ML18026A428

Pp&L Response to NRC Concerns Re Loss of Spent Fuel Pool Cooling Following Loca,Sses,Units 1 & 2.

ML18026A428
Person / Time
Site:	Susquehanna
Issue date:	08/16/1993
From:	PENNSYLVANIA POWER & LIGHT CO.
To:
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ML18026A429	List: ML18026A428 ML18030A383
References
NUDOCS 9308170357
Download: ML18026A428 (42)

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ATTACHMENTTOPLA4012PP8cLRESPONSETONRCCONCERNSREGARDINGTHELOSSOFSPENTFUELPOOLCOOLINGFOLLOWINGALOSSOFCOOLANTACCIDENTSUSQUEHANNASTEAMELECTRICSTATIONUNITS1AND2DOCKETNOS.50-387AND50-3889308i703579308ihPDRADOCK05000387pPDR 7yI ATTACHMENTTOPLA4012TABLEOFCONTENTS1.0SPENTFUELPOOL/PLANTCONFIGURATIONOVERVIEW............Page12.0TYPICALREFUELINGOUTAGEPRACTICES.......................Page23.0ACCIDENTSCENARIOS/CONFIGURATION.......................Page44.0PLANTRESPONSETOWORSTCASEACCIDENTSCENARIO...4.1SFPMAKE-UP/COOLINGCAPABILITIES4.2REACTORBUILDINGACCESS....................4.3ENVIRONMENTALIMPACTS.............~...Page5..Page5..Page7..Page

