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)
Shared Package
ML17331A062	List: ML17331A061 ML17331A063
References
AEP:NRC:0500Y, AEP:NRC:500Y, NUDOCS 9303030121
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acezr.ztu xDOCvMzmDrSxammrax SvsrmcREGULATINFORMATION DISTRIBUTIO~STEM (RIDS)iDACCESSION NBR:9303030121 DOC.DATE:

93/02/26NOTARIZED:

NODOCKETFACIL:50-315 DonaldC.CookNuclearPowerPlant,Unit1,IndianaM0500031550-316DonaldC.CookNuclearPowerPlant,Unit2,IndianaM05000316AUTH.NAMEAUTHORAFFILIATION FITZPATRICK,E.

IndianaMichiganPowerCo.(formerly IndianaaMichiganEleRECIP.NAME RECIPIENT AFFILIATION RDocumentControlBranch(Document ControlDesk)~I

SUBJECT:

Providessummaryofanalysesreptforanalytical effort.Analysesdemonstrate thatcontainment structural integrity willnotbethreateded byhydrogengeneration

&combunstion.

NimtinDZSTRZBUTZON CODE:ROZZDCOPZESRECEZVED:LTR IENCL~SZSE:~f'KSTITLE:GenericLtr88-20reIndividual PlantEvaluations NOTES:RECIPIENT IDCODE/NAME PD3-1PDINTERNAL:

ACRSHOUSTONPM NRRAN,RGL01RESMITCHELLPJ RGN1RGN-3COPIESLTTRENCL11111111111111RECIPIENT IDCODE/NAME DEAN,WAEOD/DSP/TPAB NRR/OGCBRESFLACK,JRES/DSIR/SAIB/B RGN2RGN4COPIESLTTRENCL111111337,71111DEXTERNAL'RC PDRNSIC11DNOTETOALL"RIDS"RECIPIENTS:

PLEASEHELPUSTOREDUCEWASTE!CONTACTTHEDOCUMENTCONTROLDESK,ROOMPl-37(EXT.504-2065)

TOELIMINATE YOURNAMEFROMDISTRIBUTION LISTSFORDOCUMENTS YOUDON'TNEED!TOTALNUMBEROFCOPIESREQUIRED:

LTTR24ENCL24 tIIl0IT1 IndianaMichiganPowerCompanyP.O.Box16631Columbus, OH43216RAEP:NRC:0500Y DonaldC.CookNuclearPlantUnits1and2DocketNos.50-315and50-316LicenseNos.DPR-58andDPR-74HYDROGENCONTROLPROGRAM(10CFR50.44(c))

SUBMITTAL OFANALYSESU.S.NuclearRe'gulatory Commission DocumentControlDeskWashington, D.C.20555Attn:T.E.MurleyFebruary26,1993

DearDr.Murley:

InanNRCletterdatedApril10,1989,itwasindicated thatthe10CFR50.44 hydrogencontrolrevieweffortfortheDonaldC.CookNuclearPlant,whichhadbeenterminated bytheNRCin1986,wouldbesubsumedintotheIndividual PlantExamination (IPE)effort.Asaresultofthisdirection, theIPEand10CFR50~44analysiseffortsforCookNuclearPlantwereperformed aspar'allel butseparateinterfacing programs.

IndianaMichiganPowerCompany(I&M)submitted theIndividual PlantExamination resultsinletterAEP:NRC:1082E datedMay1,1992.InletterAEP:NRC:500X datedAugust5,1992,I&Mcommitted tocompletebyFebruary28,1993,theanalysespursuantto10CFR50.44 todemonstrate theabilityofthehydrogencontrolsystemtomitigatetheconsequences ofthereleaseofhydrogenintoCookNuclearPlantcontainment duringpostulated degradedcoreaccidents.

Thepurposeofthisletteristoprovidethereportofthisanalytical effort.Theattachment tothisletterprovidesasummaryoftheanalysesrequiredby10CFR50.44 paragraph (c)(3)(vi)(A).

Thesequences selectedforanalysiswerebasedonsignificant sequences foundintheIPE.Theseanalysesdemonstrate thatthecontainment structural 9303030121'30226

.PDR'DOCK05000315PDR Dr.T.E.Murley2AEP:NRC'0500Y integrity willnotbethreatened byhydrogengeneration andcombustion, andthatnecessary equipment willsurvivetheconditions createdbytheburningofhydrogen.

