ML12226A562

Sequoyah, Units 1 and 2, Enclosure 1, Evaluation of Proposed Changes Attachment 1 Proposed Sqn Units 1 and 2 UFSAR Text Changes (Markups), Page 2.4-1 Through 2.4-41

ML12226A562
Person / Time
Site:	Sequoyah
Issue date:	08/10/2012
From:	Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation
References
TAC ME8200
Download: ML12226A562 (42)

Text

ENCLOSURE IEVALUATION OF PROPOSED CHANGESATTACHMENT IProposed SQN Units I and 2 UFSAR Text Changes (Markups)I SQN-2.4 HYDROLOGIC ENGINEERINGSON is located on the riaht hank of Chickamauaoa L ake at Te~nnessee Rivr mile (TRM'/484 F5 withplant grade at elevation 705.0 ft MSL. The plant has been designed to have the capability for safeshutdown in floods UD to the computed maximum water level, in accordance with reaulatorv position 2of RG 1.59.Determination of the maximum flood level included consideration of postulated dam failures fromseismic and hydrologic causes. The maximum flood elevation of 722.0 ft would result from anoccurrence of the probable maximum storm. Coincident wind wave activity results in wind waves of upto 4.2 ft (crest to trouah). Wind wave run uo on the Diesel Generator Buildina reaches elevation723.2 ft. Wind wave run up on the critical wall of the ERCW Intake Pumping Station and the walls ofthe Auxiliary, Control and Shield Buildinqs reaches elevation 726.2 ft.The nearest surface water user located downstream from SQN is East Side Utility at TRM 473.0, 11.7miles downstream. All surface water suoBlies withdrawn from the 98.6 mile reach of the mainstreamof the Tennessee River between Dayton, Tennessee (TRM 503.8) and the Mead Corporation inStevenson, Alabama (TRM 405.2) are listed in Table 2.4.1-1.2.4.1 Hydrologic Description2.4.1.1 Site and FacilitiesThe location of key plant structures and their relationship to the original site topography are shown onFigure 2.1.2-1. The structures which have safety-related equipment and systems are indicated on thisfigure and are tabulated below, along with the elevation of major exterior accesses.Number ofAccessesStructureAccessIntake.p.

• Pumping (1) Stairwell entrancest-UGtUleStructure (2) Access hatches(3) Cable tunnelAuxiliary andControl Buildings(1)(2)(3)(4)(5)(6)(7)Railroad access openingDoors to turbine buildingDoors to turbine buildingDoors to turbine buildingPersonnel lock to SBGeneral vent or intakeDoors to AEB and MSW16112224241114141Elevation (ft)705.0705.0690.0Shield buildingBuildingDiesel gene-ate4buldi4! RGeneratorBuildingERCW r RakelntakePumping Station(1) Personnel lock (watertight)(2) Equipment hatch(3) Personnel lock(1) Equipment access door(2) Personnel access door(3) Emergency exit(4) Emergency exit(1) Access door(2) Trash sluice(3) Deck drainage (sealedfor flood)706.0706.0732.0685.0690.0714.0714.0691.0730.0732.0722.0722.0722.0740.5725.0723.5720.011Exterior accesses are also provided to each of the class IE electrical systems manholes andhandholes at elevations varying from 700 ft MSL to 724 feet MSL, depending upon the location of2.4-1 SQN-each structure.The relationship of the plant site to the surrounding area can be seen in Figures 2.1.2-1 and 2.4.1-1. Itcan be seen from these figures that significant natural drainage features of the site have not beenaltered. Local surface runoff drains into the Tennessee River.2.4.1.2 HydrosphereThe Sequoyah Nuclear Plant (SQN) site comprises approximately 525 acres on a peninsula on thewestern shore of Chickamauga Lake at Tennessee River Mile (TRM) 484.5. As shown by Figure2.4.1-1, the site is on high ground with the Tennessee River being the only potential source offlooding. SQN is located in the Middle Tennessee Chickamauga watershed, U.S. Geological Survey(USGS) hydrologic unit code 06020001, one of 32 watersheds in the Region 06 -Tennessee RiverWatershed (Figure 2.4.1-2).The Tennessee River above SQN site drains 20,650 square miles. The drainage area atChickamauga Dam, 13.5 miles downstream, is 20,790 square miles. Three major tributaries-,Hiwassee, Little Tennessee, and French Broad Rivers,_-rise to the east in the rugged SouthernAppalachian Highlands. They flow northwestward through the Appalachian Divide which is essentiallydefined by the North Carolina-Tennessee border to join the Tennessee River which flowssouthwestward. The Tennessee River and its Clinch and Holston River tributaries flow southwestthrough the Valley and ridge physiographic province which, while not as rugged as the SouthernHighlands, features a number of mountains including the Clinch and Powell Mountain chains. Thedrainage pattern is shown on Figure 2.1.1-1. About 20 percent of the watershed rises above elevation3 000 ft with a maximum elevation of 6,684 ft at Mt. Mitchell, North Carolina. The watershed is about70 percent forested with much of the mountainous area being 100 percent forested.The climate of the watershed is humid temperate. Mean annual prccipitation for the Tonncsscc Valleyis shown by Figuro 2.4.1 2. Above Chickamauga Dam, annual rainfall averages 51 inches and variesfrom a low of 40 inches at sheltered locations in the mountains to high spots of 85 inches on thesouthern and eastern divide. Rainfall occurs relatively evenly throughout the year. See Section 2.3for a discussion of rainfall. The lowest monthly average is 2.9 inches in October. The highest monthlyaverage is 6.8 inches in March, with January a close second with an average of 6.0 inches.Major flood-producing storms are of two general types; the cool-season, winter type, and thewarm-season, hurricane type. Most floods at SQN, however, have been produced by winter-typestorms in the main flood-season months of January through early April.Watershed snowfall is relatively light, averaging only about 14 inches annually above the plant.Snowfall above the 3,000-ft elevation averages 22 inches annually. The maximumhlighest averageannual snowfall efin the basin is 63 inches GGeim at Mt. Mitchell, the highest point east of theMississippi River. The overall snowfall average above the 3,000-foot elevation, however, is only 22inches annually. 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-regulatedrivers in the United States. The TVA reservoir system is operated for flood control, navigation, andpower generation with flood control a prime purpose with particular emphasis on protection forChattanooga, 20 miles downstream from SQN.Chickamauga Dam, 13.5 miles downstream, affects water surface elevations at SQN. NermalSummerfull pool elevation is 683.0682.5 feet. At this elevation the reservoir is 58.9 miles long on theTennessee River and 32 miles long on the Hiwassee River, covering an area of 3&40036.050 acres,with a volume of 628,0622.500 acre-feet. The reservoir has an average width of nearly 1 mile,ranging from 700 feet to 1.7 miles. At SQN-4the SQN site the reservoir is about 3,000 feet wide withdepths ranging between 12 feet and 50 feet at normal pool elevation.The Tennessee Rioer abo've Chattanooga, Tenne , .f the best regulated rives in the United2.4-2 SQN-States. A prime purpose of the TVA water cntrol system 69 is flood, control#0, With pa.ticular emphasis Onprotection for Chattanooga, 20 milos, downstroam fromn SQN.There are 2-Q17 major in the TVA system from the plant, 13 Of Whi-h ha e&s.bstas ial reevdflood detention capacity during the m~ain flood season. Table 2.4.1 1 listpertinent data for TVA's mnajor dams prior to moedifications made by the Dam Safety Programn (seeTable-2.4.-5 dams (South Holston, Boone, Fort Patrick Henry, Watauga, Fontana, Norris,Cherokee, Douglas, Tellico, Fort Loudoun, Melton Hill, Blue Ridge, Apalachia, Hiwassee, Chatuge,Nottely, and Watts Bar) in the TVA system upstream from SQN, 14 of which (those previouslyidentified excluding Fort Patrick Henry, Melton Hill, and Apalachia) provide about 4.8 million acre-ft ofreserved flood-detention (March 15) capacity during the main flood season. Table 2.4.1-2 listspertinent data for TVA's dams and reservoirs. Figure 2.4.1-3 presents a simplified flow diagram for theTennessee River system. Table 2.4.1-3 provides the relative distances in river miles of upstreamdams to the SQN site. Details for TVA dam outlet works are provided in Table 2.4.1-4. In addition,there are six major non-TVA dams, previously owned by the Aluminum Company of America(ALCOA). The ALCOA reservoirs often contribute to flood reduction, but were ignored in this analysisdo not have dependable reserved flood detention capacity. The lccations of these damsand the minor dams, Nolichucky and Walters (Waterville Lake), shawn on Fiure 2.1.1-1. Table24.-122.4.1-5 lists pertinent data for the major and minor ALCOA dams and Walters Dam (WatervilleLake). The locations of these dams are shown on Fiaure 2.1.1-1.The flo-od d+etention capacity rese..ed in the TVA system arie. .....ally, with the greatest amountsduring the flood.se.ason. 2.4.1 3, containing 14 sheets, shows tributa.y and ma.n.rveseasFon coprl atig guides fr thoese reservis having major ifuence on SON flood flows. Table2.4.1 3 shows the fleouds cotrol reseratieon at the multiple PRipvce projecto above SON at thebeginning and end of the wirtervie d season and in the summer. Assured -ystem detention capacityabeve the plart varies fuom 5.6 inches OR Jaruary 4to 1.5 incrhes on Muarch 15, decreasing to 1.0 induring the summer and fall. ActuaI detention capacity may exceed these amoneats, depending uponinfloGws and powerdea~nds&.Flood control above SON is provided largely by 4412 tributary reservoirs. Tellico Dam is counted as atributary reservoir because it is located on the Little Tennessee River, although, because of canalconnection with Fort Loudoun Dam, it also functions as a main river dam. On March 15, near the endof the flood season, these provide a minimum of 44 004818500 acre-feet of detention capacity,equivalent to ximatey.5 inches on on the 4476approximately 19,500 square-mile area theycontrol. This is 90 percent of the total available above Chickamauga Reservoir. The two main riverreservoirs, Fort Loudoun and Watts Bar, provide 490,000 acre-feet, equivalent to 4-.5proiael .inches of detention capacity on the remaining area above the thaesChickamaua Dam.The flood detention capacity reserved in the TVA system varies seasonally, with the greatest amountsduring the January through March flood season. Figure 2.4.1-4 (16 sheets) shows the reservoirseasonal operating guides for reservoirs above the plant site. Table 2.4.1-6 shows the flood controlreservations at the multi ple-purpose proalcts above SON at the beginning and end of the winter floodseason and in the summer. Total assured system detention capacity above Chickamauga Dam variesfrom approximately 5.5 inches on January ito approximately 5 inches on March 15 and decreasing toapproximately 1.5 inches during the summer and fall. Actual detention capacity may exceed theseamounts, depending upon inflows and power demands.Chickamauga Dam, the elevation of which affects flood elevations at the plant, has a drainage area of20,790 square miles, 3,480 square miles more than Watts Bar Dam. There are seven maior tributarydams (Chatuge, Nottely. Hiwassee, Apalachia. Blue Ridge, Ocoee No. 1 and Ocoee No. 3) in the3,480-square-mile intervening watershed. of which four have substantial reserved capacity. On March15, near the end of the flood season, these provide a minimum of 379,300 acre-ft eguivalent to 5.9inches on the 1 ,200-sguare-mile controlled area. Chickamauga Dam contains 345,300 acre-ft ofdetention capacity on March 15 equivalent to 2.8 inches on the remaining 2,280 square miles. Figure2.4.1-4 (Sheet 1) shows the seasonal operatina auide for Chickamauaa.Elevation-storaqe relationships for the reservoirs above the site and Chickamauqa, downstream, are2.4-3 SQN-shown in Figure 2.4.1-5 (17 sheets).Daily flow volumes at the plant, for all practical purposes, are represented by discharges fromChickamauga Dam with drainage area of 20,790 square miles, only 140 square miles more than at theplant. Momentary flows at the nuclear plant may vary considerably from daily averages, dependingupon turbine operations at Watts Bar Dam upstream and Chickamauga Dam downstream. There maybe periods of several hours when there are no releases from either or both Watts Bar andChickamauga Dams. Rapid turbine shutdown at Chickamauga may sometimes cause periods of Up-sr-eamreverse flow in Chickamauga Reservoir.Based upon discharge records since closure of Chickamauga Dam in 1940, the average dailystreamflow at the plant is 32,600 cfs. The maximum daily discharge was 223,200 cfs on May 8, 1984.Except for two special operations on March 30 and 31, 1968, when discharge was zero to controlmilfoil, the minimum daily discharge was 700 cfs on November 1, 1953. Flow data for water years1951-1972 indicate an average rate of about 27,600 cfs during the summer months (May-October)and about 38,500 cfs during the winter months (November-April). Flow durations based uponChickamauga Dam discharge records for the period 1951-1972 are tabulated below.Average Daily Percent of TimeDischarge, cfs Equaled or Exceeded5,000 99.610,000 97.715,000 93.320,000 84.025,000 69.330,000 46.835,000 31.7Channel velocities at SQN average about 0.6 fps under normal winter conditions. Because of lowerflows and higher reservoir elevations in the summer months, channel velocities average about 0.3 fps.As listed on Table 2.4.1-41, there are 23 surface water users within the 98.6-mile reach of theTennessee River between Dayton, TN and Stevenson, AL. These include fifteen industrial watersupplies and eight public water supplies.The industrial users exclusive of SQN withdraw about 497500 million gallons per day from theTennessee River. Most of this water is returned to the river after use with varying degrees ofcontamination.The public surface water supply intake (Savannah Valley Utility District), originally located acrossChickamauga Reservoir from the plant site at TRM 483.6, has been removed. Savannah Valley UtilityDistrict has been converted to a ground water supply. The nearest public downstream intake is theEast Side Utility (formerly referred to as U.S. Army, Volunteer Army Ammunition Plant). This intake islocated at TRM 473.0.Groundwater resources in the immediate SQN site are described in Section 2.4.13.2.2.4.1.3 T-/A Dam Safety ProqramMost of the dams upstrcam from SON Were designed and built before the hydr metorgica.approach to spillway design had gained- its. currenpt level of acceptance. Spillway design capacity wasgenerally less than weuld be provided today. The original FSAR analyses were based on the existingdam system before dam safety modifications wcrc made and included failure of som~e upstream damsfrom oVertopping.In 1982, P/A officially began a safety review of its dams. The P/.IA DmS-afety Program wasdesigned to be consistent with Fcderal Guidelines for Dam Safety and simil!ar efforts by ether Federal2.4-4 SQN-agnis. T-echnical 6tudios and enginerin 1nay6,86 Were conRducted and physical mod~ifications.mplomon9td to onsure the hydFr4oloi anrd seismic inRtgrity of thA TVA dams and dm-nGStratc thatP./..'s dans can boe .perat.d in accor.Pd.ance. With Managem"ent Agoncy (FEMA)guidelines. Table 2.4.1 5 provides the status of P/A. Damrn Safety AS Of 1 A98These modifications enable these to safely pass the probable maximum flood. The raMininghyd~ologic- mo-dific-ations pla~nnd for Be-ar Crpeeak Da~m andd C-hic-kamauga Dam will not affect SQN ian. manner whiGh Might invalidate the reanalysis deScribed below.In 1997 98, TPA reanalyzed the nu.lcar plant design basis flood events. The purpose of thereanalysis was to evaluate the effects of the hydrologic dam safety modifications on the flooThe following methods anRd assumptions wee applied to the FeaRalysis:1. The computer programs and modeling methods were the sam speiusly used anddo-cumenRted in the FS9A.R.2. Probable maimum timae distrib`ution of precipitaoniO, PreGipitation losses andrscR'oi operating procedures nwere unchanged fonm the original 3. The orFiginal stability analyses and postulated seismic dam failure assumptions woeeGOnsepoatively assumed to occur in the same manner and in combination with the saepevosyRA-If- U;II rt---f-A -KI- M__ C-f-4,.u u. A UPPI: IAF W A Q RMi f; f I-.,- LI n i C ý4 14 T U;Ridne D~rmr Which dmntt thpir sCtrnwturl intporitv for ;; ~C;4Mire Pvnt Aih rpt.-rn n~riindof approXimately 10,000 years.* m 2ii i i i i IiA rle nlaRRed Fnoa1;iravGR 0" "hiGI-amauna r1arn aFFAGFIR the embankment te nQFFRi+ OVORG IRG)was cOnservatively assumed to have been implemented for the purpose Of calculating flEoodeffects. IUnder present existing conditions, the Chikamauga embankment would be eoroded- in the overtopping PMF event and the mxumfloo-d ele-vation at SON woul be lowerFthan that With the miannedl modlification.2.4.2 Floods2.4.2.1 Flood Historyvt,-.ia4)The nearest location with extensive formal flood records is 20 miles downstream at Chattanooga,Tennessee, where continuous records are available since 1874. Knowledge about significant floodsextends back to 1826, based upon newspaper and historical reports. Flood flows and stages atChattanooga have been altered by TVA's reservoir system beginning with the closure of Norris Dam in1936 and reaching essentially the present level of control in 1952 with closure of Boone Dam, the lastmajor dam with reserved flood detention capacity constructed above Chattanooga. Tellico Damprovides additional reserved flood detention capacity; however, the percentage increase in totaldetention capacity above the Watts BarSequoyah site is small. Thus, for practical purposes, floodrecords for the period 1952 to date can be considered representative of prevailing conditions. Table2.4.2-1 provides annual peak flow data at Chattanoogqa. Figure 2.4.2-1 shows the known floodexperience at Chattanooga in diagram form. The maximum known flood under natural conditionsoccurred in 1867. This flood eaeGhedwas estimated to reach elevation 690.5 ft at SQN site with adischarge of about 450,000 cfs. The maximum flood elevation at the site under present-day regulationreached elevation 687.9 ft at the site on May 9, 1984.2.4-5 SQN-The following table lists the highest floods at SQN site under present-day regulation:Estimated Elevation7at SQN (Feet)Discharge,at Chickamauga Dam (cfs)DateBefore RcgulatiO.March 11, 1867 6 0. 5 450,000MaFerh , 1975 686.2 105,000April 3, 1886 684.5 385,000March 7, 1917 680.0 335,000April 5, 1920 676.5 270,000Since PreSent RegulationFebruary 3, 1957 683.7 180,000March 13, 1963 684.8 205,000March 18, 1973 687.0 219,000April 5, 1977 685.0 150,000May 9,1984 687.9 250,000April120. 