95.0CONCLUSION

S..............................~...........Page12APPENDIX1:ENHANCEMENTSA1.1PROCEDUREENHANCEMENTS............~.....A1.1.1PROCEDURESREVISED:.............~.....A1.1,2PROCEDURESTOBEDEVELOPEDORREVISED..A1.2TRAININGENHANCEMENTSA1.3MODIFICATIONENHANCEMENTSA1.3.1SFPLEVELANDTEMPERATUREA1.3.2CASKSTORAGEPITDRAINLINEMODIFICATIONS.Page13.Page14.Page14.Page16.Page16.Page17.Page17.Page17APPENDIX2:UHSIMPACTANALYSIS............................Page18IGURES~~~~~~~~~~~~~~~~~~~~~~~~~~~~o~~~~~~~~~~~~~~~~~FFIGURE1:FuelPoolCooling/RHRInterfaceP&IDFIGURE2:ReactorBuildingHVACDiagramFIGURE3:PlanViewofRefuelingFloorPage22 P4~ATTACHMENTTOPLAR0121.0SPENTFUELPOOLtPLANTCONFICURATIONOVERVIEWSusquehannaSESisadualunitBWR4,withMarkIIprimarycontainments.Eachunithasaseparatereactorbuildingenclosurethatsurroundseachprimarycontainmentstructure.Bothunitsshareacommonrefuelingfloorthatspanstheentiretopelevationofbothreactorbuildings.Thisisalargeopenroomwithnointerveningwallstoseparatetheunits.Bothreactorbuildingsandthecommonrefuelingfloor,together,comprisesecondarycontainment.TheventilationandSGTSsystemstotheseareasaredesignedsuchthatthereactorbuildingofthenon-LOCAunitisisolatedfromtheLOCAunitandtherefuelingfloor.Consequently,treatmentoftheairborneradioactivityintheaccidentunitandtherefuelingfloorisprovidedbySGTS(SeeFigure1).Figure2providesaplanviewoftherefuelingfloorandindicatestherelationshipoftheSFPstothereactorvessels.TheSFPforeachunitiscentrallylocatedbetweenthereactorsandshareacommoncaskstoragepit.Likewise,theskimmersurgetanks(seeFigure3)foreachSFPalsocommunicatedirectlywiththecaskstoragepit,aswellas,theSFPoftherespectiveunit.EachUnit'sSFPisequippedwithitsownnon-safetygradeSFPcoolingandclean-upsystem.Theunitsalsoshareacommonclean-upsystem.ThecoolingwaterfortheSFPcoolingsystemisprovidedbytheservicewatersystem,whichisnon-safetygradeandnotDieselGeneratorbacked.EachSFPisequippedwithseparateconnectionstoeachloopofEmergencyServiceWater(ESW)toprovideasourceofsafetygrademake-upwater.EachofthetworedundantESWconnectionstoeachSFPcanprovidesufficientwatertomaintainwaterlevelunderboilingconditions.Duetothecommunicationofthecaskstoragepitwiththeskimmersurgetanks,addingwatertooneunit'sSFPtomaintainthewaterlevelabovetheweirwillresultinwaterlevelintheoppositeunit'sSFPtoriseabovetheweir.'achSFPisprovidedwithaconnectiontotheRHRsystemoftherespectiveunitasameansofprovidingasafetygradebackupcoolingsystem.TheconnectiontotheRHRsystemutilizesSeismicCategoryIpipingandanyoneofthefourRHRpumpscanbeusedinthismode.EachofthefourRHRpumpsthatcouldbeusedreceivespowerfromaseparateemergencydieselgenerator.'URINGOUTAGEPERIODSIMAKEUPTOTHESFPCANALSOBEPROVIDEDVIAONEOFTHETWO(2)LOOPSOFCORESPRAY.PLANTADMINISTRATIVEPROCEDURESREQUIREATLEASTONELOOPOFCORESPRAYTOBEOPERABLEATALLTIMESWHILETHESFPGATESTOTHEREACTORAREOPEN.THEREAREFOURCOMMONEMERGENCYDIESELSFORTHESTATIONANDONESPARE.ONEACHUNITIEACHRHRPUMPANDCORESPRAYPUMPISPOWEREDBYASEPARATEDIESELII~E~ITHEARHRPUMPFROMTHEADIESELITHEBRHRPUMPFROMTHEBDIESELETC.Page1 7rPlC4 I~(ATTACHMENTTOPLA40122.0TYPICALREFUELINCOUTACEPRACTICESPriortothestartofanoutage,theheatloadintheisolatedfuelpoolsissmallandthetimetoboilisrelativelylarge.Thetimetoboilfortheoutageunit'spool(lastoutagewas18monthsago)isapproximately136hoursor5.7days.'henon-outageunit'spoolunderwentthemostrecentoffload(i.e.,6monthsago)andhasatimetoboilofapproximately81hoursor3.4days.'"'hefullcoreisoffloadedduringSSESrefuelingoutages.Thecoreheatloaddecaysasafunctionoftimeduringtheoutage.ForatypicalSSESfullcoreoffload,thedecayheatwilldecreasebyapproximately28%fromthetimethecoreisplacedinthefuelpooluntilitisreturnedtothereactorandthecaskstoragepitgatesarere-installed.4Theemergencyheatload(EHL)of33.9millionBTU/houristhemaximumdesignheatloadwhichcanbeprojectedtopossiblyberesidentinoneSSESfuelpool.'heEHLcanbedissipatedbytheRHRfuelpoolcoolingmodeat5,700gpmmaintainingthefuelpooltemperatureatlessthan125'F.Thecurrent(Unit1,7threfuelingoutage)fuelpoolheatloads(thisincludestheheatofbothpoolscombined)is=28millionBTU/hour,whichislessthantheEHL.ThisheatloadiscalculatedbasedonactualSSESoperatinghistory.Inatypicalrefuelingoutage,fueloffloadingstartsonday6(6daysaftershutdown)andiscompletedbyday13.Duringtheoffloadingperiod,RHRisoperatedintheshutdowncoolingmode.Oncetheoffloadiscomplete,thecaskstoragepitgatesareremovedtherebyconnectingtheoutageunit'sfuelpoolandreactorcavitytotheoperatingunit'sfuelpool.Thisincreasestheoutageunit'seffective"pool"volumebyapproximately33%.Thispoolconfiguration(2fuelpools+caskstoragepit+reactorwell+equipmentpit)istypicallymaintaineduntilRPVreloadiscompletedonday37oftheoutage.TheRHRshutdowncoolingmodeistypicallyoperateduntilfueloffloadiscompleted(day'13),andisavailableforoperationuntilworkonthecommonportionsofRHRisinitiated.FortheUnit17threfuelingoutage,workonthecommonportionoftheRHRsystemiscurrentlyscheduledtobeginonday16andbecompletedbyday26;however,thebeginningandendofthisworkwindowisdevotedtotestingsothatthesystemcouldeasilyTHESEVALUESAREBASEDONTHESSESU26RIODATASCHEDULEDFORTHESPRINGOF1994ANDARECONSERVATIVELYCALCULATED.ACTUALTIMETOBOILWOULDBELONGER.ITSHOULDBENOTEDTHAT2/3OFTHEPREVIOUSCYCLECOREISRETURNEDTOTHEREACTORWHILE1/3WILLREMAININTHEPOOLFORSTORAGE.THISHEATLOADCONSIDERSAFULLCOREOFFLOADIAFULLFUELPOOLIANDPOWERUPRATE.Page2 I)~gf&4'IJ I~r~ATTACHMENTTOPLA4012bereturnedtoserviceduringthisperiod.TheotherloopofRHR,whichisoutofservice,iscurrentlyscheduledtobereturnedtoserviceon.day26,howeveritisavailablefor"testingonday23andcouldbeputintoserviceinanemergencysituation.Therefore,theeffective"window"whenbothloopsofRHRwouldbeoutofserviceduetomaintenanceactivitiesis7days.However,theworkbeingperformedinthisperiodistypicallyindividualtasksontheorderof8to24hourdurationsratherthana5dayactivity.Betweenday16andday26(whenRHRisnotavailable),thetimetoboiltypicallyrangesfrom40to49hours(assuming110'Ffuelpooltemperature).'histimeexistseventhougharelativelylargeheatloadispresentinthepoolbecauseofthelargevolumeofwatercreatedbytheconnectedpools.Therefore,itwouldbepossibletorestorealoopof'RHRforuseinthefuelpoolcoolingmodewithinthe40hourtimetoboiltimeframe.Also,duringthetimeperiodwhenthepoolsareconnected,theoutageunit'sfuelpoolcoolingsystemissecuredonday17andistakenoutofserviceonday21.Thesystemismaintainedavailableforseveraldaystoassuretheoperatingunit'sFPCsystemcanadequatelydissipatethefuelpoolheatload.Thus,theoperatingunit'sFPCsystemiscoolingbothfuelpoolsfromday17today30.Onday30,RHRisreturnedtoserviceintheshutdowncoolingmodeasrefuelingbegins.Typically,onday11(priortocompletionofthefueloffload),theoutageunit'sHVACsystemisisolatedfromtherecirculationplenum.Thisisdonetoassurethattheoutageunit'senvironmentisnotaffectedbyoperationoftheHVACrecirculationsystem.Thispreventstheenvironmentoftherefuelingfloor(zoneIII)and/ortheoperatingunit'sreactorbuildingfrombeingmixedwiththeoutageunitintheeventthataradiologicalreleaseoccursontherefuelingfloorortheoperatingunit.Onday48,theoutageunitistypically.reconnectedtotherecirculationplenum.Workactivitiesmayrequirereconnectionoftheoutageunittotherecirculationplenumduringtheworkactivitywindow.Afterthefuelpoolsarereturnedtoanisolatedcondition(day39),theoutageunit'sfuelpooltimetoboilisapproximately50hours,eventhoughthepoolvolumeissignificantlysmallerthanitwasduringtheoutage.Thisisbecausetheresidentfuelbundleshavehadtimetodecayandonly1/3ofthecoreremainsintheSFP.Theoperatingunit'spoolhasatimetoboilof=130hoursor5~/2days.ACTUALTIMEToBOILISEXPECTEDTOBECONSIDERABLYLONGERDUETOTHECONSERVATIVEASSUMPTIONSUSEDINTHECALCULATIONS.Page3 t)~r1U ATTACHMENTTOPLAA0123.0ACCIDENTSCENARIOS/CONFICURATIONPP8L'sevaluationoftheconcernsassociatedwithalossofSFPcoolingfollowingaLOCAorLOOPeventindicatesthatcoolingcanberestoredtotheSFP(s)priortoboiling.AdequatetimewillexistforeitherrestorationofthenormalSFPcoolingsystemorutilizingSeismicClassIconnectionstothesafety-relatedResidualHeatRemoval(RHR)system.ProceduralguidanceforrespondingtoalossofSFPcoolingiscontainedinOff-NormalandEmergencyOperatingprocedures.ThelatterprocedurespecificallyidentifiestheneedtoprovideforSFPcoolinginaLOCAsituation,whiletheOff-Normalprocedureaddressesalossofcoolingforanyreason.TheconcernsraisedregardingalossofSFPcoolingareassociatedwithaDesignBasisAccident(DBA)LOCAoraDBALOCAconcurrentwithanextendedlossofoffsitepower(LOOP).InaLOCAcondition,thenormalSFPcoolingsystemwillbeautomaticallyshedfromtheplantelectricalsystem,alongwithothernon-safetyrelatedequipment,topermitthestartupofthelargeECCSpumpsontheLOCAunit.OncealloftheECCSequipmenthasstarted,theSFPcoolingsystemanditssupportsystemscanbemanuallyrestarted.Asimilarmanual(non-mandatory)loadshedexistsinemergencyresponseprocedureswithregardtoreactorbuildingpostaccidenttemperature.However,aswiththeLOCAloadshed,theSFPcoolingsystemanditssupportsystemscouldbemanuallyrestartediftheyaremanuallyshutdown.Ifthiscannotbeaccomplished,thesafetyrelatedRHRsystemcouldbeusedtocooltheSFPinitsFuelPoolCoolingmodeofoperation.ItshouldbenotedthatthismodeofRHRdoesnotperforma"safety-relatedfunction",however,itusesthesamecomponentsasthesafety-relatedfunctionsofRHRandtheportionofSFPcoolingthatitutilizesisASMEClass3andSeismicCategoryI.InaLOOP,normalfuelpoolcoolingwouldbelostforaperiodoftimeuntilpowercouldberestored.TheSSESIPE(usingNUREC-1032criteria)indicatesthatthereisa99.53%probabilityofrestoringoffsitepowerwithin24hours.Basedonthesefactors,itisreasonabletoexpecttorestorethenormalSFPcoolingsystempriortotheSFPreachingaboilingcondition.IntheextremelyunlikelyeventthattheLOOPisofalongerduration,thesafety-relatedandemergencydieselgeneratorbackedRHRsystemcouldbeusedtocooltheSFPinitsFuelPoolCoolingmodeofoperation.Consequently,aLOCA/extendedLOOPwouldbethemostlimitingeventsinceitwouldresultinthelossofthenormalSFPcoolingforthedurationoftheevent.ALOCA/extendedLOOPcouldbepostulatedtooccurwhilebothunitsareoperatingorwhileoneunitisinarefuelingoutage.ThemostlimitingscenarioisaLOCA/extendedLOOPwherebothunitsareoperating,sinceECCSwouldberequiredtocoolbothreactorcoresandSFPs(forisolatedpools)atthesametime.However,italso'representsaconditionwherethelowestheatloads,andthuslongesttimetoboilexistsfortheSFP.TheoutagesituationrepresentsagreaterheatloadintheSFP,'utplaceslessdemandsonECCSduetothecross-tiedpoolsandoneunitshutdown.Page4 I~~1~QktIC ATTACHMENT,TOPLA4012Consequently,thedesignofSusquehannaissuchthatSFPboilingwouldnotoccurwhileoneunitisinarefuelingoutageshouldaLOCAoccurontheoperatingunitorwithbothunitsoperatingandcross-tiedSFPs.ThisstatementappliesevenifaDBALOCAwithaRegGuide1.3sourcetermisassumedconcurrentwithanextendedLOOPonbothunits.ThisisduetothefactthatthereactorcavityandbothSFPsarecross-tied;andtheoutageunit'sreactorbuildingwillremainaccessibleforthedurationofaLOCA,sinceitsHVACsystemisnormallyisolatedfromtheoperatingunitandtherefuelingfloor.CrosstyingtheSFPsprovidesforawatervolumeof173;146ft'omparedtoavolumeof48,690ft'orasingleisolatedSFP.Therefore,eventhoughtheheatloadisrelativelylarge,thetimetoboilisalwaysgreaterthan25hoursandisusuallygreaterthan40hours.Theoutagealsoprovidesthegreatestamountofmake-upcapability(ESWfrombothunitsandCoreSprayfromtheoutageunit).ThesefactorsallowsufficienttimeforoperatoractiontorestorecoolingtotheSFP.Thecross-connectingoftheSFPsallowseitherunit'scoolingsystems(i.e.,normalFuelPoolCoolingandRHRFuelPoolCoolingmode)toprovidecoolingtobothpools.Thisisaccomplishedbyutilizingoff-normalprocedureON-135(235)-001,"LOSSOFFUELPOOLCOOLING/COOLANTINVENTORY"andoperatingprocedureOP-149(249)-003,"RHROPERATIONINFUELPOOLCOOLINGMODE".TheseproceduresprovidethedetailedguidanceintermsofensuringproperSFPlevelandESWandRHRflowrates.Therefore,duringanoutage,SFPboilingwillnotoccurandtheremainderofthisresponsewillfocusonnon-outageconditionswithisolatedSFPs.4.0PLANTRESPONSETOWORSTCASEACCIDENTSCENARIO4.1SFPMAKE-UP/COOLINGCAPABILITIESTheengineeredsafetygradeSFPmake-upsystemforSusquehannaisEmergencyServiceWater(ESW).Thecapabilityalsoexiststousethesafety-relatedRHRServiceWater(RHRSW)systemviatheRHRsystemasaback-upsourceofsafetygrademake-up(notproceduralizedatthistime)~TheactionsrequiredtorespondtoaLossofFuelPoolCoolingeventaredescribedinprocedureswhichexistedatthetimetheconcernwasraised.TheuseofESWinvolvesthemanipulationofthreemanualvalves(2")perloopofESWintwodifferentareasoftheplant.Asnotedearlier,initiationofESWmake-uptoeitherSFPwillresultinbothpoolsbeingfilledwhenthepoolheightisraisedabovetheweirregardlessofwhetherornotthepoolsarecross-tied.Withthepoolsisolated,wateraddedtoonepoolwilloverflowtoitsskimmersurgetank;whichwhencompletelyfilledwilloverflowtothecaskstoragepit;whichwilloverflowtotheoppositeunits'kimmersurgetank;whichwillinturnoverflowtotheoppositeunitsSFP(seeFigure3).Instructionsexistintheprocedurestofillabovetheweirs,therebycompletelyfillingtheskimmersurgetank,andthenusingtheexistingPage5