Sincerely, PL~p~gVicePresident rbbAttachment cc:A.A.Blind-BridgmanJ.R.PadgettG.CharnoffNFEMSectionChiefA.B.Davis-RegionIIINRCResidentInspector

-Bridgman Dr.T.E.Murley3AEP:NRC:0500Y bc: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:0500Y DC-N-6015.1 ATTACHMENT TOAEP:NRC:0500Y HYDROGENCONTROLPROGRAM(10CFR50.44(c))

FORTHEDONALDC.COOKNUCLEARPLANT.SUBMITTAL OFANALYSES ATTACHMENT TOAEP'NRC:0500Y

1.0INTRODUCTION

PAGE1TheNuclearRegulatory Commission requiresin10CFR50.44thatreactorcontainments beabletoaccommodate, withoutlossofcontainment integrity ordegradation ofvitalequipment, thehydrogenthatmaybegenerated duringdegradedcoreaccidents.

Asaresult,theicecondenser containment designattheCookNuclearPlantwasrequiredtoincludehydrogencontrolsystemscapableofaccommodating anamountofhydrogenequivalent tothatgenerated fromthereactionof75Xofthecladdingintheactivefuelregionwith'team.

Thehydrogengenerated bysuchareactionhasbeenjudgedtoboundtheamountsofhydrogenlikelytobegenerated indegradedcoreaccidents inwhichcoredegradation isarrestedpriortocoremeltdown.

Inresponsetotheaboverequirement, theDistributed IgnitionSystem(DIS)wasinstalled attheCookNuclearPlant.Thissystemiscurrently operableandithasbeenreviewedandapprovedbytheNRCstaffinaSafetyEvaluation datedDecember17,1981[1].Considerable analysesandexperiments havebeenperformed todemonstrate conformance withtheaboverequirements, asrequiredby10CFR50.44paragraph (c)(3)(vi)(A).

InanNRCletterdatedApril10,1989,itwasindicated thatthefinalconfirmatory analysiseffort,whichwasterminated in1986,wouldbesubsumedintotheIndividual PlantExamination (IPE)effort.ThebaseIPEanalysiswassubmitted totheNRConMay1,1992inletterAEP:NRC:1082E

[2].Thiscurrentreportdescribes theuseoftheIPEanalysistoaddresscompliance withtherequirements of10CFR50.44.Asdescribed inthisreport,theIPEanalysiswasusedtoestablish themorelikelydegradedcoresequences.

Thecontainment responseanalysisperformed fortheIPEwasmodifiedtoincludetherequirements of10CFR50.44,andanalysisofappropriate sequences wasthenperformed.

Thecomputeranalysisofthecontainment responsetohydrogengenerating sequences providesanunderstanding ofthetimingandrelatedhydrogencombustion ratesinthevariousregionsofthecontainment.

Thisinformation isusefulindetermining heatloadsonequipment requiredtosurvivethehydrogencombustion environment.

Duetotheapproximations necessary toperformanintegrated analysisofboththereactorcoolantsystemandcontainment, thedetailedcombustion characteristics predicted bythecomputercodeonlyapproximate theconditions expectedinacontainment region,particularly forthepressureresponsetohydrogencombustion.

Incontainment regionswher'epressureresponseisofparticular

interest, hydrogenflowconditions predicted bythesequenceanalysisareusedtore-evaluate thecodepredictions basedontheresponseexpectedfromareviewof ATTACHMENT TOAEP:NRC:0500Y PAGE2applicable experiments.

Conclusions ontheadequacyoftheDISforhydrogencontrolarethendrawnonthecombination ofexperiment andanalysis, asrequiredby10CFR50.44paragraph (c)(3)(iv)(A).

Twootherhydrogencontrolsystemsareinstalled intheCookNuclearPlant,thehydrogenskimmersystemandthehydrogenrecombiners.

Thehydrogengeneration criteriaof10CFR50.44(c)(3)(vi) arewellbeyondthecapability ofeitherofthesesystems.Thehydrogenskimmersystemwasinstalled todrawairfromconfinedareasinthecontainment topreventacombustible mixtureofhydrogenfrombuildingupintheseareasintheeventofadesignbasisaccident.

