ML17331A061

Forwards FAI/93-25, DC Cook Nuclear Plant Hydrogen Control Evaluation Summary Rept, Per 10CFR50.44(c)(3)(vi)(a)

ML17331A061
Person / Time
Site:	Cook
Issue date:	02/26/1993
From:	FITZPATRICK E INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
To:	MURLEY T E NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
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ML17331A062	List: ML17331A061 ML17331A063
References
AEP:NRC:0500Y, AEP:NRC:500Y, NUDOCS 9303030121
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acezr.ztuxDOCvMzmDrSxammraxSvsrmcREGULATINFORMATIONDISTRIBUTIO~STEM(RIDS)iDACCESSIONNBR:9303030121DOC.DATE:93/02/26NOTARIZED:NODOCKETFACIL:50-315DonaldC.CookNuclearPowerPlant,Unit1,IndianaM0500031550-316DonaldC.CookNuclearPowerPlant,Unit2,IndianaM05000316AUTH.NAMEAUTHORAFFILIATIONFITZPATRICK,E.IndianaMichiganPowerCo.(formerlyIndianaaMichiganEleRECIP.NAMERECIPIENTAFFILIATIONRDocumentControlBranch(DocumentControlDesk)~I

SUBJECT:

Providessummaryofanalysesreptforanalyticaleffort.Analysesdemonstratethatcontainmentstructuralintegritywillnotbethreatededbyhydrogengeneration&combunstion.NimtinDZSTRZBUTZONCODE:ROZZDCOPZESRECEZVED:LTRIENCL~SZSE:~f'KSTITLE:GenericLtr88-20reIndividualPlantEvaluationsNOTES:RECIPIENTIDCODE/NAMEPD3-1PDINTERNAL:ACRSHOUSTONPMNRRAN,RGL01RESMITCHELLPJRGN1RGN-3COPIESLTTRENCL11111111111111RECIPIENTIDCODE/NAMEDEAN,WAEOD/DSP/TPABNRR/OGCBRESFLACK,JRES/DSIR/SAIB/BRGN2RGN4COPIESLTTRENCL111111337,71111DEXTERNAL'RCPDRNSIC11DNOTETOALL"RIDS"RECIPIENTS:PLEASEHELPUSTOREDUCEWASTE!CONTACTTHEDOCUMENTCONTROLDESK,ROOMPl-37(EXT.504-2065)TOELIMINATEYOURNAMEFROMDISTRIBUTIONLISTSFORDOCUMENTSYOUDON'TNEED!TOTALNUMBEROFCOPIESREQUIRED:LTTR24ENCL24 tIIl0IT1 IndianaMichiganPowerCompanyP.O.Box16631Columbus,OH43216RAEP:NRC:0500YDonaldC.CookNuclearPlantUnits1and2DocketNos.50-315and50-316LicenseNos.DPR-58andDPR-74HYDROGENCONTROLPROGRAM(10CFR50.44(c))SUBMITTALOFANALYSESU.S.NuclearRe'gulatoryCommissionDocumentControlDeskWashington,D.C.20555Attn:T.E.MurleyFebruary26,1993

DearDr.Murley:

InanNRCletterdatedApril10,1989,itwasindicatedthatthe10CFR50.44hydrogencontrolrevieweffortfortheDonaldC.CookNuclearPlant,whichhadbeenterminatedbytheNRCin1986,wouldbesubsumedintotheIndividualPlantExamination(IPE)effort.Asaresultofthisdirection,theIPEand10CFR50~44analysiseffortsforCookNuclearPlantwereperformedaspar'allelbutseparateinterfacingprograms.IndianaMichiganPowerCompany(I&M)submittedtheIndividualPlantExaminationresultsinletterAEP:NRC:1082EdatedMay1,1992.InletterAEP:NRC:500XdatedAugust5,1992,I&McommittedtocompletebyFebruary28,1993,theanalysespursuantto10CFR50.44todemonstratetheabilityofthehydrogencontrolsystemtomitigatetheconsequencesofthereleaseofhydrogenintoCookNuclearPlantcontainmentduringpostulateddegradedcoreaccidents.Thepurposeofthisletteristoprovidethereportofthisanalyticaleffort.Theattachmenttothisletterprovidesasummaryoftheanalysesrequiredby10CFR50.44paragraph(c)(3)(vi)(A).ThesequencesselectedforanalysiswerebasedonsignificantsequencesfoundintheIPE.Theseanalysesdemonstratethatthecontainmentstructural9303030121'30226.PDR'DOCK05000315PDR Dr.T.E.Murley2AEP:NRC'0500Yintegritywillnotbethreatenedbyhydrogengenerationandcombustion,andthatnecessaryequipmentwillsurvivetheconditionscreatedbytheburningofhydrogen.Sincerely,PL~p~gVicePresidentrbbAttachmentcc:A.A.Blind-BridgmanJ.R.PadgettG.CharnoffNFEMSectionChiefA.B.Davis-RegionIIINRCResidentInspector-Bridgman Dr.T.E.Murley3AEP:NRC:0500Ybc:S.J.BrewerW.M.Dean,NRC-Washington,D.C.D.H.Malin/K.J.TothM.L.Horvath-BridgmanJ.B.Kingseed/R.B.BennettJ.B.ShinnockW.G.Smith,Jr.AEP:NRC:0500YDC-N-6015.1 ATTACHMENTTOAEP:NRC:0500YHYDROGENCONTROLPROGRAM(10CFR50.44(c))FORTHEDONALDC.COOKNUCLEARPLANT.SUBMITTALOFANALYSES ATTACHMENTTOAEP'NRC:0500Y