~~1' il~~(~ATTACHMENTTOPLA4012skimmersurgetanklevelinstrumentationtodeterminethatthepoolsarefilledtoatleasttheweirheight.Thisinstrumentationhas1EpowerandisseismicallydesignedinaccordancewithGDC63andsection9.1.3ofNUREG-0800.Thisinstrumentationisnotenvirorimentallyqualifiedsinceitdoesnotperformafunctionidentifiedinsection7.1ofNUREG-0800orRegGuide1.97.Levelmeasurementusingthisinstrumentationisaccomplishedbyopeningadrainvalveonthetanklevelinstrumentationandobservingwhetherthereisachangeinskimmersurgetanklevel.Ifnoneoccurs,thenthepoolsarefilledabovetheweirsandindirectcommunicationwiththeskimmersurgetank.Ifachangeinleveloccurs,thenthepoollevelisbelowtheweirelevationandtheoperatorwouldaddwaterviaESWorothersystemsuntilthetanklevelisincreased.Thisprocessofperiodicallyaddingwatertocompensateforboil-offwouldthenberepeatedoverthecourseoftheeventuntilcoolingisre-established.Theabove'referencedprocedurescautiontheoperatorsagainstoverfillingtheSFPthroughuncontrolledmake-uptotheSFP.ModificationstoaddlevelandtemperatureindicationinthecontrolroomforeachSFParebeingplannedinordertominimizetheactionstakenbytheoperatorandprovideforenhancedassessmentofSFPheat-up.ProceduresalsoidentifytheRHRFuelPoolCoolingmodeasameansofcoolingtheSFP,utilizingsafety-relatedandSeismicCategoryIequipment,intheeventthenormalfuelpoolcoolingsystemcannotberestored.Thisisaccomplishedbythemanipulationofsixvalvesintwodifferentareasoftheplant.Thesevalvesrangeinsizefrom8"to16"andareallASMESectionIIImanualvalves.ThesevalvesarenotrequiredtobetestedunderASMESectionXI,however,PP8Lwillbeperformingperiodicstrokingofthesevalves.EitherloopofRHRmaybeusedinthismodeandtheinstallationofaspoolpieceisnotrequired,sincetheconnectionatSSESiscompletely"hardpiped".Pre-operationaltestdatafrombothunitsindicatesthatatleast5,700gpmcanbeachievedbyonepumpthroughoneloopofRHR.CalculationsindicatethatthisflowcanbesustainedwithmorethanadequateNPSHfortheRHRpumpsoncetheSFPhasbeenpre-filledtotheproper'level.ThislevelisspecifiedinproceduresandprovidessufficientlevelintheskimmersurgetanktoensureadequateheadfortheRHRpumps.Thisflowissufficienttomaintaintemperatures6125FatdecayheatloadsuptotheEmergencyHeatLoad.UltimateHeatSink(UHS)analysesperformedtodateindicatethatthisheatloadcanbeaccommodated.ThedesignbasiseventfortheUHSisaLOCA/LOOPwithaLOCAononeunitandasimultaneousforcedshutdownontheotherunit.Inthismode,theUHScanprovidesufficientcoolingwaterforsafetyrelatedequipmentfor30dayswiththewatertemperatureatorbelowthesystem'sdesigncoolingwatertemperature.ThereactordecayheatassumedintheUHSdesignanalysesrangesfromapproximately140MBTU/hrafter2.0hours,to36.6MBTU/hrafterday7,to22.6MBTU/hronday30oftheevent.ThisdecayheatdataisusedforboththeLOCAandthenon-LOCAunit.Page6.

