and flood inflows.OBE Concurrent With One-Half the Probable Maximum Flood Watts Bar DamStability analyses of Watts Bar Dam powerhouse and spillway sections result in the judgment that these structures will not fail. The analyses show low stresses with about 38% of all the spillway base, and about 42% of the powerhouse base, in compression.
Results are given in Figure 2.4-68. Dynamic analysis of the concrete structures resulted in the determination that the base acceleration is amplified at levels above the base. This differs from the previous analysis where amplification was not considered.Slip circle analysis of the earth embankment section results in a factor of safety of 1.52, and the embankment is judged not to fail. Results are given in Figure 2.4-69.For the condition of peak discharge at the dam for one-half the probable maximum flood the spillway gates are in the wide-open position with the bottom of the gates above the water. This condition was not analyzed because the condition with bridge failure described in the following paragraphs produces the controlling condition.Analysis of the bridge structure for forces resulting from the OBE, including amplification of acceleration results in the determination that the bridge could fail as a result of shearing the anchor bolts. The downstream bridge girders are assumed to strike the spillway gates. The impact of the girders striking the gates is assumed to fail the bolts which anchor the gate trunnions to the pier anchorages allowing the gates to fall on the spillway crest and be washed into the channel below the dam. The flow over the spillway crest would be the same as that prior to bridge and gate failure, i.e., peak discharge for one-half the probable maximum flood with gates in the wide-open position. Hence, bridge failure will cause no adverse effect on the flood.A potentially severe condition is the OBE at the onset of the main portion of one-half the probable maximum flood flow into Watts Bar Reservoir when most spillway gates would be closed during bridge failure, as described above. The gate hoisting machinery would be inoperable from being struck by the bridge with the result that the flood would crest with the gates closed and the bridge deck and girders lying on top of 2.4-32 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92the spillway piers. Analysis of the concrete portions of the dam for the headwater for this condition shows that they will not fail.For the condition described above with the most probable embankment breaching from overflow, the outflow of Watts Bar Dam would increase rapidly from about 200,000 cfs prior to the breach to about 660,000 cfs when breaching is complete. Breach time would be about 5 hours.The 660,000 cfs breach flow is the crest. The flood level at Watts Bar Dam reached elevation 717.5. Elevation at the plant site will be somewhat less, which is safely below plant grade elevation 728. This flood level was not reevaluated using the model described in Section 2.4.3.3, as amended, nor as part of the 1998 reanalysis, because it is clearly not controlling.For flow conditions between the 25-year flood and one-half the probable maximum flood, when the bottom of the gates are in the water, failure of the bridge during an OBE with consequent striking of the gates by the downstream bridge girders will result in failure of the gate lifting chains. The gates will rotate to the closed position. This condition is less severe than that described above for gates remaining closed during one-half the probable maximum flood; consequently, the resulting flood levels were not determined.Fort Loudoun DamStability analyses of Fort Loudoun Dam powerhouse and spillway sections result in the judgment that these structures will not fail. The analyses show low base stresses, with near two-thirds of the base in compression. Results are given in Figure 2.4-71.Slip circle analysis of the earth embankment results in a factor of safety of 1.26, and the embankment is judged not to fail. Results are given in Figure 2.4-72.The spillway gates and bridge are of the same design as those at Watts Bar Dam. Conditions of failure during the OBE are the same, and no problems are likely. Coincident failure at Fort Loudoun and Watts Bar does not occur.For the potentially critical case of Fort Loudoun bridge failure at the onset of the main portion of one-half the probable maximum flood flow into Fort Loudoun Reservoir, it was found that the Watts Bar inflows are much less than the condition resulting from simultaneous failure of Cherokee and Douglas, as described later.Tellico DamNo part of Tellico Dam is judged to fail. Results of the stability analyses for a typical non-overflow block and a typical spillway block are shown in Figure 2.4-73. The result of the stability analysis of the earth embankment is shown in Figure 2.4-74 and indicates a factor of safety of 1.28.
HYDROLOGIC ENGINEERING2.4-33WATTS BARWBNP-92 Norris DamResults of the Norris Dam stability analyses for a typical spillway block and a typical non-overflow section of maximum height are shown on Figure 2.4-75. Because only a small percentage of the spillway base is in compression, this structure is judged to fail. The high nonoverflow section with a small percentage of the base in compression and with high compressive and shearing stresses is also judged to fail.Figure 2.4-76 shows the likely condition of the dam after failure. Based on stability analyses the non-overflow blocks remaining in place are judged to withstand the OBE. Blocks 33-44 are judged to fail by overturning.The location of the debris is not based on any calculated procedure of failure because it is believed that this is not possible. It is TVA's judgment, however, that the failure mode shown is one logical assumption; and, although there may be many other logical assumptions, the amount of channel obstruction would probably be about the same.The discharge rating for this controlling, debris section was developed from a 1:150 scale hydraulic model at the TVA Engineering Laboratory and was verified closely by mathematical analysis.In the hydrologic routing for this failure, Melton Hill Dam was postulated to fail when the flood wave reached headwater elevation 804, based on structural analysis. The headwater at Watts Bar Dam would reach Elevation 758.1, 8.9 feet below the top of the earth embankment of the main dam; however, the West Saddle Dike would be overtopped and breached. A complete washout of the dike was assumed. The resulting water level at the nuclear plant site is 721.5, 6.5 feet below 728 plant grade. Cherokee DamResults of the Cherokee Dam stability analysis for a typical spillway block are shown in Figure 2.4-77. Based on this analysis the spillway is judged stable at the foundation base elevation 900. Analyses made for other elevations above elevation 900, but not shown in Figure 2.4-77, indicate the resultant of forces falls outside the base at elevation 1010. The spillway is assumed to fail at this elevation.The nonoverflow dam is embedded in fill to elevation 981.5 and is considered stable below that elevation. However, stability analysis indicates failure will occur above the fill line. The powerhouse intake is massive and backed up by the powerhouse. Therefore, it is judged able to withstand the OBE without failure. Results of the analysis for the highest portion of the south embankment are shown on Figure 2.4-78. The analysis was made using the same shear strengths of material as were used in the original analysis and shows a factor of safety of 0.85. Therefore, the south embankment is assumed to fail during the OBE. Because the north embankment and saddle dams 1, 2, and 3 are generally about one-half, or less, as high as the south embankment, they are judged to be stable for the OBE.
2.4-34 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92Figure 2.4-79 shows the assumed condition of the dam after failure. All debris from failure of the concrete portion is assumed to be located downstream in the channel at elevations lower than the remaining portions of the dam and, therefore, will not obstruct flow.No hydrologic results are given for the single failure of Cherokee Dam because the simultaneous failure of Cherokee and Douglas, discussed under multiple failures, is more critical.Douglas DamResults of the Douglas Dam stability analysis for a typical spillway block are shown in Figure 2.4-80. The upper part of the Douglas spillway is approximately 12 feet higher than Cherokee, but the amplification of the rock surface acceleration is the same. Therefore, based on the Cherokee analysis, it is judged that the Douglas spillway will fail at elevation 937, which corresponds to the assumed failure elevation of the Cherokee spillway.The Douglas non-overflow dam is similar to that at Cherokee and is embedded in fill to elevation 927.5. It is considered stable below that elevation. However, based on the Cherokee analysis, it is assumed to fail above the fill line. The abutment non-overflow blocks 1-5 and 29-35, being short blocks, are considered able to resist the OBE without failure. The powerhouse intake is massive and backed up downstream by the powerhouse. Therefore, it is considered able to withstand the OBE without failure.Results of the analysis of the saddle dam shown on Figure 2.4-81 indicate a factor of safety of 1. Therefore, the saddle dam is considered to be stable for the OBE.Figure 2.4-82 shows the portions of the dam judged to fail and the portions judged to remain. All debris from the failed portions is assumed to be located downstream in the channel at elevations lower than the remaining portions of the dam and, therefore, will not obstruct flow.No hydrologic results are given for the single failure of Douglas Dam because the simultaneous failure of Cherokee and Douglas, as discussed later under multiple failures, is more critical.Fontana DamFontana Dam was assumed to fail in the OBE although no stability analysis was made. Fontana is a high dam constructed with three longitudinal contraction joints in the higher blocks. Although the joints are keyed and grouted, it is possible that the grouting was not fully effective. Consequently, there is some question as to how this structure will respond to the motion of a severe earthquake. To be conservative, therefore, it is assumed that Fontana Dam will not resist the OBE without failure.Figure 2.4-83 shows the part of Fontana Dam judged to remain in its original position after failure and the assumed location on the debris of the failed portion. The location HYDROLOGIC ENGINEERING2.4-35WATTS BARWBNP-92of the debris after failure is one logical assumption based on a failure of the dam at the longitudinal contraction joints. There may be other logical assumptions, but the amount of channel obstruction would probably be about the same.The higher blocks 9 to 27 containing either two or three longitudinal joints are assumed to fail. Right abutment blocks 1 to 8 and left abutment blocks 28 and beyond were judged to be stable for the following reasons:
(1)Their heights are less than one-half the maximum height of the dam.
(2)None of these blocks have more than one longitudinal contraction joint, and some have no longitudinal joints.
(3)The back slope of Fontana Dam is 1 on 0.76 which the original stability analysis shows is flatter than that required for stability for the normal static loadings.Although not investigated, it was assumed that Nantahala Dam upstream from Fontana and Santeetlah on a downstream tributary and the three ALCOA dams downstream on the Little Tennessee River would fail along with Fontana in the OBE. Instant vanishment was assumed. Tellico and Watts Bar Dam spillway gates would be operable during and after the OBE. Failure of the bridge at Fort Loudoun Dam would render the spillway gates inoperable in the wide-open position.The Fontana failure wave would overtop and fail Tellico embankments. Transfer of water into Fort Loudoun would occur but would not be sufficient to overtop the dam or to prevent failure of Tellico. Tellico was postulated to completely fail. Watts Bar headwater would reach 761.3, 5.7 feet below the top of the embankment. No embankment failure would occur. However, the West Saddle Dike would be over topped and breached. The elevation at the plant site would be 725.2, 2.8 feet below 728 plant grade.Multiple FailuresAttenuation studies of the OBE show that above Watts Bar Dam only the simultaneous failures of Cherokee and Douglas Dams need be considered with respect to Watts Bar Nuclear Plant safety. These two dams are only 15 miles apart, and an OBE located midway between them is assumed to cause their simultaneous failure. The degree of failure and likely position of debris are judged to be comparable to that shown for single failure of these dams in Figures 2.4-79 and 2.4-82.The postulated simultaneous failures of Cherokee and Douglas Dams would reach a maximum headwater elevation of 833.8 feet at Fort Loudoun Dam, 0.55 foot above the top of the embankment. Fort Loudon would be overtopped for only about six hours to a maximum depth of 0.55 foot. Breaching analysis indicates that this short overtopping time and shallow overflow depth would not fail the dam. Although transfer of water into Tellico would occur, the maximum headwater would only reach Elevation 826, which is four feet below top of dam. At Watts Bar Dam the headwater would reach Elevation 758.2, 8.8 feet below the top of the earth embankment of the main dam. However, the 2.4-36 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83West Saddle Dike would be overtopped and breached. A complete washout of the dike was assumed. The elevation at the plant site would be 723.1, 4.9 feet below plant grade Elevation 728.
SSE Concurrent With 25-Year FloodThe SSE will produce the same postulated failure of the Fort Loudoun and Watts Bar bridges as described for the OBE described earlier. The resulting flood level at the Watts Bar plant was not determined because the larger flood during the OBE makes that situation controlling.Watts Bar DamA reevaluation using the revised amplification factors was not made for Watts Bar Dam for SSE conditions. However, even if the dam is arbitrarily re moved instantaneously, the level at the nuclear plant site would be elevation 723, 5 feet below plant grade. This flood level was not reevaluated using the runoff model described in Section 2.4.3.3 as amended because it is clearly not controlling.Fort Loudoun DamResults of the stability analysis for Fort Loudoun Dam are shown on Figure 2.4-86. Because the resultant of forces falls outside the base, a portion of the spillway is judged to fail. Based on previous modes of failure for Cherokee and Douglas, the spillway is judged to fail above elevation 750 as well as the bridge supported by the spillway piers.The results of the slip circle analysis for the highest portion of the embankment are shown on Figure 2.4-87. Because the factor of safety is less than one, the embankment is assumed to fail.No analysis was made for the powerhouse under SSE. However, an analysis was made for the OBE with no water in the units, a condition believed to be an extremely remote occurrence during the OBE. Because the stresses were low and a large percentage of the base was in compression, it is considered that the addition of water in the units would be a stabilizing factor, and the powerhouse is judged not to fail.Figure 2.4-88 shows the condition of the dam after assumed failure. All debris from the failure of the concrete portions is assumed to be located in the channel below the failure elevations.No hydrologic routing for the single failure of Fort Loudoun, including the bridge structure, is made because its simultaneous failure with other dams is considered as discussed later in this subparagraph.Tellico DamNo structural analysis was made for Tellic o Dam failure in the SSE. Because of the similarity to Fort Loudoun, the spillway and entire embankment are judged to fail in a manner similar to Fort Loudoun. Figure 2.4-89 shows after failure conditions with all debris assumed located in the channel below the failure elevation.
HYDROLOGIC ENGINEERING2.4-37WATTS BARWBNP-92No routing for the single failure of Tellico is made for the reasons given above for Fort Loudoun.Norris DamUnder SSE conditions blocks 31 to 45 (833 feet of length) are judged to fail. The resulting debris downstream would occupy a greater span of the valley cross section than would the debris from the OBE but with the same top level, elevation 970. Figure 2.4-90 shows the part of the dam judged to fail and the location and height of the resulting debris.This postulated single failure would result in peak headwater at Watts Bar of 747.9, 9.1 feet below the top of the earth portions of the dam. Routing was not carried further because it was evident that flood levels at the plant site would be considerably lower than for the Norris failure in the OBE with the one-half PMF.The discharge rating for this controlling, debris section was developed from a 1:150 scale hydraulic model at the TVA Engineering Laboratory and was verified closely by mathematical analysis. The somewhat more extensive debr is in SSE failure restricts discharge slightly compared to OBE failure conditions.Cherokee, Douglas, and FontanaConsidered separately, the SSE will pr oduce the same postulated failures of Cherokee, Douglas, and Fontana Dams as were described for the OBE. None of these single failures need to be carried downstream, however, because elevations would be lower than the same failures in one-half the probable maximum flood.Multiple FailuresAlthough considered, as discussed in the following paragraphs, TVA believes that multiple dam failures are an extremely unlikely event. TVA's search of the literature reveals no record of failure of concrete dams from earthquake. The postulation of an SSE of 0.18 g acceleration is a very conservative upper limit in itself (as stated in Section 2.5 TVA has determined this as 0.14 g). In addition, the SSE must be located in a very precise region to have the potential for multiple dam failures. In order to fail Norris, Cherokee, and Douglas dams, the epicenter of SSE must be confined to a relatively small area  the shape of a football, about 10 miles wide and 20 miles long.In order to fail Norris, Douglas, Fort Loudoun, and Tellico dams, the epicenter of an SSE must be confined to a tr iangular area with sides of approximately one mile in length. However, as an extreme upper limit the above two combinations of dams are postulated to fail as well as the combination of (1) Fontana, Fort Loudoun, and Tellico; and (2) Fontana and Douglas.An SSE centered between Fontana and the Fort Loudoun-Tellico complex was postulated to fail these three dams. The four ALCOA dams downstream from Fontana and Nantahala, an ALCOA dam, upstream were also postulated to fail completely in this event. Watts Bar Dam and spillway gates would remain intact, but failure of the roadway bridge was postulated which would render the spillway gates inoperable. At 2.4-38 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92the time of seismic failure, discharges would be small in the 25-year flood. For conservatism, Watts Bar gates were assumed inoperable in the closed position after the SSE event. Using the failure modes shown on Figures 2.4-83, 2.4-88, and 2.4-89 for Fontana, Fort Loudoun, and Tellico respectively, unsteady routing showed the failure wave overtopping Watts Bar Dam with resulting embankment failure. Initial Watts Bar embankment failure begins at headwater level 763.0. Headwater levels will continue to rise to elevation 764.7 because of no spillway discharge. This event would result in a flood level at the nuclear plant site of 720.7, 7.3 feet below 728 plant grade. This flood level was not reevaluated using the update runoff model described in Section 2.4.3.3 as amended, nor as part of the 1998 reanalysis, because it is clearly not controlling.Norris, Cherokee, and Douglas Dams were also postulated to fail simultaneously. Figure 2.4-91 shows the location of an SSE, and its attenuation, which produces 0.15 g at Norris, 0.09 g at Cherokee and Douglas, 0.08 g at Fort Loudoun and Tellico, 0.05 g at Fontana, and 0.03 g at Watts Bar. Fort Loudoun, Tellico, and Watts Bar have previously been judged not to fail for the OBE (0.09 g). The bridge at Fort Loudoun Dam, however, might fail under 0.08 g forces, falling on any open gates and on gate hoisting machinery. Trunnion anchor bolts of open gates would fail and the gates would be washed downstream, leaving an open spillway. Closed gates could not be opened. By the time of the seismic event at upstream tributary dams the crest of the 25-year flood would likely have passed Fort Loudoun and flows would have been reduced to turbine capacity. Hence, spillway gates would be closed. At least this most conservative assumption was used. As stated before, it is believed that multiple dam failure is extremely remote, and it seems reasonable to exclude Fontana on the basis of being the most distant in the cluster of dams under consideration. For the postulated failures of Norris, Cherokee, and Douglas, the portions judged to remain and debris arrangements are as given in Figures 2.4-76, 2.4-79, and 2.4-82 for single dam failure.The flood for the postulated failure combination would overtop and breach Fort Loudon Dam. Although transfer of water into Tellico would occur, the maximum headwater would only reach Elevation 820, which is 10 feet below top of dam. At Watts Bar Dam the headwater would reach Elevation 764.9, 2.1 feet below the top of the earth embankment of the main dam. However, the West Saddle Dike would be overtopped and breached. The elevation at the plant site would be 727.5, 0.5 feet below plant grade Elevation 728. This is the highest flood resulting from any combination of seismic and flood events.The flood elevation hydrograph at the plant site is shown on Figure 2.4-111.
Norris, Douglas, Fort Loudoun, and Tellico Dams were postulated to fail simultaneously. Figure 2.4-93 shows the location of an SSE, and its attenuation, which produces 0.12 g at Norris, 0.08 g at Douglas, 0.12 g at Fort Loudoun and Tellico, 0.07 g at Cherokee, 0.06 g at Fontana, and 0.04 g at Watts Bar. Cherokee is judged not to fail at 0.07 g; Watts Bar has previously been judged not to fail at 0.09 g; and, for the same reasons as given above, it seems reasonable to exclude Fontana in this failure combination. For the postulated failures of Norris, Douglas, Fort Loudoun, and Tellico, the portions judged to remain and the debris arrangements are as given in Figures HYDROLOGIC ENGINEERING2.4-39WATTS BARWBNP-922.4-76, 2.4-82, 2.4-88 and 2.4-89 for single dam failure. For this re-evaluation, Fort Loudon and Tellico were assumed to fail completely as the portions judged to remain are relatively small. This is conservative.This postulated failure combination results in Watts Bar headwater Elevation 758.9, 8.1 feet below the top of the earth embankment of the main dam. However, the West Saddle Dike would be overtopped and breached. A complete washout of the dike was assumed. The elevation at the plant site would be 722.8, 5.2 feet below plant grade Elevation 728.Douglas and Fontana were postulated to fail simultaneously. Figure 2.4-94 shows the location of an SSE and its attenuation, which produces .14 g at Douglas, .09 g at Fontana, .07 g at Cherokee, .05 g at Norris, .06 g at Fort Loudoun and Tellico, and .03 g at Watts Bar. For the postulated failures of Douglas and Fontana, the portions judged to remain and the debris arrangements are as given in Figures 2.4-82 and 2.4-83 for single dam failure. Fort Loudoun, Tellico, and Watts Bar have previously been judged not to fail for the OBE (0.09 g). The bridge at Fort Loudoun Dam, however, might fail under 0.06 g forces, falling on gates and on gate hoisting machinery. Fort Loudoun gates were assumed inoperable in the closed position following the SSE event. The Fontana failure flood wave would overtop and breach Tellico Dam and its saddle dikes. The flood from the Douglas failure would reach Fort Loudoun after Tellico has been overtopped and breached. Although Fort Loudoun gates are inoperable in the closed position, the Fort Loudoun Tellico canal would provide enough relief to keep Fort Loudoun Dam from being overtopped. The combined Douglas-Fontana failure surge would reach elevation 751.7 at Watts Bar Dam, 5.3 feet below dam top. Resulting water surface at the Watts Bar plant would reach elevation 721.2, 6.8 feet below plant grade. This flood level was not reevaluated using the model described in Section 2.4.3.3 as amended, nor as part of the 1998 reanalysis because it is not controlling.
2.4.4.2  Unsteady Flow Analysis of Potential Dam FailuresUnsteady flow routing techniques
[23] were used to evaluate plant site flood levels from postulated seismically induced dam failures wherever their inherent accuracy was needed. In addition to the  flow models described in Section 2.4.3.3 the unsteady flow models described below were used as adjuncts to route floods from postulated dam failures.Unsteady flow techniques were applied in Norris Reservoir. The Norris Reservoir model was developed in sufficient detail to define the manner in which the reservoir would supply and sustain outflow following postulated dam failure. The model was verified by comparing its routed headwater level in the one-half PMF with those using storage routing techniques. Headwater level agreed within a foot, and the model was considered adequate for the purpose.Unsteady flow techniques were also applied in Cherokee, Douglas, and Fontana Reservoirs. The reservoir models were developed in sufficient detail to define the manner in which the reservoirs would supply and sustain outflow following postulated dam failure.
2.4-40 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92 2.4.4.3  Water Level at PlantsiteThe unsteady flow analyses of different postulated combinations of seismic dam failures coincident with floods described in Section 2.4.4.1 yields a maximum elevation of 727.5, excluding wind wave effects. As shown in Table 2.4-8, it would result from the SSE failure of Norris, Cherokee, and Douglas Dams coincident with the twenty-five year flood postulated to occur in June when reservoir levels are high. A June wind with 50% exceedance probability over the 1.3-mile effective fetch is 12 miles per hour overland. Flood waves, crest to trough, are about 1.0 foot high resulting in maximum water elevation of 728.2. Runup could reach elevation 729.0 on a 3:1 earth slope. The static and dynamic effects of wind waves on structures are described in Section 2.4.3.6.2.4.5  Probable Maximum Surge and Seiche FloodingChickamauga Lake level during non-flood conditions would not exceed elevation 682.5, normal maximum pool level, for any significant time. No conceivable meteorological conditions could produce a seiche nor reservoir operations a surge
 