1.0INTRODUCTION

PAGE1TheNuclearRegulatoryCommissionrequiresin10CFR50.44thatreactorcontainmentsbeabletoaccommodate,withoutlossofcontainmentintegrityordegradationofvitalequipment,thehydrogenthatmaybegeneratedduringdegradedcoreaccidents.Asaresult,theicecondensercontainmentdesignattheCookNuclearPlantwasrequiredtoincludehydrogencontrolsystemscapableofaccommodatinganamountofhydrogenequivalenttothatgeneratedfromthereactionof75Xofthecladdingintheactivefuelregionwith'team.Thehydrogengeneratedbysuchareactionhasbeenjudgedtoboundtheamountsofhydrogenlikelytobegeneratedindegradedcoreaccidentsinwhichcoredegradationisarrestedpriortocoremeltdown.Inresponsetotheaboverequirement,theDistributedIgnitionSystem(DIS)wasinstalledattheCookNuclearPlant.ThissystemiscurrentlyoperableandithasbeenreviewedandapprovedbytheNRCstaffinaSafetyEvaluationdatedDecember17,1981[1].Considerableanalysesandexperimentshavebeenperformedtodemonstrateconformancewiththeaboverequirements,asrequiredby10CFR50.44paragraph(c)(3)(vi)(A).InanNRCletterdatedApril10,1989,itwasindicatedthatthefinalconfirmatoryanalysiseffort,whichwasterminatedin1986,wouldbesubsumedintotheIndividualPlantExamination(IPE)effort.ThebaseIPEanalysiswassubmittedtotheNRConMay1,1992inletterAEP:NRC:1082E[2].ThiscurrentreportdescribestheuseoftheIPEanalysistoaddresscompliancewiththerequirementsof10CFR50.44.Asdescribedinthisreport,theIPEanalysiswasusedtoestablishthemorelikelydegradedcoresequences.ThecontainmentresponseanalysisperformedfortheIPEwasmodifiedtoincludetherequirementsof10CFR50.44,andanalysisofappropriatesequenceswasthenperformed.Thecomputeranalysisofthecontainmentresponsetohydrogengeneratingsequencesprovidesanunderstandingofthetimingandrelatedhydrogencombustionratesinthevariousregionsofthecontainment.Thisinformationisusefulindeterminingheatloadsonequipmentrequiredtosurvivethehydrogencombustionenvironment.Duetotheapproximationsnecessarytoperformanintegratedanalysisofboththereactorcoolantsystemandcontainment,thedetailedcombustioncharacteristicspredictedbythecomputercodeonlyapproximatetheconditionsexpectedinacontainmentregion,particularlyforthepressureresponsetohydrogencombustion.Incontainmentregionswher'epressureresponseisofparticularinterest,hydrogenflowconditionspredictedbythesequenceanalysisareusedtore-evaluatethecodepredictionsbasedontheresponseexpectedfromareviewof ATTACHMENTTOAEP:NRC:0500YPAGE2applicableexperiments.ConclusionsontheadequacyoftheDISforhydrogencontrolarethendrawnonthecombinationofexperimentandanalysis,asrequiredby10CFR50.44paragraph(c)(3)(iv)(A).TwootherhydrogencontrolsystemsareinstalledintheCookNuclearPlant,thehydrogenskimmersystemandthehydrogenrecombiners.Thehydrogengenerationcriteriaof10CFR50.44(c)(3)(vi)arewellbeyondthecapabilityofeitherofthesesystems.Thehydrogenskimmersystemwasinstalledtodrawairfromconfinedareasinthecontainmenttopreventacombustiblemixtureofhydrogenfrombuildingupintheseareasintheeventofadesignbasisaccident.Inadesignbasisaccident,lessthan1Xofthezirconiumisexpectedtoreactwithwater.TheDIShasignitersinthesesameconfinedareas,whichcantakeoverforthehydrogenskimmersystemincontrollinghydrogeninthoseareasintheeventforthemoresevereaccidentconditions.Likewise,thehydrogenrecombinerswerenotintendedtocontrolhydrogenintheconcentrationsandatthegenerationratesrequiredunderthissectionoftheregulation.Theuseofhydrogenrecombinerswillbereservedforlongtermhydrogencontrolaftertheaccidentconditionshavestabilized.ThisreportonlyaddressestheeffectivenessoftheDISincontrollinghydrogen.TheexistingUFSARaddressesboththehydrogenskimmersyst:emandthehydrogenrecombiners.Section2providesasummarydescriptionofthemethodologyusedtochooseaccidentsequencesforanalysis,thecomputercodeandmodelsusedtoanalyzethosesequences,andtheresultsofthesequenceanalysis.AcompletereportonthesequenceanalysisisprovidedintheAppendix.ThecontainmentstructuraladequacyisreviewedinSection3ofthissummary,andequipmentsurvivabilityanalysisisreviewedinSection4.Section5discussestheuseoftheheadventsonthehydrogencontrolanalysis.TheconclusionsofthehydrogencontrolanalysisaresummarizedinSection6.