1998 685.9 180,000May 7, 2003 687.8 225,000There are no records of floodina from seiches. dam failures, or ice Jams. Historic information abouticing is provided in Section 2.4.7.2.4.2.2 Flood Design ConsiderationsTVA has planned the SQN project to conform with regulatory position 2 of Regulatory Guide 1.59including position 2.The types of events evaluated to determine the worst potential flood included (1) Probable MaximumPrecipitation (PMP) on the total watershed and critical subwatershedssub-watersheds, includingseasonal variations and potential consequent dam failures and (2) dam failures in a postulated SafeShutdown Eathquake (SSE) or eae-half-SSEOBE with guide specified concurrent flood conditions.Specific analysis of Tennessee River flood levels resulting from ocean front surges and tsunamis isnot required because of the inland location of the plant. Snow melt and ice iam considerations arealso unnecessary because of the temperate zone location of the plant. Flood waves from landslidesinto upstream reservoirs required no specific analysis, in part because of the absence of maiorelevation relief in nearby uostream reservoirs and because the orevailino thin soils offer small slidevolume potential compared to the available detention space in reservoirs. Seiches pose no floodthreats because of the size and configuration of the lake and the elevation difference between normallake level and plant grade.The computed maximum stillwatermaximum PMF plant site flood level in the reserVoir at the plant sitefFGM aRY-ae is elevation 741.6722.0 ft. This elevation would result from the PMP critically centeredon the watershed as described in Section 2.4.3.Maxim'um le-Vel including wave height is 722.4. This elevation would result from the probablemaximum nrecinitntion critica!lv centered on the waters'hed and a Wind waves based on an overlandwind speed of 45 Mile per hour ..e...... indF from the most critical direction miles per hour wereassumed to occur coincident with the flood peak of the resulting flood. This would create maximumwind waves up to 4.2 ft high (trough to crest).All safety related facilities syste~ms and eoiiinme.nt are hnuisped in stnr'ctures whinh nrnvide nrntectionfrom flooding for all flood conditions up to plant grade at elevation 705.0 ft. See Section 2.4.10 formore specific information.Other rainfall floods will also exceed plant grade7 elevation 705.0 ft- and will nocessitaterequire plantshutdown. Flood warning cr!teria and forecasting techniques have been developed to assure that2.4-6 SQN-grade and are deScrib.,d in Subsections 2.4.10 and 2.4.14, and Appendix 2.4A.Section 2.4.14describes emeraencv protective measures to be taken in seismic events exceedina plant arade.Seismic and GenRu-rent-flood events could create flood levels Which weould excedcause dam failuresurges exceeding plant grade elevation 705.0 ft. The maximum elevation reached in such ar event iselevation 707.9, 2.9 feet above plant grade and 11.7 feet below the controlling event probalmaximum flood (PMF), eXcluding Wind wave conRsiderationAs. In all s.uch e-Vents. therFe is adequate time-fer safe plant shutdowA~n aafte-r the seismicG event and before plant grade would be crossed. TheemnergencY protective mneasures and warning criteria are desc'ribed i'n Sub-sections 2.4.10 and 2.4.14,and Appendix 2.4A.Section 2.4.14 describes emergency protective measures to be taken in seismicevents exceeding plant grade.Most safety related bWuiding accesses are flocatedi at elevatioan 706 orabeove. The acnessecs belowelevation 706 afe withir the powerhouse and Will not be exposed to flooedwater util plant grade isexceeded. Therefore, the structres are protected fromm floedingprior touthce hnd of the cheutdoWpe~ied.Drainage to the Tennessee River has been provided te accommoAdate- runoff from the probalSpecific aralysis of Tennessee River flood levels resulting from oceanfrnet surges and tunamis is Rtereqed beGause of the inland location Of the plantoWmeltand ice jamu cursiderations ate alDs uneGecessary because of the temperate zone location Ofthe plant. Floo~d waves from landslides"E inoupstreamn reser.'eirs required no specific analysis, in pa~tbewicauhs Of th absve nhe of major elevatior relief int earby upstream run uwils and because tfetpfevailing thin soils ofer small slide volume potential cempared to the available detentio ae inteAll safety related facilities, systems, and equipment are housed in structures which provyide protectionRfromR flooding forF all flood conditions up to plant grade at elevation 705.For the condition where flooding exceeds plant grade, as described In Subsections 2.4.3 and 2.4.4, allequipment required to maintain the plant safely duFrig the flood, and for 100 days after the beginningof the flood, is either designed to operate submerged, located above the maximum flood level, orother'.iso protected.Safety Felated For the condition where flooding exceeds plant grade, as described in Sections 2.4.3and 2.4.4, those safety-related facilities, systems, and equipment located in the containment structureare protected from flooding by the shield buildfing. AlShield Buildingq structure with those accessesand penetrations below the maximum flood level in the s-hield- building are designed and constructedas wateF tkjtwatertight elements.Wind wave run up during the PMF at the Diesel Generator Building would reach elevation 723.2 ftwhich is 1 .2 ft above the operating floor. Conseguently, wind wave run up will impair the safetyfunctions of the Diesel Generator Buildino. The accesses and penetrations below this elevation in theDiesel Generator Building are designed and constructed to minimize leakage into the building.Redundant sump pumps are provided within the buildinq to remove minor leakage. Protectivemeasures are taken to ensure that all safety-related systems and equipment in the Emergency RawCooling Water (ERCW) Intake Pumping Station will remain functional when subjected to the maximumflood level.Those Class 1 E electrical system conduit banks located below the PMF plus wind wave run up floodlevel are designed to function submerqed with either continuous cable runs or qualified, type testedsplices.The turbine, cont.ro, and auxilia.y build...Turbine, Control, and Auxiliary Buildings will be allowed toflood. All equipment required to maintain the plant safely during the flood, and for 100 days after the2.4-7 SQN-beginning of the flood, is either designed to operate submerged, is located above the maximum floodlevel, or is otherwise protected.Wind WaVe FRu up during the PMF= at the diesel generator building reaches olevation 7-24.8 which is0.2 feet below the operating flori .C-Rsoquently, Wind wave rUn up will not impair the safety funRctionof systems in the diesel generator building.The accesses and penetratiodns exbelw this elevation iR the diesel generator buMildig are designed andconStruoted to minimize leakage into the buildings. Redundart sUMp pumcps ae pfrovided within tebuilding to remove minor leakage. roterative mneasures acr takenon to enue that all safety relatedsystems and equipmnt in the Emrergeny Raw Coolinqg Water (ERvW) pumt p station Will remstainfunctional when subjected to the maximum flnod level.Class E electrigal cables, lo-cated belo the Proebsable Maximumen Flood (PMF) plus wind wave acivgiand requiFed in a flood, are designed for submrerged opeiratio.2.4.2.3 Effects of Local Intense PrecipitationMaximum water levels at buildings expected to result from the local plant PMP were determined usingtwo methods: (1) when flow conditions controlled, standard-step backwater from the control sectionusing peak discharges estimated from rainfall intensities corresponding to the time of concentration ofthe area above the control section or (2) when ponding or reservoir-type conditions controlled, storagerouting the inflow hsdrograph equivalent to the PMP hydrograph with 2-minute time intervals.Structures housing safety-related facilities, systems, and equipment are protected from flooding duringa local PMF by the slope of the plant yard. The yard is graded so that the surface runoff will be carriedto Chickamauga Reservoir without exceeding the elevation of the external accesses given inParagraph 2.4.1.1 except those at the intake pumping station whose pumps can operate submerged.PMP for the plant drainage system and roofs of safety-related structures was determined fromHydrometeorological Report No. 45 [21. The probable maximum storm used to test the adeguacy ofthe local drainage system would produce 27.5 inches of rainfall in six hours with a maximum one-hourdepth of 14 inches. Depths for each of the six hours in sequence were 1.5, 2.3, 5.0. 14.0, 3.0, and 1.7inches.The separate watershed subareas and flowpaths are shown on Figure 2.4.3-22.Runoff from the 24.5 acre western plant site will flow either northwest to a 27-foot channel along themain plant tracks and then across the main access highway or to the south over the swale inPerimeter Road near the 161-ks switchyard and across Patrol Road to the river. Because the 500-kvswitchyard and TEACP building areas are essentially level, peak outflows from this subarea weredetermined using method (2). These peak outflows were then combined with discharge estimatesfrom the remaining areas, using method (1), to establish peak water surface profiles from both thenorth channel and south swale. The maximum water surface elevation is below critical floor elevation706 and occurs near the east-west centerline of the Turbine Building.The 28.9 acre eastern plant site was evaluated as two areas. Area 1 (19.7 acres) including the dieselgenerator, unit two reactor building, field services/storage buildings and adiacent areas. Runoff fromarea 1 will flow to the south along the perimeter road and across the pavement with low point elevation705.0 ft to the discharge channel. Maximum water surface elevations computed using method (1)were less than elevation 706.0 ft. Area 2 (9.2 acres) includes the office/service, unit one reactorbuilding, office/power stores buildings, intake pumping station, and adiacent areas. Runoff from area2 will flow to the north and west along the ERCW pumping station access road to the intake channeland river. Maximum water surface elevation computed using method (2) is less than elevation 706.Underground drains were assumed clogged throughout the storm. For fence sections, the Manning'sn value was doubled to account for increased resistance to flow and the potential for debris blockage.2.4-8 SQN-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.-Plansurface drainage was evaluated and found capable of passing the locGal probable maximu Ftrwithout FrGchiRg Or eXceeding the floor elevation 706, as fu-ther described, in 2-.235,Evaluation of areal variations Of prohbable maximum sterms showed that the probable-ocring in March centered in the mountains, east of the plant. The flood crest at the plant would be,hximum, disc.harge is 1,236,000 .fS. The probable maximum el1va a e n 719.6,Dam downstream.Two basic storm situations were found to have the potential to produce maximumflood levels at SON. These are (1) a sequence of storms producing PMP depths on the21,400-square-mile watershed above Chattanooga and (2) a sequence of storms producing PMPdepths in the basin above Chattanooga and below the five major tributary dams (Norris, Cherokee,Douglas, Fontana, and Hiwassee), hereafter called the 7,980-square-mile storm. The maximum floodlevel at the plant would be caused bv the March PMP 21,400-square-mile storm. The flood level forthe 7,980-square-mile storm would be slightly less.In both storms, the West Saddle Dike at Watts Bar Dam would be overtopped and breached. No otherfailure would occur. Maximum discharge at the plant is 1,331,623 cfs for the 21,400-square-milestorm. The resultinq PMF elevation at the plant would be 722.0 ft excludinq wind wave effects.2.4.3.1 Probable Maximum PrecipitationProbable maximum precipitation (PMP) for the Tennessee River watershed above SQN has beendefined for TVA by the Hydrometeorological Branch of the National Weather Service inHydrometeorological Report No. 41 Reference [1]. Two basic storm positions were evaluated. One.would produce maximum rainfall over the total watershed. The other would produce maXithe part of the basin downstreamn fromn major TVA tributary reservoirs, hereafter referred to asth7,980 square milo storm. Snowme#tThis report defines depth-area-duration characteristics, seasonalvariations, and antecedent storm potentials and incorporates orographic effects of the TennesseeRiver Valley. Due to the temperate climate of the watershed and relatively light snowfall, snowmelt isnot a factor in generating maximum floods for the Tennessee River at the plant site.Centrsolling PwouP depths for 21,00 square mile and 7,980 square mile areas are tabulated below.72 HouJr Main StormSi. Moiles Antecedent Storm. 6 H-ou 21 Hour 72 Ho-u,21,400 6.7 5 3 11.18- 16.707,980) 8-1 7.02 14.01 20.36-Two basic storms with three possible isohyetal patterns and seasonal variations described inHydrometeorological Report No. 41 were examined to determine which would produce maximum floodlevels at the SQN site. One would Droduce PMP deoths on the 21.400-sauare-mile watershed aboveChattanooga. Two isohyetal patterns are presented in Hydrometeoroloqical Report No. 41 for thisstorm. The isohvetal pattern with downstream center would produce maximum rainfall on the middleportion of the watershed and is shown in Figure 2.4.3-1.Two possible isohyotal patterns producing the total area depths are presented in Report No. 11 .Thesecond storm described in Hvdrometeoroloaical Reoort No. 41 would oroduce PMP deoths on the7,980-square-mile watershed above Chattanooga and below the five major tributary dams. The-eaeto this study is the "downstream pattern" shown in Figure 2..3- 1 The isohyetal pattern for the7,980-square-mile storm is shown in Figure 2.4.3 2. The pattern is not Orographicallygeographically2.4-9 SQN-fixed and can be moved parallel to the long axis, northeast and southwest, along the TennesseeValley. The isohyetal pattern centered at Bulls Gap, Tennessee, would produce maximum rainfall onthe uoDer oart of the watershed and is shown in Fioure 2.4.3-2.~"~'~ir ~'vvm 'nrn" 'r1"~' '~iflTr~r.nnnflT T'~ PM' ~'gIP ~r"~m '~'g~ '~'~" '"~ r'~' ""'~' "" '~*with steor All PMP storms are nine-day events. A three-day antecedent storm was postulated tooccur three days prior to the three-day PMP storm in all PMF determinations. Rainfall depthsequivalent to 40 percent of the main storm were used for the antecedent storms with uniform arealdistribution as recommended in Reoort No. 41.Potential sto~rm amounts differing by seasons were analyzed in SUfficient number to Make ccrtain thatthe March storms would be controlling. Eno~ugh centeFRngs wcrc investigated to assure that a mostposition was used.Seasonal variations were also considered. Table 2.4.3-1 provides theseasonal variations of PMP. The two seasons evaluated were March and June. The March stormwas evaluated because the PMP was maximum and surface runoff was also maximum. The Junestorm was evaluated because the June PMP was maximum for the summer season and reservoirelevations were at their highest levels. Although September PMP is somewhat higher than that inJune, less runoff and lower reservoir levels more than compensate for the higher rainfall.Storms producinig PMP abov. upstream tributaFry dams, ,hose failure has the to createmaximm flood levels, were evaluated in the original FSAR analysis. Dam safety moedifications atupstream tributaFry dams have eliminatod these potential failures aRnd subsequent plant site floodA standard time distribution pattern was adopted for alithe storms based upon major observed stormstransposable to the Tennessee Valley and in conformance with the usual practice of Federal agencies.The adopted distribution is shewn on Figure 2.4.3 3 within the limits stipulated in Chapter VII ofHydrometeorological Report No. 41. This places the heaviest precipitation in the middle of the storm.The adopted sequence closely conforms to that used by the U.S. Army Corps of Engineers. A typicaldistribution mass curve resulting from this approach is shown in Fiqure 2.4.3-3.The PMF discharae at SON was determined to result from the 21.400-souare-mile storm DroducinaPMP on the watershed with the downstream storm pattern, as defined in Hydrometeorological ReportNo. 41. The PMP storm would occur in the month of March and would produce an average of16.25 inches of rainfall in three days on the watershed above Chickamauga Dam. The stormproducing the PMP would be preceded by a three-day antecedent storm producing an average of6.18 inches of rainfall, which would end three days Drier to the start of the PMP storm. Precioitationtemporal distribution is determined bv aDDIvina the mass curve (Fiaure 2.4.3-3) to the basin rainfalldepths in Table 2.4.3-2.The critical probable Maximum stoFrm was deAtermined to be A total basin6 s~to*rm with downstreamneregraphically fixed pattern (Figure 2.4.3 1) which would fellowA an antecedent stoFrm comm~encing OnMarch 15. Translatien ef the PMP from Report Ne. 4 1 to the basin rosults in an antecedent stormproducGing an aege preiitation of 6.4 inches in three days, followed by a three day dry period,ant h en by t hPe man Pstorm~ producing an average precipitation of 16.45 inc-hes inA three days. Figure 2.4.3 4is an iehyetal map of the three day PhMP. Bar sin rainfall depths are given in Table 2.4.3 1.PMP for the plant drainage system and roofs of safety related structures was deteFrmined froMHydrmeteor'elgc3al Report No. 45 [2]. The p"r bable maximum storm used to test the adequaGy ofthe IGal ,drai.age system would -27.5 inches f rainfall in six hours with a maximu.m one houdepth of 14 inchcs. Depths for each of the six hour ien sequence e 1.5, 2.3, 3.0, and 1.72.4.3.2 Precipitation LossesF-FeGlpitatIGR lesses IR tHe pFebable maximum stoFm aFe esumatedWKH multivariable Felati()n6HIPSus. Aedh in the day to day operation of the TVA system. There relationships, develeped from a study offt a" ýWl- M, f-M C3 -, "- " W " W C1 W" "-Atýwan am -wttm to C2 V" -"--/ -2.4-10 SQN-the; week of the year, an antoccdonlt procipitation index (API), and geographic location. TheFelationGhips ar0 suc.h thit the Io6. subtraction from rainfall to compute precipitatioex is greatestat thp nf the sto"rm and decreases to Ro subtFactin When the rainfall totals from 7 to 16inches. losses become zer ORi the late part of ex(trem% e For this probable maximum flood analysis, m.edian m.oisture onditions as determined frm pastrecords were used to determine the API at the start of the storm sequence. The artecedet hs isso large, however, that the precipitation excess computedr fer the later main stom irot sensitive4tvariations in adopted initial moisture conditions. The precipitation loss in the critical probablem Aimm stor~m totals 1.13 inches, 2.30 inches in the antccedcnt storm amonOUting to 36 percent otthe 3 day 6.44 inch rainfall, and 1.83 inches in the mnain stoFrm amRounting toll1 percent of the 3 day,16.46 1nch rainfall. Table 2.4.3 1 displays the API, rain, and precipitation excGess for: each of the1 5 subwatersheds of the hydrologic model forF the SQN probable maximum floed.No precipitation loss; was applied in the pro-bable ma;ximumA stormB o the local area used to test thadequacy of the site drainage system and roofs of safety rolated struc~tures. R-unoff w..as made equatO FainfalU,A multi-variable relationship, used in the day-to-day operation of the TVA reservoir system, has beenaoolied to determine orecioitation excess directly. The relationshios were develoned from observedstorm and flood data. They relate orecioitation excess to the rainfall, week of the year. aeoaraohiclocation, and antecedent precipitation index (API). In their application, precipitation excess becomesan increasinq fraction of rainfall as the storm prowresses in time and becomes equal to rainfall in thelater part of extreme storms. An API determined from an 11-year period of historical rainfall records(1997-2007) was used at the start of the antecedent storm. The precipitation excess computed for themain storm is not sensitive to variations in adooted initial moisture conditions because of the laraeantecedent storm.Basin rainfall, precipitation excess, and API are provided in Table 2.4.3-2. The average precipitationloss for the watershed above Chickamauga Dam is 2.33 inches for the three-day antecedent stormand 1.86 inches for the three-day main storm. The losses are approximately 38% of antecedentrainfall and 11% of the PMP. resoectivelv. The orecioitation loss of 2.33 inches in the antecedentstorm compares favorably with that of historical flood events shown in Table 2.4.3-3.2.4.3.3 Runoff ModelThe runoff model used to determine Tennessee River flood hydrographs at SQN is divided into 4540unit areas and includes the total watershed above Chickamauga Dam. Unit hydrographs are used tocompute flows from these areas. The watershed unit areas are shown in Figure 2.4.3-5. The unitarea flows are combined with appropriate time sequencing or channel routing procedures to computeinflows into the most upstream tributary reservoirs, which in turn are routed through the reservoirs,using standard routing techniques. Resulting outflows are combined with additional local inflows andcarried downstream using appropriate time sequencing or routing procedures, including unsteady flowroutina. Figu-re 2.4.3 5 shows u-nit areas of the watershed uastream from SON.'rk 4FF A 1 A ; fk; .4 + .4 CC A Q A;ff- f k A i.