ML18026A417

Forwards Revised Response to NRC Station Blackout Safety Evaluation Dtd 920114,revising Diesel Generator Target Reliability to 0.975,based on NRC Position.Resolution of Cabinet Temp Concern Will Be Submitted by 920501

ML18026A417
Person / Time
Site:	Susquehanna
Issue date:	03/13/1992
From:	KEISER H W PENNSYLVANIA POWER & LIGHT CO.
To:	MILLER C L Office of Nuclear Reactor Regulation
Shared Package
ML17157B098	List: ML17157B097 ML18026A417
References
PLA-3745, TAC-M68613, TAC-M68614, NUDOCS 9203230281
Download: ML18026A417 (34)

Text

.,ACCELERATEDDISTRIBUTIONDEMONST$A.TIONSYSTEMREGULA.YINFORMATIONDISTRIBUTIO.SYSTEM(RIDS),~'7ACCESSIONNBR:9203230281DOC.DATE:92/03/13NOTARIZED:NODOCKETFACIL:50-387SusquehannaSteamElectricStation,Unit1,Pennsylva0500038750-388SusquehannaSteamElectricStation,Unit2,Pennsylva05000388AUTH.NAMEAUTHORAFFILIATIONKEISERgH.W.PennsylvaniaPower&LightCo.RECIP.NAMEREC1PIENTAFFILIATIONMILLER.C.L.ProjectDirectorateI-2R

SUBJECT:

ForwardsutilrevisedresponsetoStationBlackoutRuleperNRC920114SafetyEvaluationw/answersattachedtoallbutIoneNRCrecommendation.QueryonCRinstrumentcabinettemptobeanswerednolaterthan920501.D,DISTRIBUTIONCODE:A050DCOPIESRECEIVED:LTRENCLjSIZE:g5f~f$TITLE:ORSubmittal:StationBlackout(USIA-44)10CFR50.63,MPAA-22/0500038705000388ADRECIPIENTIDCODE/NAMEPD1-2PDINTERNAL:ACRSNRRPD2-4PMTAMNRR/DST/SELBNRR/DST/SRXB8EEXTERNAL:NRCPDRNOTES:COPIESLTTRENCL11111133111122RECIPIENTIDCODE/NAMERALEIGHiJ.AEOD/DSP/TPABNRR/DET/ESGB8DNRRDST/PLB8D1GFILE01NSICCOPIESLTTRENCL111122331111DDNOTETOALL"RIDS"RECIPIENTS:PLEASEHELPUSTOREDUCEWAS'ONTACTTHEDOCUMENTCONTROLDESK.ROOMPl-37(EXT.20079)TOELIMINATEYOURNAMEFROMDISIRIBUTIONLINISFORDOCUMENTSYOUDON'TNEED!ADDTOTALNUMBEROFCOPIESREQUIRED:LTTR19ENCL19 PennsylvaniaPower8LightCompanyTwoNorthNinthStreet~Allentown,PA18101-1179~215/774-5151HaroldW.KeiserSeniorVicePresident-Nuclear215/774<194NRl31992DirectorofNuclearReactorRegulationAttention:Mr.C.L.Miller,ProjectDirectorProjectDirectorateI-2DivisionofReactorProjectsU.S.NuclearRegulatoryCommissionWashington,D.C.20555SUSQUEHANNASTEAMELECTRICSTATIONRESPONSETOSTATIONBLACKOUTSAFf"TYEVALUATIONPLA-3745FILER41-2

Reference:

RESPONSETOTHESTATIONBLACKOUTRULEFORSUSQUEHANNASTEAMELECTRICSTATION,UNIT1AND2PACNOS.M68613ANDM68614)DatedJanuary14,1992.

DearMr.Miller:

ThisletterprovidesthePennsylvaniaPower&LightCompany(PP&L)revisedresponsetotheStationBlackout(SBO)RuleasrequiredbythereferencedNRCSafetyEvaluation.Thisresponse(attached)revisesdieselgeneratortargetreliabilityto0.975basedonyourposition,andprovidestherequestedjustificationtosupportPP&L'soriginalpositionthatSSESisonlyrequiredtocopewithaSBOeventfor4hours.However,itshouldbenotedthatathoroughevaluationwasundertakentoreviewthestaffsconcernsregardingtheneedandabilityforSSEStocopefor8hours.ResultsofthisevaluationconcludedSSEShasthecapabilitytocopefor8hoursandlongerifrequired.WiththeexceptionofafinaltechnicalresolutiontoyourquestionregardingControlRoominstrumentcabinettemperatures,theattachmentrespondsinfulltoeachofyourrecommendations.OurresolutiontothecabinettemperatureconcernwillbeforwardedtoyounolaterthanMay1,1992.9203230281920313PDRADOCK05000387PPDR

-2-FILER41-2PLA-3745Mr.C.L.MillerQuestionsregardingthisrevisedresponseshouldbedirectedtoMr.A.K.Maronat(215)774-7852.Verytrulyyours,H.W.KeiserAttachmentcc:NRC3)ocnment:ControlDeaR(original)NRCRegionIMr.G.S.Barber,NRCSr.ResidentInspector-SSESMr.J.J.Raleigh,NRCProjectManager-Rockville

~~q~,9203230281ATTACHMENTTOPLA-3745I~NTRDUCTINTheStationBlackoutRule(10CFR50.63)wasinstitutedin1988andrequiredlicenseestoassesstheirabilitytocopewithastationblackout(SBO)ofaspecifiedduration.In1989,PP&LsubmittedtheresultsofourcopingstudytotheNRC,concludingthatSusquehannaSES(SSES)mustbeabletocopewithastationblackoutfor4hoursandmaintainanEmergencyDieselGenerator(EDG)reliabilityof0.975(97.5%).InFebruaryof1991,PP&LreviseditsEDGtargetreliabilityvaluefrom0.975to0.95basedonaspraypondbypassvalvemodification.OnJanuary14,1992,NRCissueditsSafetyEvaluationoftheSSESSBOsubmittalconcludingthatSSESwasan8hourcopingplantrequiringEDGreliabilitybemaintainedat0.975.ThefollowingisanitembyitemresponsetotherecommendationsidentifiedintheNRCSafetyEvaluation.c-".STATION,::::>SL'ATCKOUT:;,::::DUR'ATION>".ltNRRKMMENDATION:ThelicenseeneedstochangetheEDGreliabilitytargetfrom0.95to0.975andthecopingdurationfrom4hoursto8hours.P~PRLRA)CopingDurationOneinputtothedeterminationofrequiredSBOcopingdurationisthe"returntime"ofextremelyhighwinds(>125mph).Aspartofouroriginalcopingassessment,PP&LcontractedwithDames&MooreConsultingEngineersforthecalculationofthis"returntime"forSSES.Dames&Mooredeterminedthisvaluetobe-6.7E-4/yr.(aboutoncein1500years)usingdataspecifictoSSES.Anyreturntimevaluelessthan1.OE-3/yr,coupledwithoursevereweatherandoff-sitepowerdesignclassification,placesSSESina4hourcopingcategory.TheNRCevaluationdidnotcredituseofsitespecificdataduetothisdatabeingapplicableforwindsat10metersofftheground,ratherthantherequiredassessmentheightof30metersfromtheground(averagetransmissiontowerheight).Itwasthereforeconcluded,basedonNUMARCTable3.2,thatthereturntimeforSSESwasmorefrequentthanonceper1000yearsandthatSSESmustcopewithaSBOfor8hours,Page1