ATTACHMENTTOAEP:NRC'0500Y2.0ACCIDENTSEQUENCEANALYSISPAGE3Inanaccidentsequencethatleadstoadegradedcore,waterinventoryislostfromthereactorcoolantsystemuntilthecoreisuncovered.Withthecoreuncovered,theremaybeinsufficientsteamtocarrythedecayheataway,resultinginaheatupofthefuelrods.Whenthefuelrodzirconiumcladdingreachesapproximately1800'F,thezirconiumbeginsreactingwithsteamtoformzirconiumdioxideandhydrogeninanexothermicreaction.Withinminutes,thecorewillreachtheuraniumdioxideandzirconiummeltingpoint,andthecorewillbegintoslump.Duringthetimeofcoreuncovery,hydrogengenerationisusuallylimitedbyalackofsteamtoarelativelylowrate.Tostoptheprogressionoftheaccident,thecoremustberecoveredwithwater.Thisrecoverywillproducealargeamountofsteamasthecoreisquenched.Thissteam,withthealreadyoverheatedcladding,willallowforalargebutbriefpeakinthehydrogengenerationrate.Thethermalshockmayalsoshattertheintactfuelrodsatthattime.Thehydrogengeneratedbythezirconiumwaterreactionisreleasedtothereactorcoolantsystemandthenoutthecoolantsystembreachintothecontainment.Thisbreachcouldbeabreakinthereactorcoolantsystemorareleasepaththroughthereactorcoolantpumpsealsorthroughthesafetyorpoweroperatedreliefvalvesiftheaccidentwasinitiatedbyatransient.Thehydrogenmayreachaburnableconcentrationincontainment,threateningequipmentbythehighheatflux.Ifthehydrogenbuildsuptoasufficientlyhighconcentrationbeforetheburnbegins,theresultingpressurepulsemayeventhreatenthecontainmentintegrity.Thissectionoverviewsthemethodologyandresultsofthesequenceanalysis.ThecompletereportonthehydrogencontrolsequenceanalysisisprovidedintheAppendixtothisreport.Theacceptancecriteriaforthishydrogencontrolanalysisarecontainmentstructuralintegrityandsurvivabilityofvitalequipment.Thevarioussequencesandanalyticassumptionsusedintheanalysisprovideabasisforshowingcompliancewiththeacceptancecriteria,whichappearsinsubsequentsectionsofthisreport.AccidentSequenceSelectionSequenceswereselectedforanalysisbasedonseveralcriteria.First,themostprobablesequenceswerechosenbasedontheIndividualPlantExamination.Thesewerethenbinnedintosimilar ATTACHMENTTOAEP:NRC'0500YPAGE4setsofsequencesbasedonthehydrogengenerationrates,andarepresentativecaseforeachsetwaschosenforanalysis.Notethatthesearenotnecessarilythemostprobablesequences.Thecorepressureisimportanttotherateofcorereflood,sinceitlimitstheECCSflowrateavailabletorefloodthecore.Thus,forhydrogengeneration,thecorepressureatthetimeofcorerecoveryistheprimaryvariableindictatingthehydrogengenerationrate.Therefore,alargeLOCAsequence,asmallLOCAsequence,andasequenceinitiatedbylossofcomponentcoolingwaterwasanalyzedtocoverthespectrumoflow,intermediate,andhighsystempressuresatcorerecovery.Thesesequencescovertherangeofnearatmosphericpressure,steamgeneratorpressure(about1100psi)andfullreactorcoolantsystempressure(above2250psi).Inaddition,severalsensitivityanalyseswereperformed.DetailedjustificationfortheselectionofthesesequencesisprovidedintheAppendix.AccidentSequenceModellingToanalyzethesequences,theMAAP3.0B[3]codewasused.Thiscodecombinesanuclearsteamsupplymodelwithanicecondensercontainmentmodel,andwasusedintheIPEanalysis.TheoriginalMAAPhydrogenburnmodelsweremodifiedtoreflectthehydrogenburncompletenesscorrelationprovidedinanearliersubmittal[4].ThiscorrelationisthesameasisusedintheHECTRcode[5,6],andwassupportedmostrecentlybytheNevadaTestSite(NTS)[7]largescalehydrogenburnexperimentsforpremixedconditions.Foranyscenarioinwhichthecoregeometryissufficientlyintacttoberecoverable,lessthan75Xofthecladdingwouldhavereacted.Tohaveareasonableexpectationofarecoverablecore,recoveryisinitiatedsothatapproximately50Xofthecorenodeshavereachedthemeltingpoint.Thecoregeometryiskeptartificiallyintacttomaximizethesurfaceareaforsteamwaterreactiononrecovery.Toachievethe75Xzirconiumcladdingreactionrequiredby10CFR50.44(c)(3)(vi),anartificialhydrogentailwasaddedtotheanalysis.ThiswassimilartothestrategyusedbytheBoilingMaterReactorswithMarkIIIcontainments[8].Amaximumignitioncriteriaof6Xhydrogenconcentrationfortypicalcontainmentregionswasusedinthisanalysis,consistentwiththemostrecenthydrogenanalysiseffortfortheCookNuclearPlant[4].Thisignitioncriteriaboundsthe5.3Xhydrogenconcentrationforapre-mixedvolumewhichissupportedbytheNTSexperiments[7].TheMAAPhydrogenburnmodelsweredevelopedbasedontheassumptionofdiscreteburnsinpre-mixedvolumes.Forcontinuousinjectionofhydrogenintoawellmixedvolume,aswould ATTACHMENTTOAEP:NRC:0500YPAGE5bethecaseformostcontainmentregionsoftheCookNuclearPlantinadegradedcoreaccident,ignitionwouldbeatasufficientlylowaveragehydrogenconcentrationthatnosignificantpressurepulsewouldtypicallybeexpected[7,8].Sincetheassumptionofignitionatamaximumof6Xhydrogenconcentrationdoesproduceasubstantialpressurepeak,thisassumptionwasusedtoprovideaconservativeboundonthepressureresponsetoahydrogenburnincontainment.Thehydrogenignitioncriterionof6Xwasusedinboththeupperandlowerregionsofcontainmentasaninitialignitioncriterion.Thefirstignitionwouldpromoteverygoodlocalmixing.Afterthefirstignition,theignitioncriterionisresettothelowerflammabilitylimitofhydrogen.Thelowerflammabilitylimitisthelowestconcentrationofhydrogenthatwillpropagateaflame,andintheMAAPcodeiscalculatedbyincludingtheaffectsoftemperatureandsteamconcentrations.ForcontainmentconditionstypicallycalculatedintheMAAPcode,thelowerflammabilitylimitisabout4.9Xhydrogen.Thecoderesultswillthenmorecloselyapproximateacontinuousburnasseenincontinuousinjectionexperiments.Thisloweringoftheignitioncriterioninthelowercontainmentisassumedtoaffectboththelowercompartmentandannularregionsofthelowercontainment,sincetheyareadjacentwithalargeinterconnectionarea.Inthepresenceofawaterfogattheoutletoftheicecondenser,theenergyrequiredtovaporizesomeorallofthewaterinthefogwouldsuppresstheflamepropagation.Therefore,anignitionandflamepropagationpenaltywouldbeexpectedinthisregion.Earlieranalysis[4]expecteda2Xpenaltyontheignitionofhydrogeninthisregion,foranignitioncriterionof8Xhydrogen.Morerecentexperimentshavemeasuredtheproductionoffogattheoutletoftheicecondenser[9]andanewanalysishasaddressedtheimpactoffogonthepropagationofhydrogenflames[10].Basedonthenewerwork,ignitionandrelativelycontinuousburningwouldbeexpectedattheoutletoftheicecondenserformostsequences.Thisworkfoundabestestimateignitioncriterionofslightlyover7Xwhenusingtheworstfogconcentrationmeasuredintheexperiments.Theicecondenserinletsteamconditionsfortypicalaccidentsequencesarelessseverethantheinletsteamconditionsoftheexperiments.Therefore,evenlowericecondenseroutletfogconcentrationswouldbeexpectedfortypicalaccidentsequences,resultinginanicecondenseroutlethydrogenignitioncriterionsignificantlylowerthan7X.However,adequateproofofthiswouldrequire'extensivework.Therefore,afoggingignitioncriterionof8Xattheoutletoftheicecondenserwasusedinthisanalysis.Theupperplenumignitioncriterionwasnotsetlowerafteraburnsincethefogactuallyinertstheincomingflowstream.