-.-.-.-..-.--..............~......made in some elements of the m.del during PMF. studios fo.r other n.ear plants and those madefrom inforsmatio gained from the 1973 flood, the largest that has- occured during present reservoirGG~ditiORG&Changes are identified when appropriate in the text. They include both additional and revised unithydroGQaphs and additional and revised unsteady flew stream; course models.Unit hydrographs were developed for each unit area for which discharge records were available frommaximum flood hydrographs either recorded at stream n stations or estimated fromreservoir headwater elevation, inflow, and discharge data using the procedures described by Newtonand Vineyard Reference [231. For non-gaged unit areas synthetic unit graphs were developed fromrelationships of unit hvdrographs from similar watersheds relatinQ the unit hvdrograph peak flow to the2.4-11 SQN-drainaae area size. time to oeak in terms of watershed slooe and lenoth. and the shade to the unithydrograph peak discharge in cfs per square mile. Unit hydrograph plots are provided in Figure2.4.3-6 (11 Sheets). Table 2.4.3-4 contains essential dimension data for each unit hydrograph.T-henumber of u-nit areA hasb in crea..d frorm 3 used previou.ly to 15. The d,4e...r.on.e include:1. Use of the model developed for the Phipps Bend study Which cOmbined the wo uRnit areas forW.1atauga River (Sugar Grovye and Watauga local) into one Unit area and divided the Chroeet GateGity uR~tarea into two unit areas (SurgoinSVille locnal and- Cheroekee local below SUrgoinsville);2 UsIeA of the model,4 developed for the Clinch River Reactor which increased the unitareas On the Clinch River from 3 to 11 and the Watts Bar locGal from 1 to 2;3. Changes to add an unsteady flow model for the PFot Loudoun T-ellico DamA complex whichincluded dividi4ng the lower L-ittle TeAnnesseet Rivemr unit Area inotoui ra (Fontaqna to Chilhoweeand Chilhowoe toRlioad the Fort Loudoun locGal unit area into three Unit areas (FrFenchBraRiver Iocal, HolstOn RiveFr Ioal aRnd Fot Ioal); 4. Combining the te unit areas above ..c.e No. 1 (Oce No. 1 Coh.e No. 3) int onunit area (Ocoee No. 1 to Blue Ridge).In addition, eight of the unit graphs have bocn revised. Fmigure 2.1.3 6, which contains 11 sheet-s,shows the unit HY9Froywph. Table 2.4.3 Lo GEuflati esuand identification of those hydregraphs which are new or-+; I iSH- un d r ia" H y ~ F"S riTributary reservoir routings, except for Tellico and Melton Hill, were made using the-GGGd~iGh...th.dstandard reservoir routing procedures and flat pool storage conditions. M44Themain river reservoirs. a.id-Tellico, and Melton Hill routings were made using unsteady flow techniques.This dffe-rs from the previous in that:1. An unsteady flow model has been added for the Fort Loudoun Tellico com..lex, and2. The Chickarfrom tho HEC 2I I I I IILam] inn I If.--I- -hRrkvP;;t44oW mRoo8t Ras P88R revksee using Me 4913 Nood data ana resuimsu-.tpr Amroornm.In the original study, the failure wave hydrograph of the moeuth of the Hiwassee River wasapproximate, for the postulated failures of Hiwasee, Apalachia and Blue Ridge dams a, r described in2.4.4.2.1. In the eassessment,an unRsteady flow model developed dUring the dam.afety studios was used as an adjunct to rou..tel the HiW..assee, Apalachia and Blue Ridge failures in theone half SSE. The model was verified by comparing model elevations in a state of steady flow witheleatinn-.omnutd b h~e staprnda;rd stpm method. ýThis; %WaS dAne for s~tpadv flow-si r~noino fromn25,000 cfs to 1,000.000 cfs.ýj ý7ý ý ý7;ýý ýUnsteady flow routings were computer-solved with athe Simulated Open Channel Hydraulics (SOCH)mathematical model based on the equations of unsteady flow, [3]. Boundary conditions proscribedtiOW HYUFOgFaphs at the 61P6tFeaFA GOURGaFy, GGal IR 9, aA HeadwateF tjtSGHaFge.j-.---...---...--... .---...--..J -~----I-.~.-.-I--.-...,~.-.----------cuPres when geometry cGntrolled.The SOCH model inputs include the reservoir geometry, upstreamboundary inflow hydrograph, local inflows, and the downstream boundary headwater dischargerelationshios based uoon ooeratino auides or ratina curves when the structure aeometrv controls.Seasonal operating curves are provided in Figure 2.4.1-4 (16 Sheets).Discharge rating curves are provided in Figure 2.4.3-7 (17 Sheets) for the reservoirs in the watershedat and above Chickamauga. The discharge rating curve for Chickamauga Dam is for the current lockconfiguration with all 18 spillway bays available. Above SQN, temporary flood barriers have beeninstalled at four reservoirs (Watts Bar. Fort Loudoun. Tellico and Cherokee Reservoirs) to increase theheight of embankments and are included in the discharge rating curves for these four dams.Increasing the height of embankments at these four dams prevents embankment overflow and failureof the embankment. The vendor supplied temporary flood barriers were shown to be stable for themost severe PMF headwater/tailwater conditions using vendor recommended base friction values. A2.4-12 SQN-sin-gle postulated Fort Loudoun Reservoir rim leak north of the Marina Saddle Dam which dischargesinto the Tennessee River at Tennessee River Mile (TRM) 602.3 was added as an additional dischargecomponent to the Fort Loudoun Dam discharge rating curve. Seven Watts Bar Reservoir rim leakswere added as additional discharge components to the Watts Bar Dam discharge rating curve. Threeof the rim leak locations discharge to Yellow Creek, entering the Tennessee River three milesdownstream of Watts Bar Dam. The remaining four rim leak locations discharge to Watts Creek,which enters Chickamauga Reservoir iust below Watts Bar Dam. A single postulated NickajackReservoir rim leak lust northeast of Nickalack Dam and back into the Tennessee River belowNickaiack Dam was added as an additional discharge component for the Nickaiack Dam.The unsteady flow mathematical model for the 49.9 mile long Fort Loudoun Reservoir was divided ntotwenty four 2.08 m~ile reaches. The moedel was verified at thrce gauged points within Fort LoudounReser'oir using 1963 and 1973 flood data configuration for the Fort Loudoun-Tellico complex is shownby the schematic in Figure 2.4.3-8. The Fort Loudoun Reservoir portion of the model from TRM 602.3to TRM 652.22 is described by 29 cross-sections with additional sections being interpolated betweenthe original sections for a total of 59 cross-sections in the SOCH model, with a variable cross-sectionspacing of about 1 mile. The unsteady flow model was extended upstream on the French Broad andHolston Rivers to Douglas and Cherokee Dams, respectively. The French Broad and Holston Rivetunsteady flow moedels werc verified at one gaged point each at m~ile 7.4 and 5.5, respectively, using1963 and 1973 flood data River from the mouth to Douqlas Dam at French Broad River mile (FBRM)32.3 was described by 25 cross-sections with additional sections being interpolated between theoriginal sections for a total of 49 cross-sections in the SOCH model, with a variable cross-sectionspacing of about 1 mile. The Holston River from the mouth to Cherokee Dam at Holston River mile(HRM) 52.3 was described by 29 cross-sections with one additional cross-section being interpolatedbetween each of the original sections for a total of 57 cross-sections in the SOCH model, with avariable cross-section spacing of about 1 mile.The Little Tennessee River was modeled from Tellico Dam, mile 0.3, through Teo!co Reservoir toCOhilho...oe Dam at mAile 33.6. a d upstream Fn-to FonA"tanAR DamR at mAi 6.0. The mode1l AIh,,.'for TellicoResep.vir to C-1hilho..ee Dam was tested for, adequacy by .cm"paring its result. with steady stateP.! #innnfAr n n .4 k 4 ~ARA; A .conveyance in the unsteady flow moedel yielded good agreement. The average conveyance correcticR.U.E. neceesa,'y In t. .a. he.. ..o. -h.....ee Quamn to make the unsteady flow model agree wth thenstandaFrd step methd was also used in the river reach fro.m Ghilhowee to Fontana Dam LittleTennessee River mile (LTRM) 0.3 to Chilhowee Dam at LTRM 33.6. The Little Tennessee River fromTellico Dam to Chilhowee Dam at LTRM 33.6 was described by 23 cross-sections with additionalsections being interpolated between the original sections for a total of 49 cross-sections in the SOCHmodel, with a variable cross-section spacing of up to about 1.8 miles.T-he-Fort Loudoun and Tellico unsteady flow models wefeare joined by a canal unsteady flow model.The canal was modeled with five equally spaced cress Sectin6 at 525 foot itrasfoMr the2,100 foot long canal an interconnecting canal. The canal was modeled using nine cross-sectionswith an average cross-section spacing of about 0.18 miles.The Fort Loudoun-Tellico complex was calibrated by two different methods as follows:(1) Using the available data for the March 1973 flood on Fort Loudoun Reservoir and for theFrench Broad and Holston rivers. The calibration of the 1973 flood is shown in Figure 2.4.3-9(2 Sheets). Because there were limited data to verify against on the French Broad andHolston rivers, the steady-state HEC-RAS model was used to replicate the FederalEmergency Management Agency (FEMA) published 100- and 500-year profiles. Tellico Damwas not closed until 1979, thus was not in place during the 1973 flood for calibration.(2) Using available data for the May 2003 flood for the Fort Loudoun-Tellico complex. Thecalibration of the May 2003 flood is shown in Figure 2.4.3-10 (3 Sheets). The TellicoReservoir steady-state HEC-RAS model was also used to replicate the FEMA published 100-and 500-year profiles.A schematic of the steadv-state SOCH model for Watts Bar Reservoir is shown in Fiqure 2.4.3-11.2.4-13 SQN-The unsteady flow routing model for the 72.4-mile-long Watts Bar Reservoir was divided into thilry four2.13 mnilo roaches. The moedel was verified At b o gaugod points within the reservoir using 1963 flooddatadescribed by 39 cross-sections with two additional sections being added in the upper reach for atotal of 41 sections in the SOCH steady state model with a variable cross-section spacing of up toabout 2.8 miles. The model also includes a iunction with the Clinch River at Tennessee River mile(TRM) 567.7. The Clinch River arm of the model goes from Clinch River mile (CRM) 0.0 to CRM 23.1at Melton Hill Dam with one additional section being interpolated between each of the original 13sections and cross-section spaces of up to about 1 mile. Another iunction at TRM 601.1 connects theLittle Tennessee River arm of the model from the mouth to Tellico Dam at LTRM 0.3 withcross-section spaces of about 0.08 miles. The time step was tested between 5 and 60 seconds whichproduced stable and comparable results over the full range. A time step of 5 seconds was used forthe analysis to allow multiple reservoirs and/or river segments to be coupled together with differentcross-section spacing. The verification of Watts Bar Reservoir for the March 1973 and the May 2003floods are shown in Figure 2.4.3-12 and Figure 2.4.3-13, respectively..TheA schematic of the unsteady flow mathematical model for Chickamauga Reservoir is shown inFigure 2.4.3-14. The model for the total 58.9-mile-long Chickamauga Reservoir was di~ided-OitO..enty eight 2.1 mile reaches prviding twenty nine equally spaced grid points. The grid point at mile483.62 is nearest to the plant, mnile 481.5. The unsteady fleow mo-delviwas verified at four gauged poitW'ithin Chickamauga Reservier using 1973 flood data. This differs from the previous submission in thatthe 19732lo a de fner vierific-ation, replacing the 1963 flood. The 1973 flood occurred drnpreparation of the FSAR and therefore, was not available fo-r ve~rification. The 1973 floo)d is the !argest;.ohic-h has occ-rurre-d si.nce, closure of SoAuth HAolrstPn -Da~m in 19A50. Comparisons between observedand computed stages in Chickamauga Rese.voir are shown in Figure 2.4.3 7described by 29cross-sections with one additional section being interpolated between each of the oriainal 29 sectionsfor a total of 53 sections in the SOCH model with a variable cross-section spacing of up to about 1mile. The model also includes a *unction with the Dallas Bay embayment at TRM 480.5. The DallasBay arm of the model goes from Dallas Bay mile (DB) 5.23 to DB 2.86, the control point for flow out ofChickamauga Reservoir. Another 'unction at TRM 499.4 connects the Hiwassee River arm of themodel from the mouth to the Charleston gage at HRM 18.9. The time step was tested between 5 and50 seconds producing stable and comparable results over the full range. A time step of 5 secondswas used for the analysis to allow multiple reservoirs and/or river segments to be coupled togetherwith different cross-section spacing. The verification of Chickamauga Reservoir for the March 1973and the May 2003 floods are shown in Figure 2.4.3-15 and Figure 2.4.3-16, respectively.it is impossible to verif' the modelsVerifying the reservoir models with actual data approaching themagnitude of the probable maximum.. flooed. The- remaining alternative was to compare the 6 4i a state of steady flow with elevationS omputed by the step mnethod. This was-done for steady fliw rang-Ingu to 1,500,000 cfs. An example shown by the rating curve of Figure2.4.3 A shows the good ag.reement PMF is not possible, because no such events have beenobserved. Therefore, using flows in the magnitude of the PMF (1,200,000 -1,300,000 cfs),steady-state profiles were computed using the HEC-RAS [241 steady state model and compared tocomputed elevations from the SOCH model. An example of the comparison between HEC-RAS andSOCH profiles is shown for Chickamauga Reservoir in Figure 2.4.3-17. This approach was applied foreach of the SOCH reservoir models. Similarly, the tailwater rating curve was compared at eachproject as shown for Watts Bar Dam in Figure 2.4.3-18. In this figure, the initial tailwater curve iscompared to results from the HEC-RAS or SOCH models.The reservoir operating guides applied during the SOCH model simulations mimic, to the extentpossible, operating policies and are within the current reservoir operating flexibility. In addition tospillway discharge, turbine and sluice discharges were used to release water from the tributaryreservoirs. Turbine discharges were also used at the main river reservoirs up to the point where thehead differentials are too small and/or the powerhouse would flood. All discharge outlets (spillwaygates, sluice gates, and valves) for proiects in the reservoir system will remain operable without failureup to the point the operating deck is flooded for the passage of water when and as needed during theflood. A high confidence that all gates/outlets will be operable is provided by periodic inspections byTVA plant personnel, the intermediate and five-year dam safety engineering inspections consistentwith Federal Guidelines for Dam Safety, and the significant capability of the emergency responseteams to direct and manage resources to address issues potentially impacting gate/outlet functionality.2.4-14 SQN-Median initial reservoir elevations for the appropriate season were used at the start of the PMF stormsequence. Use of median elevations is consistent with statistical experience and avoids unreasonablecombinations of extreme events.The flood from the antecedent storm occupies about 70% of the reserved system detention capacityabove Watts Bar Dam at the beginning of the main storm (day 7 of the event). Reservoir levels are ator above guide levels at the beginning of the main storm in all but Apalachia and Fort Patrick HenryReservoirs, which have no reserved flood detention capacity.The watershed runoff Model was verified by using it to reproduce the March 1963 and March 1973floods; the largeSt closure of South Helston Dam. This from the submission in that the 1973 floodM F ia s ddeded fo verificatioR, reping the 1957 flood. Obsen1edvolumes Of precipitation texess were used in Vreifiation. Comparchisons beaweeowbsterVed andfoxputed outflows from Wals Bar and Chickamauga Dams for the 1973 and 1963 floods arc shownin FigUrcs 2.4.3 9 and 2.4.3 10, respectively.From~ a study of the basic unis of the predicting system and its response to alteratiosivaou basicelements, iiscnlddth-at the Model servýes adequately and conservatively to determinRe mnaximumflood levels.2.4.3.4 Probable Maximum Flood FlowThe probable maximum floodPMF discharge at SQN was determined to be I 0001W1 331623 cfs.This flood would result from the 21 ,400-sguare-mile storm in March with a downstream orographically-fixed storm Dattern (Fioure 2.4.3-1).The PMF discharge hydrograph of this flood is shown in Figure 2.4.3-4419. This flood would resultItir" 0 cy CI OCY M ww"o rvczm URY9 p va y Av 5 OFF"Pa .Or '-. ga ..,r"" "Wr" I t,dosc,"bcd in Soetion 2.1...! Tho dam safet'-. modification to Fort Lodon. Teiiice. and Watts BarDams enable them to safely pass the PMF=. The west saddle dikeThe West Saddle Dike at Watts BarDam (Figure 2.4.3-20) would be overtopped and the earth embankment breached. The dischargefrom the failed West