which would reach plant grade elevation 728, some 45 feet above normal maximum pool levels. 
 
====2.4.6 Probable====
Maxi mum Tsunami FloodingBecause of its inland location the Watts Bar plant is not endangered by tsunami flooding.2.4.7  Ice EffectsBecause of its location in a temperate climate significant amounts of ice do not form on lakes and rivers in the plant vicinity and ice jams are not a source of major flooding.The present potential for generator of signifi cant surface ice at the site is less today than prior to closure of Chickamauga and Watts Bar Lakes in 1940 and 1942, respectively. This condition exists because of (1) daily water level fluctuations from operating Chickamauga Reservoir downstream and Watts Bar Reservoir upstream would break up surface icing before significant thickness could be formed, (2) flows are warmed by releases from near the bottom of Watts Bar Reservoir, and (3) increased water depths due to Chickamauga Reservoir result in a greater mass needing to be cooled by radiation compared to pre-reservoir conditions.After closure of Watts Bar in January 1942, there have been no extended periods of cold weather and no serious icing conditions in the Watts Bar Nuclear Plant site region. On several occasions, ice has formed near the shore and across protected inlets but has not constituted a problem on the main reservoirs.The lowest water temperature observed in Watts Bar Lake at the dam during the periods 1942-1953, and June 1967 to November 1973 for which records were kept, was 39 degrees on January 30, 1970, the coldest January since 1940 in the eastern part of the Basin. This lake temperature is indicative of the lowest water temperature released from Watts Bar Lake during winter months.
HYDROLOGIC ENGINEERING2.4-41WATTS BARWBNP-86The most severe period of cold weather recorded in the Valley was January and early February 1940 prior to present lake conditions at the plantsite. A maximum ice depth of five inches was recorded on the Tennessee River at Chattanooga. There were no ice jams except one small one on the lower French Broad River.Records of icing are limited and none are available at the site prior to 1942. From newspaper records, the earliest known freeze in the vicinity was at Knoxville in 1796. More recently, newspaper accounts and U.S. Weather Bureau records for Knoxville provide a fairly complete ice history from 1840 to 1940. At Knoxville the Tennessee River was frozen over 16 times, and floating ice was observed six other times.The most severe event in this period prior to 1940 was in December-January 1917-18 when ice jammed the Tennessee River at Knoxville for 1 to 2 weeks, reaching 10 feet high at some places. In late January rain and temperature rise produced flooding on the Clinch River referred to by local people as the "ice tide."  There is no record of ice jamming, however.There are no safety-related facilities at the Watts Bar site which could be affected by an ice jam flood, wind-drive ice ridges, or ice-produced forces other than a flooding of the plant itself. An ice jam sufficient to cause plant flooding is inconceivable. There are no valley restrictions in the 1.9-mile reach below Watts Bar Dam to initiate a jam, and an ice dam would need to reach at least 68 feet above streambed to endanger the plant.Intake pump suctions which will be used for the intake of river water will be located a minimum of 7.6 feet below minimum reservoir water level; hence, no thin surface ice which may form will effect the pipe intake. In the assumed event of complete failure of Chickamauga Dam downstream, the minimum release from Watts Bar Dam will ensure a 5.9 foot depth of water in the intake channel.
 