ATTACHMENTTOAEP:NRC:0500YHydrogenProductionResultsPAGE6Thethreebasecasesequencesprovideaspectrumofhydrogengenerationratesandmechanisticzirconiumoxidationfractions.Foreachcase,anon-mechanistichydrogenproduction"tail"ofO.llb/sec.wasaddedtoobtainaneffectivehydrogenproductionequivalentto758zirconiumoxidation.Thelowpressuresequenceproducedtheleastmechanisticallyproducedhydrogenandthehighestpeakhydrogengenerationrateatreflood.Thehighpressuresequenceshowedtheoppositepattern,withthelowestpeakrateonreflood.Theintermediatepressuresequenceproducedintermediateresultsonbothoftheseparameters.Thesearesummarizedbelow.MechanisticHydrogenGenerationLargeLOCASmallLOCACCWGenerationRate(lb/sec)-priortoreflood-duringreflood(peak)0.138.1.0125.0.0183.0Mechanisticoxidation19.3aHydrogenCombustionCharacteristics35.6s51.0aInthethreebasecases,thefirstburndoesnotoccuruntilthehighproductionrateassociatedwithcorerefloodhasbegun.Thisfirstburnisinthelowercontainmentforallcases.FortheCCWcase,thefirstlowercompartmentburnisnearlysimultaneouswiththefirstburnintheupperplenumoftheicecondenser.Inallcases,significantburningispredictedinthelowercompartment.Thelowercontainmentsprayskeepthesteamconcentrationinlowercontainmentsufficientlylowthattheburningisnearlycontinuous.Onlybriefperiodsofinertionbysteamwereobserved.BurningispredictedattheoutletoftheupperplenumoftheicecondenserinonlythelossofCCWsequence,althoughtheignitionpointisnearlyreachedduringrefloodinthelargebreakLOCAsequence.AlthoughthepeakhydrogenproductionrateishigherinthelargeLOCAcase,thetotalamountofhydrogengeneratedduringthelargeLOCArefloodisnotverylarge,resultinginasomewhatsmallerhydrogenconcentrationpassingthroughtheicecondenser.ThelossofCCWsequenceisalsotheonlycasethatshowshydrogenconcentrationsreachingtheignitionpointinuppercontainment.