Saddle Dike flows into Yellow Creek which ioins the Tennessee River at mile526.82, 41.82 miles above SQN.Chickamauga Dam downstream would be overtopped but was assumed net to fail as a failure wouldreduce the flood level at the site. The dam was oostulated to remain in olace, and any notentiallowering of the flood levels at SQN due to dam failure at Chickamauga Dam was not considered in theresulting water surface elevation.In the original FSAR analysis, the flood would overtop and breach the earth emnbarkmnents of FortLoudon, T-ellicO, and Watts Bar Dams upstream..A. seond candidate is tho 7,980 square mile sto ca...n -tered at Bul1l Gap, Tennessee, 50 milesnrFtheast of Knoxville, shownn in Figure 2.4.3 2. The flood from this storm would overtop and breachthe west saddle dike at Watts Bar Dam. The flood from the 7,980 square m~ile- storm.is the loss criticalstorm and would produce a prbable maximum discharge less th-ian fro-mn the total basin storm.The previous PMF. evaluations considered ' ,nvolving upstream tributary damsDouglas and Watauga. These two situations were shown at that time to be non governing. Damsafet mod-ifica3-tions have Since eliminated the potential failures- of those d-am~s.. Therefore, those twocandidate situa-tions have been eliminated.Reservoir routings started at median observedevi frthe large area P"MP sterms.Median levels were revauaeduinG Ongeratina exacrience for:'1 Tha tnt.,I nrir aid,"-J--- I2.4-15 SQN--2. The five year period, 1972 1976, for those projects whose operating guiddes were changed iBecau.se of the wet years of 1972 1975 and the operating guide changeG, Median eleVat,,ns werehigher fo'r A- of the 13 tributa' y reseroir. w.her rohutiRg iS involved.Normal reeviroeating prOcedurcs were used In the antecedent storm. These used turbine andsluice discharge in the tributary re.e..oirs. TurbiRe discharges ae. ued in.the main riv.rreservois after large, ficoPd- flAýAows develop becausc-;P Ihead- diffre.F-nfials A-rc too t- Small. lNormal operatingproceduFre were used in the stefrm, exept that tufrbine disharge was not Used in either thetributa,"/or main river dams.Concrete Section AnalysisFor concrete dam sections, factors of safety in sliding were determined by comparison of the existinqdesign headwater/tailwater levels to the headwater/tailwater levels that would occur in the PMF asdescribed in Section 2.4.3. The structures were considered safe against failure if a factor of safetygreater than 1.0 for sliding was demonstrated. The dams upstream of SQN passed this test.A IJ SAll oates were aetermineG to be oeerable witnout fa~iuere duFRin the TiOOO. ~Ate m~ain river cams*j ....I I [ tl ' I it:OUic oe TuiiV raisec. tnus rccuiFRGn no accmoiinal ocerations Dv. the i-ast c-a4 9f tnc StoFrm. WnIcn 5i I I Inerore me structures ano access roads would be !nUncatec.Spillway GatesDuring peak PMF conditions, the radial spillway gates of Fort Loudoun and Watts Bar Dams are wideopen with flow over the qates and under the gates. For this condition, both the static and dynamicload stresses in the main structural members of the Watts Bar Dam spillway gate are determined to beless than the yield stress and the stress in the trunnion pin is less than the allowable design stress.The Open radial soillwav oates at other dams upstream of Watts Bar Dam were determined to not failbv comparison to the Watts Bar Dam sDillwav cate analysis.iAeoiaR Rintal reservo~ir eiovailORS were uscc at Me sia~i Of Me sIEorm sequence u68co to Gaene MePMF to be consistent With statistical experience and to avoid unreasonable combinations ofexrmevents. As a result, 53 perccnt of the total reserved system flood detention capacity was occupied atthc start of the mnain flood. This is considered to be amply conservative. The statement made in thePSAR and subsequent versions of the FSAR that 67 percent of the reseVed system detentioncapacit wacuid at the start of the main storm was in erro. The correct percentage as; 233The remaining reserved system detention c~apacity was 67 percent. This e~r-roeous statement wasfirst made in the PSAR and was copied in subsequent statements where the routings were the same.In the revised analysis submitted in Amendment 51, all resroirS are higher or about the sameleainat the beginning of the maRin soto-rm as a res~ult of the revised- starting levels explained inSertfion 24.3.4 of the FSAR. ThiS cOnservative change results in 53 perent of the reservoirsystem detention capacity being upied at the Fstart -f the Main filE)d rFathe thaR 33 in.eis estudies.Neither the initial reservoir levels nor the operatRingules would have signigficaRnteffecn max, imumflood discharges and elevations at the plant site because hpillway apa"ities, anRd h8nce, conRditions, wore reached earl" in the flood.The procedures used to determine if and when an overtopped earth embankment would fail and theproaedures for omputinRg the effect Of such are desc-ribed in 2 4 2 a ntd 2. 4.,.3In testing the adequacy of the yard drainage system, to safely pass the site PMP, all undergrounddrains were assumed Glaced anRd the Gfqae drFain"ace to be fullWaterborne Obiects2.4-16 SQN-Consideration has been given to the effect of waterborne obiects striking the spillway gates and bentssupportinq the bridge across Watts Bar Dam at peak water level at the dam. The most severepotential for damage is postulated to be by a barge which has been torn loose from its moorings andfloats into the dam.Should the barae aDoroach the sPillwaY Portion of the dam end on. one bridae bent could be failed bvthe barae and two spillwav gates could be damaaed and possibly swept away. The loss of one bridaebent will likely not collapse the bridce because the bridge girders are continuous members and thestress in the girders is postulated to be less than the ultimate stress for this condition of one supportbeing lost. Should two -gates be swept away, the nape of the water surface over the spillway weirwould be such that the barge would likely be grounded on the tops of the concrete spillway piers andprovide a partial obstruction to flow comparable to un-failed spillway gates. Hence the loss of twogates from this cause will have little effect on the peak flow and elevation.Should the barqe approach the spillway portion broadside, two and possibly three bridge bents mayfail. For this condition the bridae would likelv collaDse on the barae and the barae would be aroundedon the tops of the soillwaY Diers. For this condition the barae would likelv around before strikina thespillway gqates because the gqates ale about 20 ft downstream from the leg of the upstream bridgqebents.Lock GatesThe lock gates at Fort Loudoun, Watts Bar, and Chickamauga were examined for possible failure withthe conclusion that no potential for failure exists. The lock gate structural elements may experiencelocalized vieldina and may not function normally followina the most severe headwater/tailwaterconditions.2.4.3.5 Water Level DeterminationsThe controlling PMF elevation at the SQN was determined to be 722.0 ft, produced by the21,400-sauare-mile storm in March and coincident with overtopping failure of the West Saddle Dike atWatts Bar Dam. The PMF elevation hydrograph of the controlling PIIF, ..esting at elevation 719.66, isshown on Figure 2.4.3 221. Computation of both the probable maximuRmF discharge hydrOgraph(FiguIe 2.4.3 11) and the elevation was accoFmplished usingthe unsteady flow techniques Elevations were computed concurrently with discharges using the SOCHunsteady flow reservoir model described in Section 2.4.3.3.The leG critical arca producing P,- MP deptho n. the 7,980 square Mile watershed wouldproduce crest elcation 718.9 at the plant site.Maximum water levels at buildings expected t , result frm the local plant PI.-P were determined siR-nl~mo methods: (1) when flow conditions controlled , standard step backwater ferom the con-trol eciousn eak discharges estimated from rainfall1 intensities corresponding to the time9 Of concenA-tration ofthe araabove the cOnMro section or (2) when pending Or r8eseVoir type conditions controlled, storagerouting the inflow hydrograph equivalent to the PMVP hydregraph with 2 min'ute time intervals-.The separate watershed,- subareas fTowpaths are ..shown.. o. F 2.4.3 1aRunoff fromF the 21.5 acre western plant site will flew e-ither norFthwest to a 27- foot channFel along themna in p la nt tracA-k s anAd- thePn across-r, .the- mai acces s h ig hwa y orF to the sou th P'over the sw abe inPeFrimeter Road n ear the 16-1 kA/ &9.Aitchyard and acror-ss Pat-rol Roaid to the river. Because the 500 01switchyard and T-EACP building areas are essentially level, peak eutffowis fro~m this. su,-ba-rea weredetermined using method (2). These peak euA94ows; wAere then combn-ined- w~ith discharge estimatesfrom the rmiigresusnmehd()tostablish peak water surface profiles from both thenorth channel and south swae. The maximum water surace elevation is belo-w critical floor elevation706 and occurs near the east west centerline of the T-urbine Building.The 28.9 acre eastern plant site was evaluated as two areas. Area 1 (19.7 acrFes) inRluding the diesel2.4-17 SQN-generator, unit tWO reactor building, fiel.d soe.PxrvicosIstorage buildings and adjacen.t areasb. Runoff fromarea-i-will flow to the south along the perimeter road and across the pavoment With l0W point elevation705.0 to the diScharge channol. Maximum water su~face elevationS cOMputed using m~ethod (1) wercless than elevation 7-06. Area 2 (9.2 acres) includes the of:AGce/seVice, unit one reactor building,officeipower stores buildings, intake pumnping station, and adjacent areas. Runoff frmarea 2 will flowto the north and west along the E=ROW pumping station access road to the intake channe! and riVcr.Un~derground drains were assum~ed clogged throughout the sto-rm. Fo-r fenc~e ssect-ions, the MeaRn4gsR value was doubled to account for increased resistance to flew and the potential for debris bloc~kage.The only stream adjacent to SQN is the Tennessee River. There are no streams within the site. The1 percent chance floodplain of the Te~nnejssee River at then site is delineated on Figure 2.4.3 14.DePt-ails nof the analyses used in the computation of the 1 percent chance flood flow and water ctcvatienare described in a study made by TVA for the Federal Insurance Administration (P!A) and publishediFebrua~' 1979[5].The only structures located in the 1 percent c-ha;nceP floodplain are transmission towers, the intakepming station skimmer wall, and the ERCWV pump station deck. The ERCW pumps are located OntrUct-res are shown on Figure 2.4.3 14.The strUctures that Iocated in the ill net flond flows nr elevaltinns The20,650 square mile drainage area is not altered and the reduction in flow area at the site igenerated from it will be minimal and will present no problem to downstream facilitis2.4.3.6 Coincident Wind-Wave ActivitySome wind waves are likely when the probable maximum flood crests at SQN. The flood would benear its crest for a day beginning about 2-1/2 days after cessation of the probable maximum storm.The day of occurrence would most likely be in the month of March or possibly the first week in April.A conservatively high velocity of 45 miles per hour over water was adopted to associate with theprobable maximum flood crest. A 45-mile- per-hour overwater velocity exceeds maximum Marchone-hour velocities observed in severe March windstorms of record in a homogeneous region asreported by the Corps of Engineers [6].That a 45-mile-per-hour overwater wind is conservatively high, is supported also by an analysis ofMarch day maximum winds of record collected at Knoxville and Chattanooga, Tennessee. Therecords analyzed varied from 30 years at Chattanooga to 26 years at Knoxville, providing samplesranging from 930 to 806 March days. The recorded fastest mile wind on each March day was usedrather than hourly data because this information is readily available in National Weather Servicepublications. Relationships to convert fastest mile winds to winds of other durations were developedfrom Knoxville and Chattanooga wind data contained in USWB Form 1001 and the maximum storminformation contained in Technical Bulletin No. 2 [6]. From the wind frequency analysis it wasdetermined that the 45-mile-per-hour overwater wind for the critical minimum duration of 20 minuteshad an 0.1 percent chance of occurrence on any given March day.The probability that this wind Might occur on the8 specific day that the probable maXimRum flood wouldc-rest is, extremely remeto. E.ven assuming that the floo9d w.Aas- to crest once during the 40 ye-ar plantlife, the probability Of the wind occurring on that particular day is in the order of 1 X 1 0~-TA es6t*iate that the probability, of the food and wind occurring n givena O the same day tobe in the ordJer of 1 x e 10~4--4~Computation of wind waves was made using the procedures of the Corps of Engineers [7]. The criticaldirections were from the north-northwest and northeast with effective fetches of 1.7 and 1.5 miles,2.4-18 SQN-respectively. For the 45-mile-per-hour wind, 99.6 percent of the waves approaching the plant wouldbe less than 4.2- and 4.0-foot-high crest to trough for the 1.7- and 1.5-mile fetches as shown onFigures 2.4.3 524 and 2.4.3-4625. Maximum water su, a...es. in the .eser..i. approaching the plantwould be 2.8 and 2.7 feet abo'e the maximum computed leVel' or ele-Vations 722.4 and 722,3,F8GPeGtively.OnlV the most critical fetch length of 1.7 miles is used to determine the design basis floodelevationsThe maximum water level attained due to the PMF plus wind-wave activity is elevation 72-,.726.2 ft atthe ERCW pump station and the nuclear island structures (shield, auxiliary, and centrol buildingqShieldAuxiliary, and Control Buildings).The wind waves approaching the Diesel Generator Building and cooling towers break before reachingthe structures due to the shallow depth of water. The topography surrounding these structures is suchthat the wind waves will break on a steeper slope (4H:1V) than the slope immediately adjacent to thestructures. This is shown by Figure 2.4.3 726.The runup estimates are on the basis that th incminnd waves break hbfnre reachingthe StrutuFe aRnd then reform for a shallwer wateFr deptfh. This reformed wave then approaches theStructure. The runups are lower than the maximum reseo-oir level due to the small wave height for therefo.r.m.e.,d wa.ve, the shallow wat.., andh, very shallow slope b'for, reaching the structure..Wind-wave runup coincident with the maximum flood level for the diesel generator buildirgDieselGenerator Building and cooling towers (Figure 2.4.3-26) is elevation 72-1.723.2. The level insidestructures that are allowed to flood is elevation 720.1. The flood elevations used as design bases aregiven in Section 2.4A.4 2.4.14.1.1.Dynamic Effect of Waves1. Nonbreaking WavesThe dynamic effect of nonbreaking waves on the walls of safety- related structures wasinvestigated using the Rainflow Method [8]. As a result of this investigation, concrete andreinforcing stresses were found to be within allowables.2. Breaking WavesThe dynamic effect of breaking waves on the walls of safety-related structures was investigatedusing a method developed by D. D. Gaillard and D. A. Molitar. The concrete and reinforcingstresses were found to be less than the allowable stresses using this method.3. Broken WavesThe dynamic effect of broken waves on the walls of safety-related structures was investigatedusing a method proposed by the U.S. Army Coastal Engineering Research Center [7]. Thismethod of design yielded concrete and reinforcing stresses within allowable limits.All safety-related structures are designed to withstand the static and dynamic effects of the waterand waves as stated in Section 2.4.2.2.2.4.4 Potential Dam Failures, (Seismically anAd Otherise-Induced)The procedures described in Appendix A of Regulatory Guide 1.59 were followed when evaluatingpotential flood levels from seismically induced dam failures.The plant site and upstream reservoirs are located in the Southern Appalachian Tectonic Provinceand, therefore, subject to moderate earthquake forces with possible attendant failure. Upstream damswhose failure has the potential to cause flood problems at the plant were investigated to determine iffailure from seismic events would endanger plant safety.2.4-19 SQN-It should be clearly understood that these studies have been made solely to ensure the safety of SQNagainst failure by floods caused by the assumed failure of dams due to seismic forces. To assure thatsafe shutdown of the SQN is not impaired by flood waters, TVA has in these studies addedconservative assumptions to be able to show that the plant can be safely controlled even in the eventthat all these unlikely events occur in must the proper sequence.By furnishing this information TVA does not infer or concede that its dams are inadequate to withstandearthquakes that may be reasonably expected to occur in the TVA region under consideration. TVAbelieves that multiple dam failures are an extremely unlikely event. The TVA Dam Safety Program(DSP), which is consistent with the Federal Guidelines for Dam Safety [251, conducts technical studiesand engineering analyses to assess the hydrologic and seismic integrity of agency dams and verifiesthat they can be operated in accordance with Federal Emergency Management Agency (FEMA)guidelines. These guidelines were developed to enhance national dam safety such that the potentialfor loss of life and property damage is minimized. As part of the TVA DSP, inspection andmaintenance activities are carried out on a regular schedule to confirm the dams are maintained in asafe condition. Instrumentation to monitor the dams' behavior was installed in many of the damsduring original construction and other instrumentation has been added since. Based on theimplementation of the DSP, TVA has confidence that its dams are safe against catastrophicdestruction by any natural forces that could be expected to occur.2.4.4.1 Dam Failure PermutationsThere are 20 major dams above SQN. Dam locations with respect to the SQN site are shown inFigure 2.4.1-3. 