====2.4.8 Cooling====
Water Canals and ReservoirsThe intake channel, as shown in Figure 2.1-5, extends approximately 800 feet from the edge of the reservoir through the flood plain to the intake pumping station. The channel, as shown in Figure 2.4-99, has an average depth of 36 feet and is 50 feet wide at the bottom. The side slopes are 4 on 1 and are designed for sudden drawdown, due to assumed loss of downstream dam, coincident with a safe shutdown earthquake.In response to multipurpose operations, the level of Chickamauga Reservoir fluctuates between a normal minimum of 675.0 feet and a normal maximum of 682.5 feet. The minimum average elevation of the reservoir bottom at the intake channel is 656 feet and the elevation of the intake channel bottom is 660 feet. The 15 foot normal minimum depth of water provided in the intake channel is more than ample to guarantee flow requirements. The intake provides cooling water makeup to the closed-cycle cooling system and the essential raw cooling water systems. The maximum flow requirement for the plant for all purposes is 178 cfs based on four ERCW pumps and six RCW pumps inservice.
2.4-42 HYDROLOGIC ENGINEERINGWATTS BARWBNP-86The protection of the intake channel slopes from wind-wave activity is afforded by the placement of riprap, shown in Figures 2.4-99 in accordance with TVA design standards, from elevation 660 to elevation 690. The riprap is designed for waves resulting from a wind velocity of 50 mph.2.4.9  Channel DiversionsChannel diversion is not a potential problem for the plant. Currently, no channel diversions upstream of the Watts Bar plant would cause diverting or rerouting of the source of plant cooling water, and none are anticipated in the future. The floodplain is such that large floods do not produce major channel meanders or cutoffs. The topography is such that only an unimaginable catastrophic event could result in flow diversion above the plant.
2.4.10  Flooding Pr otection RequirementsAssurance that safety-related facilities are capable of surviving all possible flood conditions is provided by the discussions given in Sections 2.4.14, 3.4, 3.8.1, 3.8.2 and 3.8.4The plant is designed to shut down and remain in a safe shutdown condition for any rainfall flood exceeding plant grade, up to the "design basis flood" discussed in Section 2.4.3 and for lower, seismic-caused floods discussed in Section 2.4.4. Any rainfall flood exceeding plant grade will be predicted at least 28 hours in advance by TVA's Water Resources organization. Notification of seismic failure of key upstream dams will be available at the plant approximately 27 hours before a resulting flood surge would reach plant grade. Hence, there is adequate time to prepare the plant for any flood.See Section 2.4.14 for a detailed presentation of the flood protection plan.
2.4.11  Low Wate r ConsiderationsBecause of its location on Chickamauga Reservoir, maintaining minimum water levels at the Watts Bar plant is not a problem. The high rainfall and runoff of the watershed and the regulation afforded by upstream dams assure minimum flows for plant cooling.
2.4.11.1  Low Flow in Rivers and StreamsThe probable minimum water level at the Watts Bar plant is elevation 673 and would occur in the winter flood season as a result of special Chickamauga Reservoir preflood drawdown, at which time flows would be substantial. The most severe drought in the history of the Tennessee Valley region occurred in 1925. Frequency studies for the 1874-1935 period prior to regulation show that there is less than one percent change that the 1925 observed minimum 1-day flow of 3300 cfs downstream at Chattanooga might occur in a given year. At the plantsite the corresponding minimum 1-day flow is estimated to be 2700 cfs compared to 2600 cfs in the PSAR.Although dependable flow under extreme drought conditions is sufficient to meet all plant requirements, there is the added assurance of large quantities of water in TVA's HYDROLOGIC ENGINEERING2.4-43WATTS BARWBNP-83multiple purpose tributary reservoirs upstream. Stored water at prescribed minimum pool levels in these reservoirs (Tellico Reservoir excluded) could provide more than 1,000 cfs at the Watts Bar site for 2 years with no rainfall. These minimum levels will not be violated without specific TVA Board of Directors' action in which the safety of Watts Bar would be a controlling consideration. This guarantees that adequate water would be available if needed at the Watts Bar site.In the assumed event of complete failure of Chickamauga Dam and with the headwater before failure assumed to be the normal summer level, elevation 682.5, the water surface at the site will begin to drop 4 hours after failure of the dam and will fall at a fairly uniform rate to elevation 666 in approximately 22 hours from failure. This time period is more than ample for initiating the release of water from Watts Bar Dam.The estimated minimum flow requirement for the ERCW system is 50 cfs; however, in order to guarantee both ample depth and supply of water, a minimum flow of 2,000 cfs will be released from Watts Bar Dam. With flow of 2,000 cfs water surface elevation would be 665.9 producing 5.9-foot depth in the intake channel.2.4.11.2  Low Water Resulting From Surges, Seic hes, or TsunamiBecause of Watts Bar's inland location on a relatively small, narrow lake, low water levels resulting from surges, seiches, or tsunamis are not a potential problem.
2.4.11.3  Histor ical Low WaterFrom the beginning of stream gage records at Chattanooga in 1874 until the closure of Chickamauga Dam in January 1940, the estimated minimum daily flow at Watts Bar Nuclear Plant site was 2700 cfs on September 7 and 13, 1925. The next lowest estimated flow of 3900 cfs occurred in 1881 and also in 1883.Since January 1942 low flows at the site have been regulated by TVA reservoirs, particularly by Watts Bar and Chickamauga Dams. Under normal operating conditions, there may be periods of several hours daily when there are no releases from either or both dams, but average daily flows at the site have been less than 5,000 cfs only 0.9% of the time and have been less than 10,000 cfs only 4.8% of the time.On March 30 and 31, 1968, during special operations for the control of watermilfoil, there were no releases from either Watts Bar or Chickamauga Dams during the 2-day period. Daily average releases of zero have been recorded on four other occasions during the past 25 years.Since January 1940, water levels at the plant have been controlled by Chickamauga Reservoir. Since then the minimum level at the dam was 673.3 on January 21, 1942.2.4.11.4  Future ControlFuture added controls which could alter low flow conditions at the plant are not anticipated because no sites that would have a significant influence remain to be developed.
2.4-44 HYDROLOGIC ENGINEERINGWATTS BARWBNP-892.4.11.5  Plant RequirementsThe engineering safety feature water supply system requiring river water is    the essential raw cooling water (ERCW). Also, the high pressure fire pumps perform an essential safety function during flood conditions by providing a feedwater supply to steam generators, makeup to the spent fuel pool, and auxiliary boration makeup tank. For interface of the fire protection system with the auxiliary feedwater system, see Section 10.4.9. The ERCW pumps are located on the intake pumping station deck at elevation 741.0 and the ERCW pump intake is at elevation 653.33 feet. The ERCW intake will require 5 feet of submergence. Based on a minimum river surface elevation of 665.9 feet, a minimum of 12.07 feet of pump suction submergence will be provided.In the assumed event of complete failure of Chickamauga Dam and with the headwater before failure assumed to be the normal summer level, elevation 682.5, the water surface at the site will begin to drop 4 hours after failure of the dam and will fall at a fairly uniform rate to elevation 666 in approximately 22 hours from failure. This time period is more than ample for initiating the release of water from Watts Bar Dam.The estimated minimum flow requirement for the ERCW system is 50 cfs. However, in order to guarantee both ample depth and supply of water, a minimum flow of 2,000 cfs will be released from Watts Bar Dam.This flow will give a river surface elevation of 665.9, which ensures a 5.9-foot depth of water in the intake channel and approximately 10 feet in the river. The river surface elevation is controlled by the weir effect of Hunter Shoals, elevation 661.2, located approximately 7.5 miles downstream from the site. The stage discharge rating curve at the entrance to the intake channel is shown by Figure 2.4-95. Cross sections of Hunter Shoals are shown in Figure 2.4-96. Figure 2.4-97 shows the channel profile of the Tennessee River for the reach from mile 520.0 to 521.37.A flow of at least 2,000 cfs can be released at the upstream dam, Watts Bar, through the spillway gates, the turbines or the lock. The spillway gates offer the largest flow of water. There are twenty 40-foot-wide radial gates operated by two traveling gate hoists on the deck and one of the hoists is always located over a gate. At minimum headwater elevation 735.0, one gate opened 2 feet will provide a flow of 2,000 cfs; fully open, 15,000 cfs will be provided.There are five turbines, each with a maximum flow of 9,400 cfs and an estimated speed/non-load flow of 900 to 1100 cfs. The lock culvert emptying and filling valves are electrically operated segmental type with a bypass switch located in each of the four valve control stations. These can be used at any time to open or close both filling and emptying valves.In the improbable event of loss of station service power at the dam, a 300-kVA gasoline-engine-driven generator located in the powerhouse will supply emergency power. The generator feeds into the main board when used and the emergency power is adequate to operate each of the three sources of water supply discussed.
HYDROLOGIC ENGINEERING2.4-45WATTS BARWBNP-83For concurrent loss of the upstream and downstream dams, assurance that sufficient flow will be available is provided by records of the minimum natural flow at the plantsite before construction of dams on the Tennessee River. This flow is estimated to be 2,700 cfs. Since this flow exceeds the 2,000 cfs specified above to be released through Watts Bar Dam, it is not necessary to reserve a storage volume in Watts Bar Reservoir.2.4.12  Dispersion, Diluti on, and Travel Times of Ac cidental Rel eases of Liquid Effluents 2.4.12.1  Radio active Liquid WastesA discussion of the routine handling and release of liquid radioactive wastes is found in Section 11.2, "Liquid Waste Management Systems."  The routine and nonroutine nonradiologial liquid discharges are addressed in the Watts Bar Nuclear Plant's NPDES permit (Permit No. TN0020168) and the Spill, Prevention, Control, and Countermeasure Plan (SPCC plan), respectively. The nonradiological liquid discharges are under the regulatory jurisdiction of the State of Tennessee.
2.4.12.2  Accidental Slug Releases to Surface Water An accidental release of radioactive or nonradioactive liquid from the plant site would be subject to naturally induced mixing in the Tennessee River. The worst case for a given volume, V o (cubic feet), of liquid is a release which takes place over a short period of time. Calculations have been made to determine the reduction in concentration of such a release as it progresses downstream; particular emphasis has been placed on the concentrations at the surface water intakes downstream of the plant. The model used here is based on the convective diffusion equation as applied to the dispersion in natural streams[24,25]. The major assumptions used in this analysis are: (1)The release is assumed to occur at the right bank with no diffuser induced mixing whether the release occurs at the bank or through the diffuser.
(2)The effluent becomes well mixed vertically (but not horizontally) relatively rapidly (well before reaching first downstream water intake). This assumption is usually justified in riverine situations[26,27].(3)The river flow is uniform and one-dimensional over a rectangular cross-section.Other less restrictive assumptions are described in Reference [27].
Under assumption 2, the two-dimensional form of the convective diffusion equation is sufficient and may be written as c t------u c x------+E x 2 c ux 2---------E y 2 c y 2---------+=(1) 2.4-46 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83in which C is the concentration of radioactive effluent in the river; u is cross-sectionally averaged river velocity; x and y are coordinates in the downstream and lateral directions, respectively; and E x and E y are the dispersion coefficients in the x and y directions. Following Reference [25], it is assumed that the formal dependence of E x and E y on river parameters isandin which a x and a y are empirical coefficients, U
* is the river shear velocity, and H is the river depth. Relationships between U
* and bulk river parameters may be found in any open channel hydraulics text.
[28]Equation (1) was solved for the slug release by applying the method of images[27,29] to the instantaneous infinite flow field solution of equation (1) which is given in Reference [29]
in which C 0 is the initial concentration of radioactive material in the liquid effluent, t is the time elapsed since the release of the slug and y is the distance of the release from the right bank. Equation (3) was used in the method of images solutions.2.4.12.2.1  CalculationsThe above model was applied to predict t he maximum concentrations which would be observed on the right bank of the Tennessee River at two downstream locations; the right bank concentrations will always be higher than those on the left bank. The release is assumed to occur on the right bank at Tennessee River Mile (TRM) 528; the river width is assumed constant at 1,100 feet and the river depth is assumed constant at 30 feet. The Watts Bar Dam discharge equaled or exceeded 50% of the time is 28,200 cfs.The coefficients a x and a y in Equation (2) were chosen to be 100 and 0.6, respectively; these values are based on the results in Reference [25]. The shear velocity, U
* was computed assuming a Manning's n of 0.030 to describe the bed roughness of the river.
Because the actual release volume, V 0, is not known a priori , results are presented in terms of a relative concentration, defined as C/(C 0 ,V 0). Thus, to obtain the (2a)E x a x U*H=(2b)E y a y U*H=(3)C C 0-------V 0 4 Ht E x E y----------------------------- exp  xut-2 4E x t---------------------
yy 0-2 4E y t---------------------
+-=
HYDROLOGIC ENGINEERING2.4-47WATTS BARWBNP-93concentration reduction factor C/C 0, this relative concentration must be multiplied by the release volume V 0 (in cubic feet).Calculations show that the concentrations along the right bank at the downstream water intakes will be as follows:
2.4.12.3  Effect s on Ground WaterThe plant site is underlain by terrace deposits of gravel, sand, and clay, having an average thickness of 40 feet. The deposit is variable in grain-size composition from place to place. Locally, very permeable gravel is present. Essentially all of the ground water under the site is in this deposit.Bedrock of the Conasauga Shale underlies the terrace deposit. Foundation exploration drilling and foundation excavation revealed that very little water occurs in the bedrock.The average saturated thickness of the terrace deposit is about 25 feet. Discharge from this material is mostly small springs and seeps to drainways along the margin of the site. Directions of ground water flow are discussed in Section 2.4.13.The nearest point of probable ground water discharge is along a small tributary to Yellow Creek, which at its nearest point is 2,600 feet from the center of the plant. In this direction, the hydraulic gradient (dh/dl) is 26 feet (maximum) in 2,600 feet, or 0.01. The hydraulic conductivity (K) of the terrace materials is estimated to be 48 feet/day.  (The basis for this estimate is described in Section 2.4.13.3.) Porosity (0) is estimated to be 0.15.Average ground water velocity = (K dh/dl)/O = 3.2 ft/day or 812 days average travel time through the terrace deposit to the nearest point of ground water discharge.Estimating the density of the water-bearing material to be 2.0 and the distribution coefficient for strontium to be 20, the computed average travel time for strontium indicates a period of over 200 times longer than that for water, or 1.8 x 10 5 days (almost 500 years) travel time from the plant site to the nearest point of ground water discharge. This time of travel would be further increased by accounting for the delay resulting from movement through and absorption by unsaturated materials above the water table.Water available for dilution, based on-the estimated porosity of 0.15 and a saturated thickness of 25 feet, is estimated to be 3.75 cubic feet per square foot of surface area. Water IntakeTennessee River Mile Relative Concentration (l/cu. ft.)Dayton503.82.8 x 10
-9East Side Utility(formerly Volunteer Army Ammunition Plant)473.01.3 x 10
-9 2.4-48 HYDROLOGIC ENGINEERINGWATTS BARWBNP-89In a 1000-foot wide strip extending from the plant site to the nearest point of ground water discharge, the volume of stored water would be 9.8 x 10 6 cubic feet.There are no data on which to base a computation of dispersion in the ground water system. For a conservative analysis, it would be necessary to assume that no dispersion occurs.
2.4.13  Groundwater2.4.13.1  Description and On-Site UseOnly the Knox Dolomite is regionally significant as an aquifer.
This formation is the principal source of base flow to streams of the region. Large springs, such as Ward Spring 2.7 miles west of the site, are fairly common, especially at or near the contact between the Knox Dolomite and the overlying Chickamauga Limestone. Water occurs in the Knox Dolomite in solution openings formed along bedding planes and joints and in the moderately thick to thick cherty clay overburden. The formation underlies a 1- to 2-mile wide belt 2.5 miles west of the site at its nearest point; a narrow slice, the tip of which is about one mile north of the site; and a 1- to 2-mile wide belt, one mile east of the site and across Chickamauga Lake.Within a two-mile radius of the site, there is no use of the Knox Dolomite as a source of water to wells for other than small supplies.Other formations within the site region, described in detail in Section 2.5.1.1, include the Rome Formation, a poor water-bearing formation; the Conasauga Shale, a poor water-bearing formation; and the Chickamauga Limestone, a poor to moderate water-bearing formation that normally yields no more than 25 gallons per minute (gpm) to wells.The plant site is underlain by the Conasauga Shale, which is made up of about 84% shale and 16% limestone and occurs as thin discontinuous beds (Section 2.5.1.2). Surficial materials are older terrace deposits and recent alluvial deposits, fine-grained, poorly sorted, and poorly waterbearing.The pattern of groundwater movement shown on Figure 2.4-105 indicates that recharge of the shallow water-bearing formations occurs from infiltration of local precipitation and from lateral underflow from the area north of the plant site. All ground-water discharge from the site is to Chickamauga Lake, either directly or via Yellow Creek.Potable water for plant use is obtained from the Watts Bar Utility District. Their water is obtained from 3 wells located 2.5 miles northwest of the plant.2.4.13.2  SourcesGround water sources within a two-mile radius of the site are listed in Table 2.4-10 and their locations are shown on Figure 2.4-102. Of the 89 wells listed, only 58 are equipped with pumps. Two of the thirteen spring sources listed are equipped with pumps. Seventy-nine residences are supplied by ground water, with one well HYDROLOGIC ENGINEERING2.4-49WATTS BARWBNP-83supplying five houses. Assuming three persons per residence and a per capita use rate of 75 gpd, total ground-water use is less than 10,000 gpd.Drawdown data are available only for the Watts Bar Reservation wells, as listed in the previous section.Water-level fluctuations have been observed monthly in six observation wells since January 1973. Data collection for wells 7, 8, & 9 began in December 1981. The locations of these wells are shown on Figure 2.4-104. Data for the period January 1973 through December 1975 is shown on Figure 2.4-103.As elsewhere in the region, water levels normally reach maximum elevations in February or March and are at minimum elevations in late summer and early fall. Depth to the water table is generally less than 20 feet throughout the plant site.Figure 2.4-105 is a water-table contour map of the area within a two-mile radius of the plant site, based on 48 water-level measurements made in January 1972. The water table conforms fairly closely to surface topography, so that directions of ground-water movement are generally the same as those of surface-water movement. The water-table gradient between plant site and Chickamauga Lake at maximum water-table elevation and minimum river stage is about 44 feet in 3200 feet, or 0.014.Water occurs in the Consauga Shale in very small openings along fractures and bedding planes. Examination of records of 5500 feet of foundation exploration drilling showed only one cavity, 0.6-foot thick, penetrated. Water occurs in the terrace deposit material in pore spaces between particles. The deposit is composed mostly of poorly-sorted clay- to gravel-sized particles and is poorly water bearing, although an approximately six-foot-thick permeable gravel zone is locally present at the base of the terrace deposit. The foundation excavation required only intermittent dewatering after initial drainage. The excavation was taken below the base of the terrace deposit into fresh shale. No weathered shale was found to be present; the contact between the terrace deposit and fresh shale is sharp.The average depth to the water table in the plant area, based on data collected during August through December 1970, is 17 feet; the average overburden thickness is 40 feet; the saturated overburden thickness is therefore, 24 feet. No weathered zones or cavities were penetrated in the Conasauga Shale below a depth of 85 feet, so that the average saturated thickness of bedrock is assumed to be less than 50 feet.The plant site is hydraulically isolated by Yellow Creek and Chickamauga lake to the west, south, and east; it is hydraulically isolated to the north by the relatively impermeable Rome Formation underlying the site. Therefore, it is believed that any off-site groundwater withdrawals could not result in altered groundwater movement at the site.No attempt was made to measure hydraulic properties of overburden or of bedrock at this site because of the very limited occurrence of ground water and the heterogeneity and anisotropy of the materials underlying the site.
2.4-50 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83 2.4.13.3  Acci dent EffectsAssuming a maximum annual range in saturated thickness of overburden of between 23 feet and 33 feet, and a porosity of 0.15, total water stored in this material, and the maximum volume available for dilution, ranges seasonally between 4.6 and 6.6 cubic feet per square foot of surface area. Water available for dilution in bedrock is very small and may be less than 0.01 cubic foot per square foot of surface area.Since dispersion and exchange characteristics are not known, it must be assumed that these are not factors in a release of liquid radioactive material which would then travel to discharge points at the same rate as water movement. There are no direct pathways to ground-water users since all groundwater discharge from the site is to adjacent surface-water bodies.Groundwater travel time has been estimated for water in the terrace deposit, in which essentially all ground water at the site occurs.The nearest point of possible groundwater discharge is 2600 feet west of the plant site, along a tributary to Yellow Creek. In this direction the maximum hydraulic gradient is 26 feet in 2600 feet, or 0.01. The maximum hydraulic conductivity of the terrace materials is estimated to be 48 ft/day, based on particle-size analyses of terrace-deposit materials as related to permeability
[30].or 812 days travel time from plant to nearest point of groundwater discharge.Packer tests on the Conasauga Shale in foundation holes, using water at 50 psi, showed no acceptance, although one 0.6 foot cavity was penetrated in one hole in a total of more than 5,000 feet of drilling. Therefore, no estimate of time of water travel was made for water in bedrock.
2.4.13.4  Monitoring a nd Safeguard RequirementsThe potential for the plant to affect groundwater users is very low because of its physical location, however, any provisions for radiological groundwater monitoring will be as described in the Watts Bar Monitoring Plan. A network of observation wells will be maintained as needed and ground water will be analyzed for radioactivity as required by the Technical Specifications.In the event of accidental release of radioactivity to the groundwater system, nearby groundwater users will be advised not to use their wells for drinking water until an where vmean velocity, ft/day;
=vK dh/dl 0------------------
-=Khydraulic conductivity48 ft/day;
==dh/dlhydraulicgradient.01
==0porosity0.15 (extimated average effective)
==V48.01.15------------
-3.2 ft/day
==
HYDROLOGIC ENGINEERING2.4-51WATTS BARWBNP-92investigation can be made of the extent, rate, and direction of movement of the contaminant.Monitoring and notification for both the routine and any accidental nonradioactive liquid discharges to either surface or groundwaters would be implemented as required by the facilities NPDES permit (Permit No. TN0020168) and the Spill, Prevention, Control, and Countermeasure Plan (SPCC plan), respectively. These requirements for the nonradiological liquid discharges are under the regulatory jurisdiction of the State of Tennessee.
2.4.13.5  Design B asis for Subsurface Hydrostatic LoadingThe ground water levels used for structural design are discussed in Section 2.5.4.6.Dewatering of the construction excavation is discussed in Section 2.5.4.6.
2.4.14  Flooding Pr otection RequirementsAssurance that safety-related facilities are capable of surviving all possible flood conditions is provided by the discussions given in Section 2.4.2.2, Section 3.4, Sections 3.8.1 and 3.8.4 and this section, 2.4.14.2.4.14.1  IntroductionThis subsection describes the methods by which the Watts Bar Nuclear Plant is capable of tolerating floods above plant grade without jeopardizing public safety. Since flooding of this magnitude, as illustrated in Section 2.4.2 is most unlikely, extreme steps are considered acceptable, including actions that create or allow extensive economic consequence to the plant. The actions described herein will be implemented for floods ranging from slightly below plant grade, to allow for wave runup to the design basis flood. The plant Flood Protection Plan (Technical Requirement 3.7.2) specifies the flood warning conditions and subsequent actions.
2.4.14.1.1  De sign Basis FloodThe design basis flood (DBF) is the calculated upper-limit flood that includes the probable maximum flood (PMF) plus the wave runup caused by a 21 mph overland wind; this is discussed in Section 2.4.3.6. The table below gives representative levels of the DBF at different plant locations.Design Basis Flood (DBF) LevelsProbable Maximum Flood (still reservoir)734.9DBF on lake736.2 DBF Runup on 4:1 sloped surfaces736.9 DBF Runup on vertical walls with base elevation 728.0736.9DBF Surge level within flooded structures735.4 2.4-52 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83In addition to flood level considerations, plant flood preparations cope with the "fastest rising" flood which is the calculated flood, including seismically induced floods, that can exceed plant grade with the shortest warning time. Reservoir levels for large rainfall floods in the Tennessee Valley can be predicted well in advance. By dividing the pre-flood preparation steps into two stages, a minimum of a 27 hour, pre-flood transition interval is available between the time a flood warning is received and the time the flood waters exceed plant grade. The first stage, a minimum of 10 hours long, commences upon receipt of a flood warning. The second stage, a minimum of 17 hours long, is based on a confirmed estimate that conditions will produce a flood. This two-stage scheme is designed to prevent excessive economic loss in case a potential flood does not fully develop. Refer to Section 2.4.14.4.2.4.14.1.2  Combinations of EventsBecause floods above plant grade, earthquakes, tornadoes, or design basis accidents, including a LOCA, are individually very unlikely, a combination of a flood plus any of these events, or the occurrence of one of these during the flood recovery time, or of the flood during the recovery time after one of these events, is considered incredible.
However, as an exception, certain reduced levels of floods are considered together with a seismic event. Refer to Section 2.4.14.10 and 2.4.4.
2.4.14.1.3  Post Flood PeriodBecause of the improbability of a flood above plant grade, no detailed procedures are established for return of the plant to normal operation unless and until a flood actually occurs. If flood mode operation (Section 2.4.14.2) should ever become necessary, it is possible to maintain this mode of operation for a sufficient period of time (100 days) so that appropriate recovery steps can be formulated and taken. The actual flood waters are expected to recede below plant grade within 1 to 4 days.2.4.14.1.4  Localized FloodsLocalized plant site flooding due to the probable maximum storm (Section 2.4.2.3) will not enter vital structures or endanger the plant. Any offsite power loss resulting from water ponding on the switchyard or water entry into the Turbine Building will be similar to a loss of offsite power situation as described in Chapter 15. The other steps described in this subsection are not applicable to this case. Refer to Section 2.4.2.3.
2.4.14.2  Plant Operati on During Floods Above Grade"Flood mode" operation is defined as the set of conditions described below by means of which the plant is safely maintained during the time when flood waters exceed plant grade (elevation 728.0) and during the subsequent period until recovery (Section 2.4.14.7) is accomplished.
2.4.14.2.1  Flooding of StructuresThe Reactor Building will be maintained dry during the flood mode. Walls and penetrations are designed to withstand all static and dynamic forces imposed by the DBF; minor seepage through the concrete walls and any seepage through the leading HYDROLOGIC ENGINEERING2.4-53WATTS BARWBNP-83penetrations into the annulus will be allowed to flow to the Reactor Building floor and equipment drain sump by removing the blind flange on penetration X-118. The Reactor Building floor and equipment drain sumps are more than capable of pumping this flow. The Diesel Generator Buildings also will remain dry during the flood mode since its lowest floor is at elevation 742.0. Other structures, including the Service, Turbine, Auxiliary, and Control Buildings, would be allowed to flood as the water exceeds their grade level entrances. Equipment that is located in these structures and required for operation in the flood mode is either above the DBF or suitable for submerged operation.2.4.14.2.2  Fuel CoolingSpent Fuel PoolFuel in the spent fuel pool is cooled by the Spent Fuel Pool Cooling and Cleanup System (SFPCCS), the active components of which are located above flood waters.
During the flood mode of operation, heat is removed from the heat exchangers by essential raw cooling water instead of component cooling water. The SFPCCS cooling circuit is assured of two operable SFPCCS pumps (a third pump is available as a backup) as well as two SFPCCS heat exchangers. High spent fuel pool temperature causes an annunciation in the Main Control Room indicating equipment malfunction. Additionally, that portion of the cooling system above flood water is inspected approximately every 8 hours to confirm continued proper operation. As a backup to spent fuel cooling, water from the High Pressure Fire Protection (HPFP) system can be added to the spent fuel pool.ReactorsResidual core heat is be removed from the fuel in the reactors by natural circulation in the reactor coolant system. Heat removal from the steam generators is accomplished by adding river water from the HPFP system (Section 9.5.1) and relieving steam to the atmosphere through the power operated relief valves. This transit ion from auxiliary feedwater to river water is accomplished during Stage II of the flood preparation procedures. Refer to Section 2.4.14.4.1. Reactor coolant system pressure is maintained at less than 350 psig by operation of the pressurizer relief valves and heaters. Secondary side pressure is maintained below 125 psig by operation of the power operated relief valves. At times beyond approximately 10 hours following shutdown of the plant two relief valves have sufficient capacity to remove the steam generated by decay heat. Since 10 hours is less than the minimum flood warning time available, the plant can be safely shut down and decay heat removed by operation of two power operated relief valves per unit.The earliest that the HPFP pumps would be utilized to supply auxiliary feedwater would be about 20 hours after reactor shutdown. At this time, in order to remove the decay heat from both reactor units, the water requirement to the steam generators would be approximately 300 gpm. Later times following reactor shutdown would have gradually decreasing HPFP system makeup water flow rate requirements. With the steam 2.4-54 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83generator secondary side pressure less than 125 psig, a single HPFP pump can supply makeup water well in excess of the requirement of 300 gpm. Additional surplus flow is available since there are four HPFP pumps, two powered from each emergency power train. The HPFP pump head-capacity curve is illustrated in Chapter 9.The main steam power operated relief valves are adjusted by controls in the auxiliary control room as required to maintain the steam pressure within the desired pressure range. The controls in the main control room also can be utilized to operate the valves in an open-closed manner. Also, a manual loading station and the relief valve handwheel provide additional backup control for each relief valve. The power operated relief valves would be used to depressurize the steam generators as discussed above to maintain steam generator pressure sufficiently below the developed head of the fire pumps. Note that even in the event of a total loss of makeup water flow at the time of maximum decay heat load, approximately 6 hours are available to restore makeup water flow before the steam generators would boil dry.If one or both reactors are open to the containment atmosphere during the refueling operations, then the decay heat of the fuel in the open unit(s) and spent fuel pool heat is removed in the following manner. The refueling cavity is filled with borated water (approximately 2,000 ppm boron concentration) from the refueling water storage tank. The SFPCCS pump takes suction from the spent fuel pool and discharges to the SFPCCS heat exchangers. The SFPCCS heat exchanger output flow is directed by a temporary piping connection to the Residual Heat Removal (RHR) system upstream to the RHR heat exchangers. This piping (spool piece) connection is prefabricated and is installed only during preparation for flood mode operation. (The tie-in locations in the SFPCCS and RHRS are shown in Figures 2.4-106 and 2.4-107 respectively.)  After passing through the RHR heat exchangers, the water enters the reactor vessel through the normal cold leg RHR injection paths, flows downward through the annulus, upward through the core (thus cooling the fuel), then exits the vessel directly into the refueling cavity. This results in a water level differential between the spent fuel pool and the refueling cavity with sufficient water head to assure the required return flow through the twenty-inch diameter fuel transfer tube thereby completing the path to the spent fuel pool.Any leakage from the reactor coolant system will be collected to the extent possible in the reactor coolant drain tank; nonrecoverable leakage is made up from supplies of clean water stored in the four cold leg accumulators, the pressurizer relief tank, and the demineralized water tank. Even if these sources are unavailable, the fire protection system can be connected to the auxiliary charging system (Section 9.3.6) as a backup. Whatever the source, makeup water is filtered, demineralized, tested, and borated, as necessary, to the normal refueling concentration, and pumped by the auxiliary charging system into the reactor (see Figures 2.4-108 and 2.4-109).2.4.14.2.3  Cooling of Plant LoadsPlant cooling requirements with the exception of the fire protection system which must supply makeup water to the steam generators, are met by the Essential Raw Cooling Water (ERCW) System. The intake pumping station is designed to retain full functional HYDROLOGIC ENGINEERING2.4-55WATTS BARWBNP-83capability of the ERCW system and HPFP system water intakes for all floods up to and including the DBF. The ERCW system and HPFP system water intakes also remain fully functional in the remote possibility of a flood induced failure of Chickamauga Dam.  (Refer to Sections 9.2.1 and 9.5.1.)
2.4.14.3  Warning SchemeSee Section 2.4.14.8 (Warning Plan).
2.4.14.4  Preparation for Flood ModeAn abnormal operating instruction is available to support operation of Unit 1.At the time the initial flood warning is issued, the plant could be operating in any normal mode. This means that either or both units may be at power or either unit may be in any stage of refueling.2.4.14.4.1  Reactor Initially Operating at PowerIf both reactors are operating at power, Stage I and then, if necessary, Stage II procedures are initiated. Stage I procedures consist of a controlled reactor shutdown and other easily revokable steps, such as moving flood mode supplies above the maximum possible flood elevation and making load adjustments on the onsite power supply. After scram, the reactor coolant system is cooled by the auxiliary feedwater (Section 10.4.9) and the pressure is reduced to less than 350 psig. Stage II procedures are the least easily revokable and more damaging steps necessary to have the plant in the flood mode when the flood exceeds plant grade. HPFP system water (Section 9.5.1) will replace auxiliary feedwater for steam generator makeup water. Other essential plant cooling loads are transferred from the component cooling water system to the ERCW system and the ERCW replaces raw cooling water to the ice condensers (Section 9.2.1). The radioactive waste (Chapter 11) system will be secured by filling tanks below DBF level with enough water to prevent flotation. One exception is the waste gas decay tanks, which are sealed and anchored against flotation. Power and communication cables below the DBF level that are not required for submerged operation are disconnected, and batteries beneath the DBF level are
 