Inadesignbasisaccident, lessthan1Xofthezirconium isexpectedtoreactwithwater.TheDIShasignitersinthesesameconfinedareas,whichcantakeoverforthehydrogenskimmersystemincontrolling hydrogeninthoseareasintheeventforthemoresevereaccidentconditions.

Likewise, thehydrogenrecombiners werenotintendedtocontrolhydrogenintheconcentrations andatthegeneration ratesrequiredunderthissectionoftheregulation.

Theuseofhydrogenrecombiners willbereservedforlongtermhydrogencontrolaftertheaccidentconditions havestabilized.

Thisreportonlyaddresses theeffectiveness oftheDISincontrolling hydrogen.

TheexistingUFSARaddresses boththehydrogenskimmersyst:emandthehydrogenrecombiners.

Section2providesasummarydescription ofthemethodology usedtochooseaccidentsequences foranalysis, thecomputercodeandmodelsusedtoanalyzethosesequences, andtheresultsofthesequenceanalysis.

AcompletereportonthesequenceanalysisisprovidedintheAppendix.

Thecontainment structural adequacyisreviewedinSection3ofthissummary,andequipment survivability analysisisreviewedinSection4.Section5discusses theuseoftheheadventsonthehydrogencontrolanalysis.

Theconclusions ofthehydrogencontrolanalysisaresummarized inSection6.

ATTACHMENT TOAEP:NRC'0500Y 2.0ACCIDENTSEQUENCEANALYSISPAGE3Inanaccidentsequencethatleadstoadegradedcore,waterinventory islostfromthereactorcoolantsystemuntilthecoreisuncovered.

Withthecoreuncovered, theremaybeinsufficient steamtocarrythedecayheataway,resulting inaheatupofthefuelrods.Whenthefuelrodzirconium claddingreachesapproximately 1800'F,thezirconium beginsreactingwithsteamtoformzirconium dioxideandhydrogeninanexothermic reaction.

Withinminutes,thecorewillreachtheuraniumdioxideandzirconium meltingpoint,andthecorewillbegintoslump.Duringthetimeofcoreuncovery, hydrogengeneration isusuallylimitedbyalackofsteamtoarelatively lowrate.Tostoptheprogression oftheaccident, thecoremustberecovered withwater.Thisrecoverywillproducealargeamountofsteamasthecoreisquenched.

Thissteam,withthealreadyoverheated

cladding, willallowforalargebutbriefpeakinthehydrogengeneration rate.Thethermalshockmayalsoshattertheintactfuelrodsatthattime.Thehydrogengenerated bythezirconium waterreactionisreleasedtothereactorcoolantsystemandthenoutthecoolantsystembreachintothecontainment.

Thisbreachcouldbeabreakinthereactorcoolantsystemorareleasepaththroughthereactorcoolantpumpsealsorthroughthesafetyorpoweroperatedreliefvalvesiftheaccidentwasinitiated byatransient.

Thehydrogenmayreachaburnableconcentration incontainment, threatening equipment bythehighheatflux.Ifthehydrogenbuildsuptoasufficiently highconcentration beforetheburnbegins,theresulting pressurepulsemayeventhreatenthecontainment integrity.

Thissectionoverviews themethodology andresultsofthesequenceanalysis.

ThecompletereportonthehydrogencontrolsequenceanalysisisprovidedintheAppendixtothisreport.Theacceptance criteriaforthishydrogencontrolanalysisarecontainment structural integrity andsurvivability ofvitalequipment.

Thevarioussequences andanalyticassumptions usedintheanalysisprovideabasisforshowingcompliance withtheacceptance

criteria, whichappearsinsubsequent sectionsofthisreport.AccidentSequenceSelection Sequences wereselectedforanalysisbasedonseveralcriteria.

First,themostprobablesequences werechosenbasedontheIndividual PlantExamination.

Thesewerethenbinnedintosimilar ATTACHMENT TOAEP:NRC'0500Y PAGE4setsofsequences basedonthehydrogengeneration rates,andarepresentative caseforeachsetwaschosenforanalysis.