I$~"~1CVlk0 ATTACHMENTTOPLA4012ThreeshutdownscenarioswereevaluatedtodeterminetheimpactthattheoperationoftheRHRfuelpoolcoolingmodecouldhaveontheUHSminimumheattransfer(MHT)andmaximumwaterloss(MWL)designbasisanalyses.TheMHTanalysisassumesconditionswhichresultinthehighestpotentialforpondheat-up.TheMWLanalysisevaluatesworstcaseconditionsforpondinventorylosses.Itisconcludedthatforallthreecasesevaluated,theexistingdesignbasisUHSMHTandMWLanalysesarebounding.Appendix2providesspecificdetailsofthescenariosandtheevaluation.ItisestimatedthatitwilltakeapproximatelyeighthourstoplaceRHRinserviceintheFPCmodeofoperation,excludingthetimetofilltheSFP(s)totheappropriatelevel.Thetimetofillisdependentonthepoolconfigurationandsystemavailability,butiswithinthetimetoboil.Itisestimatedthatmake-upcanbestartedwithinonehourofinitiatingactiontobegintheprocess.AssumingonlyoneloopofESWisavailableformakeup(35GPMperpool)andpoollevelisattheweirheightwhenmakeupisinitiated,themaximumtimetoreachtheappropriateSFPleveltosustainRHRsystemoperationis22.6hours.Thismaximumfilltimewouldexistwhenthepoolsareisolatedandthecaskpitisempty.Withthefuelpoolsconnectedthroughthecaskpit,thefilltimeisreducedto5hours(caskpitwouldbefull)~Inanoutagesituationwithbothpoolsconnectedtothereactorwellandequipmentpit,thefilltimewouldbe8.7hours.InthemorelikelysituationwherebothloopsofESWareavailabletoprovideSFPmake-up,filltimeswould'behalved.Filltimewouldbefurthershortenedbyuseofotheravailablemakeupsources,suchascondensatetransferandfirewatersystems.ProcedureenhancementshavebeenmadeasaresultoftheLossofFuelPoolCoolingissues.Theseprocedureenhancementsarealsoincorporatedintotheoperatorre-qualificationtrainingprogramatSSES.AdetaileddescriptionoftheenhancementsisprovidedinAppendix1.4.2REACTORBUILDINGACCESSFSARChapter18documentsPP8L'sevaluationwithregardtooperatoraccesstothereactorbuildingtoperformactionsrequiredtorespondtoanaccidentlikeTMIwheresubstantialcoredamageresulted.Thisevaluationindicatedthattherewerenooperatoractionsinthereactorbuildingrequiredtorespondtothistypeofaccident.TheFSARevaluationalsoindicatedthatnoairbornedosecontributionwasassumedinevaluatingoperatoraccess,basedonPP8L'sinterpretationofNUREG-0737.Thecontainedsourcedoseforeachroomwasbasedonthecontactdosefromapointsource.PP8Lhassubsequentlyperformedaccessevaluationsforspecificactionswhichdidconsideranairbornedosecontributiononacasebycasebasis.Anairbornedosecontributionhasbeenincludedintheevaluationsofoperatoraccessthathavebeenperformedinresponsetothisissue.Forasevereaccident,onlyoneSFPwouldbeexpectedtoboil.Thisisprimarilyduetothefactthatthenon-accidentunit'sreactorbuildingcanbeisolatedfromtheaccidentenvironmentbymanuallyclosing(fromthe'aincontrolroom)remoteactuatedsafety-Page7

)~~~rV

(~ATTACHMENTTOPLA4012relateddampers.ThesedampersopenwhenaLOCAandLOOPsignalisreceived,therebyaligningallthreeventilationzonestoSGTS(seeFigure1).WhenaLOCAsignalaloneisreceived,onlythedampersontheLOCAunitopen(permittingtheLOCAunittobeconnectedtoZoneIII),therebypreventingcontaminationofthenon-LOCAunit.ManuallyclosingthedampersonaLOCA/LOOP,withhighradiationintheaccidentunit,willaffordthesamebarrieragainstthespreadofcontaminationtothenon-accidentunitasisaffordedunderLOCAonlyconditions.ThreezonemixingisautomaticallyinitiatedwhentheLOOPconditionispresentbecauseofthelossofnormalHVACsystemstobothreactorbuildings.Sincetherecirculationairflowwouldbecutoffwhenthedampersareclosed,PP8Lhasevaluatedthetemperaturerisethatthenon-LOCAunitwouldexperienceduringthelossofrecirculationflow.Thisevaluationshowsthattemperatureswillremainwithindesignvaluesforatleast24hours.Thisprovidesampletimeforthenon-accidentunittoreachcoldshutdown(timetoreachcoldshutdownistypically6-12hours).Isolationofthenon-LOCAunitfromtheLOCAunitenvironmentwouldpermitaccesstorestorenormalFuelPoolCooling,ifoffsitepowerisavailable,orplaceRHRFuelPoolCoolingmodeinoperationshouldoffsitepowercontinuetobeunavailable,ThisenablestheoperatorstopreventSFPboilingonthenon-LOCAunit.ShouldasevereaccidentoccurwiththeaccidentconditionsdescribedinChapter18oftheFSARonUnit1,theESWvalveslocatedonEl.670'ouldbeinaccessibleforthedurationoftheresponsetotheLOCA(30daysperUltimateHeatSinkdesignbasis).Theprimaryreasonfortheinaccessibilityistheconservativeassumptionofassigningthepeakcontactdoseofthemostradioactivesourcetotheentireroom.TheremainingESWvalvesonUnit1(El.749')wouldbeaccessibleafter30hours.IftheFSARChapter18LOCAoccursonUnit2,allESWvalvesareaccessibleafter30hours.'ccesstotheRHRFPCvalveslocatedonEl.704'feitherUnit1or2wouldbeprecludedforaFSARChapter18LOCA.TheRHRFPCvalveslocatedonEL.749'reinthesamelocationastheESWvalvesandsimilarlywouldbeaccessibleafter30hoursforanFSARChapter18LOCA.Inthiscase,thetimetoboilwillbeinexcessof49hours,therebyallowingampletimefortheoperatorstotaketheactionsdescribedinSection6.1above.PP&LhasperformedcalculationstodeterminerealisticdosethatanoperatorwouldreceiveaccessingtheRHRandESWvalvesusingaReg.Guide1,3sourcetermfromairborneandcontainedsources,buttakingintoaccountdistanceandtimefactors.ForRHR,theamountofpipingcontainingtheradioactivesourceisso,largethatsignificantdistancereductionsarenotpossible.Thetimeinvolvedtoopenthelargevalvesalsoresultsinunfavorablestaytimes.Consequently,arealisticReg.Guide1.3doseevaluationwasnotperformedfortheRHRvalves.ForESW,distancereductionswerepossibleandarebasedontheproximityofthevalvestotheCoreSpraypipingwhichactsastheradiationsource.AlsoreductionsTHEESWVALVESTHATARELOCATEDONEL.670'NUNIT1ARELOCATEDONEL~683INUNIT2.THISACCOUNTSFORTHEDIFFERENCEBETWEENUNITSWITHREGARDTOFSARCHAPTER18ACCESSIBILITY~Page8