disconnected.2.4.14.4.2  Reactor Initially RefuelingIf time permits, fuel is removed from the unit(s) undergoing refueling and placed in the spent fuel pool; otherwise fuel cooling is accomplished as described in Section 2.4.14.2.2. If the refueling canal is not already flooded, the mode of cooling described in Section 2.4.14.2.2 requires that the canal be flooded with borated water from the refueling water storage tank. If the flood warning occurs after the reactor vessel head has been removed or at a time when it could be removed before the flood exceeds plant grade, the flood mode reactor cooling water flows directly from the vessel into the refueling cavity.Flood mode operation requires that the prefabricated piping be installed to connect the RHR and SFPC systems, that the proper flow to the spent fuel pit diffuser and the 2.4-56 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83RHRS be established and that essential ra w cooling water be directed to the secondary side of the RHRS and SFPCCS heat exchangers. The connection of the RHR and SFPC systems is made using pref abricated in-position piping which is normally disconnected. During flood mode preparations, the piping is connected using prefabricated spool pieces.
2.4.14.4.3  Plan t Preparation TimeThe steps needed to prepare the plant for flood mode operation can be accomplished within 24 hours of notification that a flood above plant grade is expected. An additional 3 hours are available for contingency margin. Site grading and building design prevent any flooding before the end of the 27 hour preflood period.
2.4.14.5  EquipmentBoth normal plant components and specialized flood-oriented supplements are utilized in coping with floods. All such equipment required in the flood mode is either located above the DBF, within a nonflooded structure, or is suitable for submerged operation.
Systems and components needed only in the preflood period are protected only during that period.2.4.14.5.1  Equipment QualificationTo ensure capable performance in this highly unlikely, limiting design case, only high quality components are utilized. Active components are redundant or their functions diversely supplied. Since no rapidly changing events are associated with the flood, repairability is an available option for both active and passive components during the long period of flood mode operation. Equipment potentially requiring maintenance is accessible throughout its use, including components in the Diesel Generator Building.
2.4.14.5.2  Temporary Modification and SetupNormal plant systems used in flood mode operation and in preparation for flood mode operation may require modification from their normal plant operating configuration. Such modification, since it is for a limiting design condition and since extensive economic consequences are acceptable, is permitted to allow operation of systems outside of their normal plant configuration. However, most alterations will be only temporary and inconsequential in nature. For example, the switchover of plant cooling loads from the component cooling water to essential raw cooling water system is done through valves and prefabricated spool pieces, causing little system disturbance or damage.2.4.14.5.3  Electric PowerBecause there is a possibility that high winds could destroy power lines and disconnect the plant from offsite power at any time during the preflood transition period, the preparation procedure and flood mode operation are accomplished assuming only onsite power circuits available. While most equipment requiring ac electric power is a part of the permanent emergency onsite power distribution system other components, HYDROLOGIC ENGINEERING2.4-57WATTS BARWBNP-83if required, could be temporarily connected, when the time comes, by prefabricated jumper cables.The loads that are normally supplied by onsite power but are not required for the flood are disconnected early in the preflood period. Those loads used only during the preflood period are disconnected from the onsite power system during flood mode operations. DC electric power is similarly disconnected from unused loads and potentially flooded cables.Charging is maintained for each battery by the onsite ac power system as long as it is required. Batteries that are beneath the DBF level are disconnected during the preflood period when they are no longer needed.2.4.14.5.4  Instrument, Control, Communication and Ventilation SystemsThe instrument, control, and communication wiring or cables required for operation in the flood mode are either above the DBF or within a nonflooded structure, or are suitable for submerged operation. Unneeded wiring or cables that run below the DBF
 