ATTACHMENTTOAEP:NRC:0500YPAGE7Therelativelyhighhydrogenproductionrateforthelongrefloodperiodallowssufficientconcentrationtobuildupinthisregiontoreachtheignitionpoint.Thehydrogenladenairisdrawnfromtheuppercontainmenttotheannulus,whichisaregionoflowercontainment.Withthehydrogenburningintheadjacentlowercompartmentregion,theignitioncriterionhasbeenresettothelowerflammabilitylimit.ForthesmallandlargebreakLOCAcases,theinitialignitioncriterionfortheuppercontainmentwasnotmet,butthemixtureexceededtheconcentrationofthelowerflammabilitylimitforalongperiodoftime.Itshouldbenotedthatthelowerflammabilitylimitwasexceededforthesetwocasesonlyduringthenon-mechanisticperiodofthehydrogenrelease.Thisleadstosignificantburningintheannulus.InthelossofCCWsequence,theinitialburnintheuppercontainmentresetstheignitioncriteriatothelowerflammabilitylimit,shiftingthemajorityoftheburningfromtheannulustotheuppercontainmentforthiscase,IftheuppercontainmentinitialignitioncriterionhadbeensetclosertothelowerflammabilitylimitinthesmallorlargebreakLOCAcases,asimilarpatternwouldhavebeenseen.Inanyevent,itcanbeconcludedthattheairreturningtothelowercompartmentwillhavenolargerhydrogenconcentrationthanallowedbythelowerflammabilitylimit.Thefollowingtablesummarizestheamountofhydrogenburnedineachregionforthe'basesequences.HydrogenBurntbyRegion(lbs)LargeLOCASmallLOCACCWLowerContainmentUpperPlenumUpperContainmentAnnulus160009003400060523119858346 ATTACHMENTTOAEP:NRC'0500Y3.0CONTAINMENTSTRUCTURALADEQUACYPAGE8Thecontainmentcompartmentpressureandtemperatureresultsofthesequenceanalyseswereusedtodetermineiftheacceptancecriteriaweremet.Themaximumpressurepeakisusedtodetermineifthecontainmentmaintainsstructuralintegrity.Theacceptancecriteriaof36psigwasusedfortheultimatecontainmentstructuralcapacity,asapprovedinaSafetyEvaluationfromtheNRCdatedFebruary21,1985[11].OnlyrelativelylowpressurepulsesareshowninthesequenceanalyseswhichweresummarizedinSection2andtheAppendix.Themaximumpressurepulseof28psia,or13.3psig,wasseeninthelossofCCWsequence.Thispressurepulsewascausedbytheinitialburnintheuppercontainment.Thispressureiswellbelowtheacceptancecriteriaof36psig.Inaddition,theconclusionoftheseriesofexperimentsendingintheNTSexperiments[7]wasthatlargedeflagrationsarenotexpectedinwell.mixedcontainmentatmosphereswithcontinuoushydrogeninjectioninthepresenceofactiveigniters.Thissupportstheconclusionofthesequenceanalyses.

ATTACHMENTTOAEP:NRC:0500Y4.0EQUIPMENTSURVIVABILITYPAGE9TheequipmentneededtoachieveandmaintainshutdownconditionsforadegradedcoreaccidentwereprovidedintheSafetyEvaluationReportfortheDIS[1]andarereproducedbelow.Theoriginalanalysisofthesurvivabilityofinstrumentationandequipmentutilizedheattransfercalculationsofthecriticalequipmentsupplementedbyevaluationsofequipmentsubjecttohydrogenburnenvironment[12].Thismethodologytookcreditforthesubmergenceofequipmentwhenpossible.Subsequenttothatdate,moreextensiveexperimentshavebeenperformedattheNevadaTestSitefacility,whichsupportboththemethodologyandconclusionsoftheearlieranalysis[13].Forthisstudy,survivalofthecriticalequipmenthasbeenverifiedfortheconditionscalculatedintheMAAPanalyses.EssentialEquipmenta)Narrow-rangesteamgeneratorlevelmonitorsb)Pressurizerlevelmonitorsc)Pressurizerpressuremonitorsd)RCSwiderangepressuremonitorse)Coreexitthermocouplesf)RCSloopsRTDsg)Airrecirculation/hydrogenskimmerfansh)Distributedignitionsystemcomponentsi)Containmentwaterlevelmonitoringsystemalsotobeconsidereda)Containmentisolationvalvesb)Gasketsandsealsforflanges,electricalboxes,airlocks,andtheequipmenthatch~c)ElectricalpenetrationsConsistentwiththeSafetyEvaluation[1],thepressuretransmitterslocatedinthelowercontainmentaretakenasrepresentativeofthecriticalequipment,andspecificallyanalyzedforthermalresponse.TheadequacyofthisapproachissupportedbytheextensiveNTSequipmentexperiments.Intheseexperiments,abroadrangeofequipmentwasexposedtohydrogenburnconditions,includingcables,pressuretransmitters,solenoidvalves,amotoroperatedvalve,limitswitches,afanmotor,resistancetemperaturedetectors,hydrogenigniters,andcontainmentpenetrations.Allbutafewequipmentspecimensoperatednormallyduringandafteralltests;andallcablespassedpose-testelectricalchecks.