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ATTACHMENTTOPLA-3745Toaddressthiscopingdurationconcern,PP&LinvestigatedthebasisofTable3.2inNUMARC87-00andcontractedagainwithDames&Mooretodeterminethereturntimeofwindspeedsat30meters.ConversationswithbothNUMARCpersonnelandNRCstaffindicatedthattheuseofsitespecificdataisacceptable.TheNRCcautionedthattheuseofsuchdatashouldaccountforwindspeedsof125mphat30metersandconsiderNationalBureauofStandards(NBS)publications118and124,aswellasseveralNationalOceanicandAtmosphericAdministration(NOAA)documents.NotethattheuseofsitespecificdataisencouragedinNUMARC87-00.NBS118providesamethodofscalingwindspeedstovariousheightsandprovidesmeasuredweatherdatafrom129meteorologicalstationsacrosstheUSmainland.ItisthisdatawhichPP&LandDames&MoorebelieveprovidesthebestestimatesofwindspeedreturntimesatSSES.UsingthemethodofNBS118,the125mph"fastestmile"windspeedat30metersisscaledtoa"fastestmile"windspeedof107mphat10meters(thenormalizedheightofallreportedweatherdata).UsingthedataformeteorologicalstationsclosesttoSSES,NBS118providesthefollowing"returntimes"forvariousfastestmilespeeds:FastestMileWindSpeed(mph)ReturnTimeears1,0005,00010,00050,000100,000500,0001,000,000Scranton60.8667.3470.1276.5879.3685.8288.6095.0697.84Harrisburg70.5780.4984.7594.6498.90108.79113.05122.95127.21Page2 ATTACHMENTTOPLA-3745Inaddition,Dames&Moorehavecalculatedtheprobabilityofexceedingvariouswindspeedswithin1000years,alsobasedonthedataandmethodsinapaperbyH.C.S.Thorn:ProbabilityofExceedancein1000rsScrantonHarrisburgFastestMileWindSpeed(mph)0.5000.2500.1000.0500.0057275798292879299103117Fromthefirsttableabove,onecanseethatthereturntimeofawindspeedof107mphat10metersisexpectedtobegreaterthan1millionyearsatScrantonandalmost50,000yearsatHarrisburg.Table2shows'thattheprobabilityofexceedingthe107mphwindspeedwithin1000yearsislessthan1%atScrantonandabout3%atHarrisburg.UsingthedatafromHarrisburginTable1,theexpectedreturntimeofa125mphwindat30metersis-37,500years.PP&Lalso-reviewedNBS,124forapplicability.NBS124reliesontheextrapolationofcoastalweatherdatatoinferwindspeedsinland.Further,thismethodofextrapolationassumesinterveningterraintobeopenandgrasscovered.SinceSSESislocatedwithinavalleyseparatedfromthecoastbyapproximately100milesofhillsandforest,theextrapolationishighlyinaccurate.Thus,PP&LviewsNBS124asvalidonlyforscopingcalculationsandshouldonlybeusedintheabsenceofbettertechniques/data.PP&LconsiderstheprecedingargumentsanddatasufficientjustificationfornotusingTable3.2ofNUMARC87-00fordeterminingourESWcategory.Further,thisdatashowsthatthereturntimeofwindsinexcessof125mphatSSESishighlylikelytobegreaterthan1000years.Thus,itisconcludedthattheESWcategoryof"2"originallyreportedinourcopingstudyisfullyjustified(thedataactuallyjustifiesanESWclassificationof"1"),andthatSSESremainsa"Pl"plant(perNUMARC87-00)requiringaSBOcopingtimeof4hours.B)EDGTargetReliabilityIn1991,PP&LinformedtheNRCthatforpurposesofcomplyingwiththeSBOruleourtargetEDGreliabilitywastobe0.95(95%).Inmakingthisdetermination,PP&Lreliedontheuseof"staggeredoperation"ofRHRpumpstocoolbothsuppressionpools.Staggeredoperationisrequiredbecause,althoughinprincipleanytwoEDGscancoolbothunits,inactualitytherearetwocombinationsofEDG's(AandC,orBandD)whichresultinonlyoneRHRpumpineachunitavailabletoalternatelycoolthesuppressionpools.Page3 i

eATTACHMENTTOPLA-3745TheNRCnotedthattheuseofstaggeredoperationdidnotmeetthe"connectabilitycriterion"andwasdeterminedtobeanunacceptableincreaseinoperatorburden.ThiscriterionwasexplainedindocumentationprovidedbytheNRCtoNUMARCaftersubmittaloftheSSESSBOanalysis.TheNRCconcludedthattoavoiduseofstaggeredoperation,3ofthe4EDG'swouldberequired.Further,theNRCnotedthatifonlydieselsAandBstart,nocontrolstructureHVACwouldbeavailable.PP&LhasperformedacalculationofsteadystatecontrolroomtemperatureusingthemethodinNUMARC87-00andassumingthatthemeasured,normalcontrolroomheatloadexists.Theresultofthiscalculationisthatthecontrolroomtemperaturewillnotriseabove111'FintheabsenceofnormalHVAC.Becausetemperatureremainslessthan120'F,thecontrolstructureenvironmentremainsacceptable.Basedontheinabilitytotakecreditforstaggeredoperation,PP&Lconcurswiththestaff'spositionin"requiring3of4EDGsandthereliabilitytargetvalueof0.975.:;::ST@'TIOÃ:;::'.SL'A'CEO'::,:,::COPINO.":..:.CAPASILITY::,::,::,'=:,',llNRRECMMENDATIN'heNRCmadethefollowingfourrecommendationsbasedontheirpreviousdeterminationthatPP&LhadtoaddresstheneedforSSEStocopewithan8hourStationBlackout.1)Thelicenseeneedstoconformtoan8hourcopingdurationandincreasetheEDGreliabilitytargetfrom0.95to0.975.2)ThelicenseeshouldprovideaproceduretorefilltheCSTfromtheRWSTduringanSBOevent.3)ThelicenseeshouldaddtheportableACgeneratortothelistofSBOequipment,provideproceduresforitsutilization,andapplytoitanappropriateQAprogram.TheportableacgeneratorshouldmeetthecriteriainAppendixBofNUMARC87-00.Alsothelicenseeshouldreplacebattery1D650withahighercapacitybatteryorprovidechargingcapabilitytotheexistingbatterytoextenditssupportforthe8hourSBOduration,andrecoverythereafter.Thelicenseeshouldincludealltheanalysesandrelatedinformationinsupportingdocumentationthatistobemaintainedbythelicenseeforpossiblestaffreview.4)Thelicenseeshouldprovideforstaffreviewafulldescription,includingthenatureandobjectivesofanymodificationrequired.TheanalysesandrelatedinformationshouldalsobeincludedinthesupportingdocumentationthatistobemaintainedbythelicenseeinsupportoftheSBOsubmittals.Page4 Slipl(ii0

~RP~PLRNR'2RATTACHMENTTOPLA-3745Asaddressedintheinitialsectionofthisresponse,PP&LconcludesthatSSESmustcopewithaSBOeventfor4hours.Thisconclusionissupportedby.theuseofsitespecificweatherdata(attherequiredassessmentheight).AsfortheEDGreliabilitytargetvalue,PP&LhasreviewedtheNRCconcernsandhasconcurredwiththestaff'sfindingthattheconfigurationofSSESmandatesanEDGreliabilitytargetvalueof0.975.ThisreliabilityvaluehasbeenincludedintheEDGReliabilityProgramdevelopedinaccordancewithNUMARC87-00AppendixD.PP&LhasthoroughlyevaluatedtheabilityofSSEStocope8hourswithanSBOevent,includingallareasofconcernidentifiedintheNRCSafetyEvaluation.PP&LisconfidentthatSSEShastheabilitytocopefor8hoursandlongerifrequired.SincePP&LhasdemonstratedthatSSESisa4hourcopingplantthisinformationwillnotbeprovidedinsupportofourrevisedsubmittal,butisavailableforreview.';"':;EFFECTS::.".,"OF.,:,:LOSS:;OF..'",VENTILh;TION~:;iNRRECMMENDATIThelicenseeshould:I)provideadditionalinformationand/ortechnicaljustificationfortheinitialconditionsandassumptionsusedintheheat-upanalysisforeachareaofconcern,2)withregardtoCOTTAPcomputercode,providedetailedinformationtoaddressthestaff'sconcernsasidentifiedabove,and3)re-performtheheat-upanalysisforeachareaofconcernandforan8hourcopingdurationtakingintoaccountthenon-conservatismasidentifiedintheSAICTER.P~PRLRNR-CCPPAP2C1TheuseoftheCompartmentTemperatureTransientAnalysisProgram(COITAP)computercodehasbeenpresentedtothestaffaspartofoursubmittalstoresolvesteamleakdetectionTechnicalSpecificationchanges.AttachmentAcontainsauser'smanualfortheCOTTAPcomputercodeandacopyofarecentpaperpublishedinNuclearTechnologywhichdescribesthemethodologyusedintheCOTI'APprogramandpresentssomeoftheverificationcalculationswhichhavebeenperformed.Theuser'smanualpresentssomeofthecalculationswhichwereperformedagainstproblemsthathaveexactanalyticalsolutions.ThereferredpaperpresentsthemethodologyalongwithcalculationswhichhavebeenbenchmarkedagainstcalculationsperformedwiththeCONTAINcomputerprogram.Inaddition,theprogramandcomputationpackagehavebeenindependentlyreviewedbyGilbertAssociates.PP&LalsomaintainsaQualityAssurancefile/packagefortheCOTTAPcomputercode.APage5