level will be disconnected to prevent short circuits. Instrumentation is provided to monitor vital plant parameters such as the reactor coolant temperature and pressure and steam generator pressure and level. Important plant functions are either monitored and controlled from the main control area, or, in some cases where time margins permit, from other points in the plant that are in close communication with the main control area.Communications are provided between the central control area (the Main and Auxiliary Control Rooms) and other vital areas that might require operator attention, such as the Diesel Generator Building. Ventilation, when necessary, and limited heating or air conditioning is maintained for locations throughout the plant where operators might be required to go or where required by equipment heat loads.
2.4.14.6  SuppliesThe equipment and most supplies required for the flood are on hand in the plant at all times. Some supplies may require replenishment before the end of the period in which the plant is in the flood mode. In such cases supplies on hand are sufficient to last through the short time (Section 2.4.14.1.3) that flood waters will be above plant grade and until replenishment can be supplied. 2.4.14.7  Plant RecoveryThe plant is designed to continue safely in the flood mode for 100 days even though the water is not expected to remain above plant grade for more than 1 to 4 days. After recession of the flood, damage will be assessed and detailed recovery plans developed. Arrangements will then be made for reestablishment of off-site power and removal of spent fuel. A decision based on economics would be made on whether or not to regain the plant for power production. In either case, detailed plans would be 2.4-58 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92formulated after the flood, when damage can be accurately assessed. The 100-day period provides a more than adequate time for the development of procedures for any maintenance, inspection, or installation of replacements for the recovery of the plant or for a continuation of flood mode operations in excess of 100 days.
2.4.14.8  Warning PlanPlant grade elevation 728.0 can be exceeded by rainfall floods and closely approached by seismic-caused dam failure floods. A warning plan is needed to assure plant safety from these floods.The warning plan is divided into two stages:  Stage I, a minimum of 10 hours long and Stage II, a minimum of 17 hours so that unnecessary economic consequences can be avoided, while adequate time is allowed for preparing for operation in the flood mode. Stage I allows preparation steps causing minimal economic consequences to be sustained but will postpone major economic damage until the Stage II warning predicts a likely forthcoming flood above grade.2.4.14.8.1  Rainfall FloodsProtection of the Watts Bar Plant from rainfall floods that might exceed plant grade utilizes a flood warning issued by TVA's Water Management. TVA's climatic monitoring and flood predicting systems and flood control facilities permit early identification of potentially critical flood producing conditions and reliable prediction of floods which may exceed plant grade well in advance of the event.The Watts Bar Nuclear Plant flood warning plan provides a minimum of 27 hours to prepare for operation in the flood mode, 3 hours more than the 24 hours needed. Four additional preceding hours would be available to gather and analyze rainfall data and produce the warning. The first stage, Stage I, of shutdown begins when there is sufficient rainfall on the ground in the upstream watershed to yield a projected plantsite water level of elevation 714.5 in the winter months (October 1 through April 15) and elevation 726.5 in the summer (April 16 through September 30). This assures that additional rain will not produce water levels to elevation 727.0 in less than 27 hours from the time shutdown is initiated. The water level of elevation 727.0 (one foot below plant grade) allows margin so that waves due to winds cannot disrupt the flood mode preparation.The plant preparation status is held at Stage I until either Stage II begins or TVA's Water Management determines that floodwaters will not exceed elevation 727.0 at the plant. The Stage II warning is issued only when enough additional rain has fallen to predict that elevation 727.0 (winter or summer) is likely to be reached.
2.4.14.8.2  Seismically-I nduced Dam Failure FloodsOnly one postulated combination of seismically induced dam failures and coincident storm conditions was shown to result in a flood which could exceed Elevation 727 at the plant. Watts Bar plant protection from this flood utilizes TVA's Water Management forecast system to identify when a critical combination exists. Stage I shutdown is initiated upon notification that a critical dam failure combination has occurred or loss of HYDROLOGIC ENGINEERING2.4-59WATTS BARWBNP-92communication prevents determining a critical case has not occurred. Stage I shutdown continues until it has been determined positively that critical combinations do not exist. If communications do not document this certainty, shutdown procedures continue into Stage II activity. Stage II shutdown  continues to completion or until lack of critical combinations is verified.
2.4.14.9  Basis Fo r Flood Protection Plan In Rainfall Floods 2.4.14.9.1  OverviewLarge Tennessee River floods can exceed plant grade elevation 728.0 at Watts Bar Nuclear Plant. Plant safety in such an event requires shutdown procedures which may take 24 hours to implement. TVA flood forecast procedures are used to provide at least 27 hours of warning before river levels reach elevation 727.0. Use of elevation 727.0, 1 foot below plant grade, provides enough margin to prevent wind generated waves from endangering plant safety during the final hours of shutdown activity.
Forecast will be based upon rainfall already reported to be on the ground.To be certain of 27 hours for preflood preparation, flood warnings with the prospect of reaching elevation 727.0 must be issued early when lower target elevations are forecast. Consequently, some of the warnings may later prove to have been unnecessary. For this reason preflood preparations are divided into two stages. Stage I steps requiring 10 hours are easily revokable and cause minimum economic consequences. The estimated probability is less than 0.0032 that a Stage I warning will be issued during the 40-year life of the plant.Added rain and stream-flow information obtained during Stage I activity will determine if the more serious steps of Stage II need to be taken with the assurance that at least 17 hours will be available before elevation 727.0 is reached. The probability of a DBF occurring during the 40-year life of the plant is very small.Flood forecasting, to assure adequate warning time for safe plant shutdown during floods, will be conducted by TVA's Water Management.
2.4.14.9.2  TVA Forecast SystemTVA has in constant use an extensive, effective system to forecast flow and elevation as needed in the Tennessee River basin. This permits efficient operation of the reservoir system and provides warning of when water levels will exceed critical elevations at selected, sensitive locations.Elements of the present (1998) forecast system above Watts Bar Nuclear Plant include the following:
(1)Ninety-eight (98) rain gages, and measure rainfall, with an average density of 165 square miles per rain gage. Of these, 54 are GOES Data Collection Platform (DCP) Satellite telemetered gages, and 27 are Data Logger telephone telemetered gages which depend upon commercial telephone lines, and 17 are observer gages located at TVA hydro and fossil plants and 2.4-60 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92non-TVA hydro plants. In the case of commercial telephone line failure, field personnel can be notified by radio to interrogate and provide data from the 27 Data Logger gages.The telephone gages are interrogated on a two hour interval on the even hour (Central prevailing time) to obtain hourly rainfall readings. During flood periods, the gages can be interrogated more frequently if desired. The satellite gages transmit hourly rainfall data every 3 hours during normal operations. In addition, the satellite gages event report when 0.1 inch or greater rainfall accumulates. The normal and event transmissions are conveyed on separate satellite channels. Personnel at the TVA installations record six-hour rainfall data. Information from these sites is available for the normal forecast run at 6 a.m. Central time.
(2)Streamflow data are available from 23 stream gages in the system. Of these, 12 are GOES Data Collection Platform satellite telemetered gages, and 11 are Data Logger telephone telemetered gages which depend upon commercial telephone lines.The telephone gages are interrogated on a two hour interval on the even hour (Central prevailing time) to obtain 15-minute stage readings. During flood periods, the gages can be interrogated more frequently if desired. The satellite gages transmit 15-minute stage data every 3 hours during normal operations. Random stream gage transmission is currently being tested. Information from these sites is available for the normal forecast run at 6 a.m.
Central time.
(3)Hourly headwater elevation, tailwater elevation, and discharge data are received from 14 TVA and 4 non-TVA hydro plants. More frequent data can be obtained during flood operations.
(4)Weather forecasts including quantitative precipitation forecasts received at least twice daily and at other times when changes are expected.
(5)Computer programs which translate rainfall into streamflow based on current runoff conditions and which permit a forecast of flows and elevations based upon both observed and predicted rainfall. A network of UNIX workstation computers are utilized and are designed to provide backup for each other. One computer is used primarily for data collection, with the others used for executing forecasting programs for reservoir operations. The time interval between receiving input data and producing a forecast is less than 4 hours.
Forecasts normally cover at least a 3-day period.As effective as the forecast system already is, it is constantly being improved as new technology provides better methods to interrogate the watershed during floods and as the watershed mathematical model and computer system are improved. Also, in the future, improved quantitative precipitation forecasts may provide a more reliable early alert of impending major storm conditions and thus provide greater flood warning time.
HYDROLOGIC ENGINEERING2.4-61WATTS BARWBNP-83TVA's normal operation produces daily forecasts by 12 noon made from data collected at 6 a.m. Central time. When serious flood situations demand, personnel of Reservoir Operations work around the clock with forecasts as frequent as at 6-hour intervals.
2.4.14.9.3  Basic AnalysisThe forecast procedure to assure safe shutdown of Watts Bar Nuclear Plant for flooding is based upon an analysis of 17 hypothetical PMP storms, including their antecedent storms. They enveloped potentially critical areal and seasonal variations and time distributions of rainfall. To be certain that fastest rising flood conditions were included, the effects of varied time distribution of rainfall were tested by alternatively placing the maximum daily PMP on the first, the middle, and the last day of the 3-day main storm. In each day the maximum 6-hour depth was placed during the second interval except when the maximum daily rain was placed on the last day. Then the maximum 6-hour amount was placed in the last 6 hours. The warning system is based on those PMP storm situations which resulted in the shortest time interval between watershed rainfall and elevation 727, thus assuring that this elevation could be predicted at least 27 hours in advance.The procedures used to compute flood flows and elevations for those flood conditions which establish controlling elements of the forecast system are described in Section 2.4.3 as amended. The analyses of the remaining floods which identified the critical flood conditions were made using earlier versions of the procedures described in Section 2.4.3.2.4.14.9.4  Hydrologic Basis for Warning SystemA minimum of 27 hours has been allowed for preparation of the plant for operation in the flood mode. An additional 4 hours for communication and forecasting computations is provided to translate rain on the ground to river elevations at the plant. Hence, the warning plan provides 31 hours from arrival of rain on the ground until elevation 727 could be reached. The 27 hours allowed for shutdown at the plant consists of a minimum of 10 hours of Stage I preparation and an additional 17 hours for Stage II preparation that is not concurrent with the Stage I activity.Although river elevation 727, 1 foot below plant grade to allow for wind waves, is the controlling elevation for determining the need for plant shutdown, lower forecast target levels are used in some situations to assure that the 27 hours pre-flood transition interval will always be available. The target river levels differ with season.During the October 1 through April 15 "winter" season, Stage I shutdown procedures will be started as soon as target river elevation 714.5 has been forecast. Stage II shutdown will be initiated and carried to completion if and when target river elevation 727 has been forecast. Corresponding target river elevations for the April 16 through September 30 "summer" season are elevation 726.5 and elevation 727.Inasmuch as the hydrologic procedures and target river elevations have been designed to provide adequate shutdown time in the fastest rising flood, longer times 2.4-62 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83will be available in other floods. In such cases there will be a waiting period after the Stage I, 10-hour shutdown activity during which activities shall be in abeyance until weather conditions determine if plant operation can be resumed, or if Stage II shutdown should be implemented.Resumption of plant operation following just Stage I shutdown activities will be allowable only after flood levels and weather conditions have returned to a condition in which 27 hours of warning will again be available.2.4.14.9.5  Hydrologic Basis for Target StatesFigure 2.4-110, in four parts, shows how target forecast flood elevations at the Watts Bar plant have been determined to assure adequate warning times. The floods shown are the fastest rising probable maximum floods at the site. Only the principal storm in which the PMP occurs has been shown. These have been preceded 3 days earlier by a 3-day storm having 40% of the main storm rainfall.Figure 2.4-110 (A,B,C) shows the winter PMP which would produce the fastest rising flood which would cross plant grade and variations caused by changed time distribution. The fastest rising flood occurs during a PMP when the 6-hour increments increase throughout the storm with the maximum 6 hours occurring in the last period. Figure 2.4-110 (A) shows the essential elements of this storm which provides the basis for the warning plan. In this flood 8.7 inches of rain would have fallen 31 hours (27 + 4) prior to the flood crossing elevation 727 and would produce elevation 714.5 at the plant. Hence, any time rain on the ground results in a predicted plant elevation of 714.5 a Stage I shutdown warning will be issued. Examination of Figure 2.4-110 (B and C) show that following this procedure in these noncritical floods would result in a lapsed time of 47 and 49 hours between when 8.7 inches had fallen and the flood would exceed elevation 727.An additional 3.8 inches of rain must fall promptly for a total of 12.5 inches of rain to cause the flood to exceed elevation 727. In the fastest rising flood, figure 2.4-110 (A), this rain would have fallen in the next 8 hours. A Stage II warning would be issued within the next 4 hours. Thus, the Stage II warning would be issued 8 hours after issuance of a Stage I warning and 19 hours before the flood would exceed elevation 727.0. In the slower rising floods, Figure 2.4-110 (B and C), the time between issuance of a Stage I warning and when the 12.5 inches of rain required to put the flood to elevation 727.0 would have occurred, is 18 and 12 hours respectively. This would result in issuance of a Stage II warning not less than 4 hours later or 25 or 33 hours before the flood would reach elevation 727.0.The summer flood, shown by Figure 2.4-110 (D), with the maximum 1-day rain on the last day provides controlling conditions when reservoirs are at summer levels. At a time 31 hours (27 + 4) before the flood reaches elevation 727.0, 11.6 inches of rain would have fallen. This 11.6 inches of rain under these runoff conditions would produce elevation 726.5, so this level becomes the Stage I target. An additional 0.2 inch of rain must fall promptly for a total of 11.8 inches of rain to cause the flood to exceed elevation 727.0. In this fastest rising summer flood, Figure 2.4-110 (D), this rain would have fallen in the next hour. A Stage II warning would be issued within the HYDROLOGIC ENGINEERING2.4-63WATTS BARWBNP-83next 4 hours. Thus, the Stage II warning would be issued one hour after issuance of a Stage I warning and 26 hours before t he flood would exceed elevation 727.0.The above criteria all relate to forecasts which use rain on the ground. In actual practice quantitative rain forecasts, which are already a part of daily operations, would be used to provide advance alerts that the need for shutdown may be imminent. Only rain on the ground, however, is included in the procedure for firm warning use.Because the above analyses used fastest possible rising floods at the plant, all other floods will allow longer warning times than required for physical plant shutdown activities.In summary, the predicted target levels which will assure adequate shutdown times are:2.4.14.9.6  Communications ReliabilityCommunication between projects in the TVA power system is via (a) TVA-owned microwave network, (b) Fiber-Optics Systems, and (c) by commercial telephone. In emergencies, additional communication links are provided by Transmission Power Supply radio networks. The four networks provide a high level of dependability against emergencies.The hydrologic network for the watershed above Watts Bar that would be available in flood emergencies if commercial telephone communications are lost includes 61 rainfall gages (17 at power installations and 54 satellite gages). The Reservoir Operations is linked to the TVA power system by all five communication networks. The data from the satellite gages are received via a data collection platform-satellite computer system located in the Reservoir Operations office. These are distributed over the watershed such that reasonable flood forecasting can be done from this data while the balance of data is being secured from the remaining hydrologic network stations.The preferred, complete coverage of the watershed employs numerous rainfall and stream-flow locations above the Watts Bar plant (See Section 2.4.14.9.2). Involved in the communications link to these locations are routine radio, radio satellite and the commercial telephone system networks. In an emergency, available radio communications would be called upon to assist.Forecasts Elevations at Watts BarforforSeasonStage I shutdownStage II shutdownWinter (October 1 - April 15)714.5727 Summer (April 16 - September 30)726.5727 2.4-64 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92The various networks proved to be capable of providing the rain and streamflow low data needed for reliable forecasts in the large floods of 1957, 1963, 1973, and 1984.2.4.14.10  Basis for Flood Protection Plan in Seis mic-Caused Dam FailuresFloods resulting from combined seismic and flood events can closely approach plant grade, thus requiring emergency measures. The 1998 reanalysis showed that only one seismic dam failure combination coincident with a flood, i.e., the SSE failure of Norris, Cherokee and Douglas concurrent with the 25-year flood, would result in a flood approaching plant grade. As shown in Table 2.4-8 all other candidate combinations of events would create flood levels well below plant grade Elevation 728. Dam failure during non-flood periods would not present a problem at the plant as resulting flood levels for all candidate combinations would be well below plant grade. The reanalysis showed that failure of the controlling combination in a non-flood period and at summer flood guide levels would produce Elevation 725.2 at the plant, 2.8 feet below plant grade. All other combinations in non-flood periods would produce elevations much lower.The time from seismic occurrence to arrival of failure surge at the plant in the critical event is about 50 hours as shown in Figure 2.4-111 and is adequate to permit safe plant shutdown in readiness for flooding.The warning scheme for safe plant shutdown is based on the fact that a combination of critically centered large earthquake and rain produced flood conditions must coincide before the floodwave from seismically caused dam failures will approach plant grade. In flood situations, an extreme earthquake must be precisely located to fail Norris, Cherokee and Douglas dams before a flood threat to the site would exist.The warning system utilizes TVA's flood forecast system to identify when flood conditions will be such that seismic failure of criticaldams could cause a floodwave to approach elevation 728 at the plant site. These conditions combined with any concern by TVA Water Management that failure of a single upstream dam has occurred or is imminent will lead to an early warning. A Sage I warning is declared once failure of Norris, Cherokee and Douglas Dams has been confirmed.If loss of or damage to an upsteam dam is suspected, efforts will be made by Hydro Operations to determine whether dam failure has occurred. If the critical case has occurred or it cannot be determined that it has not occurred, Stage I shutdown will be initiated in time to assure the 27 hour flood preparation period. Once initiated, the flood preparation procedures will be carried to completion unless it is determined that the critical case has not occurred.Communications between the plant, dams, power system control center, and TVA Water Management at Knoxville are accomplished by microwave networks,  fiber options networks, radio networks, and commercial telephone service. These systems are described in FSAR Section 9.5.2.3.
HYDROLOGIC ENGINEERING2.4-65WATTS BARWBNP-922.4.14.11  Special Condition AllowanceThe flood protection plan is based upon the minimum time available for the worst case. This worst case provides adequate preparation time including contingency margin for normal and anticipated plant conditions including anticipated maintenance operations. It is conceivable, however, that a plant condition might develop for which maintenance operations would make a longer warning time desirable. In such a situation the Plant Manager determines the desirable warning time. He contacts TVA's Water Management to determine if the desired warning time is available. If weather and reservoir conditions are such that the desired time can be provided, special warning procedures will be developed, if necessary, to ensure the time is available. This special case continues until the Plant Manager notifies TVA's Water Management that maintenance has been completed. If threatening storm conditions are forecast which might shorten the available time for special maintenance, the Plant Manager is notified and steps taken to assure that the plant is placed in a safe shutdown mode in the minimum time determined available for the threatening storm conditions.REFERENCES (1)National Weather Service, "Probable Maximum and TVA Precipitation for Tennessee River Basins up to 3,000 Square Miles in Area and Durations to 72 Hours," Hydrometeorological Report No. 45, 1969, with Addendum of June 1973.
(2)U.S. Army Corps of Engineers, "Standard Project Flood Determination,: Civil Works Engineer Bulletin 52-8, March 1952.
(3)SCS National Engineering Handbook, Section 4, Hydrology, July 1969.
(4)U.S. Weather Bureau, "Probable Maximum and TVA Precipitation Over The Tennessee River Basin Above Chattanooga,"  Hydrometeorological Report No. 41, 1965.
(5)Newton, Donald W., and Vineyard, J. W., "Computer-Determined Unit Hydrographs From Floods," Journal of the Hydraulics Division, ASCE, Volume 93, No. HY5, September 1967.
(6)Garrison, J. M., Granju, J. P., and Price, J. T., "Unsteady Flow Simulation in Rivers and Reservoirs," Journal of the Hydraulics Division, ASCE, Volume 95, No. HY5, Proceedings Paper 6771, September 1969, pages 1559-1576.
(7)Eagleson, Peter S., "A Distributed Linear Model for Peak Catchment Discharge," Proceedings, The International Hydrology Symposium, September 1967, Fort Collins, Colorado, Volume 1.
(8)Kulandaiswamy, V. C., "A Nonlinear Approach to Runoff Studies," Proceedings, The International Hydrology Symposium, September 1967, Fort Collins, Colorado, Volume 1.
2.4-66 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92 (9)Ardis, C. V., Jr., "A Nonlinear Channel Routing Model, "Proceedings, Theme 1, May 1971 Flow Symposium, Instrument Society of America, Pittsburgh, 1974.(10)Reference deleted by Amendment 63.
(11)Cristofano, E. A., "Method of Computing Erosion Rate for Failure of Earthfill Dams," Engineering and Research Center, Bureau of Reclamation, Denver, 1966.(12)"The Breaching of the Oros Earth Dam in the State of Ceara, North-East Brazil," Water and Water Engineering, August 1960.
(13)National Climatic Center, Asheville, North Carolina, "Extreme Wind Study for Selected Stations in the Tennessee Valley," prepared under Contract No. TV-36522A, August 1975.
(14)U.S. Army Corps of Engineers, "Computation of Freeboard Allowances for Waves in Reservoirs," Engineering Technical Letter No. 1110-2-8, August 1966.(15)U.S. Army coastal Engineering Research Center, "Shore Protection Planning and Design," Third Edition, 1966.
(16)Anderson, Paul, "Substructure Analysis and Design," 1948.
(17)Hinds, Julian, Cregar, William P., and Justin, Joel D., "Engineering For Dams," Volume 11, Concrete Dams, John Wiley and Sons, Incorporated, 1945.(18)Bustamante, Jurge I., Flores, Arando, "Water Pressure in Dams Subject to Earthquakes," Journal of the Engineering Mechanics Division, ASCE Proceedings, October 1966.
(19)Chopra, Anil K., "Hydrodynamic Pressures on Dams During Earthquakes," Journal of the Engineering Mechanics Division ASCE Proceedings, December 1967, pages 205-223.
(20)Zienkiewicz, O. C., "Hydrodynamic Pressures Due to Earthquakes," Water Pressures Due to Earthquakes," Water Power, Volume 16, September 1964, pages 382-388.
(21)Tennessee Valley Authority, "Sedimentation in TVA Reservoirs," TVA Report No. 0-6693, Division of Water Control Planning, February 1968.
(22)Reference deleted by Amendment 63.
(23)Price, J. T. and Garrison, J. M., Flood Waves From Hydrologic and Seismic Dam Failures," paper presented at the 1973 ASCE National Water Resources Engineering Meeting, Washington, D. C.
HYDROLOGIC ENGINEERING2.4-67WATTS BARWBNP-83 (24)Fisher, H. B., "Longitudinal Dispersion in Laboratory and Natural Systems" Keck Laboratory Report KH-R-12, California Institute of Technology, Pasadena, California, June 1966.
(25)Fisher, H. B., "The Mechanics of Dispersion in Natural Streams," Journal of the Hydraulics Division, ASCE Vol. 93, No HY6, November 1967.
(26)Yotsukura, N., "A Two-Dimensional Temperature Model for the Thermally Loaded River with Steady Discharge" Proceedings of the Eleventh Annual Environmental and Water Resources Engineering Conference, Vanderbilt University, Nashville, Tennessee, 1972.
(27)Almquist, C. W., "A Simple Model for the Calculation of Transverse Mixing in Rivers with Application to the Watts Bar Nuclear Plant," TVA, Division of Water Management, Water Systems Development Branch, Technical Report No. 9-2012, March 1977.
(28)Henderson, E. M., Open Channel Flow, MacMillen, 1966.
(29)Carlslaw, B. S. and J. C. Jaeger, Conduction of Heat in Solids, Oxford University Press, London England, 1959.
(30)Johnson, A. E., 1963, Application of Laboratory Permeability.
(31)Stoker, J. J., "Water Waves," Interscience Publishers, Inc., New York, 1966, Up. 333-341.
(32)Bretschneider, C. L., "Wave Refraction, Diffraction and Reflection Chapter F of Estuary and Coastline Hydrodynamics. MIT Hydrodynamic Lab, Cambridge, Massachusetts.
(33)Keulegan, G. H., "Wave Damping Effects of Fibrous Screens," Research Report H-72-2. Corps of Engineers, Vicksburg, Mississippi, 1972.
2.4-68 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83Table 2.4-1  Facts About Major TVA Dams and Reservoirs HYDROLOGIC ENGINEERING2.4-69WATTS BARWBNP-83a. Volume at top of gates.Table 2.4-2  Facts About Non-TVA Dam and Reservoir Projects ALCOAProjectsRiver Drainage  Area,Sq. MilesMilesAboveMouthMaximum Height, Feet  Length, Feet  Area ofLake, AcresLength  of Lake Miles  Total aStorage, Acre-  Feet  Construction  Started Major Dams CalderwoodCheoah Chilhowee Natahala Santeetlah Thorpe (Glenville)Little TennesseeLittle Tennessee Little Tennessee Natahala Cheoah West Fork Tuckasegee1,8561,6081,976  108 176    36.7 43.7 51.4 33.6 22.8  9.3  9.7232225 91250 212150  916  7501,3731,042 1,054  900  536  5951,6901,605 2,8631,462 8 10  8.9  4.6 7.5  4.5 41,160 35,030 49,250138,730 158,250 70,8101928191619551930 19261940Minor Dams Bear CreekCedar Cliff East Fork  Tuckasegee
 