ATTACHMENTTOAEP'NRC:0500YPAGE10HydrogenBurnThermalEffectonEquipmentInthesequenceanalyses,thehighinitialignitioncriteriainthevariousregionsallowsthemaximumamountofhydrogentoreturntothelowercontainmentvolumes.Thiswillmaximizethehydrogenburninginthelowervolumes,whichwillmaximizethethermalloadonequipmentinthosevolumes.Itwasshownabovethatthehydrogentobereturnedtothelowercompartmentislimitedtothelowerflammabilitylimitintheuppercontainment.However,inallbutthelossofCCWcase,thehighuppercontainmentignitioncriterionforcestheburningtobeintheannularregionsurroundingthelowercompartment,whichmaximizestheheatflowintothelowercompartment.InthelossofCCWcase,thebulkofthisburningoccursintheuppercontainment.Asimple,thinsteel(1/4")heatstructurewasaddedtotheMAAPmodeltorepresentapieceofequipment.Thepeaktemperatureofthisheatstructurewasusedasanindicatorofthemostsevereconditionsinthelowercompartmentforfurtheranalysis.ThelargebreakLOCAbasecasewasfoundtobelimitingforthermalresponse,sincethehydrogenburnsinthatregionoccurredshortlyafterblowdownwhentheequipmentisstillquitehot.ThisistrueeventhoughthesmallbreakLOCAcasepredictedovertwicetheamountofhydrogentoburninthelowercompartment.Toensurethelimitingloadsontheequipmentwereobtained,twovariationsofthelargebreakLOCAcasewereanalyzed.First,twoinsteadofonecontainmentairrecirculationfanswereassumedtobeoperating.Thisisshowntonotsignificantlyaffectthehydrogenburncharacteristicsandlocations;thebasecaselargeLOCAwasfoundtoremainlimiting.ThesecondvariationofthelargebreakLOCAcasewastousecoreparametersrepresentativeofUnit2insteadofUnit1.Unit1wasoriginallychosensinceitcontainsmorezirconiumthanUnit2.Unit2,however,.operatesata5Xhigherpower.Inaddition,thefuelrodarrayinUnit,2is17x17insteadof15xl5,withagreatersurfaceareaforzirconiumoxidation.TheUnit2sensitivitycaseresultsinaslightlygreaterpeakhydrogengenerationrateatreflood,andaslightlygreaterpeakequipmenttemperatureinthelowercompartment.AthirdsensitivitywithapotentialinteresttoequipmentthermalresponseistheCEQfanfailurecase.Althoughfanfailureisnotexpectedasdiscussedbelow,itwastheintentofthissensitivitytodeterminewhethersurvivalofthecontainmentairrecirculation(CEQ)fanwasnecessarytoobtain,acceptableequipment ATTACHMENTTOAEP:NRC:0500YPAGE11survivabilityresults.ThelossofCCWsequenceprovidesthegreatestchallengetothefans,sothatbasecasewasmodifiedtoassumeCEQfanfailureatthetimeofthefirstburnintheuppercontainment.Thelowercirculationflowhastheeffectofincreasingthehydrogenconcentrationexitingtheicecondenser,wheremostofthehydrogenburningnowoccurs.TheimpactoftheCEQfanfailurewasfoundtohavenoeffectofthepeakequipmenttemperatureinthelowercompartment.AthermalmodelofaFoxboropressuretransmitterwasdevelopedtoobtainthetemperatureresponseofthetransmitterinternals.TheexternalconditionsforthisheattransfercalculationwerecalculatedbytheMAAPcodeforthelimitingsequenceforthermalresponse,theUnit2largebreakLOCA.Theanalysisdeterminedthetemperatureofthepressuretransmittercover,theairinsidethecover,andthesurfaceoftheelectronicsinsidethecover.Theresultsindicatethattheelectronicstemperatureisnotexpectedtoexceed200'F.TheNTSexperimentalmeasurementsoftheelectronicsofaFoxboropressuretransmitterreached246'F,andcontinuedtofunction.Therefore,essentialequipmentisconcludedtosurvivethethermalenvironmentcausedbyhydrogenburningundertherulesof10CFR50.44(c)(3)(iv)(A).ContainmentAirRecirculationFanTheassumptionofthehighignitioncriterionof8Xhydrogenconcentrationattheicecondenseroutletduetofog'ginghasasignificantimpactontheevaluationofthesurvivabilityofContainmentAirRecirculationfans.Givenamoremoderatefoggingignitionpenaltyattheicecondenseroutlet,.significantburningwouldbeexpectedthere.Asdescribedabove,theignitioncriterionof8Xincludessignificantconservatismintheestimationofthefogconcentrationsattheicecondenseroutlet.Asaresultofhydrogenburningintheupperplenum,insufficienthydrogenwouldbeexpectedtobuildupintheuppercontainmenttosupportaglobalburnonabestestimatebasis.Aglobalburnisaburnthatpropagatesthroughalargefractionofavolume,consumingasignificantfractionofthehydrogen.AglobalburninitiatedatarelativelyhighhydrogenconcentrationinthisregionhasbeenshownbeforetocausethecollapseoftheContainmentAirRecirculationfanhousing[14].However,basedontheevaluationofcontinuousinjectionexperimentsprovidedbelow,ahydrogenburninducedpressureexcursionsufficienttodestroythefansisnotexpected.IntheMAAPanalysespresentedintheAppendix,theinitialpressureriseof10psidwhichaccompaniedhydrogenburningintheuppercompartmentisduetotheconservatismemployedinthe ATTACHMENTTOAEP'NRC:0500YPAGE12analysis,i.e.,ignitioncriterionof6vol.XHzandtheuseoftheHECTRcodeburncompletenesscorrelation.TheHECTRcodeburncompletenesscorrelationrepresentsanupperboundofscatteredburncompletenesstestdataofpremixedcombustioninaclosedchamberwithoutcontinuousinjection.IntheNTStestswithcontinuousinjection,theobservedpressurerisewasmodestcomparedtothatwithoutinjection.Theuppercompartmentisanopenthrough-flowvolumewithcontinuousinjectionofhydrogenfromtheupperplenum.Thepressureriseassociatedwithburningisexpectedtobesmall.Therefore,thehydrogenmodellingcombinationisoverlyconservativeinthepredictionofpressurepulsesfortheCookNuclearPlantuppercontainmentregion.InsightsgatheredfromtheNTStestssupportthisobservation[7,15].Althoughpressurepulsesduetohydrogenburningofupto6psidwereobservedinNTScontinuousinjectiontestsatthetimeoffirstignition,thesepressurepulseswereonlyseenforspecialconditions.Incaseswhereasignificantpressurepulsewasobserved,awideboundarylayerofacombustiblemixtureofhydrogengrewuntilitcameincontactwithanigniter.Thepressurepulsewasduetotherapidpropagationofthehydrogenburnthroughthisboundarylayer.Theboundarylayerwasfedbytheinjectionsourceofhydrogenandsteam.TheconfigurationandhydrogeninjectionsourceintheCookNuclearPlantuppercontainmentdiffersfromthisscenario.Thehydrogeninjectionsourceintheuppercontainmentisdiffusewithamaximumhydrogenconcentrationof8X,inertedbyfog.Therateofincreaseinhydrogenconcentrationintheuppercompartmentisveryslow(40,000cfmfanflowatamaximum8Xconcentrationintothe746,000cu.ft.volumeuppercontainment).Containmentsprayinduceduppercompartmentflowsareexpectedtobehigh(intherangeofseveralmeters/second[16]),promotinggoodmixing.Noboundarylayerbetweenignitableandnon-ignitableregionsshouldexist,andcombustionshouldinitiateatthelowerflammabilitylimit.Therefore,asignificantpressureproducingdeflagrationisnotexpectedintheCookNuclearPlantuppercontainment.Forthisregion,therateofhydrogenburningwillrisetoequalthehydrogenflowrateintouppercontainment.Therefore,theCEQfansareconcludedtosurvivetheconditionscausedbyhydrogenburningundertherulesof10CFR50.44(c)(3)(iv)(A).Eventhoughthefansarenotexpectedtofailduetoaburnintheuppercontainment,asasensitivityanalysisthese'answereassumedtofailatthefirstburninuppercontainment.Sincethissensitivityanalysisdoesnotproducemoresevereresultsthanthebasecaseanalyses,itcanbeconcludedthatthedesignfunctionoftheCEQfanswouldhavebeenmet,andthatfailureoftheCEQfanswouldhavebeenacceptable.