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; Norris,Melton Hill, Fontana, and Tellico Dams between Fort Loudoun and Watts Bar: and Chatuqe, Nottely,Hiwassee, Apalachia, Blue Ridge, Ocoee No. 1, Ocoee No. 2, and Ocoee No. 3 emptying intoChickamauqa Reservoir. These were examined individually, and in getufpscombinations, to determineif failure might result from a seismic event and. if suhso would failure or failures occurringGcnurent4Iyconcurrent with storm runoff weu4-create nritalmaximum flood levels at the plant.Two sotuation wer Reaid: (1) a one half Safe Shutdown Earthquake (SSE=) as definod inSubsection 2.5.2, imposed concurrently With one half th p ,robable m :axim.um. flood and (2) a SafeShutdwn Earfthquake (SSE) as defined ir Subsectien 2.5.2, imposed contUrhrentl with a 25 yearflood. Ncither of these conditionRS would croate levcls greater than the h;Ydrologic probable maximAumflood at SQN, described previously in 2.4.3. Details of the da~m f-ailur-e analysis aro discussed innoOGBOR lt.4.4.4, Dam FamuFe r-eFFRUt=tIC'RII he~ proiUdueUes r~ei eU LO in r-\eru~dLUIX V~~d r-\%U IP.AJ II .Appendix A, were followed for evaluating potential flood levels from seismically induced dam failures.In accordance with this guidance, seismic dam failure is examined using the two specified alternatives:(1) the Safe Shutdown Earthquake (SSE) coincident with the peak of the 25-year flood and atwo-year wind speed applied in the critical direction,(2) the Operating Basis Earthquake (OBE) coincident with the peak of the one-half PMF and atwo-year wind speed applied in the critical direction.The OBE and SSE are defined in Section 2.5.2.4 as having maximum horizontal rock accelerationlevels of 0.09 q and 0.18 q respectively. As described in Section 2.5.2.4, TVA agreed to use 0.18 q asthe maximum bedrock acceleration level for the SSE.Failure Of Chickamauga Da,,, downstream, can affoct cooling wat.r supplies at the plant.Consequently for conser.atism, an arbitray fail'ue was imposed. This resulting would notbe critical to plant operation, as discussed in Section 2.4.11.6. From the seismic dam failure analysesmade for TVA's operating nuclear plants, it was determined that five separate, combined events havethe potential to create flood levels above plant grade at Watts Bar Nuclear Plant. These events are asfollows:2.4-20 SQN-(1) The simultaneous failure of Fontana and Tellico Dams in the OBE coincident with one-halfPMF.(2) The simultaneous failure of Fontana, Tellico, Hiwassee, Apalachia, and Blue Ridge Dams inthe OBE coincident with one-half PMF.(3) The simultaneous failure of Norris and Tellico Dams in the OBE coincident with one-half PMF.(4) The simultaneous failure of Cherokee, Douglas, and Tellico Dams in the OBE coincident withone-half PMF.(5) The simultaneous failure of Norris, Cherokee, Douglas, and Tellico Dams in the SSEcoincident with a 25-year flood.Tellico has been added to all five combinations which was not included in the original analyses forTVA's operating nuclear plants. It was included because the seismic stability analysis of Tellico is notconclusive. Therefore, Tellico was postulated to fail.2.4.4.1 Reservoir _DescriptionCharactoristics of dams that influence ivoer cenditions at SQN are contained in Tables 2.4.1 1 and2.44 2. location with respect to the plant as shewn on Figure 2.1.1 1. safety criteFia.:ere not inore~porated in the design of dams6 upstream froM SQN, eXcopt TellicO and_ Norris. Thosehaving a potential to influehnce plant flodinRg levels examined, as de,. ribcd in Scctio-inElevation storage relationship, and seasenally varying steoage allocatiens in the major projects areshown On the 14 she-ets of Figure 2.4.1 3.2.4.4.2 Dam F~ailure PermutationsThe plant site and upstreamA reservoirs arc located in the Southern AppalachiaR T-ectonic ProVinceand, therefore, su1bject to moderate ea~thquake for~es with possible attendant failure. All upstreadams, whose fa.iure has the potential to cause flood problems at the plant, were indestigated todetermine if failure fromn seimSFic Or hydrologic eventS would endanger plant safety. Potential failurefrem both seiscn and hydraonlgic eeAnts and the esuflinsg conseque nce are discused in this section.it should be cleary understood that these studies have been made solely to ensure the safety of SQNagainst failWe by floods. caused frFo exessive rainfall Or by the assumphed failure Of dams due toseismFic forces. To assure that safe shutdown of SQN is, not impaired by flood wators, TVA has inthese stuidios; a-d-deAd censervative assumptio-ns to coenservative assumptions to be able to show thatthe plant can be safely controlled even in the event that all these unlikely events occur in just thepro)per sequence. TVA is of the stronRg opinionR that the chances~_ of the assumed events occurringapproach zero9 probability.B3y furnishing this- info~rm~ation, TVA does RAM inferF Or concede that its dams6 are inadequate tow~ithstand great floods, and~er ea~thquakes that may be reasonably expected to occur in the TVreio unjder consideration. TVA has a programn Of inspection and main~tenance carried out on aregular schedlule to keep its damsG safe. Isrmnainof the dams6 to help keep check en theirbehavioar Wars, installedin many of the dams6 duFrig original construction. O-the-r instruSmenaBItionA hasbeen added since and isstill being added a6 the need may appear or as new techniques becom~eavafilab~eIn sheot, TVA has confidence that its dams, are safe against catastrophic destruction by any naturalforces6 th-at coeuld- beP oXoocte~d to_ occur.2 4 4 2 1 RAORmir_ F=iiiir An;;IvrRi2.4-21 SQN-Seismic failure aRna!yss consisted of the following:r i i i

• il l I I 4I IP mP r iI1. _eterminaven of tne water level at te plant during one half the M~t With f u, reser o.rs i its,creSts were aumimented by noee waves tro4e tnh Peostuilateet tailure Oft u,6toamn edars drinG aenie halfSSE.J2. 'Ueterm:nAtien of the w.atper level -at the olant drinp Ea 2!iea;r flood full rpeervirs if iU restsf.... r .. ....-- ý --- jwere augmented by flood waves ftrom the postulated faiUreto upstreamn damns during a SafShutdoWn Earthquake (SSE+.The one half SSE Identified in conditionR 1 is defincd in FSAR Section 2.5.2.4 as having a peakhorizontal acceleration value of 0.09 g at the rock foundation. The discussion in Stin2-5,2.4vshows the eXtFreRe conservatism contained in the analy6is.In the 1998 reanalysis all potentially critical seismic events involvYing dam failure upstream of the plantsite were reevaluated. The six events included the postulated one half SSE, failure of (1) Norris, (2)Fontana, (3) Cherokee Douglas, and (1) Fontana Hiwassee Apalachia Blue Ridge during one half theLoudoun Tellico during a 25 year flood.Seismic- failure of upstream dams during nonflood periods pose no threat to the plant-.,summtreof the result of the ......an.lysis isgiven ,in T-able2.41. 1. SU0Nandupstream damsae ,located asshownR, .. Figure 2..1 1. The highest flood level.at SON from different seismic damfailure and flood combinations; would be elevationF 70)7.9 from simultaneous failure Of Fon~tana Darn Onthe Little Tennessee River and Hiwassee, Blue Ridge, and Apalachia Dams OR the Hiwassee Riverduring a ene half 6afe shutdown earthquake coincGident with one half the PMF=. This includesimprov~emets resulting fromn modifications pe~fermed- fo-r the Dam Safety Programn. Wind waves couldraie te eevaionto7096 i th reervir Runup could reach elevation 710.4 On a 4:4 slope toelevation 712.8 On a VeFtical wall in shallow (4.9 feet) water, and to elevation 710.4 en Oa vFtiGal wall indeep wateF.Only stn ather seismic dam failure combination With conident foimmdbs could cause elevatiors abovepat g~ade.Plant safety would be assured by shutdOgn prier to these floods crossing plart grade, elevation 705,using the warning system described in Appendix 2.1A.T-he effect of postulated seismic bridge failure and resulting failure Of spillway gate anchors at WattsBar and Fort Loui-doaun Dams would not cr-eate a safety hazard at SQN.Prer-e dwesConcrete StructuresThe standard method of computing stability is used. The maximum base compressive stress, averagebase shear stress, the factor of safety against overturning, and the shear strength required for ashear-friction factor of safety of 1 are determined. To find the shear strength required to provide asafety factor of 1, a coefficient of friction of 0.65 is assigned at the elevation of the base underconsideration.AG stated in Sec~tion 2.4.1.2, all of the original stability analyses and postulated dam failueassum...ptions in the 1998 FeaRalyses were coRseprvtively assumed to occu in the same manner and incombination with the same postulated rainfall events.The analyses for earthquake are based on the pseudo-static analysis method as given by Hinds [10]2.4-22 SQN-with increased hydrodynamic pressures determined by the method developed by Bustamante andFlores [11]. These analyses include applying masonry inertia forces and increased water pressure tothe structure resulting from the acceleration of the structure horizontally in the upstream direction andsimultaneously in a downward direction. The masonry inertia forces are determined by a dynamicanalysis of the structure which takes into account amplification of the accelerations above thefoundation rock.No reduction of hydrostatic or hydrodynamic forces due to the decrease of the unit weight of waterfrom the downward acceleration of the reservoir bottom is included in this analysis.Waves created at the free surface of the reservoir by an earthquake are considered of no importance.Based upon studies by Chopra [12] and Zienkiewicz [13], it is eu*TVA's judgment that before waves ofany significant height have time to develop, the earthquake will be over. The duration of earthquakeused 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 effectof silt on structures is not considered. There is only a small aFmo-nt of silt noW present, and th Theaccumulation rate is slow, as measured by TVA for many years [14].EmbankmentEmbankment analysis was made using the standard slip circle method, except for Chatuge andNottely Dams where the Nemark method for the dynamic analysis of embankment slopes was used.The effect of the earthquake is taken into account by applying the appropriate static inertia force to thedam mass within the assumed slip circle (pseudo-static method).In the analysis, the embankment design constants used, including the sheer strength of the materialsin 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 throughthe soil has been assumed based on previous studies pertaining to TVA nuclear plants. Thesestudies have indicated maximum amplification values slightly in excess of two for a rather wide rangeof shear wave velocity to soil height ratios. For these analyses, a straight-line variation is used with anacceleration at the top of the embankment being two times the top of rock acceleration.As discussed in Section 2.4.3, temporary flood barriers are installed on embankments at Cherokee,Watts Bar, Fort Loudoun and Tellico Reservoirs. However, the temporary flood barriers are notrequired to be stable following an OBE or SSE and are not assumed to increase the height of theembankments for these loading conditions.Flood RoutingThe runoff model described in Section 2.4.3.3, which includes unsteady flew medels for criticalrospoer/irs and riVer roaches6, Was used to reevaluate plant Site flood- leVels re-sulting from thepestulated SSE and one;, half SRI= dam failu- r cob The remaining eventS prodIuced plant6site flooed levels sufficiently lower than the controlling9 events and wore not evaluated, was used toreevaluate five potentially critical seismic events involving dam failures above the plant. Other eventsaddressed in five earlier studies (the postulated OBE single failures of Watts Bar and Fort Loudoun;the postulated SSE combination failure of Fontana and Douglas, the postulated SSE combinationfailure of Fontana, Fort Loudoun, and Tellico; the SSE combination failure of Norris, Douglas, FortLoudoun and Tellico, and the single SSE failure of Norris) produced plant site flood levels sufficientlylower than the controlling events and therefore were not re-evaluated.The procedures prescribed by Regulatory Guide 1.59 require seismic dam failure to be examinedusing the SSE coincident with the peak of the 25-year flood, and the OBE coincident with the peak ofone-half the PMF.Reservoir operating procedures used were those applicable to the season and flood inflows.2.4-23 SQN-ThiG s-ction was rev..,, with a major rearrangoment to l'cato the ..nrol +.n, e...t.. .Valu.,atod in thevvI

• J Ill1 uuQ anayiS.. .irst AnA te non. contro,- in. eVentS. Wnin wo not re cacuate later. I Te no noconroiiing events aro ieR in tne zi-'oN- Tar nlistry.One-half SSE Concurrent With One-Half the Probable Maximum FloodPrevious evaluations have been made which determined flood levels at SQN for potentially criticalevents. Re-evaluations made later using the updated runoff model described in Section 2.4.3.3 andincluding the Dam Safety Program modifications did not determine flood levels for those events whichwere previously shown to clearly not be controlling. The 1998 analysis for determining the effects ofthe Dam Safety Program modifications determined that non-flood related seismic dam failure eventsclearly pose no threat to the plant. Flood levels were determined for six combined seismic/floodevents. Only two of these controlling seismic/flood events would exceed plant grade. These twoevents consist of multiple dam failures on (1) Little Tennessee/Hiwassee, and (2) Clinch/UpperTennessee rivers with flood levels at SQN of El. 707.9 and 706, respectively. The following is detaileddescriptions of the potentially critical controlling events including reevaluated flood levels, followed bybrief descriptions of the non-controlling failure events previously evaluated.* I I D" I lJ f li *ml ......Altflugfl conirde Fe, as aiscussed iR the TolloWing paragrapfls, T VA iDelieVos thlat mnultiple damnfailuros aro an extremely unlikely event. TVA's search of the literature reeal no recOrd- of failure-oconcrete dams erm earthquake. The postulation of an SSE Of 0.18 g acceleration is a veryoRnserFative upperF im it in itself (as stated in Scrtion., 2.5.2). In addition, the SSE must beo ol atod in a.Fcn' precise seg!pa to have the potential for multiple dam failures.SSE= In onrder to fail three dams Nforri, heenkte, and Douglas the epiceste r of a SSE m'ust boconfined to a relatively small area, the shape of a football, about 10 miles wide and 20 miles long. Inorder to fail four dams Norris, Douglas, Fort Loudoun, and Teolco the epicenter of an SSE= m:ust bcnfinedJ to a tiangular arean With sides -f approximately 1 mile in length. However, as ar extremeupper limit the above tWo com~binatfionRs of dams are postulated to fail as well as the Gembinatiens of(1) Fort Loudoun, Tollico, and Fontana; (2) Fontana and Douglas; and (3) Fontana ;And the sixHiwa;rsse River dams& The 1098 Fe analysis, determined that only the fir-st ton com.rbinations arecontrolling and need to be consi;dereFPd_. Only the Norris Cherokee Douglas event would oxceoed plang -deelevatinOne half SSE= Attenu atioin studies of the one half SSE= show that there arc three combinatiOns atsomultaneous failures Of morGe than one dam which need to be conRsidered With respect to SQN safety.:hich are discussed below. These are (1) Cherokee Douglas, (2) Fontana Hi4wassec Apalachia BuRidge, and (3) Hiwassee Apalachia Bllue Ridge Gsoee No 1. Nottely. The 19998 re analysisdetermined that only the first two comFbinationRs are controlling and need to be considered. Only theFoentana Hiwasse Apalachia Blue Ridge evenAt woul)exeed plant graeThe following descriptionRs arc first forthe contro9lling events for which flooAd- 'levels o~realuaefothe_ 1998 rFeanalysis, followed by the non contro9lling evenIts ýw~hic~h wer-e not Fe analyzed in 1998.One half S-SEFOBE Concurrent With One-Half the Probable Maximum Flood (Controlling Events)Watts Bar DamStability analyses of Watts Bar Dam powerhouse and soillwav sections result in the iudament thatthese structures will not fail. The analyses show low stresses in the spillway base, and thepowerhouse base. Original results are given in Figure 2.4.4-1 and were not updated in the currentanalysis. Dvnamic analysis of the concrete structures resulted in the determination that the baseacceleration is amplified at levels above the base. The original slip circle analysis of the earthembankment section results in a factor of safety greater than 1, and the embankment is iudged not tofail as shown in Figure 2.4.4-22.2.4-24 SQN-For the condition of peak discharge at the dam for one-half the probable maximum flood the spillwaygates are in the wide-open position with the bottom of the gates above the water. This condition wasnot analyzed because the condition with bridge failure described in the following paragraphs producesthe controlling condition.Analysis of the bridge structure for forces resulting from the OBE, including amplification ofacceleration results in the determination that the bridge could fail as a result of shearing the anchorbolts. The downstream bridge girders are assumed to strike the spillway gates. The impact of thegirders striking the gates is assumed to fail the bolts that anchor the gate trunnions to the pieranchorages allowing the gates to fall on the spillway crest and be washed into the channel below thedam. 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.Previous evaluations determined that if the dam was postulated to fail from embankment overtoppingin the most severe case (gate opening prevented by bridge failure) that the resulting elevations atSQN would be several ft below plant grade elevation 705.0 ft. Therefore, this event was notreevaluated.Fort Loudoun DamStability analyses of Fort Loudoun Dam powerhouse and spillway sections result in the iudgment thatthese structures will not fail. The analyses show low base stresses, with near two-thirds of the base incompression. The original results given in Figure 2.4.4-2 were not updated for the current analysis.Slip circle analysis of the earth embankment results in a factor of safety of 1.26, and the embankmentis iudged not to fail. The original results given in Figure 2.4.4-3 were not updated in the currentanalysis.The spillway gates and bridge are of the same design as those at Watts Bar Dam. Conditions offailure during the OBE are the same, and no problems are likely. Coincident failure at Fort Loudounand Watts Bar does not occur.For the potentially critical case of Fort Loudoun bridge failure at the onset of the main portion ofone-half the probable maximum flood flow into Fort Loudoun Reservoir, in an earlier analysis it wasfound that the Watts Bar inflows are much less than the condition resulting from simultaneous failureof Cherokee, Douglas, and Tellico Dams as described later.Tellico DamAlthough, not included in the original analyses for TVA's operating nuclear plants, The concreteportion of Tellico is iudged to fail completely because the seismic stability analysis of Tellico is notconclusive. No hydrologic results are given for the single failure of Tellico because the simultaneousfailure of Tellico Dam with other dams discussed under multiple failures is more critical. Theembankments at Tellico are stable (Figure 2.4.4-23)..4-Norris DamReuls f the Norris Dam stability analyses for a typical 6pillWay block and a typical non oeverfowsection of height ;;r r.hwn n Figure 2.4.4 8. Because only a small percentage Of thespillway bare is in compre..ion, this structure is judged to fail. The high non ov..ow section .ith -small percentage o the base in compression ande with high comprE) si.. and shearing stre.ses is alsojudged to ailAlthough an evaluation made in 1975 by Agbabian Associates concluded that Norris Dam would notfail in an OBE (with one-half PMF) or SSE (with 25-year flood), the original study postulated failure inboth seismic events. To be consistent with prior studies, Norris was conservatively postulated to fail.2.4-25 SQN-Figure 2.4.4-94 shows the likelypostuIated condition of the dam after OBE failure. Based on stabilityanalys 6, the non oVeoflOW blocks rem~aining in placo aro judged to withstand thc- o-no half SSE.vi,^ t^:l k ...... ,,4. .... * .vPAtf.,"L -A,2 ";4 t f.i ; -rV rlI,.The location of the debris is not based on any calculated procedure of failure because it is believedthat this is not possible. It is TVA's judgment, however, that the failure mode shown is one logicalassumption; and, although there may be many other logical assumptions, the amount of channelobstruction would probably be about the same.The discharge rating for this controlling, debris section was developed from a 1:150 scale hydraulicmodel at the TVA Engineering Laboratory and was verified closely by mathematical analysis.in the hydrologic routing for this failure, MeltOn Hill DamR was postulated to fail when the flood wavereached headwater elevation 804, based On Structural analysis. The headwator at Watts Bar Damnw:ould reach elevation 758.1, 8.9 fcct below top of dam. The west saddle dike at Watts Bar Damw:ould be overtopped and brcachcd. A cOmnplete washout of the dike was assumed. The resultinlgw~ater level at the nuclear plant site is 698.1. 