East Fork Tuckasegee    75.3    80.7  4.8  2.4215165  740  600  476  121  4.6  2.4 34,711  6,31519521950 Mission  (Andrews)
Queens Creek Wolf Creek East Fork TuckasegeeHiwasseeQueens Creek Wolf Creek
 
East Fork Tuckasegee West Fork Tuckasegee 292      3.58    15.2    24.9    54.7106.1  1.5  1.7 10.9  3.1 50 78180140 61 390  382  810  385  254 61  37  176  39    9 1.46  0.5  2.2  1.4  0.5 283    817 10,056  1,797    18319241947195219521949Walters  (Carolina P&L)Pigeon 455 38.0200 870 340 5.5 25,3901927 2.4-70 HYDROLOGIC ENGINEERINGWATTS BARWBNP-50Table 2.4-3  Flood Detention Capacity TVA Projects Above Watts Bar Nuclear PlantStorage Reserved for Flood Control - Acre Feet  Project January 1  March 15  Summer TributaryDouglas1,252,0001,019,000  67,000 Watauga  223,000  154,800  108,300 South Holston  289,800  221,000  106,500 Boone  91,700  40,400    4,300 Cherokee1,014,000  812,000  59,000 Fontana  737,000  583,000  23,000 Tellico  126,000  126,000  32,700Norris1,470,0001,113,000  512,000 Main RiverFort Loudoun  111,000  111,000  30,000 Watts Bar  379,000  379,000  165,000Total5,693,5004,559,2001,107,800 HYDROLOGIC ENGINEERING2.4-71WATTS BARWBNP-89Table 2.4-4  Location of Surface Water Supplies in the 58.9 Mile Reach of the Mainstream of the Tennessee River Between Watts Bar Dam (Trm 529.9) and Chichamagua Dam (Trm 271.0) Plant NameUse (MGD)Location(Bank)Approximate  Distance From Site(River Miles)Type SupplyWatts Bar Dam#TRM  529.9 1.1 (Upstream) IndustrialWatts Bar Steam Plant## TRM  529.9  R 1.1 (Upstream) IndustrialWatts Bar Nuclear Plant### TRM  528.8  R 0IndustrialCity of Dayton1.78TRM  503.8  R25  (Downstream)MunicipalSequoyah Nuclear Plant1615.68TRM  483.6  R45.2 (Downstream)IndustrialEast Side Utility5.00TRM  473  L55.8 (Downstream)MunicipalChickamagua Dam#TRM  47157.8 (Downstream)Industrial# Water usage is not metered. Flow Rate fluctuates as needed and is directed by power control center in Chattanooga.## Not active at this time time. If plant is reactivated, new numbers will be needed.### Not in operation at this time. When operational maximum intake will be
- 115 million gallons per day.
 
2.4-72 HYDROLOGIC ENGINEERINGWATTS BARWBNP-32Table 2.4-5  Probable Maximum Storm Rainfall and Precipitation Excess (Page 1 of 2) Antecedent Storm  Main StormIndex No. Area  Rain, Inches P e , a InchesRain, Inches P e , b Inches  1  2  3 4  5AshevilleNewport, French Broad
 
Newport, Pigeon
 
Embreeville Nolichucky Local6.446.446.44 6.446.442.994.044.04 4.044.0417.4018.5019.30 15.1015.5014.7216.5117.3113.1113.51  6  7 8  9 10Douglas LocalLittle Pigeon River French Broad Local
 
South Holston Watauga6.446.44 6.446.446.444.864.04 4.194.524.0417.1020.90 18.6012.3013.3015.8818.91 16.8110.7011.31 11 12 13 14 15Boone LocalFort Patrick Henry Gate City Surgoinsville Local Cherokee Local below Surgoinsville6.446.446.446.446.444.044.864.834.864.8614.1014.4012.3014.6015.8012.1113.1811.0813.3814.58 16 17 18 19 20Holston River LocalLittle River Fort Loudoun Local Needmore Nantahala6.446.44 6.446.446.444.524.04 4.042.992.9917.1021.50 17.6021.2021.5015.5019.51 15.6118.5218.82 21 22 23 24 25Bryson CityFontana Local Little Tennessee Local -
Fontana to Chilhowee Dam Little Tennessee Local -
Chilhowee to Tellico Dam Watts Bar Local above Clinch River6.446.446.446.446.442.992.992.99 4.044.0419.1020.7024.00 21.0015.8016.4218.0221.32 19.0113.81 26 27 28 29 30Norris Dam Coal Creek
 
Clinch Local Hinds Creek
 
Bullrun Creek6.446.44 6.446.446.444.864.52 4.524.524.6813.8014.60 14.9015.3015.7012.5813.19 13.4913.8914.29 HYDROLOGIC ENGINEERING2.4-73WATTS BARWBNP-83 a. Adopted API prior to antecedent storm, 1.0 inch.
: b. Computed API prior to main storm, 3.65 inches.
31 32 33 34 35Beaver CreekClinch Local (5 areas)
 
Local above mile 16 Poplar Creek Emory River6.446.446.446.44 6.444.524.524.524.52 4.5216.1015.3015.3014.90 13.1014.6913.8913.8913.4911.69 36 37 38 39 40Local Area at MouthWatts Bar Local below Clinch River Chatuge Nottely Hiwassee Local6.446.446.446.446.444.524.522.992.992.9914.9014.4021.4019.1018.9013.4912.9918.7216.4216.22 41 42 43 44 45Apalachia Blue Ridge Ocoee No. 1, Blue Ridge to Ocoee No. 1
 
Lower Hiwassee Chickamauga Local6.446.446.446.446.442.992.994.044.194.5217.9022.1018.3015.2014.5015.2219.4216.3113.4113.09Average above  Watts Bar Dam Chickamauga Dam6.446.444.204.1416.3416.4614.5614.63Table 2.4-5  Probable Maximum Storm Rainfall and Precipitation Excess (Continued) (Page 2 of 2) Antecedent Storm  Main StormIndex No. Area  Rain, Inches P e , a InchesRain, Inches P e , b Inches 2.4-74 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83Table 2.4-6  Unit Hydrograph Data (Page 1 of 2)
Unit Area No.Name Drainage    Area,  Sq. Miles Duration, Hours Q p C p T p W 50 W 75 T B1French Broad River at Asheville945615,000.271435121662French Broad River  Newport to Asheville a913635,000.531212 71083Pigeon River at Newport a666626,600.561211 6784Nolichucky River at Embreeville805627,300.581414 9825Nolichucky Local378610,600.401216 9876Douglas Local a832647,930.27 6 8 6607Little Pigeon River  at Sevierville353615,600.621210 61028French Broad River Local b2076 7,500.511211 8609South Holston703616,000.5318241710010Watauga b468617,700.531213 78411Boone Local a669622,890.16 613 89012Fort Patrick Henry636 3,200.40 8 8 66413North Fork Holston River672612,260.60243325108 14Surgoinsville Local b299610,280.481213 96615Cherokee Local below Surgoinsville b554618,750.481214 76616Holston River Local b2896 6,800.551822159617Little River at Mouth b379411,730.681614 89618Fort Loudoun Local b323620,000.29 610 63619Little Tennessee River at Needmore a4366 9,130.4918231212620Nantahala a916 3,770.451012 77021Tuckasegee River at Bryson City a  6556 26,000.431012 7 5822Fontana local a  389616,350.4610 9 5 9423Little Tennessee River  Local, Fontana-Chilhowee b  406616,900.5812 9 5 8424Little Tennessee River  Local, Chilhowee-Tellico Dam b  650617,000.61182111 72 HYDROLOGIC ENGINEERING2.4-75WATTS BARWBNP-8325Watts Bar Local above Clinch River b  293611,300.30 8 9 7 8426Norris Dam  2912643,300.07 615 811827Coal Creek b  36.62 2,150.64 89 5 4028Clinch Local b 22.252 1,350.10 2 8 5 3429Winds Creek b  66.42 2,620.68 9 7 5 5430Bullrun Creek b  1042 2,400.47142114 8431Beaver Creek b  90.52 2,600.58141410 8832Clinch Locals (5 areas) b111.252 1,350.10 2 8 5 3433Local above mi. 16 b    372 4,490.95 6 4 3 4634Poplar Creek b  1362 2,800.61202513 8835Emory River at Mouth b  865634,000.37 913 8 8736Local area at Mouth b    322 3,870.95 6 3 2 4637Watts Bar Local below Clinch River b  427616,300.36 9 9 7 8438Chatuge Dam a  189613,570.34 6 6 5 5439Nottely Dam a  215613,500.29 6 54 8040Hiwassee Local  564613,800.36121812124 41Applachia Local  506 2,900.54 9 6 4 9042Blue Ridge Dam a 232611,920.24 6 7 4 5443Ocoee No. 1 to Blue Ridge b 363617,000.37 811 7 3644Lower Hiwassee b1087632,500.9323161013645Chickamauga Local b 780632,000.38 914 7 36 Definition of Symbols Q p  = Peak discharge in cfs C p  =Snyder coefficient T p  = Time in hours from beginning of precipitation excess to peak of unit hydrograph W 50 = Width in hours at 50% of peak discharge W 75 = Width in hours at 75% of peak discharge T B  = Base length in hours of unit hydrograph
: a. Revised
: b. NewTable 2.4-6  Unit Hydrograph Data (Continued) (Page 2 of 2)
Unit Area No.Name Drainage    Area,  Sq. Miles Duration, Hours Q p C p T p W 50 W 75 T B 2.4-76 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92a.Includes failure of the West Saddle Dike at Watts Bar Dam.Table 2.4-7  Flood Flow And Elevation SummaryDischarge,  CFS    Elevation1.Storm producing PMP depths on the7,890-square-mile watershed with center at Bulls Gap a1,288,000  734.92.Storm producing PMP depths on the21,400-square-mile watershed above Chattanooga a1,230,000  734.7 HYDROLOGIC ENGINEERING2.4-77WATTS BARWBNP-32a.Includes failure of five ALCOA dams--Nantahala, upstream; Santeetlah, on a downstream tributary; and Cheoah, Calderwood, and Chilhowee, downstream. Fort Loudoun gates are inoperable in open position.b.Watts Bar tailwater elevation. Elevation at nuclear plant will be less. Not re-evaluated in 1998 reanalysis.c.Not re-evaluated in 1998 reanalysis.
d.Gate opening at Fort Loudoun prevented by bridge failure.e.Gate opening at Watts Bar prevented by bridge failure.Table 2.4-8  Floods From Postulated Seismic Failure of Upstream Dams(Plant Grade is Elevation 728)Watts Bar    Nuclear Plant    ElevationOBE Failures With One-half Probable Maximum Flood1.Norris721.52.Cherokee-Douglas723.1 f3.Fontana a725.2 f4.Watts Bar  Gate opening prevented by bridge
 
failure715.5 b5.Fort Loudoun  Gate opening prevented by bridge
 
failureNo elevations calculated; would be significantly less than for Cherokee-Douglas failure,  line 2.SSE Failures with 25-Year FloodNo elevations calculated; would be considerably lower than for Norr is failure in OBE with 1/2 PMF. 6.Norris 7.Norris, Cherokee, Douglas d727.5 8.Norris, Douglas, Fort Loudoun, Tellico722.8 9.Fontana-Douglas d721.2 c10.Fontana, Fort Loudoun, Tellico e720.7 c 2.4-78 HYDROLOGIC ENGINEERINGWATTS BARWBNP-63Table 2.4-9  Sheets 1 and 2 Deleted By Amendment 63 HYDROLOGIC ENGINEERING2.4-79WATTS BARWBNP-92Table 2.4-10  Well and Spring InventoryWithin 2-mile Radius of Watts Bar Nuclear Plant Site(1972 Survey Only) (Page 1 of 4)Map LocationEstimated ElevationIdent No.LatitudeLongitudeDepthGround Water Surface---------feet------------
Casing Size Pump Data  135°36'08"87°47'03"200+  743  712 0.5 *No pump  235°36'24"84°47'41" 59  726  723 0.5 *No pump  335°36'10"84°47'50"102  721  704 0.5 *No pump  435°36'00"84°47'48" 43.5  730  718 0.5 *No pump  535°35'42"84°47'49" 45  710  687 0.5 *No pump  635°35'55"84°47'48"  6  705  705 2.5 *No pump  735°36'04"84°48'16"107  710  684 0.5 *No pump  835°36'11"84°48'16" 30  702  684 4.0 *No pump  935°36'23"84°48'06" **  -  740  -  No pump 1035°37'15"84°49'04" 99  742  696 0.5 1/3 hp 1135°37'06"84°49'10" 87  753  Unknown 0.5 1/2 hp 1235°37'03"84°49'04"150  704  700 0.5 1/2 hp 1335°37'05"84°49'02"175  704  698 0.5 1 hp 1435°37'15"84°49'01"140  740  720 0.5 1 hp 1535°37'03"84°48'48" 83  729  693 0.5Hand pump  1635°36'46'84°48'18"205  780  665 0.5Submerged, Unknown  1735°36'34"84°48'13" 28  768  768 0.51 hp  1835°36'30"84°48'20" 95  794  777 0.51 hp  1935°35'35"84°48'52"111  713  715 0.6No pump, 1 gpm  2035°36'54"84°49'10" 68  710  Unknown 0.5Unknown  2135°36'18"84°49'24"125  725  695 0.51/2 hp  2235°36'20"84°49'20"130  729  655 0.53/4 hp  2335°35'20"84°48'55"225  730  715 0.51 hp  2435°35'15"84°48'56" 79  715  705 0.51/2 hp  2535°35'44"84°49'07" 14  805  804 8.0No pump  2635°35'46"84°49'31"385  718  Unknown 0.51/2 hp  2735°35'29"84°49'16"240  770  600UnknownUnknown  2835°37'14"84°47'04"***  -Watts Bar Lake735 - 745  -2, 50 hp=500 gpm 2935°37'19"84°45'57"100  706  660 0.51 hp 3035°36'39"84°45'59" 65  714  unknown 0.51/2 hp 3135°35'49"84°46'15"Spring  -  710  -No pump 2.4-80 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92 3235°36'19"84°45'21" 32.5  747  7402'-10"SquareWindlass and bucket,no pump 3335°35'26"84°46'44"Spring  -  800  -No pump 3435°35'25"84°47'02"120  725  705Unknown4 hp 3535°35'12"84°47'15"225  730  710 0.5No pump 3635°35'19"84°47'25"110  734  715 0.53/4 hp 3735°35'15"84°47'25"175  730  710 0.7No pump 3835°35'14"84°47'27"100  730  710 0.73/4 hp 3935°37'26"84°45'50" 40  710  702 0.51/4 hp 4035°35'16"84°47'28"165  725  705 0.53/4 hp 4135°35'19"84°47'30"110  734  695 0.53/4 hp 4235°35'14"84°47'28" 73  724  724 0.5No pump 4335°35'14"84°47'22"105  724  720 0.51/2 hp 4435°35'12"84°47'29"Spring  -  710  -1/2 hp 4535°35'15"84°47'16"125  730  690 0.51/
2 hp 4635°35'09"84°47'31"105  730  722 0.51-1/2 hp 4735°35'14"84°47'41"164  764  755 0.51-1/2 hp 4835°36'55"84°45'35"Spring  -  720  -3/4 hp 4935°35'00"84°47'50"100  748  708 0.51-1/2 hp 5035°34'48"84°47'42" 80  710  688 0.53/4 hp 5135°35'02"84°47'38"100  750  720 0.51/2 hp 5235°34'58"84°47'34" 99  722  711 0.52 hp 5335°34'55"84°47'37" 54  719  691 0.53/4 hp 5435°34'44"84°47'48" 52  718  703 3.0Not used 5535°34'39"84°47'50"257  720  692 0.55 gpm for five houses,lowered well 20 feet 5635°34'39"84°47'29" 56  701  691 0.51hp 5735°34'37"84°47'32"252  714  602 0.5125 gph, 1 hp 5835°34'59"84°47'33"Spring  -  710  -Not used 5935°35'03"84°47'38"Spring  -  730  -Cattle pond 6035°35'04"84°47'58"Spring  -  710  -Not usedInvestigation made on January 10-11, 1972. *Residence purchased for Watts Bar Nuclear Plant construction. **Spring fed pond of approximately 50 feet in diameter.***Watts Bar Dam, Steam Plant, and Pete Smith Resort water supply taken from Watts Bar Lake.Table 2.4-10  Well and Spring InventoryWithin 2-mile Radius of Watts Bar Nuclear Plant Si te (Continued)(1972 Survey Only) (Page 2 of 4)Map LocationEstimated ElevationIdent No.LatitudeLongitudeDepthGround Water Surface---------feet------------
Casing Size Pump Data HYDROLOGIC ENGINEERING2.4-81WATTS BARWBNP-836135°36'58"84°45'22"NA*750NANANA6235°36'50"84°45'24"NA710NANANA6335°35'42"84°47'32"150742INK**0.5Yes6435°37'16"84°49'00"100740500.33Yes6535°36'29"84°48'20"200710190.5Yes6635°36'52"84°49'08"70-83700INK0.5Yes6735°36'50"84°49'08"70-83700INK0.5Yes6835°36'49"84°49'09"70-83700INK0.5Yes6935°36'47"84°49'10"70-83700INK0.5Yes7035°37'03"84°49'09"NA750NANANo7135°37'05"84°49'10"NA750NAHand dugNo7235°35'41"84°49'16"NA720NANANA7335°35'43"84°48'48"NA800NANANA7435°36'53"84°48'49"INK720INKINKYes7535 35'07"84
°47'58"100+760Below RiverINKYes7635°35'07"84°48'00"INK740INKINKYes7735 35'06"84
°48'01"NA720NANANA7835°35'08"84°48'01"NA720NANANA7935°35'09"84°47'54"NA800NANANA8035°35'11"84°47'42"NA760NANANA8135 35'14"84
°47'41"NA760NANANA8235°35'13"84°47'37"400+760INK0.5Yes8335°35'14"84°47'37"300+760INK0.5Yes8435°35'10"84°47'34"NA740NANANA8535°35'14"84°47'31"NA720NANANA8635-35'18"84
°47'26"450720200.125Yes8735°35'24"84°47'14"300740INKINKYes8835°35'17"84°47'15"300730INK0.5Yes8935°35'19"84°47'12"265730INK0.5Yes9035°35'18"84°47'12"150730INK0.5Yes9135°35'17"84°47'09"NA730NANANA9235°35'14"84°47'13"NA720NANANA9335°35'06"84°47'17"210720200.5YesTable 2.4-10  Well and Spring InventoryWithin 2-mile Radius of Watts Bar Nuclear Plant Si te (Continued)(1972 Survey Only) (Page 3 of 4)Map LocationEstimated ElevationIdent No.LatitudeLongitudeDepthGround Water Surface---------feet------------
Casing Size Pump Data 2.4-82 HYDROLOGIC ENGINEERINGWATTS BARWBNP-839435°35'08"84°46'58"130760150.5Yes9535°35'08"84°46'55"NA800NANANA9635°35'19"84°46'41"80990200.5Yes9735°35'22"84°46'34"600960INK0.5Yes9835°35'39"84°46'34"INK740INKINKYesS-9935°37'04"84°48'59"Spring710 - -NoS-10035°35'45"84°49'04"Spring840 - -NoS-10135°35'40'84°49'14"Spring730 - -NoS-10235°35'16"84°46'44"Spring980 - -NoS-10335°35'06"84°46'57"Spring800 - -No*none available, many of these residences appeared to be summer houses, 2-3 attempts to locate home owners in the evening hours and on the weekend were unsuccessful.  **Information not known by homeowner.
  ***No pump sizes were known by current homeowners.Table 2.4-10  Well and Spring InventoryWithin 2-mile Radius of Watts Bar Nuclear Plant Si te (Continued)(1972 Survey Only) (Page 4 of 4)Map LocationEstimated ElevationIdent No.LatitudeLongitudeDepthGround Water Surface---------feet------------
Casing Size Pump Data HYDROLOGIC ENGINEERING2.4-83WATTS BARWBNP-83Table 2.4-11  Deleted by Amendment 83 2.4-84 HYDROLOGIC ENGINEERINGWATTS BARWBNP-92Table 2.4-12  Deleted by Amendment 92 HYDROLOGIC ENGINEERING2.4-85WATTS BARWBNP-92Table 2.4-13  Deleted by Amendment 92 2.4-86 HYDROLOGIC ENGINEERINGWATTS BARWBNP-83(1) Actual crest length is 600 ft. Length reduced by 150 ft. to conservatively account for decreased flow through fence.(2) Actual crest length is 1080 ft. Length reduced 50% to conservatively account for decreased flow through fence.Table 2.4-14  Weir Length Description and Coefficientsof Discharge For Areas 3 and 4(Sheet 1 of 1)Weir Parameters            Watershed  Area  Description    Length Feet  Description      of Control      Coefficient of Discharge"C" in  Q=CLH3/2    3Area bounded by Reactor and Turbine Buildings to the west, embankment to the north, and railroad tracks to the east and south. 450(1)Main plant track, elevation = 728.0 3.0  555Transformer yard track, elevation = 728.25
 