~tof ATTACHMPITTOPLA-3745Intheoriginalcopingassessment,twobasicCOTTAP2calculationswereperformed:anassessmentofDominantAreasofConcern(DACs);andanevaluationofcontrolroomcabinets.ForBWRs,theDACsaretheHPCIandRCICrooms,andthemainsteamtunnel(NUMARC87-00).Themainsteamtunnelisconsideredbecause,apparentlyatsomeplants,HPCIandRCICareisolatedonhightemperatureinthetunnel.AtSSES,theHPCVRCICisolationsdonotcomefrommainsteamtunneltemperaturebutfromsensorslocatedonthe683footelevationofthereactorbuildingcommontobothHPCIandRCICpiping.DuringSBO,onlytheRCICisolationlogicispowered.Thus,forSSES,themainsteamtunnelisnotatrueDAC.Thecommonpipingarea,calledtheRHRpipingareainthecalculation,isaDAC.PP&LrecalculatedtheDACtemperaturesusingCO1TAP2and"conservative"inputs.Inputsincludeduseof"maximumnormal"roomtemperaturespertheFSAR.Outsideairtemperaturewasassumedtobeaconstant95'F.Theinfluence.ofhotpiping(includingfluedheads)wasaddedtotheHPCI,RCIC,RHRpipingarea,andthemainsteamtunnel.(TheabsenceofthishotpipeloadingcausedthecooldownofthemainsteamtunnelnotedintheSAICTechnicalEvaluationReport).Noengineeringreferenceforacon'cretethermal'conductivityof0.7couldbefound.However,thisvaluewaschangedfrom1.0to0.7,pertheTER.Theactualinputdeck,andthejustificationforallinputvaluesused,appearsinthedetailedcalculation.TheresultsoftheCOTTAP2calculationsarepresentedinthetablesbelow.OriginalSubmittal:Temperature('F)NewCalculation:ROOM8hours72hours8hours72hoursHPCIRCICRHRPipingMSTunnel113118123114117117114107125150119130171FromTable3,thetemperaturesoftheDACsremainlessthanthe180'Foperabilitylimit,evenat72hours.Theinclusionofthehotpipe.loadsdoescause,significantincreasesintunneltemperatures.Page6 0ATTACHMENTTOPLA-3745Temperature('F)ROOMRHRPipingMSTunnelCOTTAP2at72hours130171NUMARC87-00176Table4presentsacomparisonofthetwohottestDACtemperaturesascalculatedbybothCOTTAP2andthemethodofNUMARC87-00.WhileitappearsthattheNUMARCmethodproduces"conservative"results,itmustbenotedthattheNUMARCcalculationproducesasteadystate,infinitetimeresult.TheCOTTAP2resultsarenotsteadystatebuttimedependent,andat72hoursthetemperaturesintheseroomsarestillincreasing.Atlongerandlongertimes,onewouldexpectbetteragreementbetweenthetwomethods.Theresultsoftheabovetableshowthattheagreementbetweenthetwomethodsisquitegood.TheTERmadereferenceto"oscillatory"temperatureprofiles.ReviewoftheoriginalCOTI'AP2workrevealednosuchprofiles.Thereviewersmaybereferringtotemperatureprofileswhichpeakanddropintheshortterm,thencontinuealongtermtemperaturerise(Figure1).ThelargeearlypeakiscausedbyACmotorheatloadswhichdecayaway.Atlatertimes,theroomisheatedbysurroundingwalls.Thisresultisconsistentwithexpectedbehavior.ThereviewersquestionedPP&L'suseofCOTTAP2forcalculationofinstrumentcabinettemperaturesandseveralassumptionsusedinthesecalculations.TheoriginalimpetusforusingCORI'AP2tocalculatecabinettemperatureswasthedesiretoavoidopeningcontrolstructurecabinetdoorsandnotimposeunnecessaryoperatorburden.PP&LconcurswiththeNRCthatmodificationsareneededtotwoassumptionsusedinthecabinettemperaturecalculations.TheNRCquestionedouruseof120'Fasthecontrolroomtemperature,implyingsuchatemperaturewasoverlyconservative.Inresponse,theinfinitetimecontrolroomtemperature,assumingmeasurednormaloperatingheatloads,hasbeencalculatedusingthemethodofNUMARC87-00.Theresultingcontrolroomtemperatureis111'F.TheTERquestioneduseof180'Fastheoperabilitylimitofcontrolroominstruments.Basedoninformationreceivedfromequipmentmanufacturers,wecurrentlybelievethecorrectlimitis140'F,andareperformingareevaluationonthisbasis.ThisevaluationwillbecompletedandsubmittedtotheNRCnolaterthenMay1,1992,Page7