6.9 fect bclow plant grade 705.No hydrologic results are given for the single failure of Norris Dam because the simultaneous failure ofNorris and Tellico Dams, discussed under multiple failures, is more critical.2. Fontana DamFon-tana; Da~m w~as a4s~su-med- to fail; in the one half SSE, although no stability analysis was made.is a high darn constructed with three longitudinal contraction joints in the highcr blGorc.A structJural defect in Fontana Dam ws;as found in October of 972 and conssist of a crngitudinal crack~~~~~~~~~~~f pn Af t .-. , 1,- ,+ ~ ..h,- r.., 1.,-. r..,.-71 A A 19\ C4r~ fI,-,.,i.-..... .,4S'£rr J.*l nlIX 1 flFigure 2.4.4 17). Only these three blocks ahe cracked, and there is no evidence that any other po-tionof the dam is weakened.Studies and tests, undertaken with the concurrence of a bo~ard Of pF!Yate consulting engioeerS,that this cracking was caused by a longitudinal thru st crpeatd by a cOmbinati*n of long concrete growth and expansion due to temperature rise in the summer months. This thrust tends topush the cuR'ed blocks upsteam. The studies and tests Will continue unti there is established a basisfor design of permnanent m:easures to conAtrol:) the fu-ture behayior of the damn.The strengthening Work has reestablished the structural integrity of the cracke-d blc l.~though thejoints 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. Tobe ..nse..atiy., therefore, i is.assumed that Fonta-a Dam Will nOt the one half SSE withoutFigure 2.1 ,t16 s;how the part of Fontana Dam judged to remain oiginal position after failureand the assumed location of the debris of the failed portion. The location of the after falure isone a6sumption based on a failure Of the dam at the InOgitudinal joints. There maybe other assumptions, but the amonl int of channel obstruction would probably be aboh ut thesam~e.The, higher blocks 9 27, containing either two Aor three longitudinal joints, are assu..med to fail. Rightabutment blocks 1 8 and left abutment blocks 28 and beyond were judged to be stable for the1. Their heights are less than one half the maximum height of the dam.22. Nne of theA-se b.ks haven more than- one lAgitudinAal cRtFacGtio joit, anAd ISo have nolongitudinal joints.2.4-26 SQN-3. The back slope o~f Fontana Dam is one On 0.76, Which the original stability analysis shows is flatterthan that required for stability for the normal static loadings.Although not investigated, it was assumed that Nantahala Dam, from Fontana ,ndSanteotlah On a downstream tributary, and the three ALCOQA dams, downstream On the LittleTennessee River, Cheoah, Ca~derweod, an~d Chilhowoe, would fail along with Fontana in the one halfSSE. Instant Vanishment was assumed. Tel"icI ad Watts Bar Dam spillway gates would be operableduring and afte~r the onRe half RSS1E. Failure of the bridge at Fort Loudoun Dam would rendcr thespillway gates inopcrablo in the wide open position.The flood wave would overtop Tellico Dam and its saddle dikes. Tran.fe of water into Fo- t Leudounw~ould occur but would not be s~uffic~ient to ovYertop the damn or to prevent failure of Tellico Dam. Tellicowas postulated to completely fail. Watts Bar headwater would reach elevation 761 .3, 5.7 feet belotop of d m. The Watts Bar west saddle dike would be overtopped and breached. A completw~ashout of the dike was assumed. The elevation at the plant site would be 702.8, 2.2 feet below plantg~ade.3.-Cherokee-ueul.as DamThe simultaneous failurc of Cherokec and Douglas Dams could occur WhcR the half SSE islocated midway be,-een the dams which are just 15 miles apart.Results of the original Cherokee Dam stability analysis for a typical spillway block are shown in Figure2.4.4-405. B edo this analysis, theThe spillway is judged stable at the foundation base elevation900.0 ft. Analyses made for other elevations above elevation 900.0 ft, but not shown in Figure 2.4.4 05, indicate the resultant of forces falls outside the base at elevation 1010.0 ft. The spillway isassumed to fail at that elevation.The non-overflow dam is embedded in fill to elevation 981.5 ft and is considered stable below thatelevation. However, original 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 towithstand the GRe4half-SSEOBE without failure.Results of the originlanalysis for the highest portion of the south embankment are shown on Figure2.4.4-146. The analysis was made using the same shear strengths of material as were used in theoriginal analysis and shows a factor of safety of 0.85. Therefore, the south embankment is assumedto fail during the one-half SSE. Because the north embankment and saddle damsSaddle Dams 1, 2,and 3 are generally about one-half or less as high as the south embankment, they are judged to bestable for the e ehalf- SSOBE.Figure 2.4.4 27 shows the assumed condition of the dam after failure. All debris from the failure ofthe concrete portion is assumed to be located downstream in the channel at elevations lower than theremaining portions of the dam, and therefore, will not obstruct flow.No hydrologic results are given for the single failure of Cherokee Dam because the simultaneousfailure of Cherokee, Douglas, and Tellico Dams discussed under multiple failures, is more critical.Douglas DamResults of the original Douglas Dam original-stability analysis for a typical spillway block are shown inFigure 2.4.4-4138. The upper part of the Douglas spillway is approximately 12 feet higher thanCherokee, but the amplification of the rock surface acceleration is the same. Therefore, based on theCherokee analysis, it is judged that the Douglas spillway will fail at elevation 937.0 ft, whichcorresponds 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 elevation927.5 ft. It is considered stable below that elevation. However, based on the Cherokee analysis, it is2.4-27 SQN-assumed to fail above the fill line. The abutment non-overflow blocks 1-5 and 29-35, being shortblocks, are considered able to resist the e half-SSE-OBE without failure.The powerhouse intake is massive and backed up downstream by the powerhouse. Therefore, it isconsidered able to withstand the ene-half-SSEOBE without failure.Results of the original analysis of the saddle damSaddle Dam shown on Figure 2.4.4 49 indicate afactor of safety of one. Therefore, the saddle damSaddle Dam is considered to be stable for the ene-half SSEOBE.Figure 2.4.4 510 shows the portions of the dam judged to fail and the portions judged to remain. Alldebris from the failed portions is assumed to be located downstream in the channel at elevations lowerthan the remaining portions of the dam and, therefore, will not obstruct flow.These-failures, in with one half the probable maximum. flood, would oyertop Fort Loudonfor only 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, but would not fail the dam. At Watts Bar the werst saddie dike would be ovcrtoppeand broached. A complete washout of thedie as assurncd. Crest level at SON would be elovation701.1, 3.9 feet below plant. No hydrologic results are given for the single failure of Douglas Dambecause the simultaneous failure of Cherokee, Douglas, and Tellico Dams as discussed later undermultiple failures. is more critical.Fontana DamThe original hydrological analysis used a conservative seismic failure condition for Fontana Dam. Asubsequent review which takes advantage of later earthquake stability analysis and dam safetymodifications performed for the TVA DSP has defined a conservative but less restrictive seismicfailure condition at Fontana. This subsequent review used a finite element model for the analysis andconsidered the maximum credible earthquake expected at the Fontana Dam site. Figure 2.4.4-11shows the part of Fontana Dam iudged to remain in its original position after postulated failure.No hydrologic results are given for the single failure of Fontana Dam because the simultaneous failureof Fontana and Tellico Dams, as discussed later under multiple failures, is more critical.Multiple FailuresPrevious attenuation studies of the OBE above Watts Bar Dam result in the iudgment that thefollowing simultaneous failure combinations require reevaluation:(1) The Simultaneous Failure of Fontana and Tellico Dams in the OBE Coincident with One-HalfPMFFigure 2.4.4-11 shows the postulated condition of Fontana for the OBE event. Tellico wasconservatively oostulated to comoletelv fail.The seismic failure scenario for Fontana and Tellico include postulated simultaneous and completefailure of non-TVA dams on the Little Tennessee River (Cheoah, Calderwood, and Chilhowee) and onits tributaries (Nantahala and Santeetlah). Failure of the bridge at Fort Loudoun Dam would render thespillway gates inoperable in the wide-open position. Watts Bar Dam spillway gates would be operableduring and after the OBE.Watts Bar Dam headwater would reach 756.13 ft, 13.87 ft below the top of the embankment. TheWest Saddle Dike at Watts Bar Dam with top elevation of 757.0 ft would not be overtopped. The peakdischarge at SQN would be 775,899 cfs. The elevation at SQN would be 702.2 ft, 2.8 ft below plantgrade elevation 705.0 ft.(2) The Simultaneous Failure of Fontana, Tellico, Hiwassee, Apalachia, and Blue Ridge Dams inthe OBE Coincident with One-Half PMF2.4-28 SQN-Fontana, Tellico, Hiwassee, Apalachia and Blue Ridge Dams could fail when the OBE is located withina flattened oval-shaped area located between Fontana and Hiwassee Dams (Figure 2.4.4-12). Failurescenarios for Fontana, Tellico, Hiwassee, Apalachia, and Blue Ridge Dams include postulatedsimultaneous failure of non-TVA dams on the Little Tennessee River (Cheoah, Calderwood andChilhowee) and on its tributaries (Nantahala and Santeetlah).Based on previous attenuation studies, the OBE event produces maximum ground accelerations of0.09 q at Fontana, 0.09 q at Hiwassee, 0.07 q at Apalachia, 0.08 q at Chatuge, 0.05 q at Nottely, 0.03q at Ocoee No. 1, 0.04 q at Blue Ridge, 0.04 q at Fort Loudoun and Tellico, and 0.03 q at Watts Bar.Figure 2.4.4-11 shows the postulated condition of Fontana Dam after failure. Hiwassee, Apalachia,Blue Ridge, and Tellico Dams are postulated to completely fail. Chatuge Dam is iudged not to fail inthis defined OBE event.Nottely Dam is a rock-fill dam with large central impervious rolled fill core. The maximum attenuatedground acceleration at Nottely in this event is only 0.05 g. A field exploration boring program andlaboratory testing program of samples obtained in a field exploration was conducted. During the fieldexploration program, standard penetration test blow counts were obtained on both the embankmentand its foundation materials. Both static and dynamic (cyclic) triaxial shear tests were made. TheNewmark Method of Analysis utilizing the information obtained from the testing program was used todetermine the structural stability of Nottely Dam. It is concluded that Nottely Dam can resist theattenuated ground acceleration of 0.054 q with no detrimental damage.Ocoee No.1 Dam is a concrete gravity structure. The maximum attenuated ground acceleration is0.03 g. Based on past experience of concrete dam structures under significantly higher seismicground accelerations, the Ocoee No. 1 Dam is 'udged to remain stable following exposure to a 0.03 qbase acceleration with amplification.Ocoee No. 1 and Ocoee No. 3 Dams, downstream of Blue Ridge Dam, would be overtopped and werepostulated to completely fail at their respective maximum headwater elevations. Ocoee No. 2 Damhas no reservoir storage and was not considered.Fort Loudoun and Watts Bar spillways would remain operable. The Fontana failure wave wouldtransfer water through the canal from Tellico into Fort Loudoun, but it would not be sufficient to overtopFort Loudoun Dam. The maximum headwater at Fort Loudoun would reach elevation 817.13 ft, 19.87ft below the top of the dam. Watts Bar headwater would reach elevation 756.13 ft, 13.87 ft below thetop of dam. The West Saddle Dike at Watts Bar with a top elevation of 757.00 ft would not beovertopped.The peak discharae at the SQN site oroduced bv the OBE failure of Fontana. Tellico. Hiwassee.Apalachia, and Blue Ridge coincident with the one-half PMF is 918,880 cfs. The peak elevation is706.3 ft, 1.3 ft above 705.0 ft plant grade.(3) The Simultaneous Failure of Norris and Tellico Dams in the OBE Coincident with One-HalfPMFFigure 2.4.4-4 shows the postulated condition of Norris Dam for the OBE event. Tellico wasconservatively postulated to completely fail in this event.In the hydrologic routing for this failure, Melton Hill Dam would be overtopped and was postulated tofail when the flood wave reached headwater elevation 817.0 ft, based on the structural analysis andsubsequent structural modifications performed at the dam as a result of the Dam Safety Program.The headwater at Watts Bar Dam would reach elevation 762.96 ft, 7.04 ft below top of dam. The WestSaddle Dike at Watts Bar with top at elevation 757.0 ft would be overtopped and breached. Acomplete washout of the dike was assumed. Chickamauga headwater would reach 701.05 ft, 4.95 ftbelow top of dam. The embankments at Nickalack Dam would be overtopped but was postulated notto breach which is conservative.2.4-29 SQN-The peak dischar-ge at the SQN site produced by the OBE failure of Norris and Tellico Damscoincident with the one-half PMF is 912.939 cfs. The oeak elevation is 706.3 ft. 1.3 ft above 705.0 ftplant grade.(4) The Simultaneous Failure of Cherokee, Douclas, and Tellico Dams in the OBE Coincidentwith One-Half PMFFioures 2.4.4-7 and 2.4.4-10 show the postulated condition after failure of Cherokee and DoualasDams, respectively. Tellico was conservatively postulated to completely fail.In the hydrologic routing for these postulated failures, the headwater at Watts Bar Dam would reachelevation 763.1 ft. 6.9 ft below the too of the dam. The West Saddle Dike at Watts Bar with a tooelevation of 757.0 ft would be overtopped and breached. A complete washout of the dike is assumed.Chickamauga Dam headwater would reach 702.95 ft, 3.05 ft below the top of the dam. Theembankments at Nickaiack Dam would be overtopped but were conservatively postulated not tobreach.The peak discharge at the SQN site produced by the OBE failure of Cherokee, Douglas, and Tellicowith the one-half PMF is 930.585 cfs. The oeak elevation is 708.6 ft. 3.6 ft above 705.0 ft olant arade.This is the highest flood elevation resulting from any combination of seismic events. The floodelevation hydrograph at the plant site is shown on Figure 2.4.4-18.-. Fontana, Hiwa.see, Apalachia, and Blue Ridge Damsi,Fontana, Hiwassee, Apalachia, and Blue Ridge Dams coul-d- fail wA.hen the ono half SSE is located,,thi. the fotball shaped area shown .i Figure 2.4 1.4T-his cvcnt prodUccs maximum ground accelerations of 0.09 g at Fontana, 0.09 g at Hiwassce, 0.07 gat Apalachia, 0.08 g at Chatuge, 0.05 g at Not+ely, 0.03 g at Ocoee NO. 1, 0.04 g at Blue Ridge, 0.04 -gat Fort Loudoun and Tellico), and 0.03 g at Watts Bar. Failuro is postulated for Fontana and Hiwassecfor an oarthguakc epicenter located anywherc within the- foogtball 1shaped arca shown on F~igure -2.4.418. Ground accelerations shown for the various dams6 arc maximum that Gould occur for cpiccnterlocGated at Yarious pointS in the deScribed area and would not occur simultaneouslY. Fort LoudoUn,Tellico, and Watts Bar Dams and spillway gates would rem~ain intact. The degrec of Fontana failureand likely position of are judged to be comparable to that shown for single failure in Figure2.4.4 16. Hiwassee, Apalachia, and Blue Ridge Dams were assumed to com~pletely disappear.Chatuge was judged not to fail as the acceleration is less than for the one half SSE=: centered at thedam.,Nottely Dam is a rockfill dam with large ceRntal iFmpeViou shOlled fill Gore. The FmaXimum attenuateground aceleatioen at Nottely is only 0.054 g. A field exploration bering program and laborato5g'testing programn of samples obtaine-d in -A field exploration was conducted#_ý_. Dur4_ing the field explorationprogram, standard penetration tests blow counts were o-btained- oM both the_ embankment anditfoudatonmaterials. Both static and dynamic (cyclic) triaxgial s-hear tests were made. This informnationRwas u se'd ithe Newmark Me..thod of Analysis. The "Newma. Method of Analysis" (Newma.., N. M.,"Effects of Earthquake On Dam.. of Embankments," Getechnique 15A140 141, 156, 1065) utilizingtheinformnation obtained- from the testing program was used_ to deAter4m.ine_ th~e structuMI-ral stability of Nettely_Dam. W.