ATTACHMENTTOAEP:NRC'0500YPAGE13Therearetwodesignobjectivesforthesefans.First,thefansareintendedtoprovidegoodcirculationofthesteamreleasedinthelowercontainmentthroughtheicecondensertoreachuppercontainment.Thisensuresthattheicecondenseranduppercontainmentspraysremovesteameffectively,keepingthecontainmentpressuretowithinitsdesignbasisvalueof12psig.However,duetothefactthatthesubjectdegradedcoreaccidentconditionsarewellbeyondthedesignbasis,theacceptancecriterionforcontainmentpressureforthisanalysisisthecontainmentultimatestrengthof36psig.Thesequenceanalyzedshowsthat,evenwithapostulatedfanfailure,thepeakcontainmentpressureis13.3psig,(28psia)whichiswellbelowthecontainmentultimatestrengthof36psig.TheseconddesignbasisfortheContainmentAirRecirculationsystemissupportfortheHydrogenSkimmerSystem(HYS)flows.TheHYSdrawsgasesfromthesteamgeneratorandpressurizerdoghousesandthecontainmentdomeregiontopreventcombustibleconcentrationsofhydrogenfromaccumulatinginadesignbasisaccident,inwhichasmallpercentageofthecladdingisassumedtoreactwithsteam.Forthedegradedcoreaccidentsequences,theHYSwouldbegreatlyoverloadedandthiscriteriacannotbemet.Fordegradedcoreaccidents,theDIStakesover,eliminatingtheneedforHYSoperation.