[~lrg,~(ATTACHMENTTOPLA4012instaytimewerepossiblebasedonasimulatedwalkdownbyanoperator.ThedoseanoperatorwouldexperienceaccessingtheESWvalvesonEL.670'ntheUnit1reactorbuilding24hoursforaRegGuide1.3sourcetermandrealisticassumptionsis4.22Rem.Therealisticassumptionsaredistanceofthevalvesfromthesourceandawalkdowntransittimeinsidethereactorbuildingof1.8minutestoandfromthevalvesandatimeof1minutetoopeneachofthetwovalves(2minutestotalforvalveopening).Similarly,thedosetoanoperatoropeningthe4ESWvalves(1minuteeachvalve)onEL.749'slessthan1.6rem.4.3ENVIRONMENTALIMPACTSPPRLisperforminganassessmentoftheenvironmentaleffectsresultingfromaboilingSFPassumingoperatoraccesstotheLOCAunitisnotpossible.Theseeffectsincludefloodingandtheelevatedheatload/humidityimposeduponequipmentinthereactorbuildingduetotheboiloff.ThedeterminationoftheenvironmentaleffectsisbasedupontakingoperatoractionstomitigatetheeffectsofaboilingSFP,intheunlikelyeventcoolingcannotberestoredtotheSFP.TheprincipaloperatoractiontolimittheenvironmentalimpactofaboilingSFPisshuttingdownthereactorbuildingrecirculationsystem.Turningofftherecirculationsystemwillpreventthespreadoftheboilingenvironmenttotheaccidentunit'sreactorbuilding.'lso,preliminaryevaluationsindicatethatturningofftherecirculationsystemwillstillpermittheSGTSsystemtomaintainanegativepressureinsecondarycontainmentsincethemassofsteamaddedbytheboilingpoolislessthanthecapabilityoftheSGTSsystem.Itshouldbenotedthattheprimarypurposeofthereactorrecirculationsystemistomixthepost-accidentenvironmentsoastoprovideauniformconcentrationofairborneradiationwithinthereactorbuilding.Whileprocedureshavenotbeenrevisedyettoreflectshuttingdowntherecirculationsystem,theneedtomitigatetheenvironmentfromaboilingpoolisrecognizedinemergencyplanprocedures,therebyallowingtheemergencyorganizationtotakethisaction.EP-PS-102,"TechnicalSupportCoordinator:EmergencyPlan-PositionSpecificProcedure"providesspecificinstructionstotheTechnicalSupportCoordinatortomonitortheSFPandtakeactionstoprecludeboiling.TheTechnicalSupportCoordinatorisapager-activatedpositionunderPPBL'sEmergencyPlanandwouldbeactivatedtorespondintheeventofanaccident.Thesteamfromtheboilingpoolisexpectedtocondenseonthestructuralsurfacesoftherefuelingfloorelevation,withalargeportioncondensingoutintheformofrainwithoutdirectcontactwiththesesurfaces.Aportionoftheboiloff(=10%)willberemovedviatheSGTSsystemandtheremaining100%relativehumidityairwillcondensethroughouttheTHESEENHANCEMENTSHAVENOTBEENPROCEDURALIZEDASOFTHEDATEOFTHISREPORT.THEYAREPLANNEDTOBEINCORPORATEDINTOEP-PS-102.Page9 l~ATTACHMENTTOPLAP012refuelingfloor.9Thiscondensatewillfinditswaytothereactorbuildingsumproomfromtherefuelingfloorviathedrainagesystem.Sincetherefuelingfloorisacommonarea,thedrainsontheUnit1sidewilldraintoUnit1andUnit2dr'ainstoUnit2.Therefore,thecondensatewouldbeequallysplitbetweentheunits.Basedonthis,anassessmentwasperformedtodeterminetheextentoffloodingthatwouldresultfromaboilingSFP.Forthefloodingassessment,adecayheatcorrespondingtoanisolatedSFPattheendofanoutage(day55)waschosen.Thisresultsinaboiloffrateequivalentto=11gpmfortheisolatedSFP.Useoftheboiloffrate(ratherthanthemaximummakeupcapabilityofESW)isappropriatesinceoff-normalproceduresdirecttheoperatorstoperiodicallyfilltheSFPtooffsetboiloffrather'thanleavingthevalvesopencontinuously.ThedesignoftheUltimateHeatSink,fromwhichtheESWsystemtakessuction,includessufficientvolumeforESWtoprovidemakeuptotheSFPforaperiodof30daysat35gpm.UsingthisasthedurationoftheLOCA,andtheboiloffratefromtheHVACanalysis,thetotalvolumeofwaterthatwouldboiloff,assumingnooperatoractiontorestorecoolingwithin30daysis:11gal/minx30daysx60min/hrx24hr/day=475,200gallonsMoistureextractedbySCTS(=10%)=-47520gallonsTOTAL=427,680gallonsThisvolumewouldthenbesplitequallybetweenthetwounits,asdescribedabove,suchthatapproximately213,840gallonswouldaccumulateinthebasementofeachreactorbuilding.Ifoffsitepowerisunavailableforthesumppumps,thecondensatewouldoverflowthesumpandstarttoaccumulateonthefloor.Watertightdoorsratedfora23footheadofwaterisolatetheSumproomfromtheECCSroomsexceptforanadjacentCoreSprayPumpRoom."Therefore,waterwouldbegintoaccumulateinthesetworoomsatthesamerate.TheotherCoreSprayroomisprotectedbywatertightdoorsandthereforeisnotsubjecttoflooding.ItshouldbenotedthatonlyoneloopofCoreSprayisrequiredtoassistinlongtermcorecoolingatthispointintheLOCA,sothatthefloodingofoneCoreSprayroomdoesnotrepresentathreattolongtermcorecooling.ThevolumeoftheSumproom/CoreSprayPumproomcombinationissuchthatwatercouldaccumulatetoadepthof11feetwithinfor30daysatthe11gpmboil-offrate.Thisiswellwithinthe23'ootdesignlimitofthedoors.Therefore,fortheisolatedpoolcase,theSumpRoom/CoreTHESGTS-HEATERSAREDESIGNEDFOR100~oHUMIDITYAIRANDAREEQUIPPEDWITHDEMISTERSsHEATERSANDDRAINSTOREMOVETHEMOISTURE~THEAFFECTEDCORESPRAYPUMPROOMISTHE"A"PUMPROOMsWHICHCONTAINSTHE"A"&"C"CORESPRAYPUMPS.Page10 ATTACHMENTTOPLA4012SprayPumpRoomcombinationprovidesadequatevolumeforaccumulationofboiloffovera30dayaccidenteventduration.ApreliminaryassessmentofthetemperatureimpacttothereactorbuildingundertheseconditionsindicatesthatEnvironmentalQualification(EQ)temperaturelimitsareexceededforasmallnumberofsafetyrelatedequipmentintheunlikelyeventofpoolboiling,withoutactionstorestorecoolingtotheSFP.TheassessmentindicatesthatwhenthereactorbuildingHVACrecirculationsystemisshutdownattheonsetofboiling,thetemperatureswithintheaccidentunit'sreactorbuildingwillremainwithinEQlimitsforthemajorECCScomponents.ThepeaktemperatureintheECCSswitchgearandloadcenterroomswillreachamaximumtemperatureof=105at30daysintoaLOCA/extendedLOOP.ThistemperatureslightlyexceedstheEQlimitof104'F,butiswellwithinthecapabilitiesoftheequipmenttoperformitsfunctionforthebriefperiodoftimeitwillbeoperatingabovetheEQtemperature.Theroomtemperaturesfor15additionalinstruments/MCCs/panelswillbemoresignificantlyexceededat30days.However,anevaluationoftheimpactofthehighertemperaturesindicatesthattheLOCAqualificationlifewouldbereducedfrom100to46daysforthemosttemperaturelimitingdevice."AreviewofthesafetyfunctionofthesecomponentsindicatesthattheyperformtheirfunctionsveryearlyintheLOCAeventandwouldnotberequiredtooperateatthetimetheirEQtemperatureswouldbeexceeded.Evenifthecomponentsweretofail,onlythefailureinthree480VACMCC'swouldresultinanyECCSfunctionsbeingaffected.ThefailureofcomponentswithintheseMCC'scouldcausethe"C"RHRandCoreSpraypumpstobelost;however,atthetimeintheeventwhenthiswouldhappen(day20-55),therewouldstillbesufficientRHRandCoreSpraypumpsavailabletocoolthereactorcore.Insummary,thecapabilitiesdescribedaboveincombinationwiththeproceduresdiscussedinthisreportprovideampleassurancethattheconsequencesofapostulatedboilingSFPwillbemitigated.Consequently,adequatelongtermreactorcorecoolingcanbemaintained,alongwithSFPcoolingandmakeuptoaboilingSFP.THEREDUCTIONINLIFEWOULDOCCURAFTERTHEEQTEMPERATUREISEXCEEDEDWHICHWOULDBEATLEAST20DAYSAFTERTHESFPBEGINSTOBOIL.Page11 ATTACHMENTTOPLA401