<r ATTACHMENTTOPLA-3745';:;CONTAPC41i22lT,!ISOLATION','RREMMENDATION'helicenseeshouldlistthevalvesidentifiedinanappropriateprocedureandidentifytheactionsnecessarytoensurethatthesevalvescanbefullyclosed,ifcontainmentisolationisrequiredduringanSBOevent.Thevalveclosureshouldbeconfirmedbypositionindication(local,mechanical,remote,processinformation,etc.)P&LRThepenetrationswhichhavebeenidentifiedbytheNRCasrequiringtobeproceduralizedaretheResidualHeatRemoval(RHR)andCoreSpray(CS)suctionlinesalongwiththeContainmentSprayline.ContainmentisolationoftheselineshasbeenaddressedandapprovedbytheNRCpriortothissubmittal.Thefollowingidentifiesthatapprovedapproach.SusquehannaSESFSARsection6.2.4.3.6statesinpartthat"Containmentisolationprovisionsforcertainlinesinengineeredsafetyfeatureorengineeredsafetyfeature-relatedsystemsmayconsistofasingleisolationvalveoutsidecontainment.Asingleisolationvalveisconsideredacceptableifitcanbeshownthatthesystemreliabilityisgreaterwithonlyoneisolationvalveintheline,thesystemisclosedoutsidecontainment,andasingleactivefailurecanbeaccommodatedwithonlyoneisolationvalveintheline."Additionally,section6.2.4.3.6.3states,"AlthoughstrictlyspeakingtheHPCI,RCIC,CS,andRHRpumpsuctionlinesdonotconnectdirectlytotheprimarycontainment,theyareneverthelessevaluatedto10CFR50AppendixA,GeneralDesignCriteria56.Theselinesareeachprovidedwithoneremotemanuallymotoroperatedgatevalveexternaltothecontainmentandusetherespectivepipingsystemsasthesecondisolation,barrier..FortheRHRandCSvalvesthehandswitchesarekeylocked".Furtherinvestigationintothisissuerevealsthatsection6.2.4oftheNRCSafetyEvaluationReport(NUREG0776)forSusquehannaSSESdocumentstheNRCapprovalofmeetingthealternativeacceptancecriteriaspecifiedinsection6.2.4oftheStandardReviewPlan.Thissectionsummarizesthesealternativeacceptancecriteriaalongwithspecificallyidentifyingthelinesfoundacceptableviathismethod.Basedontheaboveexplanationwebelievethatcontainmentisolationisestablishedandcontainmentintegritywillbemaintained.Page8 tg~04'L ATTACHMENTTOPLA-3745:1'R'O.CEDURFS.:;::lANDl,TRAXNING,',REMMEATIThestaffexpectsthelicenseetoimplementtheappropriatetrainingtoassureaneffectiveresponsetoanSBOevent.PP&LRNEAppropriateplantpersonnelwillbetrainedonanyneworrevisedproceduresinaccordancewiththerequirementsofInitiative2,NUMARC87-00andReg.Guide1.155,section3.4.'-;:QUALITY>'A'SSUR'A'NCE'"'.AND;:::TECHggCAL"'-::,SPECIPICATION~):'RREMMEATIThestaffexpectsthattheplantprocedureswillreflecttheappropriatetestingandsurveillancerequirementstoensuretheoperabilityofthenecessarySBOequipment,'P&L'f4ItisPP&LsintenttosatisfytheQualityAssurance(QA)requirementsofReg.Guide1.155byupgradinganexistingproceduretoincorporateStationBlackout.ThisprocedureaddressesalltheReg.GuideQArequirementsandwillrequirethenecessaryInspectionsandTeststobeperformedinaccorda'ncewiththeOperationalQualityAssuranceProgram.::-;ED6'!RELIA'SILIIYiPROGRAM::::..":NRRKMMENDATIN'helicenseeshouldcompletetheimplementationofanEDGreliabilityprogramwhichmeetstheguidanceofRG1.155,Section1.2andprovideascheduleforitscompletion.ConfirmationthatsuchaprogramisinplaceorwillbeimplementedshouldbeincludedinthedocumentationsupportingtheSBOsubmittalsthatistobemaintainedbythelicensee.Page9 00'I0 ATTACHMENTTOPLA-3745PP&LRReg.Guide1.155specifiesthateachutilityestablishanEDGperformancemonitoringprogram.NUMARC87-00AppendixDcontainsguidanceforthedevelopmentandimplementationofsuchaprogram.PP&Lhascommittedtoimplementaprogramofreliabilitymonitoringand,asindicatedabove,PP&LmustmaintainanEDGreliabilityatorabove97.5%aspartofourSBOcopingstrategy.TheReg.GuideandNUMARCprovide"triggervalues"fordeterminingcompliancewithtargetreliability.NRCreviewersindicatedthatlackofthisdatainoursubmittalhinderedassessmentofSSESEDGreliability.Atthe97.5%reliabilitylevel,complianceisassumedifthefailurestostart/loadarelessthanorequalto3,4,and5outofthelast20,50and100startattempts,respectively.Asof2/10/92thefailurestostart/loadineachcategorywere0,0,and3,respectively.Thus,today,PP&Lcanaccepttheincreasedreliabilitytargetof97.5%.PP&L'sEmergencyDieselGeneratorreliabilitymonitoringprogramhasbeendevelopedanddocumentedinNuclearDepartmentAdministrativeProcedure-QA-0401entitled"EmergencyDieselGeneratorMonitoringProgram."ThisprocedurecomplieswiththereliabilityrequirementsdelineatedinAppendixDofNUMARC87-00,Rev.1.Reliabilitywillbemonitoredagainstasetof"triggervalues"withactionsspecifiedforvariouslevelsoftriggervalueexceedance.Page10 l~rvO.d4 ROOMTEMPERATURERESPONSETOASTATIONBLACKOUT200180160140~I-120I-1008010203040TIME(HRS)50607080LegendgHVACEQUIPRM0EXHfANRM~HVACEQUIPRM0HVACEQUIPRM6RECIRCPLENUM COTTAP:ACOMPUTERCODEFORSIMULATIONOFTHERMALTRANSIENTSINSECONDARYCONTAINMENTSOFBOILINGWATERREACTORS~~~"7MARKA.CHAIKOandMICHAELJ.MURPHYPennsylvaniaPower&LightCompany,Allentown,Pennsylvania18101ReceivedDecemberI,1989AcceptedforPublicationSeptember12,1990TheCompartmentTransientTemperatureAnalysisProgram(COTTAP)wasdevelopedbythePennsylva-niaPower&LightCompanyforpostaccidentboilingwater'reactor(BWR)secondarycontainmentthermalanalysis.Thecodemakesuseofpreviouslydevelopedimplicittemporalintegrationmethodsandsparsema-trixinversiontechniquestoallowmodelingofanen-tireBWRsecondarycontainment.Investigationsweremadewithamodelconsistingof121compartmentsand767heat-conductingslabs.Thesimulationpre-sentedinvolvesthenumericalintegrationof20101or-dinarydifferentialequationsovera30-hsimulationperiod.TwohoursofCPUtimewererequiredtocarryoutthecalculationonanIBM3090computer.TheCOTTAPcodeconsidersnaturalconvectionandradi-ationheattransferbetweencompartmentairandwalls'hroughadetailedflnitedifferencesolutionoftheslabconductionequations.Heatadditionfromhotpipingandoperatingequipment,andcoolingeffectsassociatedwithventilationflowsandcompartmentheatremovalunitsarealsoincluded.AdditionalcapabilitiesofCOTTAPincludemodelingofcompartmentheatupre-sultingfromsteamlinebreaksandsimulationofnat-uralcirculationcoolingincompartmentswithflowpathsatdifferingelevations.I.INTRODUCTIONUnderpostaccidentconditions,boilingwaterreac-tor(BWR)secondarycontainmentventilationsystemstypicallyisolatetopreventfissionproductreleasetotheenvironment.Sincecooledairisnolongercircu-latedthroughthesecondarycontainment,increasedcompartmenttemperaturesresult.Predictionsofpost-accidentcompartmenttemperaturesarenecessarytodeterminewhethersafety-relatedequipmentissub-jectedtotemperaturesthat'exceeditsmaximumdesignvalues.Safety-relatedequipmentmustbeoperableun-derpostaccidentconditionsinordertoeffectthesafeshutdownofthereactor.Afteranaccident,thesecondarycontainmentventilationsystemoperatesinarecirculationmodetopromoteairmixingbetweencompartmentsandtodilutelocallyconcentratedradioactiveisotopes.OriginaldesigncalculationsforPennsylvaniaPower&LightCompany's(PP&L)SusquehannaSteamElectricStation(SSES)assumedthatairrecircula-tionprovidedenoughmixingtoproduceafairlyuniformtemperaturedistributionthroughoutallsec-ondarycontainmentcompartments.Forthisreason,asingle-compartmenttransient.modelwasusedinthesimulationofpostaccidentconditions.Recentinvesti-gationsbasedonsteady-statecalculationshaveshown,however,thatsignificanttemperaturevariationscanexistbetweencompartments.ThesetemperaturevariationswerelargeenoughtopromptadetailedNUCLEARTECHNOLOGYVOL.94APR.199l ChaikoandMurphyPOSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSISmulticompartmenttransientanalysisofthesecondarycontainment.ToreanalyzethepostaccidenttransientbehavioroftheSSESsecondarycontainment,PP&LdevelopedtheCompartmentTransientTemperatureAnalysisPro-gram(COTTAP).Developmentofthisprogrambeganafteranevaluationofavailablecodesrevealedthatnonewerecapableofperformingasufficientlydetailedsimulationowingtothelargenumberofheat-conduct-ingstructuresfoundintheSSESsecondarycontain-ment.Forexample,theCONTEMPTcode,'hichisprobablythemostwidelyusedcontainmentanalysisprogram,canmodelasmanyas999compartmentsbutislimitedto99heat-conductingslabs.Incontrast,COTTAPcanmodelupto1200heat-conductingslabsand300compartments.Italsocontainsmodelsthatdescribeheatdissipationfromoperatingelectricalequipmentandprocesspiping.ACOTTAPmodeloftheSSES-1and-2secondarycontainmentstructuresconsistsof-120compartmentsand800heat-conduct-ingslabs.TheCONTAINcode2isamorerecentlydevelopedcontainmentsimulationprogramwithcomplexmod-elingcapabilities.Itis,however,designedspecificallyforprimarycontainmentsimulationandisnotwellsuitedforsecondarycontainmentmodelingbecauseithasnoprovisionsforenergyinputtocompartmentsfromheatloadssuchaselectricalpanels,lighting,mo-tors,andhotpiping.AdescriptionoftheCOTTAPcode,includingas-sumptions,governingequations,numericalsolutionmethods,andcodelimitationsisgiveninSec.II.Rep-resentativeresultsoftheSSES-1and-2secondarycon-tainmentanalysisarepresentedinSec.III,andcodeverificationisdiscussedinSec.IV.II.DESCRIPTIONOFTHECOTTAPCODEII,A.CompartmentMassandEnergyBalancesTheCOTTAPcodeallowsforairandwatervapormasstransferbetweencompartmentsbymeansofforcedventilation,leakage,andnatural,circulationflows.Aforcedventilationflowmodeldescribesheat-ing/ventilating/airconditioningsystems,andaleakagemodelsimulatesintercompartmentflowsthathregen-eratedbypressuredifferentials.Inaddition,anaturalcirculationmodelsimulatesgravity4rivenflowsbetweencompartmentsconnectedbyflowpathsatdifferingelevations.Steamcanalsobeaddedtoacompart-mentasaresultofpipebreaksorremovedthroughcondensationandrain-out.AirandwatervapormassconservationequationsforacompartmentwithNventilationpaths,NIleakagepaths,andN,naturalcir-culationpathsaregivenbyHNcVgWojYoj+gWgYIJ+gWoj(Y<jY)J-1j~ijmianddpIvuJvlV-"=gWj(1-Y,j)+gWg(1-YIJ)dljaijaiH~+gWy(Y-Ycj)+W~-Woold-Wlo>j=l(2)whereV=compartmentvolume(m3)t=time(s)pp=compartmentairandwatervapordensities,respectively(kg/m3)WJWIJWj-massflowratesassociatedwithj'thventilation,leakage,andcir-culationpaths,respectively(kg/s)Y=massfractionofairwithincom-partmentYj,YIJ--airmassfractionsindonorcom-partmentsforventilationpathjandleakagepathj,respectivelyY~--massfractionofairinadjoiningcompartmentassociatedwithcir-.culationpathjWq,=rateofsteamadditionduetopipebreaks(kg/s)Wd=steamcondensationrate(kg/s)W=rain-outrate(kg/s).ThevaluesWjandWljarepositiveforflowintothecompartmentandnegativeforflowoutofthecom-partment,whereasthecirculationrateWjisalwaysapositivequantity.Ventilationpathsaredescribedby'heirassociatedmassflowratesandidentificationnumbersofsourceandreceivingcompartments.Ven-tilationflowscanbetrippedofforonatanytimedur-ingatransientbysupplyingappropriatetrip-logicdata.Leakage,circulation,andpipebreakmodelsaredis-cussedinSec.II.Calongwithotherspecialpurposemodels.Informulatingthecompartmentenergybalance,itisassumedthatairbehavesasanidealgas.Moreover,-'orthetransientsofinterest,partialpressuresofwa-tervaporaretypically(Iatm.Therefore,itisassumedthatthesteamspecificenthalpydependsonlyontem-perature,i.e.,thevaporenthalpyisequaltotheen-thalpyofsaturatedsteamatthetemperatureofthe.gasmixture.Thepartialpressureofwatervaporwithinacompartmentiscomputedfromtheidealgasequationofstate,andthetotalcompartmentpressureiscalcu-latedasthesumoftheairandwatervaporpartialpressures.Withtheseassumptions,thecompartmentenergybalancebecomesNUCLEARTECHNOLOGYVOL.94APR.1991 Pb,k=totalcompartmentpressureifpipecontainssaturatedliquid(Pa)Pb<<ak=pipefluidpressureifpipecontainssaturatedsteam(Pa)hg(Pb,k)=specificenthalpyofsaturatedwatervaporatpressurePb,k(J/kg)hi(T)=specificenthalpyofsaturatedliquidwaterattemperatureT(J/kg)TJ,T>--donorcompartmenttemperaturesforventilationpathjandleakagepathj;respectively(K)TJ--temperatureinadjoiningcompart-mentassociatedwithcirculationpathj(K).Compartmentheatloadsfromlighting,electricalpan-els,motors,andmiscellaneousequipmentaremain-tainedconstantunlesstheyaretrippedon,off,orexponentiallydecayedduringthetransient.Hotpipingandroomcoolerloadsvarywithcompartmenttemper-atureandcanalsobetrippedonoroff.Inaddition,hotpipingheatloadscanbeexponentiallydecayedusingtheheatloaddecaymodeldiscussedinSec.(3)II.C.7.+(1-Yy)hg(T))-(1-Y)hg(T)],whereChaikoandMurphyPOSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSISVPaT+PaCpa(T)dhg(T)dT+P>rdTdr=-VTC(T)--Vh(T)-dPadP~dCdj'VTR-"+R,-+Qligitt+Qpanel+Qmotor+Qcooler+Qpiping+Qmisc+Qslab+Qbreak+Wbsilg(Pbreak)Wro)1J(T)-Wcoadhg(T)iVu+gWt>J[Y>>r)To)Cpa(Ttrj)+(IYoj)hg(Tpj)]J>>>1iVI+gWlj[Yi)TJJCpa(Tj))+(1Yg)hg(T(J)])=INc+gWcj[Yc)TcJCpa(TcJ)YTCpa(T)J=lT=compartmentgastemperature(K)Cp,(T)=specificheatofairattemperatureT(J/kgK)hg(T)=specificenthalpyofsaturatedwatervaporattemperatureT(J/kg)R,=idealgasconstantforair(288.7J/kgK)R=idealgasconstantforwater(461.4J/kgK)Qligbt,Qpanel>>Qmotor>Qcooler>>Qpiping>Qrnisc=compartmentheatloadsduetolight-ing,electricalpanels,motors,aircoolers,hotpiping,andmiscellane-ousequipment(J/s)Q,i,b=rateofheattransfertocompartmentair/watervapormixturefromsur-roundingslabs(J/s)II.B.SlabModelInthesecondarycontainmentofaBWR,compart-mentwalls,ceilings,andfloorsaregenerallyconcreteslabsthatrangeinthicknessfrom-0.3to-2m.Todeterminetheheattransferratebetweenacompart-mentatmosphereandtheboundingconcreteslabs,theone-dimensionalheatconductionequation(4)issolvedforeachslab.Here,T,(K)istheslabtemper-ature,andx(m)isthespatialcoordinate.Sincethethermaldiffusivityns(m/s)issuppliedasinputforeachslab,materialsotherthanconcretecanbemod-eledprovidedthatslabsareofuniformmaterialcom-position.Thisone-dimensionaldescriptionassumesthatslabedgeeffectsdo.notsignificantlyaffecttheoverallrateofheattransfer.BoundaryconditionsonslabtemperaturearegivenbyQb,k=heattransferratetoair/watervapormixturefromliquidexitingbreakasitcoolstocompartmenttemperature(J/s)and[Tl(r)Ts(0r)]aT,h,BxoksWb,--massflowrateofsteamexitingbreak(kg/s)46NUCLEARTECHNOLOGYVOL.94APR.1991 ChaikoandMurphywhereT>(t),T2(t)=temperaturesofcompartmentsad-jacenttotheslabk,=slabconductivity(J/msK)L,=slabthickness(m)h~,h2=heattransfercoefficients(J/mzsK).ThesolutionofEq.(4)subjecttoEqs.(5)and(6)givestheratesofenergytransferfromtheslabsurfacestotheadjacentgasmixtures.Thecoefficientshiandhzaccountfornaturalconvection,radiation,andcondensationheattransfer.Intheabsenceofcondensation,thecoefficienthlcanbeexpressedashi--ht+h/p,(7)whereh>andh~,arethenaturalconvectionandra-diationcomponents,respectively.NaturalconvectioncoefficientsareexpressedintermsoftheNusseltnumber,whichinturnisafunc-tionoftheRayleighandPrandtlnumbers.Fortheco-efficienthl,theappropriaterelationisNu=-=f(Ra,Pr),h)Ct.k(g)(~,+1)h/I:'4+a+b-c)elm,auaTau~(10)wherewhereCt.--slabcharacteristiclengthk=gasthermalconductivityandtheRayleighandPrandtlnumberstureare,respectively,definedbyo=Stefan-Boltzmannconstant(5.669x10sJ/mzsK4)e,=slabemissivityT,=averagetemperature,whichisdefinedbyTau=[(T"+Tsurf)/2)',(l1)forthegasmix-gpCI.lTs(0,t)-TI(t)ldvierp~ITICk(9)wherePOSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSISfreeconvectionfromaverticalplate.Forhorizontalslabs,free-convectioncoefficientsdependonwhetherthesurfaceisbeingheatedorcooledbythesurround-inggasmixture.AsrecommendedbyHolman,4thecorrelationofFujiiandImurasisusedwiththemod-ifiedcharacteristiclengthproposedbyGoldsteinetal.~tocomputethecoefficientforanarbitrarilyshapedslabwithheatedsurfacefacingupwardorcooledsur-facefacingdownward.Incaseswheretheuppersur-faceiscooledorthelowersurfaceisheated,thecorrelationsofLloydandMoran7areused.Diatomicgasessuchasnitrogenandoxygenarees-sentiallytransparenttothermalradiation;however,theemissivityofwatervaporwithrespecttothermalradi-ationissignificant.InCOTTAP,radiantenergyex-changebetweenaslabsurfaceandwatervaporcontainedwithinthesurroundinggasmixtureismodeledthroughtheuseofaneffectiveradiationheattransfercoeffi-cient[seeEq.(7)].Fortheapplicationsofinterest,tem-peraturedifferencesbetweenaslabsurfaceandthesurroundinggasmixturearerelativelysmall(typically(5K).Therefore,thefollowingapproximaterelationproposedbyHottelandSarofimforsmalltempera-turedifferencesisusedtocomputetheradiationcoef-ficient:whereg=accelerationduetogravity(9.8m/sz)p=coefficientofthermalexpansion(K')v=kinematicviscosity(mz/s)n=thermaldiffusivity(m/s)p=dynamicviscosity(kg/ms)Cv=specificheatoftheairhvatervapormixture-~(J/kgK).T=gastemperature(K)T~=slabsurfacetemperature(K)e,=emissivityofwatervaporevaluatedatT,u.TheCess-Lian'quations,whichgiveananalyticalapproximationtotheemissivitychartsofHottelandEgbert,"areusedtocomputethewatervaporemis-sivity.InEq.(10),chasthevalue0.45,andaandbareobtainedthroughdifferentiationoftheCess-Lianemis-sivityequationsGasmixturepropertiesusedinthecalculationoffreeconvectioncoefficientsareevaluatedatthethermalboundarylayertemperature,whichistakenastheav-erageoftheslabsurfacetemperatureandthebulkgastemperature.Forverticalslabs,coefficientsarecalculatedfromthecorrelationproposedbyChurchillandChu3forand81n[e(T,PP,PL)]aBin(PL)8ln[e(T,PP,PL,)]8ln(T)(12)NUCLEARTECHNOLOGYVOL.94APR.199147 losure',forin-ndcondensa-gwalls.Fora-nsationalonebecomingsat-ain-out)formgsmpartmentrel-ativehumiditylessthanorequaltounity,therainoutrateW(kg/s)iscalculatedfromthefollowingempir-icalmodel:surfacetemperaturedropsbelowthedewpoint(thesaturationtemperatureofwaterevaluatedatthepar-tialpressureofwatervaporinthecompartment)oftheair/watervapormixture.Heattransfercoefficientsforcondensationconditionsarecalculatedusingtheexper-imentallydeterminedUchida"correlation,whichin-cludesthediffusionalresistanceeffectofnoncondensibleW,=200(RH-0.99)max(WC,i)ifRH)0.99andgasesonsteamcondensationrates.InCOTTAP,initialcompartmenttemperatures,pressures,andrelativehumiditiesarespecifiedasin-putdata.Aninitialslabtemperatureprofileisdeter-minedbycomputingthesteadysolutiontoEqs.