===3.0 4Area===
consisting of the switchyard area west of the condenser tube access track and south of the Turbine Building. 590East condenser tube access track elevation = 728.22
 
===3.0 1220Perimeter===
road, elevation = 728.0 3.0Area consisting ofthe switchyard area east of the condenser tube access track and south of the transformer
 
yard track 540(2)East and southend of switchyard area, elevation = 728.0
 
===3.0 HYDROLOGIC===
ENGINEERING2.4-87WATTS BARWBNP-921. Watershed areas 1 - 4 are shown on Figure 2.4-40a; 150-acre area north of site shown on Figure 2.4-40b. 2. Maximum elevation reached at the construction access road.Table 2.4-15  Drainage Area Peak Discharge(Sheet 1 of 1)Watershed  Area 1      Description      Drainage Area    (Acres)
Maximum Elevation1Channel formed by the west end of the switchyard and the adjacent embankment.15.92728.85Backwater was computed in the channel from the road leading to the chemical holdup ponds to the gatehouse and Office Building. The estimated peak discharge at the road (15.92 acres) was 570 cfs. Discharges at upstream locations were decreased proportional to drainage area.2Natural drain with flow to the west from the perimeter road to the access road.67.0728.81Backwater was computed from the crossing the perimeter road, to the Reactor, Diesel Generator, and Waste Wvaporation System Buildings. The estimated peak discharge at the access road was 6053 cfs. This includes flow from area 2 (67 acres), flow over the construction access road north of the site (100 acres), and flow from 60 acres to the northwest of the site. Discharges at upstream locations were decreased proportional to drainage area.3Pool bounded by Reactor and Turbine Buildings to the west, embankment to the north, and railroad tracks to the east and south.22.9728.87The inflow hydrograph was routed with a starting elevation of 728.0 and outflow over the main and transformer yard railroad tracks.Flow reach extending from the main railroad track to a section between the east Reactor Ruilding and embankment to the north.10.0728.79Backwater was computed from the main railroad track to the Reactor Building. The estimated peak discharge at the railroad was 420 cfs. Discharges at upstream locations were decreased proportional to drainage area.4Pool consisting of the switchyard area west of the condenser tube access track and south of the Turbine Building.11.4728.50The inflow hydrograph was routed with a starting elevation of and outflow to the south and west over the perimeter road, and to the east over the condenser tube access track.Pool consisting of the switchyard area east of the condenser tube access track and south of the transformer yard track.6.2728.75The inflow hydrograph was routed with a starting elevation of 728.0 and outflow to the south and east toward the perimeter road.
Northof SitePool bounded by the embankment to the south of the access railroad to the east.50725.67The inflow hydrograph was routed with a starting elevation of 716 (invert of double 96-inch pipe) and outflow through the double 96-inch pipe.Pool bounded by the dike to the east, the access highway to the west, and the construction access road to the south.100735.28 2The inflow hydrograph routed with a starting elevation of 727.1 (invert of 81- by 59-inch pipe arch) and outflow through the pipe arch and over the construction access road.
HYDROLOGIC ENGINEERING2.4-88WATTS BARWBNP-92Table 2.4-16  Dam Safety Modification Status (Hydrologic)Dam*Dam ModificationYear CompletedMain River DamsFort Loudon-TellicoFort Loudon Dam was raised 3.25 feet with a concrete wall to elevation 833.25. A 2000-foot uncontrolled spillway with crest at Elevation 817 was added at Tellico Dam.
1989Watts BarEmbankment of main dam was raised 10 feet with earthfill/concrete wall to Elevation 767. West Saddle Dike was not modified. Top of Saddle Dike remains at Elevation 757.
1997NickajackSouth embankment was raised 5 feet with earthfill/concrete wall to Elevation 657. A 1900-foot roller-compacted concret e overflow dam with top at Elevation 634 was added below the north embankment.
1992GuntersvilleEmbankments were raised 7.5 feet with earthfill and concrete walls to Elevation 617.5.1996Tributary DamsLittle Bear CreekEmbankment was raised 4.5 feet.
1998BeechEmbankment was raised 4.5 feet with earthfill to Elevation 475.5.1992Blue RidgeThree (3) additional spillway bays were added in 1982. Embankment was raised 7 feet with earthfill/concrete wall to Elevation 1713, and a 320-foot uncontrolled spillway with crest at Elevation 1691 was added in 1995.
1995BooneEmbankment was raised 8.5 feet with earthfill to Elevation 1408.5.1984Cedar CreekEmbankment was raised 5.5 feet with concrete wall to Elevation 605.1997 ChatugeEmbankment was raised 6.5 feet with earthfill to Elevation 1946.5.1986CherokeeA portion (600 feet) of the non-overflow dam was raised 7.75 feet to Elevation 1089.75.1982DouglasA portion of the non-overflow dam was raised 13.5 feet to Elevation 1022.5, and eight saddle dams were raised 6.5 feet with earthfill to Elevation 1023.5.
1988NottelyEmbankment was raised 13.5 feet with rockfill to Elevation 1807.5.1988Upper Bear CreekEmbankment was raised 4 feet with concrete wall to Elevation 817.1997 WataugaEmbankment was raised 10 feet with rockfill to Elevation 2012.1983FontanaDam post-tensioned 1988Melton HillDam post-tensioned 1988*These dam safety modifications enable these projects to safely pass the probable maximum flood (PMF).Note: Plans are to armor the embankment at Chickamauga and Bear Creek Dams to permit overtopping.
HYDROLOGIC ENGINEERING2.4-89WATTS BAR WBNP-83Figure 2.4-1  Tennessee River Basin Mean Annual Precipitation 35-Year Period 1935-1969
 
HYDROLOGIC ENGINEERING2.4-90WATTS BAR WBNP-92Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-2  General Plan Elevation & Sections Watts Bar Hydro Project HYDROLOGIC ENGINEERING2.4-91WATTS BAR WBNP-92Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-3  General Plan Elevations & Sections Fort Loudon Project HYDROLOGIC ENGINEERING2.4-92WATTS BAR WBNP-92Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-3a  General Plan Elevations and Sections Fort Loudon Project HYDROLOGIC ENGINEERING2.4-93WATTS BAR WBNP-32Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-4  Norris Dam Plan-Elevations and Sections HYDROLOGIC ENGINEERING2.4-94WATTS BAR WBNP-32Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-5  General Plan Elevations & Sections - Melton Hill Project HYDROLOGIC ENGINEERING2.4-95WATTS BAR WBNP-32Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-6  General Plan Elevation And Sections - Fontana Project HYDROLOGIC ENGINEERING2.4-96WATTS BAR WBNP-92Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-7  General Plan Elevation & Sections - Douglas Project HYDROLOGIC ENGINEERING2.4-97WATTS BAR WBNP-92Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-8  General Plan Elevations & Sections - Cherokee Project HYDROLOGIC ENGINEERING2.4-98WATTS BAR WBNP-32Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-9  General Plan Elevation & Sections - Fort Patrick Henry Project HYDROLOGIC ENGINEERING2.4-99WATTS BAR WBNP-92Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-10  General Plan Elevations & Sections - Boone Project HYDROLOGIC ENGINEERING2.4-100WATTS BAR WBNP-92Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-11  General Plan Elevations &. Sections - Watauga Project HYDROLOGIC ENGINEERING2.4-101WATTS BAR WBNP-63Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-12  General Plan Elevation & Sections - South Holston Project HYDROLOGIC ENGINEERING2.4-102WATTS BAR WBNP-63Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-13  General Plan Elevation & Sections - Tellico Project HYDROLOGIC ENGINEERING2.4-103WATTS BAR WBNP-63Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-14  General Plan Elevation &. Sections - Chickamauga Project HYDROLOGIC ENGINEERING2.4-104WATTS BAR WBNP-63Figure 2.4-15  Multiple-Purpose - Reservoir Operations Watts Bar Project HYDROLOGIC ENGINEERING2.4-105WATTS BAR WBNP-63Figure 2.4-16  Multiple-Purpose - Reservoir Operations - Fort Loudoun Project HYDROLOGIC ENGINEERING2.4-106WATTS BAR WBNP-63Figure 2.4-17  Multiple-Purpose - Reservoir Operations Norris Project HYDROLOGIC ENGINEERING2.4-107WATTS BAR WBNP-63Figure 2.4-18  Multiple-Purpose - Reservoir Operations - Fontana Project HYDROLOGIC ENGINEERING2.4-108WATTS BAR WBNP-63Figure 2.4-19  Multiple-Purpose - Reservoir Operations - Douglas Project HYDROLOGIC ENGINEERING2.4-109WATTS BAR WBNP-63Figure 2.4-20  Multiple-Purpose - Reservoir Operations - Cherokee Project HYDROLOGIC ENGINEERING2.4-110WATTS BAR WBNP-63Figure 2.4-21  Multiple-Purpose - Reservoir Operations - Boone Project HYDROLOGIC ENGINEERING2.4-111WATTS BAR WBNP-63Figure 2.4-22  Multiple-Purpose - Reservoir Operations - Watauga Project HYDROLOGIC ENGINEERING2.4-112WATTS BAR WBNP-63Figure 2.4-23  Multiple-Purpose - Reservoir Operations - South Holston Project HYDROLOGIC ENGINEERING2.4-113WATTS BAR WBNP-63Figure 2.4-24  Multiple-Purpose - Reservoir Operations - Tellico Project HYDROLOGIC ENGINEERING2.4-114WATTS BAR WBNP-63Figure 2.4-25  Tennessee River-Mile 529.9 - Reservoir Areas And Volumes - Watts Bar Project HYDROLOGIC ENGINEERING2.4-115WATTS BAR WBNP-63Figure 2.4-26  Multiple-Purpose -Reservoir Operations - Chickamauga Project HYDROLOGIC ENGINEERING2.4-116WATTS BAR WBNP-63Figure 2.4-27  Tennessee River Mile 602.3 -Reservoir Areas And Volumes - Fort Loudoun Project HYDROLOGIC ENGINEERING2.4-117WATTS BAR WBNP-63Figure 2.4-28  Clinch River Mile 79.8 -Reservoir Areas And Volumes - Norris Project HYDROLOGIC ENGINEERING2.4-118WATTS BAR WBNP-63Figure 2.4-29  Clinch River Mile 23.1 - Reservoir Areas and Volumes - Melton Hill Project HYDROLOGIC ENGINEERING2.4-119WATTS BAR WBNP-63Figure 2.4-30  Little Tennessee River Mile 61.0 - Reservoir Areas and Volumes - Fontana Project HYDROLOGIC ENGINEERING2.4-120WATTS BAR WBNP-63THIS PAGE INTENTIONALLY BLANK HYDROLOGIC ENGINEERING2.4-121WATTS BAR WBNP-63Figure 2.4-31  French Broad River Mile 32.3 - Reservoir Areas And Volumes - Douglas Project
 