25.0CONCLUSION

SPP&LhasthoroughlyevaluatedtheconcernsassociatedwiththeSFPCsystematSSESandhavedeterminedthatsafeoperationisassured.Theoriginaldesignofthesystems,structures,andcomponentsatSSESadequatelyaddressesalossofSFPCoolingconcurrentwithLOCAand/orLOOPevents.Inaddition,adequateresponsecapabilityexiststopreventSFPboilingatSSES.Theseconclusionsarebaseduponthefollowing:1.BasedontheSSESIPE,theprobabilityofaDBALOCAwithanextendedLOOPanda,boilingSFPisontheorderof10".2.Timetoboilistypicallymuchgreaterthan25hoursatanypointinwhichtheaccidentscenarioisofconcern.SufficienttimewillbeavailabletotakeappropriateoperatoractionstorestoreSFPcoolingandpreventboiling.3.ESWmakeuptotheSFPswilleventuallyfillbothpools,thereforeaccesstotheaccidentunitisnotrequiredtoprovidemakeupwatertoitsSFP.4.CoolingcanberestoredpriortoSFPboilingbyeither:a)restorationofnormalSFPCsystem,orb)thesafetygradeRHRsystem(FPCmode).5.ProcedureshavebeenimprovedandoperatorshavebeentrainedtoassuretheproperresponsetoalossofSFPcooling.ModificationstoinstallimprovedlevelandtemperatureindicationtotheSFPswillfurtherstrengthentheoperatorresponsetothisevent.6.Accesstothenon-LOCAunitisalwaysassuredduetothecapabilitytoisolateitsventilationsystemfromtheaccidentunitfromthemaincontrolroom.7.Modificationsarebeingevaluatedtosupportremovalofthecaskstoragepitgatesduringnon-outageperiodswillprovidecapabilitytoutilizethenon-LOCAunitSFPCsystem,ifavailable,ortheRHRFPCAmodeduringallaccidentconditionstopreventbothSFPsfromreachingaboilingcondition."Page12 ATTACHMENTTOPLA<012APPENDIX1:ENHANCEMENTSPage13 I~P ATTACHMENTTOPLA4012Asaresultoftheengineeringevaluations,PP8Lhasmadeenhancementsandisconsideringfurtherimprovementsintheareaofmodifications.ConsiderationisbeinggiventoremovingthecaskstoragepitgatesatSSEStoprovideadditionalflexibilityinrespondingtoalossofSFPCoolingevent.Inaddition,procedures'avebeenupdatedtoimproveoperatorawarenessoftheconcerns,andoperatortraininghasbeenprovidedtoenhanceresponsetoalossofSFPCoolingevent.TheSFPmonitoringequipmentmeetslicensingrequirements;however,enhancementsarebeingplannedinordertoimproveoperatorresponsetosuchevents.Adetaileddiscussionofthevariousenhancementsfollows.A1.1PROCEDUREENHANCEMENTSA1.1.1PROCEDURESREVISED:1.ON-135(235)-001,Rev.12,"LOSSOFFUELPOOLCOOLINC/COOLANTINVENTORY~(DATED12/22/92)Thisrevisionidentified:Thatthepoolscanbecrosstiedshouldpoolcoolingnotbeabletobereestablished.(Thisactionincreasesthetimetoboilandmakeseitherunits'ystemsavailabletocoolormakeuptobothpools.)Thatfireprotectionwatercanbeusedtomakeuptothepools.(Providesanadditionalsourceofmakeupwatertothosealreadyidentifiedintheprocedure.)Alternatemethodsfordeterminingfuelpoollevelshouldaccesstotherefuelingfloorberestricted.(Allowsleveldeterminationviauseoftheskimmersurgetankinstrumentationshouldnormalleveldetectionmethodsnotbeavailable.)CautionsshouldpoolboilingoccurwiththeventilationsystemsforzoneI,II,IIIisolatedregardingincreasedairborneradiation,thepotentialneedtoevacuatetherefuelingfloorandpotentialimpactstosafetyrelatedequipmentinthereactorbuildings.(Drawsspecificattentiontothepotentialimpactsofaboilingpool.)Theneedtomaintainpoollevel,notifyHPandmonitorbuildingreleasesshouldpoolboilingoccur.Allavailablemeansshouldbeemployedtocoolthepoolspriortoallowingthepoolstoboil.(Increasedtheemphasistonotallowthepoolstoboil.)Page14 ATTACMMENTTOPLA40122.ON-104(204)-001,U¹1:PCAF1-92-1390toRev.7&U¹2:PCAF2-92-0605toRev.,7~RESPONSETOLOSSOFOFFSITEPOWERIDATED12/17/92ThischangeprovidesinstructionsuponlossofoffsitepowerthatthefuelpoolcoolingsystemwilltripandthatON-135(235)-001"LOSSOFFUELPOOLCOOLING/COOLANTINVENTORY"(describedabove)shallbeperformed.3OP149(249)003~RHROPERATIONINFUELPOOLCOOLINGMODEU¹1:PCAF1-92-1389toRev.9RU¹2:PCAF2-92-0604toRev.9,Date:12/15/92:ThatshouldanRHRflowof6000gpmberequired,thatcontrolledstepincreasesto6000gpmshouldbeachievedallowingstabilizedconditionstobereachedateachstepincrease.(Thisassurespoolleveldoesnotdecreaseduetopoolcoolingsuchthatoperationatthehigherflowratesisnotadverselyimpacted.)Rev.11forU¹15U¹2,Date:4/21/93:Theneedtofillthefuelpooltoanappropriatelevelof8inchesbelowthefuelpoolcurbtoobtainRHRflowofapproximately6000gpm.ItalsoidentifiedthatfuelpoolfilImethodsaredelineatedinON-135(235)-001,(DATED12/2/92),"LOSSOFFUELPOOLCOOLING/COOLANTINVENTORY".FillingthefuelpoolstoanappropriateleveltoassureproperNPSHfortheRHRfuelpoolcoolingmodeofoperationisbasedonthepre-operationaltestingperformedontheRHRfuelpoolcoolingmode(ref.pre-operationaltestreportsP49.1andP249.1)andisfurtherconfirmedbyPP8LcalculationM-RHR-039Rev.0issued5/17/93.ThespecifiedheightprovidesanadequateheadofwatertoassureNPSHbykeepingtheskimmersurgetankfullduringRHRoperation.ThusadequateNPSHisassuredwhenthefuelpoolheightisadequatelymaintainedandmonitored.Acautiontocloselymonitorfuelpoollevelduringfillingastheadditionofcoldwatercouldcauseafuelpoolleveldrop.AcautiontocloselymonitorfuelpoollevelwhenRHRisplacedinserviceasthecoolingofthepoolcouldcausetheleveltodecrease.4.EP-PS-102,Rev.6,"TECHNICALSUPPORTCOORDINATOR:EmergencyPlan-PositionSpecificProcedure",DATE12/30/92ThischangeaddedasectiondiscussingtheconcernsassociatedwithlossofFPCevents.Theaddedsectionprovidesinstructionstodeterminewhenpoolboilingcanbeexpectedandtheactionsthatcanbetakentopreventormitigatetheconsequencesoffuelpoolboiling.Includedarecyclespecifictimetoboilcurves.Page15 JI ctATTACHMENTTOPLA4012A1.1.2PROCEDURESTOBEDEVELOPEDORREVISED1.OUTAGEPLANNING:EnhancementstotheSSESoutageplanningprocesswillbemadetoprovideforformalengineeringevaluationoftheSSESoutagescheduleforconformancetotheSSESdesignbasis.AdministrativecontrolstoNuclearDepartmentAdministrativeProceduresandfunctionalunitprocedures,asnecessary,willbemade.TheSSESUnit1fall1993refuelingoutageevaluationiscompleteandiscurrentlyundergoingreview.2.VALVESTROKINGPROCEDURES:A.ProcedureswillbedevelopedtoperformvalvestroketestingonthemanuallyoperatedRHRFuelPoolCoolingvalves,Theseprocedureswillbeimplementedduringthenextsetofunitoutages.B.ProcedureswillbeimplementedtotesttheESW(aspartofISIprogramtestingon2yrintervals)makeupvalves.ProceduresareissuedforUnit1(andimplemented)andproceduresforUnit2willbedevelopedandareplannedtobeperformedbytheendoftheyear.3.REVISIONTOEP-PS-102FORHVACACTIONSThischangewouldprovidedirectiontoshutdowntheReactorBuildingRecirculationfansifSFPboilingappearsimminentanditwillnotbepossibletorestorecoolingtotheSFPbecauseofaccessibilitytothereactorbuildingorotherreasons.Italsowillprovidedirectionfortheisolationofthenon-accidentunitfromtherecirculationplenumtopreventthespreadofairborneradiation.A1.2TRAININGENHANCEMENTSSSESoperatorshavebeeninformedoftheissuesandprocedurechangesthrough"hotbox"trainingandthroughthequarterlyOperationsre-qualificationtrainingprogram.Thetrainingconsistedofareviewoftheconcerns,theengineeringevaluationresults,andprocedurechangeswhichresulted.Additionally,engineeringsupportpersonnelreceivedabriefingoftheissuesandevaluationresultsinthefirstquarterof1993.Page16