Notethatthesearenotnecessarily themostprobablesequences.

Thecorepressureisimportant totherateofcorereflood,sinceitlimitstheECCSflowrateavailable torefloodthecore.Thus,forhydrogengeneration, thecorepressureatthetimeofcorerecoveryistheprimaryvariableindictating thehydrogengeneration rate.Therefore, alargeLOCAsequence, asmallLOCAsequence, andasequenceinitiated bylossofcomponent coolingwaterwasanalyzedtocoverthespectrumoflow,intermediate, andhighsystempressures atcorerecovery.

Thesesequences covertherangeofnearatmospheric

pressure, steamgenerator pressure(about1100psi)andfullreactorcoolantsystempressure(above2250psi).Inaddition, severalsensitivity analyseswereperformed.

Detailedjustification fortheselection ofthesesequences isprovidedintheAppendix.

AccidentSequenceModelling Toanalyzethesequences, theMAAP3.0B[3]codewasused.Thiscodecombinesanuclearsteamsupplymodelwithanicecondenser containment model,andwasusedintheIPEanalysis.

TheoriginalMAAPhydrogenburnmodelsweremodifiedtoreflectthehydrogenburncompleteness correlation providedinanearliersubmittal

[4].Thiscorrelation isthesameasisusedintheHECTRcode[5,6],andwassupported mostrecentlybytheNevadaTestSite(NTS)[7]largescalehydrogenburnexperiments forpremixedconditions.

Foranyscenarioinwhichthecoregeometryissufficiently intacttoberecoverable, lessthan75Xofthecladdingwouldhavereacted.Tohaveareasonable expectation ofarecoverable core,recoveryisinitiated sothatapproximately 50Xofthecorenodeshavereachedthemeltingpoint.Thecoregeometryiskeptartificially intacttomaximizethesurfaceareaforsteamwaterreactiononrecovery.

Toachievethe75Xzirconium claddingreactionrequiredby10CFR50.44(c)(3)(vi),

anartificial hydrogentailwasaddedtotheanalysis.

ThiswassimilartothestrategyusedbytheBoilingMaterReactorswithMarkIIIcontainments

[8].Amaximumignitioncriteriaof6Xhydrogenconcentration fortypicalcontainment regionswasusedinthisanalysis, consistent withthemostrecenthydrogenanalysiseffortfortheCookNuclearPlant[4].Thisignitioncriteriaboundsthe5.3Xhydrogenconcentration forapre-mixed volumewhichissupported bytheNTSexperiments

[7].TheMAAPhydrogenburnmodelsweredeveloped basedontheassumption ofdiscreteburnsinpre-mixed volumes.Forcontinuous injection ofhydrogenintoawellmixedvolume,aswould ATTACHMENT TOAEP:NRC:0500Y PAGE5bethecaseformostcontainment regionsoftheCookNuclearPlantinadegradedcoreaccident, ignitionwouldbeatasufficiently lowaveragehydrogenconcentration thatnosignificant pressurepulsewouldtypically beexpected[7,8].Sincetheassumption ofignitionatamaximumof6Xhydrogenconcentration doesproduceasubstantial pressurepeak,thisassumption wasusedtoprovideaconservative boundonthepressureresponsetoahydrogenburnincontainment.

Thehydrogenignitioncriterion of6Xwasusedinboththeupperandlowerregionsofcontainment asaninitialignitioncriterion.

Thefirstignitionwouldpromoteverygoodlocalmixing.Afterthefirstignition, theignitioncriterion isresettothelowerflammability limitofhydrogen.

Thelowerflammability limitisthelowestconcentration ofhydrogenthatwillpropagate aflame,andintheMAAPcodeiscalculated byincluding theaffectsoftemperature andsteamconcentrations.

Forcontainment conditions typically calculated intheMAAPcode,thelowerflammability limitisabout4.9Xhydrogen.

Thecoderesultswillthenmorecloselyapproximate acontinuous burnasseenincontinuous injection experiments.

Thisloweringoftheignitioncriterion inthelowercontainment isassumedtoaffectboththelowercompartment andannularregionsofthelowercontainment, sincetheyareadjacentwithalargeinterconnection area.Inthepresenceofawaterfogattheoutletoftheicecondenser, theenergyrequiredtovaporizesomeorallofthewaterinthefogwouldsuppresstheflamepropagation.