HYDROLOGIC ENGINEERING2.4-122WATTS BAR WBNP-63Figure 2.4-32  Holston River Mile 52.3 - Reservoir Areas And Volumes - Cherokee Project HYDROLOGIC ENGINEERING2.4-123WATTS BAR WBNP-63Figure 2.4-33  S.F. Holston River Mile 8.2 - Reservoir Areas and Volumes - Fort Patrick Henry Project HYDROLOGIC ENGINEERING2.4-124WATTS BAR WBNP-63Figure 2.4-34  South Fork Holston River Mile 18.6 - Reservoir Areas and Volumes - Boone Project HYDROLOGIC ENGINEERING2.4-125WATTS BAR WBNP-63Figure 2.4-35  Watauga River Mile 36.7 - Reservoir Areas And Volumes - Watauga Project HYDROLOGIC ENGINEERING2.4-126WATTS BAR WBNP-63Figure 2.4-36  S.F. Holston River Mile 49.8 - Reservoir Areas And Volumes - South Holston Project HYDROLOGIC ENGINEERING2.4-127WATTS BAR WBNP-63Figure 2.4-37  Little Tennessee River Mile 0.3 - Reservoir Areas And Volumes - Tellico Project HYDROLOGIC ENGINEERING2.4-128WATTS BAR WBNP-63Figure 2.4-38  Tennessee River Mile 471.0 - Reservoir Areas And Volumes - Chickamauga Project HYDROLOGIC ENGINEERING2.4-129WATTS BAR WBNP-63Figure 2.4-39  Deleted by Amendment 63 HYDROLOGIC ENGINEERING2.4-130WATTS BAR WBNP-50Figure 2.4-40  Tennessee River Mile 464.2 - Distribution Of Floods At Chattanooga, Tennessee HYDROLOGIC ENGINEERING2.4-131WATTS BAR WBNP-50Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-40a  Main Plant Site Grading And Drainage System For Flood Studies  Sheet 1 HYDROLOGIC ENGINEERING2.4-132WATTS BAR WBNP-50Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-40a  Main Plant Site Grading and Drainage System For Flood Studies  Sheet 2 HYDROLOGIC ENGINEERING2.4-133WATTS BAR WBNP-50Figure 2.4-40a  Main Plant Site Grading and Drainage System For Flood Studies  Sheet 3 HYDROLOGIC ENGINEERING2.4-134WATTS BAR WBNP-50Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-40b  Main Plant General Plan HYDROLOGIC ENGINEERING2.4-135WATTS BAR WBNP-50Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-40c  Yard Site Grading and Drainage System For Flood Studies HYDROLOGIC ENGINEERING2.4-136WATTS BAR WBNP-89Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-40d-1  Main Plant Plant Perimeter Roads Plan and Profile Sheet 1 HYDROLOGIC ENGINEERING2.4-137WATTS BAR WBNP-89Figure 2.4-40d  Main Plant Plant Perimeter Roads Plan and Profile  - Sheet 2 HYDROLOGIC ENGINEERING2.4-138WATTS BAR WBNP-50Figure 2.4-40d  Main Plant Plant Perimeter Roads Plan and Profile  - Sheet 3 HYDROLOGIC ENGINEERING2.4-139WATTS BAR WBNP-50Figure 2.4-40e  Access Highway TVA DWG 1001H202 R4  - Sheet 1 HYDROLOGIC ENGINEERING2.4-140WATTS BAR WBNP-50Figure 2.4-40e  Access Highway TVA DWG. 1001H201 R4  - Sheet 2 HYDROLOGIC ENGINEERING2.4-141WATTS BAR WBNP-50Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-40f  Main Plant  Main Plant Tracks Plan - Sheet 1 HYDROLOGIC ENGINEERING2.4-142WATTS BAR WBNP-50Figure 2.4-40f  Main Plant Main Plant Tracks Sections & Profiles  - Sheet 2 HYDROLOGIC ENGINEERING2.4-143WATTS BAR WBNP-50Figure 2.4-40f  Main Plant Main  Plant Tracks Sections & Profiles  - Sheet 3 HYDROLOGIC ENGINEERING2.4-144WATTS BAR WBNP-50Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-40g  Yard, Grading Drainage and Surfacing Transformer & Switchyard - Sheet 1 HYDROLOGIC ENGINEERING2.4-145WATTS BAR WBNP-50Figure 2.4-40g  Yard, Grading Drainage and Surfacing Transformer & Switchyard - Sheet 2 HYDROLOGIC ENGINEERING2.4-146WATTS BAR WBNP-50Figure 2.4-40g  Yard, Grading Drainage and Surfacing Transformer & Switchyard  - Sheet 3 HYDROLOGIC ENGINEERING2.4-147WATTS BAR WBNP-83Figure 2.4-40h  Probable Maximum Precipation Point Rainfall HYDROLOGIC ENGINEERING2.4-148WATTS BAR WBNP-50Figure 2.4-40i  Deleted by Amendment 83 HYDROLOGIC ENGINEERING2.4-149WATTS BAR WBNP-83Figure 2.4-40j  Deleted by Amendment 83 HYDROLOGIC ENGINEERING2.4-150WATTS BAR WBNP-83Figure 2.4-40k  Deleted by Amendment 83 HYDROLOGIC ENGINEERING2.4-151WATTS BAR WBNP-83Figure 2.4-40L  Deleted by Amendment 83 HYDROLOGIC ENGINEERING2.4-152WATTS BAR WBNP-83Figure 2.4-41  Probable Maximum March Isohyets  (21,400-sq. mi. downstream)  1st 6 Hours (IN.)
HYDROLOGIC ENGINEERING2.4-153WATTS BAR WBNP-83Figure 2.4-42  Probable Maximum March Isohyets  (7980 Sq. Mi.)  1st 6 Hours (IN.)
HYDROLOGIC ENGINEERING2.4-154WATTS BAR WBNP-83Figure 2.4-43  Rainfall Time Distribution Adopted Standard Mass Curve HYDROLOGIC ENGINEERING2.4-155WATTS BAR WBNP-83Figure 2.4-44  72-Hour March Probable Maximum Storm Depths (IN) Tennessee River Watershed Above Chickamauga Dam HYDROLOGIC ENGINEERING2.4-156WATTS BAR WBNP-32Figure 2.4-45  Hydrological Model Unit Areas HYDROLOGIC ENGINEERING2.4-157WATTS BAR WBNP-32Figure 2.4-46  6-Hour Unit Hydrographs  Sheet 1 of 11 HYDROLOGIC ENGINEERING2.4-158WATTS BAR WBNP-32Figure 2.4-46  6-Hour Unit Hydrographs  Sheet 2 of 11 HYDROLOGIC ENGINEERING2.4-159WATTS BAR WBNP-32Figure 2.4-46  6-Hour Unit Hydrographs  Sheet 3 of 11 HYDROLOGIC ENGINEERING2.4-160WATTS BAR WBNP-32Figure 2.4-46  6-Hour Unit Hydrographs Sheet 4 of 11 HYDROLOGIC ENGINEERING2.4-161WATTS BAR WBNP-32Figure 2.4-46  6-Hour Unit Hydrographs Sheet 5 of 11 HYDROLOGIC ENGINEERING2.4-162WATTS BAR WBNP-32Figure 2.4-46  6-Hour Unit Hydrographs Sheet 6 of 11 HYDROLOGIC ENGINEERING2.4-163WATTS BAR WBNP-32Figure 2.4-46  2-Hour Unit Hydrographs Sheet 7 of 11 HYDROLOGIC ENGINEERING2.4-164WATTS BAR WBNP-32Figure 2.4-46  2-Hour Unit Hydrographs Sheet 8 of 11 HYDROLOGIC ENGINEERING2.4-165WATTS BAR WBNP-32Figure 2.4-46  6-Hour Unit Hydrographs Sheet 9 of 11 HYDROLOGIC ENGINEERING2.4-166WATTS BAR WBNP-32Figure 2.4-46  6-Hour Unit Hydrographs Sheet 10 of 11 HYDROLOGIC ENGINEERING2.4-167WATTS BAR WBNP-32Figure 2.4-46  6-Hour Unit Hydrographs Sheet 11 of 11 HYDROLOGIC ENGINEERING2.4-168WATTS BAR WBNP-32THIS PAGE INTENTIONALLY BLANK HYDROLOGIC ENGINEERING2.4-169WATTS BAR WBNP-32 iFigure 2.4-47a  Watts Bar Probable Maximum Flood Fort Loudon - Tellico Outflow
 
2.4-170HYDROLOGIC ENGINEERINGWATTS BAR WBNP-92Figure 2.4-47b  Fort Loudon Dam Rating Curve HYDROLOGIC ENGINEERING2.4-171WATTS BAR WBNP-92Figure 2.4-47c  Tellico Dam Rating Curve 2.4-172 HYDROLOGIC ENGINEERINGWATTS BAR WBNP-92Figure 2.4-48  General Plan Elevation & Sections HYDROLOGIC ENGINEERING2.4-173WATTS BAR WBNP-92Figure 2.4-49  Hydrologic Model Verification - 1973 Flood 2.4-174 HYDROLOGIC ENGINEERINGWATTS BAR WBNP-32Figure 2.4-50  1973 Flood-Chickamauga Reservoir Unsteady Flow Model Verification HYDROLOGIC ENGINEERING2.4-175WATTS BAR WBNP-32Figure 2.4-51  Steady- State Model Verification  Watts Bar Dam Tailwater Rating Curve 2.4-176HYDROLOGIC ENGINEERINGWATTS BAR WBNP-92Figure 2.4-52  Watts Bar Nuclear Plant Probable Maximum Flood Discharge HYDROLOGIC ENGINEERING2.4-177WATTS BAR WBNP-32Figure 2.4-53  West Saddle Dike Location Plan and Section 2.4-178 HYDROLOGIC ENGINEERINGWATTS BAR WBNP-32Figure 2.4-54  Watts Bar Probable Maximum Flood -Watts Bar Embankment Failure HYDROLOGIC ENGINEERING2.4-179WATTS BAR WBNP-92Figure 2.4-55  Watts Bar Dam Rating Curves 2.4-180HYDROLOGIC ENGINEERINGWATTS BAR WBNP-32Figure 2.4-56  Watts Bar Probable Maximum Flood  Watts Bar Dam Outflow HYDROLOGIC ENGINEERING2.4-181WATTS BAR WBNP-92Figure 2.4-57  Watts Bar Probable Maximum Flood  Watts Bar Headwater Elevation 2.4-182 HYDROLOGIC ENGINEERINGWATTS BAR WBNP-32Figure 2.4-58  Watts Bar Probable Maximum Flood  Chickamauga Headwater Elevations HYDROLOGIC ENGINEERING2.4-183WATTS BAR WBNP-32Figure 2.4-59  Chickamauga Darn Rating Curves 2.4-184HYDROLOGIC ENGINEERINGWATTS BAR WBNP-32Figure 2.4-60  Watts Bar Probable Maximum Flood  Chickamauga Outflow HYDROLOGIC ENGINEERING2.4-185WATTS BAR WBNP-39Figure 2.4-61  Watts Bar Probable Maximum Flood  Water Levels Before and After Embankment Failure 2.4-186HYDROLOGIC ENGINEERINGWATTS BAR WBNP-39Figure 2.4-62  Relative Bore Height (After J. J. Stroker, REF. 31)
HYDROLOGIC ENGINEERING2.4-187WATTS BAR WBNP-39Figure 2.4-63  Assumed Limits of Embankment Failure  Wave Expansion 2.4-188HYDROLOGIC ENGINEERINGWATTS BAR WBNP-32Figure 2.4-64  Watts Bar Nuclear Plant Probable Maximum Flood Elevation HYDROLOGIC ENGINEERING2.4-189WATTS BAR WBNP-92Figure 2.4-65  Tennessee River - Mile 514-530 - Watts Bar Nuclear Plant Flood and Thalweg Profile 2.4-190HYDROLOGIC ENGINEERINGWATTS BAR WBNP-39Figure 2.4-66  Extreme Value Analysis 30-Minute Wind Speed From The Southwest Chattanooga, TN 1948-74 HYDROLOGIC ENGINEERING2.4-191WATTS BAR WBNP-92Figure 2.4-67  Watts Bar Nuclear Plant Wind Wave Fetch 2.4-192HYDROLOGIC ENGINEERINGWATTS BAR WBNP-63Figure 2.4-68  Powerhouse & Spillway Results of Analysis For Operating Basis Earthquake - Watts Bar Dam HYDROLOGIC ENGINEERING2.4-193WATTS BAR WBNP-63Figure 2.4-69  Embankment Results of Analysis For Operating Basis Earthquake 2.4-194 HYDROLOGIC ENGINEERINGWATTS BAR WBNP-83Figure 2.4-70  Deleted by Amendment 83 HYDROLOGIC ENGINEERING2.4-195WATTS BAR WBNP-83Figure 2.4-71  Powerhouse & Spillway Results of Analysis For Operating Basis Earthquake - Fort Loudoun Dam 2.4-196HYDROLOGIC ENGINEERINGWATTS BAR WBNP-83Figure 2.4-72  Embankment Results Of Analysis For Operating Basis Earthquake - Fort Loudoun Darn HYDROLOGIC ENGINEERING2.4-197WATTS BAR WBNP-63Figure 2.4-73  Nonoverflow & Spillway Results of Analysis For Operating Basis Earthquake - Tellico Dam 2.4-198HYDROLOGIC ENGINEERINGWATTS BAR WBNP-63Figure 2.4-74  Embankment Results For Analysis For Operating Basis Earthquake - Tellico Darn HYDROLOGIC ENGINEERING2.4-199WATTS BAR WBNP-63Figure 2.4-75  Spillway & Nonoverflow Results of Analysis For OBE & 1/2 PMF-Norris Dam 2.4-200 HYDROLOGIC ENGINEERINGWATTS BAR WBNP-63 THIS PAGE INTENTIONALLY BLANK HYDROLOGIC ENGINEERING2.4-201WATTS BAR WBNP-63Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-76  Analysis For OBE & 1/2 PMF Assumed Condition of Dam After Failure Norris Dam
 
HYDROLOGIC ENGINEERING2.4-202WATTS BAR WBNP-63Figure 2.4-77  Spillway & Nonoverflow Results of Analysis For Operating Basis Earthquake -Cherokee Dam HYDROLOGIC ENGINEERING2.4-203WATTS BAR WBNP-63Figure 2.4-78  Embankment Results of Analysis For Operating Basis Earthquake - Cherokee Dam HYDROLOGIC ENGINEERING2.4-204WATTS BAR WBNP-63Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-79  Assumed Condition of Dam After Failure PBE And 1/2 Probable Max Flood - Cherokee Dam HYDROLOGIC ENGINEERING2.4-205WATTS BAR WBNP-63Figure 2.4-80  Spillway & Nonoverflow Results of Analysis For Operating Basis Earthquake - Douglas Dam HYDROLOGIC ENGINEERING2.4-206WATTS BAR WBNP-63Figure 2.4-81  Saddle Dam No. 1 Results of Analysis For Operating Basis Earthquake - Douglas Dam HYDROLOGIC ENGINEERING2.4-207WATTS BAR WBNP-63Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-82  Douglas Dam Assumed Condition of Dam After Failure aBE And 1/2 Probable Maximum Flood - Douglas Project HYDROLOGIC ENGINEERING2.4-208WATTS BAR WBNP-63Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-83  Fontana Dam Assumed Condition of Dam after Failure aBE And 1/2 Probable Maximum Flood - Fontana Dam HYDROLOGIC ENGINEERING2.4-209WATTS BAR WBNP-63Figure 2.4-84  Deleted by Amendment 63 HYDROLOGIC ENGINEERING2.4-210WATTS BAR WBNP-63Figure 2.4-85  Deleted by Amendment 63 HYDROLOGIC ENGINEERING2.4-211WATTS BAR WBNP-63Figure 2.4-86  Spillway Results of Analysis For SSE Earthquake Fort Loudoun Dam HYDROLOGIC ENGINEERING2.4-212WATTS BAR WBNP-63 Figure 2.4-87  Embankment Results of Analysis For SSE Earthquake Fort Loudoun Dam HYDROLOGIC ENGINEERING2.4-213WATTS BAR WBNP-63Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-88  Fort Loudoun Dam Assumed Condition of Dam After Failure SSE Combined With a 25 Year Flood - Fort Loudoun Dam HYDROLOGIC ENGINEERING2.4-214WATTS BAR WBNP-63Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-89  Tellico Dam Assumed Condition of Dam After Failure SSE Combined With a 25 Year Flood Tellico Project HYDROLOGIC ENGINEERING2.4-215WATTS BAR WBNP-63Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-90  Norris Dam SSE + 25 Year Flood Judged Condition of Dam After Failure - Norris Dam HYDROLOGIC ENGINEERING2.4-216WATTS BAR WBNP-63Figure 2.4-91  SSE With Epicenter In North Knoxville Vicinity HYDROLOGIC ENGINEERING2.4-217WATTS BAR WBNP-35Figure 2.4-92  Time and Date Flood Hydrographs HYDROLOGIC ENGINEERING2.4-218WATTS BAR WBNP-35Figure 2.4-93  SSE With Epicenter In West Knoxville Vicinity HYDROLOGIC ENGINEERING2.4-219WATTS BAR WBNP-35Figure 2.4-94  Location of SSE For Simultaneous Failure of The Douglas and Fontana Dams HYDROLOGIC ENGINEERING2.4-220WATTS BAR WBNP-35Figure 2.4-95  Tennessee River Mile 523.2 Watts Bar Nuclear Plant Rating Curve HYDROLOGIC ENGINEERING2.4-221WATTS BAR WBNP-35Figure 2.4-96  Cross Sections Tennessee River (mile 521.00) (mile 520.70) (mile 520.60)
HYDROLOGIC ENGINEERING2.4-222WATTS BAR WBNP-35Figure 2.4-97  Channel Profile Tennessee River (mile 520.0 to mile 521.37)
HYDROLOGIC ENGINEERING2.4-223WATTS BAR WBNP-57Security-Related Information - Withheld Under 10CFR2.390Figure 2.4-98  Main Plant General Grading Plan HYDROLOGIC ENGINEERING2.4-224WATTS BAR WBNP-57Figure 2.4-99  Grading Plan Intake Channel HYDROLOGIC ENGINEERING2.4-225WATTS BAR WBNP-83Figure 2.4-100  Deleted by Amendment 83 HYDROLOGIC ENGINEERING2.4-226WATTS BAR WBNP-33Figure 2.4-101  Deleted by Amendment 33 HYDROLOGIC ENGINEERING2.4-227WATTS BAR WBNP-83Figure 2.4-102  Wells And Spring Inventory Within 2-Mile Radius of Watts Bar Nuclear Plant Site HYDROLOGIC ENGINEERING2.4-228WATTS BAR WBNP-83Figure 2.4-103  Water-Level Fluctuations In Observation Wells at The Watts Bar Site HYDROLOGIC ENGINEERING2.4-229WATTS BAR WBNP-50Figure 2.4-104  Locations of Ground - Water Observation Wells HYDROLOGIC ENGINEERING2.4-230WATTS BAR WBNP-50Figure 2.4-105  Generalized Water-Table Contour Map January 1972 HYDROLOGIC ENGINEERING2.4-231WATTS BAR WBNP-50Figure 2.4-106  Mechanical - Flow Diagram Fuel Pool Cooling and Cleaning System HYDROLOGIC ENGINEERING2.4-232WATTS BAR WBNP-50Figure 2.4-107  Powerhouse Units 1 & 2 Flow Diagram - Residual Heat Removal System HYDROLOGIC ENGINEERING2.4-233WATTS BAR WBNP-50Figure 2.4-108  Schematic Flow Diagram Flood Protection Provisions Open Reactor Cooling (Unit 1 Shown, Unit 2 Similar)
HYDROLOGIC ENGINEERING2.4-234WATTS BAR WBNP-50Figure 2.4-109  Schematic Flow Diagram Flood Protection Provisions Natural Convection Cooling (Unit 1 Shown, Unit 2 Similar)
HYDROLOGIC ENGINEERING2.4-235WATTS BAR WBNP-32Figure 2.4-110  Watts Bar Nuclear Plant Rainfall Flood Protection Plan Basis For Safe Shutdown For Plant Flooding HYDROLOGIC ENGINEERING2.4-236WATTS BAR WBNP-92Figure 2.4-111  Douglas PMF Failure Wave at Watts Bar Plant}}

Latest revision as of 11:46, 14 January 2025

Final Safety Analysis Report (Fsar), Amendment 93, Section 2.4 Hydrologic Engineering Through Figure 2.4-111
ML091400522
Person / Time
Site: Watts Bar Tennessee Valley Authority icon.png
Issue date: 04/30/2009
From:
Tennessee Valley Authority
To:
Office of Nuclear Reactor Regulation
References
Download: ML091400522 (236)
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