(4),(5),and(6)correspondingtotheinitialcompartmentconditions.Thisimpliesthatcompartmentshavebeenmaintainedattheirinitialconditionslongenoughforslabstoattainsteady-statetemperatureprofiles.W,=0.0ifRHs0.99,(16)whereRH=relativehumidityWs=totalsteamflowrateintothecompartment(kg/s)C,i=constantthatissuppliedaspartoftheinputdata(kg/s).ChaikoandMurphyFOSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSISwhereisolationofapipebreak(duetovalvecP,=a'rpat'alprcssue(Pa)stance)acompartmentbeginstocoolationcontinuestooccuronsurroundinP=watervaporpartialpressure(Pa)sufficientlyfastcooldownrate,condedoesnotpreventcompartmentairfromurated,andthusmoisturedroplets(rCondensationonaslabsurfaceoccurswhenthewithintheamixture.TomaintaincoII.C.SpecialPurposeModelsTheCOTTAPcodeincludesspecializedmodelstosimulatetheeffectsofpipebreaks,hotpiping,andcompartmentaircoolers.Leakageandnaturalcircu-lationmodelsarealsoincludedtodescribeintercom-partmentmasstransfer.Inaddition,thecodeincludesasimplifiedslabmodel,aheatloaddecaymodel,andacompartmentmodelinwhichtemperature,pressure,andrelativehumidityarespecifiedasafunctionoftime.II.C.l.PipeBreakModelWithinthescopeofthepresentmodel,pipesmaycontainsteamorsaturatedliquidwater.Inputdatade-finethetotalmassflowthroughthebreakWb,(kg/s)alongwiththetimeatwhichthebreakdevelopsandthelengthoftimeoverwhichfluidlossoccurs.Forpipescontainingsaturatedliquid,thesteamflowrateWb,exitingthepipe(kg/s)iscalculatedfromtheen-ergybalanceWbihy(P>)=Wbslig(P)+(Wbi-Wbs)h/(P),(14)whichdescribestheisenthalpicexpansionoffluidfrompipepressureP~tocompartmentpressureP.Theliq-uidfraction,whichdoesnotflashasitleavesthepipe,isassumedtocooltocompartmenttemperature,andthedissipatedsensibleheatistransferreddirectlytothecompartmentair/watervapormixture.Forthecasewhereapipecontainssteam,allofthemassandenergyexitingthebreakisdepositeddirectlyintothecompart-mentgasmixture.Rain-outphenomenacanbeimportantincompart-mentscontainingpipebreaks.Forexample,following48II.C.2.HotPipingModelInmanysecondarycontainmentcompartments,themajorheatsourceconsistsofpipingthatcontainsreactorsteamorcoolant.Theheatadditionratetoacompartmentairhvatervapormixturefromahotpipeiscalculatedfromalp(<gUp7rLpDp[Tj'(t)]>(I7)where.~Up=overallheattransfercoefficient(J/m2sK)L~=pipelength(m)D~=outsidediameterofthepipe(orinsulationifthepipeisinsulated)(m)Tj--pipefluidtemperature(K)T=compartmenttemperature.Theoverallheattransfercoefficientiscalculatedbythecodebasedoninitialcompartmentconditions;theco-efficientisthenmaintainedconstantthroughoutthetransient.II.C.3.AirCoolerModelCoolingunitsareusedinanumberofsecondarycontainmentcompartmentstoremoveheatgeneratedbyequipmentsuchasemergencycorecoolingsystems(ECCS)injectionpumpsandhigh-voltagebusesandtransformers.HeatremovalratesofcoolingunitsarecalculatedfromQcool(t)Ccool(T(t)Tcool(t)j~(Ig)NUCLEARTECHNOLOGYVOL.94APR.199t ChaikoandMurphyPOSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSISwhereT,/(t)=averageoftheinletandoutletcoolingwatertemperaturesC,/=constantthatiscomputedfromspec-ifiedinitialvaluesofthecoolingloadQ,/,theinletcoolingwatertempera-ture,thecoolingwaterflowrate,andthecompartmenttemperatureT.Anenergybalanceonthecoolingwateryieldstheout-letcoolingwatertemperature.II.C.4.LeakageModelsTheCOTTAPleakagemodelsimulatespressure-inducedintercompartmentalmasstransferthroughopeningssuchasdoorwaysandventilationducts.In-tercompartmentleakageiscalculatedbybalancingthepressuredifferentialbetweenthecompartmentswithanirreversiblepressureloss.Thus,theleakageratesat-isfiesP(t)-P,(t)Kinesia(t)[Win(t)](19)2p//(l)AwwhereP1,Pz=pressuresofthecompartmentsassociatedwiththeleakagepath(Pa)WN=leakagerate(kg/s)K~=irreversiblepressurelosscoefficientA//,--leakagearea(m)p//,=gasdensitywithinthecompartmentsup-plyingtheleakageflow(kg/m).Itisassumedthatinertialeffectsdonotsignificantlyaffectleakagerates.II.C.5.NaturalCirculationModelAnaturalcirculationmodelsimulatesgravity-drivenmixingincompartmentsconnectedbyflowpathsatdifferingelevations.ThecirculationrateW,(kg/s)isobtainedfromThismodelalsodescribesintercompartment,gravity-drivencirculationflowsthatcandevelopatopendoor-ways(seetheanalysisofBrownandSolvason'.II.C.6.ThinSlabModelThedetailedslabmodeldiscussedinSec.II.Bisnotrequiredtodescribeheattransferthroughthinslabsthathavelittlethermalcapacitance.Slabsofthistype,e.g.,refuelingfloorwalls,havenearlylineartem-peratureprofiles,andthustheheatflowthroughathinslabcanbecalculatedbytheuseofanoverallheattransfercoefficientU.Therateofheattransferthroughathinslabisobtainedfromq/s(r)=UisA[T1(>)-T2(/)],(21)whereA=thinslabheattransferarea(m)TjTz=temperaturesofthecompartmentssepa-ratedbytheslab(K).ValuesofU(J/msK)aresuppliedaspartofthecodeinputdata(onevalueforeachverticalslabandtwovaluesforeachhorizontalslab).Forhorizontalslabs,twovaluesofUarerequiredbecausefree-convectionfilmcoefficientsdependonthedirection,upwardordownward,ofheatflowthroughtheslab.II.C.7.Heal-LoadDecayModelCoolingofacomponentsuchasapipefilledwithhotstagnantfluidorapumpthathasceasedoperat-ingissimulatedthroughtheuseofalumped-param-eterheattransfermodel.Mostcompartmentsinthesecondarycontainmenthavealargethermalcapacitybecauseoftheboundingconcreteslabs.Itisthereforeassumedthatthecomponenttemperaturechangesonafastertimescalethanthecompartmentairtemper-ature;i.e.,theairtemperatureisassumedtoremainfairlyconstantduringthecooldownofthecomponent.Withthisassumption,thecomponentheatdissipationrateQc(t)isgovernedby7'Q'"=-Q(/)(22)d/W-g['()'()](")K//[Alp2(t)]+KN/[ANpi(/)]JwhereQc(/o)=Qco(23)wherep1,pz--densitiesoftheair/watervapormixtureswithinthetwoadjacentcompartments(kg/m)(hereitisassumedthatp2isthegasdensityforthecoolercompartment)E,E/--elevationsoftheupperandlowerflowpaths(m)A,A/--upperandlowerflowpathareas(m).NUCLEARTECHNOLOGYVOL.94APR.1991McCwVcUcAc(24)whereM,=massofthecomponent(kg)Ci~=specificheatofthecomponent(J/kgK)49and7,(s'),thethermaltimeconstantofthecompo-nent,isgivenby ChaikoandMurphyPOSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSISU,=overallheattransfercoefficient(J/m2.sK)A,=componentheattransferarea(m2).InEq.(23),to(s)isthetimeatwhichthecooldownprocessbegins,andQ<<,whichissuppliedasinputdata,istheheatdissipationratepriortocooldown.So-lutionofEqs.(22)and(23)givestheexponential-decayapproximationusedinCOTTAPtomodelheatdissi-pationofcoolingcomponents.Thecomponenttimeconstanty,isspecifiedasinputdataexceptinthecaseofhotpiping,whereitiscalculatedbythecodefromthepipingdescriptiondata.II.C.8.Time-DependentCompartmentModelWiththetime-dependentcompartment(TDC)model,environmentalconditionswithinacompart-mentarespecifiedasafunctionoftime;i.e.,temper-ature,pressure,andrelativehumidityversustimearesuppliedastabularinputdata.Thismodelisparticu-larlyusefulforrepresentingoutsideairconditions,in-cludingsolarandthermalradiationeffects.Theinfluenceofsolarandlong-waveatmosphericradiationonexteriorbuildupsurfacescanbedescribedbyspec-ifyingtheeffectiveSol-Airtemperature'ntheTDCinsteadoftheactualoutsideairtemperature.Insec-ondarycontainmentanalysis,theTDCmodelisalsousefulfordescribingtransientconditionswithintheprimaryreactorcontainment,whicharegenerallyknownfromtheresultsofdetailedlicensingbasiscal-culations.dTsl=GTpssxx(25)wherei=1,2,3,...,N,thenumberofequallyspacedgridpointsTp--slabtemperatureatgridpointiTp=finitedifferenceapproximationtothesecond-orderspatialderivativeatgridpointi.FollowingtheapproachusedbyPirkleandSchiesser'3intheMOLsolutionofparabolicequa-50II.D.NumericalSolutionNlethodsAnenergybalanceandtwomassbalancesaresolvedforeachcompartmenttodeterminegastemperature,airmass,andwatervapormass.Inaddition,theone-dimensionalheatconductionequationissolvedforeachslab.Beforecomputingthenumericalsolutionofthegoverningequations,partialdifferentialequationsdescribingheatflowthroughslabsareapproximatedbysetsofordinarydifferentialequations(ODEs).Thisisaccomplishedthroughapplicationofthemethodoflines(MOL).IntheMOL,afinite.differenceapprox-imationisappliedonlytothespatialderivativeinEq.(4),givingtions,fourth-ordercentraldifferenceformulasareusedtocomputeTtatinteriorgridpoints:Asix-pointslopingdifferenceformulaisusedtoap-proximateTpati=2andi=N-1:ITsxx2=-2(10Tsi15Ts24Ts3+14Ts4-'6T,s+T,6)+O(~)(27)and1TsxxNl2(10TSN15TsN-l4TsN-2+14TsN-3-6TsN-4+TsN-5)+O(~4).(28)Fortheendpoints,wherethenormalderivativesarespecifiedthroughconvectiveboundaryconditions,thefollowingfinitedifferenceapproximations,recom-mendedbyPirkleandSchiesser,'3areusedtocom-puteTI41532T=---Ti+96T2-36T3+-T4sxxt12626ssS3sTss50t3,Tsxl+O(h)(29)34andI415TsN=---TN+96TNi-36TN2sxx323+-TsN-3--TsN-4+506TsxN2+O(a)(30)InEqs.(29)and(30),thenormalderivativesTsxiandT~areevaluatedinaccordancewithEqs.(5)and(6),theconvectiveboundaryconditions;i.e.,hiTsxl-(TlTsI)sandh2Tsx2----(TsN-T2)s(31)NUCLEARTECHNOLOGYVOL.94APR.199l1Tsxxi=122(-Tsi-2+16Tsi-i-30Tsi+16Tsl+i128,-Ts'+2)+O(h),(26)wherei=3,4,...,N-26=spacingbetweengridpoints.

ChaikoandMurphyPOSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSISAllgovernirigequationsarenowexpressedintermsofODEsoftheformdy-=F(y,t)withy(0)=yedL'32)SolutionsofEq.(32)exhibitrapidinitialadjust-mentsincompartmentairtemperaturecausedbytherelativelysmallthermalcapacitanceoftheaircontainedwithinthecompartment.Moreover,slabtemperaturesundergorapidinitialchangesinnarrowregionsneartheboundaries,resultingintheformationofspatialthermalboundarylayers.InthenumericalintegrationofEq.(32),smalltimestepsarerequiredtosimulatetheseinitialtransients.Astheinitialtransientresponsedecays,however,itisdesirabletoincreasestepsizesinordertoreducethecomputationtimerequiredtofol-lowtheslowlyvaryingpartofthesolution.Equations,suchasEq.(32),whichexhibitinitialtemporalbound-arylayerstructuresaretermedstiffdifferentialsystems(seethediscussioninRef.16),andbecauseofstabil-itylimitations,theycannotbesolvedefficientlywithexplicitintegrationschemes.Forthisreason,anim-plicitschemewasselectedforCOTTAP.NumericalintegrationofthegoverningEq.(32)iscarriedoutwiththeLSODEScode,'hichusestheimplicitbackwarddifferentiationmethodsproposedbyGearforthesolutionofstiffsystems.TheLSODEScodealsoemployssparse'matrixinversiontechniquesinsolvingtheimplicitfinitedifferenceequations.Withthesenumericalintegrationfeatures,itisfeasibletocarry'outtheintegrationofthelargedifferentialsys-temsthatariseinthesimulationofsecondarycontain-menttransients.Asanillustrationoftheproblemdimension,simulationoftheSSES-1and-2secondarycontainmentsunderpostaccidentconditionsrequiredthesolutionof20101coupledODEs.Fortheselarge-scaleproblems,reevaluationofcode-calculatedslabheattransfercoefficientsateverytimestepleadstounacceptablylongcomputationtimes.Toalleviatethisdifficulty-,thefrequencyofre-evaluation(numberofstepsbetweenreevaluationofcoefficients)isaparametersuppliedasinputtothecode.Sensitivitycalculationsonsmall-scaleproblemsrepresentativeofpostaccidentsecondarycontainmenttransientsindicatethatcoefficientscanbereevaluatedasinfrequentlyasoncepertenstepswithoutintroducingsignificanterrorsintheresults.TheCPUtimerequire-mentswerereducedbyafactorof4whencoefficientswerereevaluatedateverytenthtimestep.1.Fissionproducttransportamongcompartmentsisnotmodeled.II.E.CodeLimitations.inModelingAccidentScenariosThefollowingmodelinglimitationshavebeeniden-tifiedinthecurrentversionoftheCOTTAPcode:2.Coolermodelingdoesnotdescribemoisturere-movalunderconditionswherethecoolingcoiltemper-.atureisbelowthedewpointoftheinletgasmixture.3.Pipebreakmodelingisvalidonlyforlinescon-tainingsteamorsaturatedliquid;breaksinvolvingthereleaseofsubcooledliquidcannotbedescribed.4.Compartmentfloodingeventscannotbesimu-latedbecauseallliquidisassumedtoexitthroughcom-partmentfloordrains.III.RESULTSOFSSESSECONDARYCONTAINMENTANALYSISFORPOSTACCIOENTCONDITIONSThissectiongivesrepresentativeresultsforaCOT-TAPsimulationofthecombinedSSES-1and-2sec-ondarycontainmentsunderpostaccidentconditions.ThethermalresponsesoftheUnits1and2secondarycontainmentsarecoupledbyheattransferthroughcommonwallsthatseparatethetwostructures.TheSSESmodelconsists.of105compartments,16time-dependentcompartments,767slabs,38thinslabs,and505heatloads.Thesimulationwascarriedoutfor30handrequired124minofCPUtimeonanIBM3090computer.NotethatmostoftheCPUtimeisrequiredtosimulatetherapidlyvaryingpartofthetransientthatoccurswithinthefirstfewhoursoftheevent.Thus,substantiallylongersimulationtimesdonotsig-niflcantlyincreaseCPUtimerequirements.Forthisanalysis,itisassumedthataloss-of-coolantaccident(LOCA)occursinSSES-1andafalseLOCAsignal(aspurioussignalthatindicateslossofreactorcoolantandleadstoventilationsystemisola-tionandoperationofECCSinjectionpumps)isgen-eratedonSSES-2.Underpostaccidentconditions,ECCSinjectionpumpscomprisethekeyequipmentwithinthesecondarycontainmentstructure.TheECCSconsistsoftheresidualheatremoval(RHR),corespray,andhigh-pressurecoolantinjection(HPCI)sys-tems.Thesesystemsreceiveelectricalpowerfromhigh-voltagebusescontainedwithinemergencyswitchgearandloadcenterrooms.FigureIshowsthecalculatedtemperatureresponsewithinaSSES-1RHRpumproom(eachunitcontainstwoRHRpumproomsandtwocorespraypumprooms).Initially,theairtemper-atureincreasesrapidlybecauseofthesmallthermalca-pacitanceoftheairwithinthecompartment.Asairtemperatureincreases,abalancebetweencompartmentheatsourcesandlossestocompartmentaircoolersandslabsbeginstodevelop.Atthistime,air.temperaturestartstoincreaseontheslowtimescalegovernedbytheslabthermalcapacityandtransportproperties.Aninitialrapidtemperaturerisefollowedbyamuchslowertemperatureincreaseischaracteristicofallcom-partmentheatuptransients.After1hofoperation,thisparticularRHRpumpswitchesfromtheinjectionmodeofoperationtothesuppressionpoolcoolingNUCLEARTECHNOLOGYVOL.94APR.199151-ChaikoandMurphyPOSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSIShC320E316I-E3316o314312051015202530Time(h)Fig.1.SimulationofpostaccidenttemperatureresponsewithinSSES-IRHRpumproomforLOCAonSSES-IandfalseLOCAonSSES-2.317~316.~~315I-314Eo313E312Q311X310051015202530Time(h)Fig.3.SimulationofpostaccidenttemperatureresponsewithinSSES-IHPCIpumproomforLOCAinSSES-IandfalseLOCAinSSES-2.mode.Asaresultofincreasedcompartmentheatloadsassociatedwiththechangeinoperatingmode,thetem-peratureagainincreasesrapidlyuntilanewbalancebetweentheheat-generationandheat-lossratesisat-tained.ThetemperatureresponsewithinaSSES-IcorespraypumproomisshowninFig.2.Coresprayop-erationbeginsatthestartoftheeventandceasesIhlater.Temperaturedecreasesrapidlyatthispointbe-cause,oncepumpoperationisterminated,nosignif-icantheatloadsremaininthecompartment.Figure3illustratesthetemperatureresponseoftheSSES-IHPCIsystem,whichalsobeginsoperationatthestartoftheaccident.Inthiscase,however,compartmenttemperaturecontinuestoincreasewhenthesystemceasesoperationatIhintothetransient.Thisoccursbecausepipingheatloadswithinthiscompartmentaresubstantial.WhenHPCIpumpoperationstops,anas-sociatedroomcoolingunitalsoceasesoperation.Uponshutdownofthecoolingunit,slowlydecayingpipingheatloadsrapidlyincreasecompartmenttemperatureuntilabalancebetweenheatgenerationandheatlossestocompartmentslabsisapproached.Figure4givesthetemperaturewithinaSSES-Iloadcenterroomthat~317PE~316I-E3315CC~314V)313O051015202530Time(h)Fig.2.SimulationofpostaccidenttemperatureresponsewithinSSES-IcorespraypumproomforLOCAinSSES-IandfalseLOCAinSSES-2.