~e concF~lude Nottely DamA can easily resist the attenuated ground accGeleration of 0.054 g wtno detrimental damage.Qrcooot No. 1 Dam is aconcete gravity strucwtu re. The maximuim attenuated groun~d acceleration is0.03 g. The 0.03 g with the proper am~plification wvas u-sed- to- analyze the structural stability-Otstructures at Ocooc No. 1. The metho of ana'ysis used was the same as deScribed previously underm i vIAI 1 A L, .4 R! ;Ii g gl MICI "Ot 0 RQ el" E)Vet-tUFR RG. 8 GORG U e t e aFA W RGI a...In the original analysis, the failure wave hydregraph was approximated for the H;iw..as..ee Rivr a..t itsM.outh for thet; fal ures o. ef H iwasse.e, Apalachia ad Blue Ridge DaM. In the 1.9-9 e analyis 2.4-30 SQN-unte-ady flow model in S-ctifn 2.4.3.3 developed during the da-m s"afty studi.o Was Ueas an adjunc~t to routo the Hiwassoe, Apalachia and Blue Ridge faIluresin the simultAneous-1 f-ailurc of Fontana, HiWassec, Apalachia, and Blue Ridge Dams, the Fontan-afail.ur wavo would oe.top aRd fil the- Ttellico .mbankmonts. TraRnfer of water i'to Fo="rt Loudounwould occur but would not b-e suiffic-ient to overtop the dam Or to preVent failurze of Tollico. Tellico waspostulated to com~pletely fail. Watts Bar headwater would- re;ach elevatio~n 761.3, 5.7 foot below top-ofdamn. The west sa-dd-le d-iko at Watts BRar would be overtepped. A comAplete washout of the dike downto ground elevation was assumed. This flooed woave comFbined with th-at of HiwassqCee, Blue Ridge, andApaJa~hi Dams would pe-,rP a mnaxi~m-um flood- ee at the pl~ st of 70., .feet aboveplant grade. This is the highest flood resultiRg from any combination of and floodPeunts Th satae .h-hvdrnor;nh ;t the leant site is sho,.w.n on Fieure 2 4 4 21SSE Concurrent With 25-Year Flood (Controlling Events)The SSE will produce the same postulated failure of the Fort Loudoun and Watts Bar bridqes asdescribed for the OBE described earlier. The resulting flood level at the SQN was not determinedbecause 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 SSEconditions. However, even if the dam is arbitrarily removed instantaneously, the level at the SQNbased on previous analyses would be below elevation 705.0 ft plant grade.Fort Loudoun DamResults of the original stability analysis for Fort Loudoun Dam are shown on Fiaure 2.4.4-13. Becausethe resultant of forces falls outside the base, a portion of the spillway is 'udged to fail. Based onprevious modes of failure for Cherokee and Douglas, the spillway is judged to fail above elevation750.0 ft as well as the bridae suDported bv the soillwav niers.The results of the original slip circle analysis for the highest portion of the embankment are shown onFiqure 2.4.4-14. 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 OBEwith no water in the units. a condition believed to be an extremely remote occurrence durino the OBE.Because the stresses were low and a large percentage of the base was in compression, it isconsidered that the addition of water in the units would be a stabilizing factor, and the powerhouse is4udged not to fail.Figure 2.4.4-15 shows the condition of the dam after assumed failure. All debris from the failure of theconcrete portions is assumed to be located in the channel below the failure elevations.No hydroloqic routing for the sinqle failure of Fort Loudoun, includinq the bridge structure, is madebecause its simultaneous failure with other dams is considered as discussed later in thissubparagraph.Tellico DamNo hvdrologic routing for the sinqle failure of Tellico is made because its simultaneous failure withother dams is more critical as discussed later in this sub-paragraph.Norris DamAlthough an evaluation made in 1975 by Agbabian Associates concluded that Norris Dam would notfail in the SSE (with 25 year flood), Norris Dam was postulated to fail. The resulting debrisdownstream would occupy a greater span of the valley cross section than would the debris from the2.4-31 SQN-OBE but with the same top level, elevation 970.0 ft. Figure 2.4.4-16 shows the part of the dam judgedto fail and the location and heiaht of the resultina debris.The discharae ratinq for this controllinq, debris section was developed from a 1:150 scale hydraulicmodel at the TVA Engineering Laboratory and was verified closely by mathematical analysis. Thesomewhat more extensive debris in SSE failure restricts discharge slightly compared to OBE failureconditions.No hydrologic routing for the single failure of Norris was made because the simultaneous failure withCherokee, Douqlas and Tellico Dams, discussed under multiple failures, is more critical.CherokeeThe SSE is iudaed to oroduce the same Dostulated failure of Cherokee as was described for the OBE.The sinale failure does not need to be carried downstream because elevations would be lower thanthe same OBE failure in one-half the probable maximum flood.DouglasThe SSE is iudged to produce the same postulated failure of Douglas as was described for the OBE.The single failure does not need to be carried downstream because elevations would be lower thanthe same OBE failure in one-half the probable maximum flood.Multiple Failures5. NorriG, Cherokee, and DouglasNorris, Cherokee, and Douglas Dams werc also pestulatcd- to fail soimultancously. Figure 2.4.4 2shows the !Eoca;tion. Of _An SSE_, and it6 attenuation, which produ~ec 0.15 g at Norris, 0.09 g atCherokee and Douglas, 0.08 g at Fort Loudeun and Tollico, 0.05 g at Fontana, and 0.03 g at WattsBar. Fort Loudoun, TelliGG, and Watts. Bar have boen judged not to fail for the one half SSE(acceleration value of 0.0-9 g) (see following discussion of non controling events). The bridge at FrLoudoun DamR, however, m~ight fail under 0.08 g forces, falling OR any open gates, and on gate hofistingm~achinery. TFrunion anchor belts of open gates would fail and the gates would be washeddownstream, leaVing an open Spillway. Cloced gates cou-ld not be opened. The mest coeorasetiveassumption war, used that at the time of the seismAic event on the upstreamA tributary dame, the Gcrest Ofthe 25 year glood would likely have passed Fort Leudoun and flows would have been reduced toturbine capacity. Hcnce spillway gates would be closed. As stated before, it is believed that multipled-am. fiailure is extremely remote, and it seems reasonable to exclude Fontan~a on the basis of bein'g thcmost distant in the cluster of dams under consideration. For the postulated failur~es of Norris,Cherokee, and Douglas, the pertions judged to rem~ain and debris arran~gemenRt are as given iFigures 2.4.4 9, 2.4.4 12, and 2.4.4 15, respectively.The SSE will produc~e the same postulated failures of Chero~kee and Douglas Dams6 as were describedfo-r the onRe half SSE.For N~rris under SSE condibonsG, blgcks, 31 45 (883 feet of length) are judged to fail. The resultingdebris downstream would occupy a greater span of the valley cross section than would the debris fromthe one half SSE but with the same top level, elevation 97-0. Figure 2.4.4-280 siheows the part of thecontrolling debris section was developed from a 1:150 scale hydraulic moedel at the TVAEniergLabe~atory and was verfified closely by mathematical analysis. The somewhatimoare exesiedebriin SSE= failre restricts discharge slightly comnparedtonehlSEfaurcndinsThe flooed- fo-r the postulated f-aiure cmitonwould overtep and breac;;-h Fort Loudoun Damn.Although transfer of water into Tellfico would occur, it would not be sufficpient to oveto th dam AtWlatts Bar Dam the; headwator wouldd reach 761.9, 2.1 feet below the top of the ea;rth erhmbnmt ofAtha ~ ~ ~ +k --im -4m IUniarta4a~e r4IaiL rII~a'~ AI.,tt D- k-!, --n ,,I n ,a4-- 4n krc-hAM--rI2.4-32 SQN-Resulting Wate-r SurlfaceP at SQN would reach elevation 706. This is 1.0 foot higher than plant gradeThis is the highest flood resulting from any combination of SSE seismic and flood eve-nts. The floodelevatiOn Flow and stage hydrOgraphs at the plant site is shown On Figure 2.4.4 30.6. Norris, Douglas, Fort Loudoun, and TellicoNorriS, Douglas, Fort Loudoun, and Tellico Dams were pestulatcd to failsmlanosy FigUre 2.4.431 shOWs the location of an SSE, and Its attenuation, which produces 0.12 g at Norris, 0.08 g atDougla.0.12g ateFortLoudou and Telio,0.07gatCherokee, 0.06 g at.Fontana,and.0. gWaftt Bar. Cherokee i6 judged net to fail at 0.07 g; Watts Bar has previously been judged not to fall at0.09 g; and, for the same resn as given above, It seems Fea6onable to exclude FmOntana in this-failure combination. For the postulattedd flaillurmes Of Norris, Douglas, ForFt Loudoun, and TellicO, theportiens judged to remain and the debFris arrangements are gi vn in F 9, 2.4.4 15,2.4.4 26, and 2.4.4 27, respectively. For analysis Fort Loudoun and Telli.o were postulatedto fail com+pletely as the potions judged to remain are relatively small.The SSE will produce the same postulated failure of Douglas Dam as was described for the one halSSE,Results of the stability analysis for Fort Loudun Dam are shownR o F.igue 24. Because themresultantof foce falls outside the base, a paFtion of the spillway is judgs tod Rfil. Ba previos,modes of failure for Cherokee and Douglas, the spillway is judged to fail above elevation 7-50 as welas the bridge supported by the spillway piers.The results of the Slip Gircle analysis for the highest poretio of the embankment aFe sho-wn o InFigure 2.4.4 25. Because the factOr of safety is less than one, the embankment is assumed to fai.No analysis was made for the powerhouse under SSE. However, an analysis was; Made for the onehal;f SS2-E with no water in the units, a condition believed to beP eXtrPemcly remote to occur durig hone half SSE. Because the stresses were lOW and a large percentage of the base was incompression, it is considered that the addition of water in the units woulId be a stabilizing factor, andthe pGeweho)use is judged net to fail.Fmigure 2.4.4 26 shows the codtio f the- rdam after asmdfailu,_re. All debris from the failure of theconrGete poFtion is assume-- -d to be locGated in the channel below the failure elevatiosNo structural analysis was made for Tellico Dam failure in the SSE=. Ber.aus~e of the similarity to FrLoudoun, the spillway and entire embankment are judged to fail In a mnanner similar to Fort LOUdGun.F~igure 2.4.4 27 sheows afterF failure conpditions with all debris assumed locatpd inA the channel below theThis postulated failure cmiaonresul-ts in Wattsý Bar htqadwater elevation 758.9, 8.1 foet belowabove the top o-f the_ em-bank~menpt of the mnain damn. The west saddle dike at Watts Bar Dam would beovertopped and broac~hed. A com:plete washout of the dike woas asssumed. The resulting water- level atSQN would be elevation 699.3, 5.7 feet below plant grade 705.O~ halIf SSE QGRGUFF8,f VAJth G~ HlJIf th P~bal Maiu .Ev M .~I.,1. Watts Bar DamStability analyses of Watts Bar Dam powerhouse and spillway s~ections result in the judgment thatthese structures will net fail!. The- a;nalyses ShOW loW stresses with about 38 percent of the sp"iwaybase in co.mpreSion ;and- about 42 percent of the powerhouse bion. Results aregiven in Figure 2.4.4 1. Dynamic analysis of the concrete structures resulted in the determination thatthe ba;se acreoerationR is amplified at levels above the base.The slip cirle analysis of the eaFth embankment section results in Ra fator Of safety of 1.52, and the2.4-33 SQN-!-- ^ A A ýAM-14uAAK-Mj04T2Ims iut; :uuuu uf h4A +;!I kil "UU~.I PrIVRAI !F4 rtuuru J Z7Normally for the condition of peak discharge at the damR f4or one half the PMF=, the spillway gates wulbe in the wide open position (Figure 2.4.4 3). But, a~ly4 of the bridgo Structure for for~es resultingfrom a on-e h~alf SSE, including amnplificat'on of acceleration results in the determination that the bridgecould fail as a result of shearing the anchor bolts. The dOWnstrcam bridge girder-s could 6trike thespillway gates. The impact of the girders striking the gates, could fail' the bolts Which anchor the gattru-nninps, to the pier anchorages allowing the gates to fall. The flow ever the spiliWay crest would bethe same as that prier to bridgc and gate f-ailure. Hencc, bridge failure Will cause no adverse effect Onthe flood.A potentially con~eGedition is the bridge falling when most spillway gates would be closed. Thegate heisting machine~' would be inoperable after being struck by the bridge. As a result, the floodw:ould crest with the gates closed and the bridge deck and girders lying OR top of the spillway piersAnalysis of the concrete podtions of the dam for the headwM.atfor for this condition shows that theyw liRot f4aFloo-d lvl at SON for all the conditions described above is safely below plant grade elevation 7052. FEA Loudoun DamStability analyses of Foed Loudoun Darn po~werhouse and spillway sections result in the judgment thatthese structures will Rat fail. The analyses show low base stresses, With near tWO thirds of the as icompesson.Results are giiven in FiOgure 2.4.4 4.Slip circle an~alysis of the cadth embankment result in a factor of safety of 1.26, and the emba~knkentis judged not to fail. Results are given in Fiegure 2.4.4 5.The spiliway gates and bridge arc of the same design as those at W~atts Bar DamA. ConAditions Offailure during a one half SSE are the same, and no problems- aRep li6kely. Coincident f-aUilure- at FGedLoudoun and Watts Bar does nOt occur.ForF the potentially critisal caste Of FAed Loudoun bridge failure at the onRset of the main peodion of onehalf the probable m-axi~m.um flooed- flow, into Faed Leudeun ReceF'eiF, It was found that the Watts BarinflowVs areFP mHuch less than the condition resulting fromR simYultaneous failur-e of Chwerkee and Douglas-.3. Toellico DamNo padt of Tellico Dam is judged to fail. Results of the stability analyses for a typical non GVe~fOWblock and a typical spillway blocGk are shown in Figure 2.4.1 6. The result of the stability analysisothe earth emnbankment is shown in Figur~e 2.4.4 7 and ind.icates6 A- factor of safety of 1.28.4. Cherokee DamNo hydrologic r~esults are give-n fo-r the GIngle failure of Cheroakeee Damri bec-a-usee the simul---ta-neous--rfailure of Chero~kee and Douglas is mne-re c~ritic-,al.5. etiqa6 Dam4No) hydrolo~gic results are given for the single failure o~f Douglas Dam because the simultaneous failureo-f Che'rokee and- Douglas. is more critical.6.Hiwassee~t River Dams-Hiwaccee Dam was assumed to fail in the one half SSE. No hydrologic results are given for the singlefad, rA efHiwAgslso Da;m because its4r simul.taneous failre wth ther dams is more critical.7. Apalahi~a2.4-34 SQN-A.ala.chi DWam, was ;- isA'Jmd to tfail an thA on, hiltf SSE Nio hdrloic rul- t;, ar rivn ftr thp Sirle-Z A --ta GA. la -am A- re 9-;-; W-6 61 1 + A -I I N; A A A A a Ii 9 M.B. Blue R~geBlue Ridgc Dam was assumed to fail in the oRne half SSE. No are given for thesinglo failur eof Blue Ridge Dam bccausc its simultanoouIS failu-re- with otho-r dsis mon-rR- criticalR-.9. Ocoee No.-1Ocnoecl ro-sh. 1 Dam was assnuodI to fail in the Pon half SSE. No hydrologic result6 arc giren for theSingle failure Of Ococe No. 1 Dam bccause its simultanous failure with other dams is more critical.Nottely Dam wau assumed to fail in the one half SSE. No hydrologic results afe giVcn for the singlefailure of Nottely Dam because issimultaneous failure with other damns is more critical.11. ChatugeGhatuge Dam is a ho gee o, nmpepwieur. rolled fill dam. With the epicenter of the one half SSElocated at the dam, the maximum ground accelcration atI Cha;tuge is 0.09g g. Gron, d accelerationsg othis mtagnitude should have no detrimcn~ta! effects On a well cOnstructed compacted oadthfillembankment. We knew of no failueresf compacted carth embankment slopes fromn earthquakemotions. F~ailures to date have been associated with o~ther liquefaction of hydraulic fill embankmcn~tSof liquefaction of loose granular foundatien materials. The rolled embankment materials in Chatugeare no~t sensitive to liquefaction. To Yerif' these conclusion analysis using the "Ncwmark Methodfothe Dynamic Analysis of EmbakmeRnt Slopes" (New'mark, N. M., of Ea-thquake o. [Dams ofFEmbankments," Geetechnique 15-440 141, 156, 1965) was made to determine the structural stabilityof Chatuge. We conducted a field exploration boring program and laboraton.' testing program ofsamples obtained in the field exploration. DuFrig the field exploration program, standard penetratiotests blow cn,,ts were obtained On both the embankment and its foundatioRn mFateials. Both staticand dynamic (cycIli) triaxial shear tests were made. This information was used in the NewmarMethod of Analysis. We concluded from the Analysis that the Chatuge Dam can easily resist theqround acceleration Of 0.09 g With no detrimnental damageK .vv12. Hiw:assee. Aoalachia. BluJe Ridee. Ocoee Ne. 1. and .NoelevHiwassee, Apalachia, Blue Ridge, Ococe No.1, and Ngttely Damsr could fail when the one half SSE iscritcaly !oted Allfiv das wore assumned to cOmnpletely disappear in this event. Resulting crslevel at SQN would be below plant grade 705.1. Watts Bar DamA reeAv'aluation waS nnt made ..r Dam condi SS t Apevieus evaluation haddetermined that even if the dam is arbitrarily remeved instantaneously, the level at the nucl'ear plantsite w~ould- be below plant grade.2. Fo-rt Loudoun DamNo hydrologic routing fo the single failure- of Fot L=-udeun, including the bridge ifs Madebecause Its simulitaneous failure with Tellico and Fontana, as well as with Tolfico), Norris, and Douglas,3. Toqllico Da;m2.4-35 SQN-No ro)uting for the Gingle failure of Tellice is made fo-r the re-arons given above for Fort Loudo-un.4. Norris DamThis postulated Single failure would result in peak headwator at Watts Bar bolow the top of the earthPG~t4GR&-Gf the damn. Routing waS not carried furAther bec~ause it was evident that flood levels6 at theplant site would be considerably lower than for the Norris failure in the one half SSE combined with theo~e half MF.5. Hiwassee River Dams Considered SeparatelyNo structural analyses were made for Chatuge, Nottely, Blue Ridge, Ocoee No. 1, Hiwassee, andA palachia in the SSE= Instead, all six dams were postulated to fail OpelyNo roguting for the failure of the six Hiwassee dams alone i6 m~ade because their simultaneous failure4:th FonRtana is considered as discussed earlier in this subparagraph.-6. Cherokec, Douglas, and Fontana Considered SeparatelyThe SSE= will produce the same postulated failures of Chero~kee, Douglas, and Fon)tana Dams as weredescribed for the one half SSE. None of these failures need to be carried downstream, however,because elevations would be lower than the same failures in one hal;f the probable mxumflood.47. Fort Loudoun. Tellico. and FontanaA~ c~~p "nnt'~rnd hctnnn Fnntin~ inn th~ Fnrt I nirlni'n Thilirn comnI~" '*'i~' nn5~t'¶I1tn~d In fiji thr~'rthree dams. The four ALCOA dams downstreamR fromn Fn~tana and Nantahala, an ALCOA dam,ups~treamn were also postulated to fail completely in this event. W~atts Bar Dam and spillway gatesw:ould remain intact, but tailure of the roadway bridge was postulated whic-hwoould- render the spillwaygates inoperable. At the time of seismnic failure, discharges would be small in; the 25 year flood. F-orGOnseR'atism, Watts Bar gates w~ere _assumed inoperable in the closed position after the S-S-EmetThis event would result in a flooed- level at the nuclear plant site below 705 plant grade.8. Douglas and FontanaDouglas and Fontana wore postulated to fail si~m.ultanReously. The locration ofRan SSE required tofiboth darns would produce 0. 