<~g~2ATTACHMENTTOPLA4012A1.3MODIFICATIONENHANCEMENTSA1.3.1SFPLEVELANDTEMPERATUREAnIMOCEMSlevelmeasurementsystemwhichhasbeenseismicallydesigned,butnotqualifiedwillbeinstalled."Thesystemincludesanewprobemountedonanewseismicallydesignedbracketinthefuelpoolonelevation818'.Theprobeoutputrequiresthreeconductorswhichwillberoutedinembeddedconduitonelevation818'otheLowerRelayRoomintheControlStructure.AwallmountedelectronicspanelwillbeinstalledintheLowerRelayRoomwhichincludesaleveltransmitter.Theoutputoftheleveltransmitterwillbewiredtoadedicatedrecorderinthemaincontrolroomonabackrowpanel.ThetemperaturemeasurementsystemwillutilizethespareRTDintheexistingtemperaturesensorwhichisseismicallymountedinthefuelpool.ThisisalreadywiredouttoapanelonEL.818',andwillberoutedtoatemperaturetransmitterinthenewwallmountedelectronicspanelintheLowerRelayRoom.Theoutputofthetemperaturetransmitterwillberoutedtothededicatedrecorderinthecontrolroombackpanelusedforlevel.PowerforbothinstrumentloopsandtherecorderwillbenonClass1E,butwillbesuppliedfromaClass1Esourcethroughanisolatorsoastoprovideadditionalreliability.Thismodificationiscurrentlyscheduledtobeinstalledinthe1stquarterof1994.A1.3.2CASKSTORAGEPITDRAINLINEMODIFICATIONSPPALisconsideringnotinstallingthegatesbetweenthecaskstoragepitandSFPsduringnon-outageperiods.ThiswillgreatlyimprovetheabilitytorespondtoaLossofSFPcoolingeventsinceeitherunits'ystemscouldbeusedtocoolbothSFPs.However,whilethisimprovestheresponsetoalossofSFPcoolingevent,itincreasestherisktoaSFPdraindowneventthroughvalvemis-operation.Duringoutages,whenthegatesareremoved,additionalmeasuressuchasthetemporaryinstallationofastandpipeoverthecaskpitdrainaretakentopreventinadvertentdraindown.PP&Lisevaluatingvariousoptionsforinstallingpermanentphysicalbarrierstoassurethatinadvertentdraindowndoesnotoccur.ThesemeasureswillretaintheabilitytodraindownthepitforspentfuelcaskmovementswhileprovidingpositiveprotectionagainstdraindownduringperiodswhenthecaskpitiscrosstiedtotheSFPs.FORMAISEISMICQUALIFICATIONUNDERPP&L'SSQRTPROGRAMISNOTREQUIREDBASEDONTHESAFETYFUNCTIONOFTHEINSTRUMENTATION.,Page17