-309ejE308I-E3cc~3078CO306051015202530Time(h)Fig.4.SimulationofpostaccidenttemperatureresponsewithinSSES-IloadcenterroomforLOCAinSSES-IandfalseLOCAinSSES-2.52NUCLEARTECHNOLOGYVOL.94APR.1991 supplieselectrthiscompartmstantthroughoutthetransient.Fromtheresultsofthisanalysis,itisdeterminedthatunderpostaccidentconditions,someoftheequip-mentwithinthesecondarycontainmentwouldbeex-posedtotemperaturesthatexceedtheirqualificationvalues.Consequently,componentswerereassessedforoperationathighertemperatures,andinsomein-stancesequipmentwasrelocatedtocompartmentswithlesssevereenvironmentalconditions.Furthermore,aprocedurewasdevelopedtoinstructplantoperatorstoshednonessentialelectricalloadswithin24hafteranaccidentinordertomoderatethetemperaturere-sponseswithinsecondarycontainmentcompartments.K310P~~305COTTAP---CONTAIN300IChaikoandMurphyPOSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSISicalpowertoemergencyequipment.In315ent,heatloadsremainessentiallycon-IV.EVALUATIONOFCODEACCURACYAspartoftheverificationprocessfortheCOT-TAPcode,calculationalresultswerecomparedwiththoseobtainedwiththeCONTAIN(Ref.2)program,whichhasbeenverifiedthroughcomparisonwithex-perimentaldata.'AlthoughtheCONTAINcodedoesnotaccommodateadirectheatinput(suchasfromoperatingmechanicalorelectricalequipment)toacompartment,usefulproblemscanneverthelessbeformulatedinordertoinvestigatethemodelingandcomputationalaccuracyofCOTTAP.Twosuchprob-lemswereformulatedforcodeverification.ThefirstproblemteststheCO%I'APcompartmentmassanden-ergybalancecalculationsandtheslabheattransfersimulation.Thisproblemconsistsofasinglecompart-mentthathasa1000-m3volumeandcontainsairat300Kand101325-Painitialtemperatureandpressure.Concreteslabs,whichrangeinthicknessfrom0.1to1m,formthewallsofthecompartment.Allslabshaveauniform,initialtemperatureof300K.Toaddheattothecompartment,theairincontactwiththeoutersurfaceofoneslab(theslabthatis0.1mthick)issud-denlyincreasedto400Katt=0.Inaddition,at50sintothetransient,airwithatemperatureof500Kisin-jectedintothecompartmentata0.26kg/sflowrate.Outersurfacetemperatureriseandairinjectioncon-ditionswereselectedtoeffectsignificant,butnotex-cessive,temperatureandpressureresponse.Figures5and6presentacomparisonoftheCOT-TAPandCONTAINcalculationresultsforthefirsttestproblem.Thetemperatureandpressuresimula-tionsbothshowexcellentagreement;notethatthepressureresponsecurvesgiveninFig.6completelyoverlap.In-Fig.5,theinitialtemperatureincrease,whichisduetoinjectionofhotairintothecompart-ment,beginstoleveloffat-0,5h.Heatadditionbymeansofconductionthroughtheexternallyheatedslabthenbeginstooccur,causingafurtherbutlessrapidincreaseintemperature.Thesecondtestproblemconsideredforcodever-0.200.180.160.14Q-0.12-COTTAP---CONTAIN0.100246810Time(h)Fig.6.ComparisonofCOTTAPandCONTAIN.compart-mentpressuresimulationsfortestprobleml.ificationinvolvesmodelingofcompartmenttempera-tureandpressurebehaviorunderconditionswherehigh-energysteamisinjectedintothecompartment.Inthisproblem,condensationeffectsstronglyinfluencetherateoftemperatureandpressureincrease.Com-partmentphysicaldescriptiondataarethesameasthatfortestproblem1.Inthiscase,however,theonlyheatsourceisthesteamenteringthecompartmentata0.20kg/sflowrateanda2.7756x106J/kgenthalpy.Thisflowrateandenthalpyarecharacteristicofasmallsteamleakwithinasecondarycontainmentcom-partment.Figures7and8showacomparisonofthe0246810Time(h)Fig.5.ComparisonofCOTTAPandCONTAINcompart-menttemperaturesimulationsfortestproblemI,NUCLEARTECHNOLOGYVOL.94APR.I99t53 ChaikoandMurphyPOSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSIS450~4oo'50300-COTTAP---CONTAINACKNOWLEOGMENTSTheauthorsthankJackG.Refling,JamesE.Agnew,MarkR.Mjaatvedt,andLeonardJ.Westfortheirmanyhelpfulsuggestionsduringthecourseofthiswork.WealsothankLisaWalshfortypingthemanuscript.REFERENCES1.C.C.LIN,C.ECONOMOS,J.R.LEHNER,G.MAISE,andK.K.NG,"CONTEMPT4/MOD4:AMulti-compartmentContainmentSystemAnalysisProgram,"BNL-NUREG-51754,BrookhavenNationalLaboratory(1984).05101520Timelh)Fig.7.ComparisonofCOTTAPandCONTAINcompart-menttemperaturesimulationsfortestproblem2.0.6osg0.4IPn0.3-Q.2.K.K.MURATAetal.,"User's.ManualforCONTAIN1.1:AComputerCodeforSevereNuclearReactorAccidentContainmentAnalysis,"NUREG/CR-5026,SandiaNa-tionalLaboratories(1989).3.S.W.CHURCHILLandH.H.S.CHU,"CorrelatingEquationsforLaminarandTurbulentFreeConvectionfromaVerticalPlate,"Int.J.HeatMassTransfer,18,1323(1975).4.J.P.HOLMAN,HeatTransfer,4thcd.,p.250,McGraw-HillBookCompany,NewYork(1976).5.T.FUJIIandH.IMURA,"NaturalConvectionHeatTransferfromaPlatewithArbitraryInclination,"Int.J.HeatMassTransfer,15,755(1972).6.R.J.GOLDSTEIN,E.M.SPARROW,andD.C.JONES,"NaturalConvectionMassTransferAdjacenttoHorizontalPlates,"Int.J.HeatMassTransfer,16,1025(1973).0.20.1COTTAP---CONTAIN7.J.R.LLOYDandW.R.MORAN,"NaturalConvec-tionAdjacenttoHorizontalSurfaceofVariousPlanforms,"ASME74-WA/HT-66,AmericanSocietyofMechanicalEngineers(1974).05101520Time(h)Fig.8.ComparisonofCOTTAPandCONTAINcompart-mentpressuresimulationsfortestproblem2.COTTAPandCONTAINsimulationresults.There-sultsshowgoodagreementeventhoughthecodesem-ployconsiderablydifferentapproachesinthecalculationofcondensationratesonslabsurfaces.TheCOTTAPcodeusestheexperimentallydeterminedUchida'ondensationcoefficient,whileCONTAINcarriesoutadetailedcomputationofthethermalre-sistancesassociatedwiththegasboundarylayerandthecondensatefilm.8.D.Q.KERN,ProcessHeatTransfer,p.690,McGraw-HillBookCorupany,NewYork(1950).9.H.C.HOTTELandA.F.ballot'tM,RadiativeTransfer,McGraw-HillBookCompany,NewYoit(1967)'1~10.R.D.CESSandM.S.LIAN,"ASimpleParameteriza-tionfortheWaterVaporEmissivity,"Int.J.HeatTransfer,98,676(1976).11.H.C.HOTTELandR.B.EGBERT,"RadiantHeatTransmissionfromWaterVapor,"Am.Inst.Chem.Eng.,38,531(1942).12.H.UCHIDA,A.OYAMA,andY.TOGO,"Evalua-tionofPost-IncidentCoolingSystemsofLight-WaterPowerReactors,"Proc.3rdInt.Conf.PeacefulUsesofAtomicEnergy,Geneva,Switzerland,1964,Vol.13,p.93,UnitedNations(1965).54NUCLEARTECHNOLOGYVOL.94APR.1991 ChaikoandMurphy13.W.G.BROWNandK.R.SOLVASON,"NaturalCon-vectionThroughRectangularOpeningsinPartitions-IVer-ticalPartitions,"Int.J.HeatMassTransfer,5,859(1962).14.ASHRAEHandbook1985Fundamentals,AmericanSocietyofHeating,RefrigeratingandAir-ConditioningEn-gineers,Atlanta,Georgia.15.J.C.PIRKLE,Jr.andW.E.SCHIESSER,"DSS/2:ATransportableFORTRAN77CodeforSystemsofOrdinaryandOne,TwoandThree-DimensionalPartialDifferentialEquations,"presentedat1987SummerComputerSimula-tionConference,Montreal,Canada,1987.18.K.K.MURATAandK.D.BERGERON,"Experimen-talValidationoftheCONTAINCode,"Proc.11thLWRSafelyInformationMtg.,Gaithersburg,Maryland,October24-28,1983,SAND-83-1911C,SandiaNationalLaborato-ries(1983).19.K.K.MURATAetal.,"CONTAIN:RecentHighlightsinCodeTestingandValidation,"Proc.Int.Mtg.LightWaterReactorSevereAccidentEvaluation,Cambridge,Massa-chusetts,August28-SeptemberI,1983,AmericanNuclearSociety(1983).16.C.W.GEAR,NumericalInitialValueProblemsinOr-dinaryDifferentialEquations,Chap.11,Prentice-Hall,En-glewoodCliffs,NewJersey(1971).POSTACCIDENTBWRSECONDARYCONTAINMENTTHERMALANALYSIS17.A.C.HINDMARSH,"ODEPACK,ASystematizedCollectionofODESolvers,"ScientificComputing,Vol.I,p.55,R.S.STEPLEMANetal.,Eds.,IMACSTransac-tionsonScientificComputation,North-HollandPublishingCompany,Amsterdam(1983).MarkA.Chaiko[BS,1980,andMS,1983,chemicalengineering,Penn-sylvaniaStateUniversity(PSU);PhD,appliedmathematics,LehighUniver-sity,1989]isaprojectengineer-nuclearsystemsatthePennsylvaniaPower&LightCompany.Hiscurrenttechnicalinterestsincludeboilingwaterreactorstabilityanalysisandthermal-hydraulicmodelingofreactorsystems.MichaelJ.Murphy(BS,mechanicalengineering,1982,andMS,nuclearengineering,1986,PSU)isaprojectengineer-nuclearsystemswiththePenn-sylvaniaPower&LightCompany.Heiscurrentlyinvolvedinsimulationofanticipatedtransientwithoutscramandsevereaccidentanalysis.NUCLEARTECHNOLOGYVOL.94APR.199155