ATTACHMENTTOAEP:NRC:0500Y5.0REACTORHEADVENTSPAGE14ThereactorheadventswereinstalledintheCookNuclearPlantinresponseto10CFR50.44(c)(3)(iii)toventahydrogenbubbleinthereactorheadintheeventofadegradedcoreaccidentwithsignificanthydrogengeneration.ThisheadventisalsousedintheEmergencyOperatingProcedurestoaidinvesseldepressurizationafterallothermechanismshavefailed,includingboththeprimaryandsecondarypoweroperatedreliefvalves.Thereactorheadventventstothelowerlevelofuppercontainment,andassuchisapotentialhydrogensourcethatcanbypasstheignitersinthelowercontainmentandicecondenserupperplenum.Theprimarypurposefortheheadventistorelievea"hardbubble"afterhydrogengenerationhasoccurred.Atthistime,itisassumedthatthecoreiscovered,andthathydrogenhasaccumulatedinthereactorhead.Sincethecoreiscovered,notimecriteriaexistsforthespeedofventingthisbubble.TheEmergencyOperationProceduresdirecttheoperatortoreadthehydrogenconcentrationintheuppercontainmentbeforeventingthehydrogen,andlimitthetimeofventingsothatacombustiblemixtureofhydrogencouldnotaccumulateintheuppercontainment.Thehydrogencouldthenberemovedbythehydrogenrecombiners.Sincetheventingprocedureexplicitlypreventsacombustiblemixturefromaccumulating,thisuseofthereactorheadventissupported.Theseconduseoftheheadventistorelieveprimarysystempressurewhenallotherdepressurizationsystemfail.Giventhenumberofsystemfailuresneededtoreachthispoint,thisuseisconsideredextremelyunlikely.TheheadventgeometryandflowcharacteristicsareverysimilartothecontinuousinjectionexperimentsperformedatNTS[7,15).Iftheheadventisusedtoaidindepressurizingthecore,amixtureofsteamandhydrogenwillbereleasedatahighflowrateandmomentumtotheuppercontainment.ForthisconfigurationintheNTSexperiments,aslowapproachtoignitionwasfound,withnosignificantpressurepulsewhenignitionoccurred.Infact,theonlycaseswheresignificantpressurepulseswereseenintheNTScontinuousinjectionexperimentswerethosecaseswithonlybottomigniters.TheCookNuclearPlantuppercontainmenthasignitersbothintheupperdomeoftheuppercontainmentandonthesteamgeneratorandpressurizerdoghousewalls.AsseenintheNTStestswithcontinuousinjectionofajetofhydrogenandsteam,ignitionwouldeitherbeatapointwherethejetpassedarelativelylowigniter,orasthehydrogenreachedthetopofthecontainment.Ineitherevent,ignitionwouldoccurwhilethehydrogenoccupiesarelativelysmallportionofthecontainmentvolume,andapressurepulsesufficientto ATTACHMENTTOAEP:NRC'0500YPAGE15damageordestroytheCEQfanswouldnotoccur.Therefore,theuseofheadventstodepressurizetheprimarysystemintheeventofadegradedcoreaccidentisacceptable.

ATTACHMENTTOAEP'NRC:0500Y6.0SUMMARYANDCONCLUSIONSPAGE16Tomeetthehydrogencontrolrequirementsof10CFR50.44,theDistributedIgnitionSyst:emwasinstalledattheCookNuclearPlant.AsrequiredbySection(c)(3)(vi)ofthatregulation,analyseshavebeencompletedtosupportthedesignofthehydrogencontrolsystem.TheanalyseswerebasedontheaccidentsequencesidentifiedintheCookNuclearPlantIndividualPlantExamination.Theseanalysesassumedthatthecorewasrecoveredbeforethecorebecameseverelydegraded,andthat75Xofthezirconiuminthecorereactedwithsteamtogeneratehydrogen.ThecontainmentconditionsthatresultedfromthishydrogenburninginthepresenceoftheDistributedIgnitionSystemwasthencalculated.Theregulationrequiresthatthecontainmentmaintainsitsstructuralintegrity,andthattheequipmentnecessarytomaintainsafeshutdownandcontainmentintegritybecapableofperformingtheirfunctionduringandafterexposuretotheenvironmentcreatedbythehydrogenburning.Theanalysesshowthatthemaximumpressurepredictedforhydrogenburnconditionsisfarlessthantheultimatestructuralcapability.Inaddition,themaximumtemperaturecalculatedinimportantequipmentisshowntobelessthanthetemperaturerequiredtothreatenthecapabilityofthatequipment.Therefore,theanalysesshowthatthedesignoftheDistributedIgnitionSystemissufficienttocontrolhydrogenundertherequirementsof10CFR50.44.

APPENDIXTOATTACHMENTTOAEP:NRC:0500YHYDROGENCONTROLPROGRAM(10CFR50.44(c))FORTHEDONALDC.COOKNUCLEARPLANTSUBMITTALOFANALYSES

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