14 g at Douglas, 0.009 gat Fontana, 0.07 g at Chero~kee, 0.05 g at Norris,0.06 g at ranF I=auaUn) aRia i ciiica, aria 0.03 g at Watts Bar. i-or Mne postluated m.aIiures of Deugiasand Font.ana, the potions ju"dged to roman and the dbris arrangements aed as given in Figures2.4.4 15 and 2.1.4 16. Fort Loudoun, T-ellico, and WaI;tts, Bar haepviulbenjddnotoalfonr the_ OBE (0).09 o ). The bridge at Loud.oun Damn, however, might fail u. n d 06 g f -oes, fallingOR gates and OR gate hoisting mnachinery. Fort Loudoun gates wore assumned inoperable in the closedpo)sition folloEwing the SSE Gevet. ReSUltn~g water sU~face at SQN would be below plant grade.91 Fontana and Hiwoassee River DamsFonRtana and six Hiwassec River dams Hiwassee, Apalachia, Chatuge, Nottly, Blue Ridge, andOcoe-e- No. 1 were postulated to fail simultaneously. For) the postulated failure of Fontana, the portionjudged to remain and the_ debris_ a;rraneet ar as given in Fmigure 2.4.4 16. The six HiwasseedaR-msR wereM as~sume-d to fail completely. Fort Loudeun, Toellico, and Watts Bar are judged not to fail'NA1,th all gates operable. The=Fontana surge comhined;, with that of ther six ia,,ee Ri;vr dar-mswounIldreach an elevation at the plant site below the plant grade.2.4.4.2.2 Failue Analys ,All upstream auu GW~tiuam dams6 which could have Sinfraton flood level at SQwore examined for po-te-ntial; fa-ilu-reA during all fiood conditions, which would have the potential tov2.4-36 SQN-Produ~e mnaximum plant flood levels includinG the dam PMF at the ind-iVidui-al unstroam; dams16EncRGcte secUonS W8er eoxam~noo Tar ovenuMrng -Ana- norizentai snear and sldang. zspillway gates.:ere examined for stability at potentially critical wa-ter lelsand against failure fromn being Struck bywater borne objects. Leocks and- lock] gts wer xamnined forF stability, and earth em~bankmonets wcrcexa nd for erosion due to overtopping.During the SQN PMFl the only failure would be the west saddle dike a;t Waifs Bar. C-hicka;mauga Damwould be overtoonoed but wsxas ~oprse~vatively assumed not to fa4l.I I IiPOF conrGete dam sections, comparisonG were made oetween thle original design fleadwater andtaihA4ater le'els and those that would prevail in the PMF. if the oveFturning moments and horizontalforces were not inrGeased by more than 20 percent, the structure eecnidered safe againstfailure. All upstFeam dams passed this test except Douglas, Feor Loudoun, and Watts Bar Originaldesigns showed the spillway section.s÷ of these dhams to be mos..t vulnerable. These splway sections:erae examined in futher detail and judged to be stable.During peak PMF= conditions the radial spillway gates of Fmort Loudoun and Watts Bar DamsG will bewide epenn with flow over the gates and under the gates. For this cnGdition both the static anddynamic load stresses in the main structural mnembers of the gate will be less than the yield stress by af-ctor of three. The stFres in the trunniop pin is less than the allowable design stress by a factorgrFeater than 10. The trunnion pin is prevented from disledgment by a key inft the gate anchorageassembly and fitting into a slot in th. in.The gates were also investigated for the cndition n when rising headwatFr firsFt begins te eXceedthe bottom of the gates in the wide open position. This condition produces the largest forces tendingto retate the Fradial gate upward. InR the wide Poition the gates are dogged against steel gatesteps anchored to the conrGete piers. The stressqes in the gate stop members are less than the yieldstress Of the- material by afactOr Of 2L.It is concluded that the above listed margins are sufficient to provide assurance also that the gates willnet f-;il as a esult of additional stresses whiGh may result fFom possible vibrations of the gates Consideration has been given to the effect of water borne objectS striking the spillway gates and bentSsupporting the bridge- ac-ross W.atts Bar Dam at pealk ;.watte~r llevel at the dam. The most severepotential for damage would be by a barge which has been torn loose from its moo..rgs and floats the-aShould the barge h the spillway portion of the dam end 9o, one bridge bent could be failed bythe barge and two spillway gates could be damaged and possibly swept away. The loss of onRe bridgebon-;t will1 not collapse the bridge because the bridge girders are continuou 10SMembers; and the str~ess inthe girders Will be less than the ul-tima;tetrs forF this condition Of one support befing lost. Should twogates be swept away, the nappe of the water su~face over the sp~iway Weir would be such that thebarge would be grounded on the tops of the conrGete spillway weir-s and provide a partial obstuctionto- flowN comparable to unfailed spillway gates. Hence the loss of two gates frolm this nau se will havelittle effect on the peak flow and loVa;tion.Should the barge approach the spillway portion broadside, two and possibly thFree bidge bohnts couildbe failed. For this condition, the bridge would collapse On the barge and the barge would be groundedonA the tops of the spillway weirs. This would be probable because the approach velocity Of the bargew:ould be fromF 4 to) 7 Mi les per hour and the bottomA of the barge would be about six inches above thetops of the weirs. For this- coend-ition the barge would be grounded before striking the spillway gatos2.4-37 SQN-henause theo gates aro abut20- feePt dontcmfom the leg of the upstroamA bridcio bents.wLegk-GatesThe lock gates at Fort Loudoun, Watts Bar, aRd Chickamauga were examined for possible fai'ure withthe conclusion that no potential for failure exists because the gates are designcd for a differentialhydrostatic head greater than that which exists d-ring the probable m.aximum flood,Eimbnkhnel mnn D a~nh4nin the 1998 reanalysis, the only embankment would be the wesot saddle dike at Watts BaF Dam.Chickamauga Dam, downstreamR of the plant, would be overtopped but was assumed not to fail. Thissis conse awtive as failure of Chickamauga Dam would slightly lower flood elevations at the plant.The adopted relationship to c.mpute the rate of erosion in an earth dam, failure is that developed andused by the Bureau of Reclamation in With 4is safety of dams prOgram Theexpression relates the volume of eroded fill material to the volume of water flowing through the breach.The equabo i~&LQsoil-Ke-Qw'ater-whe~eAS..- Vol.um.e of soil eroded n.each tme periodPý -nnQiRS4if (4r MFnnnrtionamV~r 4 Tflot solnl in .. ..diScharge relationships in this studye -Base Of natural logarithm systemrbHa~Wher-eb -Base length of evefl(eW channel at any given timeH- H"daui head at any given time-~j Developed angle Of friction Of 6ol0atril AGOnsewative value of 13 degrees was adopted formaterials in the dams investiciated.Solving the equation, which was computerized, involves a tria! and error procedure over short depthanRd time in.rements. In the program., depth changes of 0.1 foo0t Or less are used to keep timeincr emets to less than one second during rapid failure and up to about 350 seconds prior tobreaGhýýThe so..lution of an earth embankment breach begins by so.v.ng the er.ion equation ursn aheadwatorel.. ation hydr.graph a..um.ing no failure. Erosion is pestulated to occur across the entireearth secAtioA ;;Ad to start at the down..tream. edge; whAe heA;d4 wat-r elevations reac.hed a se-leteddepth above the dam top elevation. Subsequently, when erosio;An reachesr the upstream edge of theembankment, breaching and rapid lowerin~g of the emnbankmnent begins. T-hereafter, comnputations,incl'ude headwater adiustments for inrGeased reservoir Gut-flGw resulting from the breach.Watts Bar West Saddle Dike Embankment Failure2.4-38 SQN-Figure 2.4 A 37 is a general plan of Waftt Bar .hoWing elevations and sectiens. Figure 2.4.4 38 is atopographic Map of the general Vicinity of Watts Bar Dam, Figure 2.4.4 39 is a general plan andsection of the west saddle dike.The west saddle dike .a 3xmnd and found subject to aiur from.r GYcropping. This failure wasassumed to be a complete washout and add to the discharge fromn Watts Bar Dam.Some v...fi.ation for the breaching com.putational p.rocedures ilustrated above was obtained bcomparison with actual failures reported in the literature and in inforFm~al d-iscGussion With hydrologic-engi neer. These repo ..ts show that ove.topped earth cmbankmentsdo n ot necessarily fail. EaFthemb-ankm.e.-nts have sustained overtopping Of several feet f.o several hours before failurFe ocurred.An extreme example is Ores earth dam in Brazil [17] which was, overtopped to a depth otfaprxmately 2.6 feet along a 2,000 foot length fo-r 12 ho-urs beforep bre-ac-hing began. Once an earthembhank~men-t s breached, failure tends to progress rapidly, however. How rapidly depends upon thematerial and headwate~rdenths dijrnn faiure Gemniete fiailt res comniited in this and other stujd Fnhav. va...ri.d from about one h-af t. six hou.rs a.ft.r initi ......... I'" .................vvThis, is ncnsistent with ArtualChiGkamauqa EmbaRkmeRt F=ai!uFe-in thedewRn---- ý I I --..rlnl; Ianalysis:I thela iIluru Af [A;t-RR [:rmeajikmRtl-fI: :11 "MPr M--...ruKJl:u; .... .-arurrM- ONP rP"HIPAC rAHUuu 44000 uI.'uiI. AT TPA ulAri[ F- u.9 M-1ui.ruiri iriKridiiAiim.pro.em.ents are planned for Chickamauga Dam, which if implemented, would prevent failrc.Therefore, although overtopped in the PMVF, the damA was assumed net to fail in deteFrmining floodelevations at the plant. This assumRption is conservative.TVA considered the following multiple SSE dam failure combinations.(5) The Simultaneous Failure of Norris, Cherokee, Douglas and Tellico Dams in the SSECoincident with 25-year FloodThe SSE must be located in a very precise region to have the potential for multiple dam failures. Inorder to fail Norris. Cherokee. Doualas. and Tellico Dams. the eoicenter of SSE must be confined to arelatively small area the shaoe of a football. about 10 miles wide and 20 miles Ione.Figure 2.4.4-17 shows the location of an SSE, and its attenuation, which produces 0.15 g at Norris,0.09 q at Cherokee and Douqlas, 0.08 q at Fort Loudoun and Tellico, 0.05 q at Fontana, and 0.03 q atWatts Bar. Fort Loudoun 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 q forces, falling on any open gatesand on aate hoistina machinery. Trunnion anchor bolts of ooen aates would fail and the aates wouldbe washed downstream, leaving an open spillway. Closed gates could not be opened. By the time ofthe seismic event at upstream tributary dams the crest of the 25 year flood would likely have passedFort Loudoun and flows would have been reduced to turbine capacity. Hence, spillway qates wouldbe closed. As stated before, it is believed that multiple dam failure is extremely remote, and it seemsreasonable to exclude Fontana on the basis of beina the most distant in the cluster of dams underconsideration. For the postulated failures of Norris, Cherokee, and Douglas the portions iudged toremain and debris arrangements are as given in Figures 2.4.4-16, 2.4.4-7, and 2.4.4-10, respectivelv.Tellico is conservatively postulated to completely fail.As discussed in Section 2.4.3, temporary flood barriers are installed on embankments at Fort Loudounand Tellico Reservoirs. The temoorarv flood barriers are assumed to fail in the SSE and are thus notcredited for increasing the height of the Fort Loudoun or Tellico Reservoirs embankments. The floodfor this postulated failure combination would overtop and breach the south embankment and MarinaSaddle Dam at Fort Loudoun. At Watts Bar Dam, the headwater would reach elevation 765.54 ft, 4.46ft below the top of the earth embankment of the main dam. However, the West Saddle Dike with topat elevation 757.0 ft would be overtopped and breached. The headwater at Chickamauga Dam wouldreach elevation 701.14 ft. 4.86 ft below too of dam. The embankments at Nickaiack Dam would be2.4-39 SQN-overtopped but was conservatively postulated not to breach.The maximum discharge at SQN would be 974,937 cfs. The elevation at the plant site would be706.0 ft, 1.0 ft above 705.0 ft plant grade. This is the highest flood elevation resulting from anycombination of seismic events.In addition to the SSE failure combination of Norris, Cherokee, Douglas, and Tellico identified as thecritical case, three other combinations were evaluated in earlier studies. These three originallyanalyzed combinations produced significantly lower elevations and were therefore not reevaluated.These include the following:1. Norris, Douglas, Fort Loudoun, and Tellico2. Fontana, Fort Loudoun, and Tellico3. Fontana and DouglasIn order to fail Norris, Douglas, Fort Loudoun, and Tellico Dams, the epicenter of an SSE must beconfined to a triangular area with sides of approximately one mile in length. However, as an extremeupper limit the above combination of dams is postulated to fail as well as the combination of (1)Fontana, Fort Loudoun, and Tellico; and (2) Fontana and Douglas.Norris, Douglas, Fort Loudoun, and Tellico Dams were postulated to fail simultaneously. Figure2.4.4-19 shows the location of an SSE, and its attenuation, which produces 0.12 q at Norris, 0.08 q atDouglas, 0.12 q at Fort Loudoun and Tellico, 0.07 q at Cherokee, 0.06 q at Fontana, and 0.04 q atWatts Bar. Cherokee is iudged not to fail at 0.07 q: Watts Bar has previously been iudged not to fail at0.09 q; and, for the same reasons as given above, it seems reasonable to exclude Fontana in thisfailure combination. For the postulated failures of Norris, Douglas, Fort Loudoun, and Tellico, theportions iudged to remain and the debris arrangements are as given in Figures 2.4.4-16, 2.4.4-10,2.4.4-15 and 2.4.4-20 for single dam failure. Fort Loudoun and Tellico were postulated to failcompletely as the portions iudged to remain are relatively small. This combination was notreevaluated because previous analysis showed it was not controlling.An SSE centered between Fontana and the Fort Loudoun-Tellico complex was postulated to fail thesethree dams. The four ALCOA dams downstream from Fontana and Nantahala, a Duke Energy dam(formerly ALCOA) upstream were also postulated to fail completely in this event. Watts Bar Damwould remain intact. This flood level was not reevaluated because previous analysis showed it wasnot controlling.Douglas and Fontana Dams were postulated to fail simultaneously. Figure 2.4.4-21 shows thelocation of an SSE and its attenuation, which produces 0.14 q at Douglas, 0.09 q at Fontana, 0.07 g atCherokee, 0.05 g at Norris, 0.06 g at Fort Loudoun and Tellico, and 0.03 q at Watts Bar. For thepostulated failures of Douglas and Fontana Dams, the portions judged to remain and the debrisarrangements for Douglas Dam are as given in Figures 2.4.4-10 and 2.4.4-11 for Fontana dam failure.Fort Loudoun and Watts Bar Dams have previously been iudged not to fail for the OBE (0.09 q).Postulation of Tellico failure in this combination has not been evaluated but is bounded by the SSEfailure of Norris, Cherokee, Douglas and Tellico.2.4.4.32 Unsteady Flow Analysis of Potential Dam FailuresUnsteady flow routing techniques [261 were used to evaluate plant site flood levels from postulatedseismically induced dam failures wherever their inherent accuracy was needed. FoF PMFdeterminations unsteady In addition to the flow models described in Section 2.4.3.3. wore used- frouting floodsG from.. postulated 6eiSm°ically ind"uc-.ed. damn failures, of tributary dams, additional unsteadyflow models were used as adjuncts to those described in Section 2.4.3.3models described below wereused to develop the outflow hydrographs from the postulated dam failures. The HEC-HMS storagerouting was used to compute the outflow hydrograph from the postulated failure of each dam exceptmain river dams. In the case of dams which were postulated to fail completely (Hiwassee, Apalachiaand Blue Ridge), HEC-RAS or SOCH was used to develop the outflow hydrograph. For Tellico Dam,the complete failure was analyzed with the SOCH model.2.4-40 SON-Un'stoeay ,ow tecnigques w..e applie, in Neoris Resew(*i. The Norr-s Resepe.ir model wM%developed in sufficiot detail to do-fine the m~annor in Which the roserv~oir mouln upyan uti,4,,,,,,,,,,,.,,4~~~~~~ ~ h..,. ., .-,.. ,_,-1 suppl a.nd,, ,, sustain.u.flW fo...Wi, g postulated dam fa..u.e. The mRO .. utdowas vefrified by fa Mpaire g its outed heoadwaterlevel in the one half PMF= with thoso using storagc routing techniqueS. Headwater level agreed withina foot, and the model was co~nsidered adequate for the purpose-.Unstoady flow techniques wcrc also applied in Cherokee, Douglas, and Fon~tana Reser~'oirs. ThereseR'oier mo-dels; werP-e developed in sufficient detail to define the mtanner in w~hich the re~sepvoir-s wouldsupply and sustain outflowA. followinAf'g postulated dam failure. The failure time and initial reservoirelevations for each dam were determined from a pre-failure TRBROUTE analysis. HEC-HMS wasused to develop the post failure outflow hydrographs based on the previously determined dam failurerating curves. The outflow hydrographs were validated by comparing the HEC-HMS results with thosegenerated by simulations using TRBROUTE.2.4.4.43 Water Level at Plant SiteMaxim water level at the plant from- differet postulated co,-mhination Of e.-.-, seismicdafilur ,.escoincident With floods would be elevation 707.8, excGluding wind wave effects. it would result from theone half SSE fafilure of Fontana, Hiwassee, Apalachia, and Blue Ridge Damns coincident with one-halfthe probable maximum flood. March win~d with one percent eXceodance probability over the 1.4 mileeffective fetch from the critical nrOth northwest direction is 26 miles per hour over land. This wouldcause reev )rwvs to reach elevation 7-09.6. Runup could reach elevation :710.1 on a smoo~th 4:1slope, elevation 712.8 9R a Yectical wall in shallow (4.9 feet) water, and elevation 710.4 OR a Ye~ticalw-all in deep water.The unsteady flow analyses of the five postulated combinations of seismic damfailures coincident with floods analyzed yields a maximum elevation of 708.6 ft at SON excludino windwave effects. The maximum elevation would result from the OBE failure of Cherokee. Doualas andTellico Dams coincident with the one-half PMF flood postulated to occur in March. Table 2.4.4-1provides a summary of flood elevations determined for the five failure combinations analyzed.Coincident wind wave activity for the PMF is described in Section 2.4.3.6. Wind waves were notcomputed for the seismic events, but superimposed wind wave activity from guide specified two-yearwind speed would result in water surface elevations several ft below the PMF elevation 722.0 ftdescribed in section 2.4.3.2.4.5 Probable Maximum Surqe and Seiche Floodinq (HISTORICAL INFORMATION)Chickamauga Lake level during non-flood conditions could be no higher than elevatin 685.441, top gates, and i; not likely to would not exceed elevation 682.5 ft, normal summe maximum pool level, forany significant time. No conceivable hurricane Or cyclonic typo windsmeteorological conditions couldproduce the over 20 feet ef wave height required tea seiche nor reservoir operations a surge whichwould reach plant grade elevation 705.0 ft, some 22 ft above normal maximum pool level.2.4.6 Probable Maximum Tsunami Floodin.q (HISTORICAL INFORMATION)Because of its inland location, SON is not endangered by tsunami flooding.2.4.7Ilee -it 9 o ~a Rd LanRds idesQ (141 S- TO RI GAL IN F RMIA T. 1 -0 14 ectBecause of the location in a temperate climate; significant amounts of ice do not form on4theTeRnessee Valley rivers and lakes. SON is In no danger from ice floodig,, .lakes and rivers in theplant vicinity and ice iams are not a source of maior flooding.Flood waves from landslides into upstream reservoirs pose no danger because of the absence ofmajor elevation relief in nearby upstream reservoirs and because the prevailing thin soils offer smallslide volume potential compared to the available detention space in reservoirs.2.4-41