~~I~~'Li~kATTACHMENTTOPLA-4012APPENDIX2:UHSIMPACTANALYSISPage18 ATTACHMENTTOPLA4012ThedesignbasiseventfortheUltimateHeatSink(UHS)isaLOCA/LOOPwithaLOCAon.oneunitandasimultaneousforcedshutdownontheotherunit.Inthismode,theUHScanprovidesufficientcoolingwaterforsafetyrelatedequipmentfor30dayswiththewatertemperatureatorbelowthesystem'sdesigncoolingwatertemperature,ThedecayheatassumedintheUHSdesignanalysesforeachreactorrangesfromapproximately140MBTU/hrafter2.0hours,to36.6MBTU/hrafterday7,to22.6MBTU/hronday30oftheevent.ThisdecayheatdataisusedtheanalysisforboththeLOCAandthenon-LOCAunit."ThreeshutdownscenarioswereevaluatedtodeterminetheimpactthattheoperationoftheRHRFuelPoolCooling(FPC)modecouldhaveontheUHSminimumheattransfer(MHT)andmaximumwaterloss(MWL)designbasisanalyses.TheMHTanalysisassumesconditionswhichresultinthehighestpotentialforpondheat-up.TheMWLanalysisevaluatesworstcaseconditionsforpondinventorylosses.Itisconcluded,thatforallthree,theexistingdesignbasisUHSMHTandMWLanalysesarebounding.Thescenariosevaluatedare:CASE1Unit1shutdownforrefueling.Coreisoff-loadedandaheatloadof33.9MBTU/HRisresidentintheconnectedpools.Inthisscenario,thisunit'sRHRFPCmodeisusedtocoolthepool.Unit2experiencestheLOCA.ALOOPoccursconcurrently.Inthiscase,intermsofheatloadtotheUHS,theUnit1reactordecayheatisreplacedbytheheatloadfromthefuelpools.Asindicatedabove,theheatloadfromthefuelpoolsisexceededbythereactordecayheatrateforatleast7daysintotheaccident.ThedesignUHSMHTtemperatureresponsepeaksatabout1.8daysintothetransient.Therefore,theUHSMHTdesignbasisscenarioboundsthisshutdowncasesincetheLOCAunitreactordecayheatcontributionisthesameforbothcases,andthedesigncase'snon-LOCAunitdecayheatratefarexceedstheheatloadcontributionfromthefuelpoolsduringthecriticalperiodforpondheat-up'otential(i.e.,lessthan3days).CASE2Unit1hasjustcompletedarefuelingoutageandtheheatloadintheconnectedfuelpoolsis7.7MBTU/hr(basedonU17RIOdecayheatvalues).Timetoboilis3.6days.Unit1orUnit2hastheLOCA.Page19 r4~tttC./

ATTACHMfNTTOPLA4012ALOOPoccursconcurrently.RHRFuelPoolCoolinginitiatedonday2.Non-LOCAunitiscooledbyshutdowncoolinguntilday2whenRHRisswappedbetweenthefuelpoolcoolingandshutdowncoolingmodes.TheshutdownscenarioforthiscaseisidenticalasthatfortheUHSMHTdesignbasisscenarioexceptthat,approximatelytwodaysintotheaccident,thenon-LOCAunitRHRheatexchangerinshutdowncoolingmodeisswappedbetweenfuelpoolcoolingandshutdowncoolingmodesasrequiredto.maintainshutdowncoolingandpreventthefuelpoolsfromboiling.ThisconditionisalsoboundedbytheUWSMHTdesignbasisanalysisinthat:a.Thefuelpoolcoolingheatloadof7.7MBTU/hrislessthanthedesignbasisreactordecayheatrateforthe30dayaccident.b.Switchingthenon-LOCAunitRHRheatexchangertofuelpoolcoolingatapproximatelytwodaysintothetransienteffectivelyreducestheheatloadintothespraypondatthistime.Subsequentnon-LOCAunitRHRheatexchangerswappingbetweenshutdowncoolingandfuelpoolcoolingmodeswillresultinalowerthandesignintegratedpondheatloadfortheperiodbetween2and30days.Consequently,theUHSdesigntemperaturewillnotbeexceeded.c.*AnaddedconservatisminthisassessmentisthattheUHSMHTdesignanalysisassumesbothunitsreactor.decayheatratebasedon2effectivefullpoweryears(EFPY)ofoperationwhereasinthiscaseoneunithasjustreturnedfromarefuelingoutageandthusgeneratesmuchlessdecayheat.CASE3Unit1hasjustcompletedarefuelingoutageandtheheatloadintheconnectedfuelpoolsis7.7MBTU/hr(basedonU17RIOdecayheatvalues).Timetoboilis3.6days.Unit2orUnit1hastheLOCA.ALOOPoccursconcurrently.RHRFuelPoolCoolinginitiatedonday2.Alternateshutdowncoolingisusedtocoolthenon-LOCAunitandRHRfuelpoolcoolingusedtocoolthefuelpoolsstartingonday2.Page20

<I~.ATTACHMENTTOPLA4012Theshutdownscenarioforthiscaseis~essenttatlthesameastheUHSMHTdesignbasisscenarioexceptthatamaximumof7.7MBTU/hroffuelpoolsheatloadsisaddedatabout2daysintothetransient.ThiseventisdeemedtobeboundedbytheUHSMHTdesignbasisanalysisinthat:a.AsindicatedintheassessmentforCase2above,thedesignbasisdecayheatforbothunitsisidenticalandequivalent,to2EFPYofoperation.However,thiscase'snon-LOCAunitisassumedtohavejustreturnedfromarefuelingoutage,inordertomaximizethefuelpoolheatload,andthusgenerateslessdecayheat.b.TheUHSdesigndecayheatrate2daysaftershutdownisover60%higherthanthatafter,say,onemonthofoperation.Thisconservativeestimateresultsinover30MBTU/hrexcessdecayheatattwodaysintothetransientascomparedtothe7.7MBTU/hraddedheatloadfromthefuelpools.c.Asanaddedconservatism,calculationsalsodemonstratethatthetwoloops/foursprayarraysoperationrequiredforthiscaseafter2daysismoreefficientforpondcoolingthanthesingleloop/twoarraysoperationusedindesignbasisanalyses.UHSSUMMARYThus,ithasbeendemonstratedthatalltheaboveshutdownscenariosfortheUHSresponsetouseoftheRHRFuelPoolCoolingmodeareboundedbythedesignbasisUHSMHTanalysis.TheUHSMWLresponsetotheseconditionsisconsideredboundedbythedesignUHSMWLanalysisinthat:a.ThedesignbasisUHSMWLanalysismaximizesdriftandevaporationwaterlossesbyassuming2RHRheatexchangersinserviceperunitforthedurationofthe30datransient.bTheworstcasescenariofromaUHSMWLstandpoint,Case3,maypotentiallyuse2RHRheatexchangersperunitbutonlyaftertwodaysintothetransient.c.TheUHSMWLdesignbasisdecayheatloadishigherthanthatofthefuelpoolcoolingscenariosandthusresultinspraywatertemperaturesandconsequently,higherevaporativelosses.d.ThedesignbasisUHSMWLanalysisassumeslossofpondinventoryforfuelpoolmake-up(70CPMstarting24hrs.intothetransient)whichis,ofcourse,avoidedifthefuelpoolsarenotallowedtoboil.Page21 rw.!'+.k ATTACHMENTTOPLA4012FICURESPage22

REFUELINGFLOORUNITNlRECIRCREACTOR~SUCTIONBLDGRECIRCDISCHARGEUNITN2REACTORBLDGSGTSFlGURE1 LMIT2LAITIHHgISlKN4SKPARATERANTtÃYFTTSTTOIAlKPITI-CII-CIV'LVKPITSI0IIKACTIN'IKlDSTTNAGEAD1AQQQtHNKhREACTORBUILDING=L.8IS'-0 UNIT2~~UNITI~y)'SPENT)UELNKIKKERSUlNK174KCASKPIT:~~BKIKNEISllRGRTANKg~SPAT25307IA253011825309IA25107025309OA2535OO2530loa~~2S3O9O8253S2530108P253o918FROHESIIFROMES1125300125302110FUELPOOL1530011301153019AlORINTOCLEANNIOSup.POOLORYHELLSPRAVTOLPCj251060251FoodIKILTEX%,IARINHEATEXCH,HV251F003ARHRAPINPALOOPFROHSUPPRFSSIONPOOLHV251F006AHV251FoolAPBSUSERVICENAIERIBIA18FUELPOOLCOOLIHOPUIIP8 0s'.+4ka