Therefore, anignitionandflamepropagation penaltywouldbeexpectedinthisregion.Earlieranalysis[4]expecteda2Xpenaltyontheignitionofhydrogeninthisregion,foranignitioncriterion of8Xhydrogen.

Morerecentexperiments havemeasuredtheproduction offogattheoutletoftheicecondenser

[9]andanewanalysishasaddressed theimpactoffogonthepropagation ofhydrogenflames[10].Basedonthenewerwork,ignitionandrelatively continuous burningwouldbeexpectedattheoutletoftheicecondenser formostsequences.

Thisworkfoundabestestimateignitioncriterion ofslightlyover7Xwhenusingtheworstfogconcentration measuredintheexperiments.

Theicecondenser inletsteamconditions fortypicalaccidentsequences arelessseverethantheinletsteamconditions oftheexperiments.

Therefore, evenlowericecondenser outletfogconcentrations wouldbeexpectedfortypicalaccidentsequences, resulting inanicecondenser outlethydrogenignitioncriterion significantly lowerthan7X.However,adequateproofofthiswouldrequire'extensive work.Therefore, afoggingignitioncriterion of8Xattheoutletoftheicecondenser wasusedinthisanalysis.

Theupperplenumignitioncriterion wasnotsetlowerafteraburnsincethefogactuallyinertstheincomingflowstream.

ATTACHMENT TOAEP:NRC:0500Y HydrogenProduction ResultsPAGE6Thethreebasecasesequences provideaspectrumofhydrogengeneration ratesandmechanistic zirconium oxidation fractions.

Foreachcase,anon-mechanistic hydrogenproduction "tail"ofO.llb/sec.wasaddedtoobtainaneffective hydrogenproduction equivalent to758zirconium oxidation.

Thelowpressuresequenceproducedtheleastmechanistically producedhydrogenandthehighestpeakhydrogengeneration rateatreflood.Thehighpressuresequenceshowedtheoppositepattern,withthelowestpeakrateonreflood.Theintermediate pressuresequenceproducedintermediate resultsonbothoftheseparameters.

Thesearesummarized below.Mechanistic HydrogenGeneration LargeLOCASmallLOCACCWGeneration Rate(lb/sec)-priortoreflood-duringreflood(peak)0.138.1.0125.0.0183.0Mechanistic oxidation 19.3aHydrogenCombustion Characteristics 35.6s51.0aInthethreebasecases,thefirstburndoesnotoccuruntilthehighproduction rateassociated withcorerefloodhasbegun.Thisfirstburnisinthelowercontainment forallcases.FortheCCWcase,thefirstlowercompartment burnisnearlysimultaneous withthefirstburnintheupperplenumoftheicecondenser.

Inallcases,significant burningispredicted inthelowercompartment.

Thelowercontainment sprayskeepthesteamconcentration inlowercontainment sufficiently lowthattheburningisnearlycontinuous.

Onlybriefperiodsofinertionbysteamwereobserved.

Burningispredicted attheoutletoftheupperplenumoftheicecondenser inonlythelossofCCWsequence, althoughtheignitionpointisnearlyreachedduringrefloodinthelargebreakLOCAsequence.

Althoughthepeakhydrogenproduction rateishigherinthelargeLOCAcase,thetotalamountofhydrogengenerated duringthelargeLOCArefloodisnotverylarge,resulting inasomewhatsmallerhydrogenconcentration passingthroughtheicecondenser.

ThelossofCCWsequenceisalsotheonlycasethatshowshydrogenconcentrations reachingtheignitionpointinuppercontainment.

ATTACHMENT TOAEP:NRC:0500Y PAGE7Therelatively highhydrogenproduction rateforthelongrefloodperiodallowssufficient concentration tobuildupinthisregiontoreachtheignitionpoint.Thehydrogenladenairisdrawnfromtheuppercontainment totheannulus,whichisaregionoflowercontainment.

Withthehydrogenburningintheadjacentlowercompartment region,theignitioncriterion hasbeenresettothelowerflammability limit.ForthesmallandlargebreakLOCAcases,theinitialignitioncriterion fortheuppercontainment wasnotmet,butthemixtureexceededtheconcentration ofthelowerflammability limitforalongperiodoftime.Itshouldbenotedthatthelowerflammability limitwasexceededforthesetwocasesonlyduringthenon-mechanistic periodofthehydrogenrelease.Thisleadstosignificant burningintheannulus.InthelossofCCWsequence, theinitialburnintheuppercontainment resetstheignitioncriteriatothelowerflammability limit,shiftingthemajorityoftheburningfromtheannulustotheuppercontainment forthiscase,Iftheuppercontainment initialignitioncriterion hadbeensetclosertothelowerflammability limitinthesmallorlargebreakLOCAcases,asimilarpatternwouldhavebeenseen.Inanyevent,itcanbeconcluded thattheairreturning tothelowercompartment willhavenolargerhydrogenconcentration thanallowedbythelowerflammability limit.Thefollowing tablesummarizes theamountofhydrogenburnedineachregionforthe'basesequences.

HydrogenBurntbyRegion(lbs)LargeLOCASmallLOCACCWLowerContainment UpperPlenumUpperContainment Annulus160009003400060523119858346 ATTACHMENT TOAEP:NRC'0500Y

3.0 CONTAINMENT

STRUCTURAL ADEQUACYPAGE8Thecontainment compartment pressureandtemperature resultsofthesequenceanalyseswereusedtodetermine iftheacceptance criteriaweremet.Themaximumpressurepeakisusedtodetermine ifthecontainment maintains structural integrity.

Theacceptance criteriaof36psigwasusedfortheultimatecontainment structural

capacity, asapprovedinaSafetyEvaluation fromtheNRCdatedFebruary21,1985[11].Onlyrelatively lowpressurepulsesareshowninthesequenceanalyseswhichweresummarized inSection2andtheAppendix.

Themaximumpressurepulseof28psia,or13.3psig,wasseeninthelossofCCWsequence.

Thispressurepulsewascausedbytheinitialburnintheuppercontainment.

Thispressureiswellbelowtheacceptance criteriaof36psig.Inaddition, theconclusion oftheseriesofexperiments endingintheNTSexperiments

[7]wasthatlargedeflagrations arenotexpectedinwell.mixedcontainment atmospheres withcontinuous hydrogeninjection inthepresenceofactiveigniters.

Thissupportstheconclusion ofthesequenceanalyses.

ATTACHMENT TOAEP:NRC:0500Y

4.0 EQUIPMENT

SURVIVABILITY PAGE9Theequipment neededtoachieveandmaintainshutdownconditions foradegradedcoreaccidentwereprovidedintheSafetyEvaluation ReportfortheDIS[1]andarereproduced below.Theoriginalanalysisofthesurvivability ofinstrumentation andequipment utilizedheattransfercalculations ofthecriticalequipment supplemented byevaluations ofequipment subjecttohydrogenburnenvironment

[12].Thismethodology tookcreditforthesubmergence ofequipment whenpossible.

Subsequent tothatdate,moreextensive experiments havebeenperformed attheNevadaTestSitefacility, whichsupportboththemethodology andconclusions oftheearlieranalysis[13].Forthisstudy,survivalofthecriticalequipment hasbeenverifiedfortheconditions calculated intheMAAPanalyses.

Essential Equipment a)Narrow-range steamgenerator levelmonitorsb)Pressurizer levelmonitorsc)Pressurizer pressuremonitorsd)RCSwiderangepressuremonitorse)Coreexitthermocouples f)RCSloopsRTDsg)Airrecirculation/

hydrogenskimmerfansh)Distributed ignitionsystemcomponents i)Containment waterlevelmonitoring systemalsotobeconsidered a)Containment isolation valvesb)Gasketsandsealsforflanges,electrical boxes,airlocks,andtheequipment hatch~c)Electrical penetrations Consistent withtheSafetyEvaluation

[1],thepressuretransmitters locatedinthelowercontainment aretakenasrepresentative ofthecriticalequipment, andspecifically analyzedforthermalresponse.

Theadequacyofthisapproachissupported bytheextensive NTSequipment experiments.

Intheseexperiments, abroadrangeofequipment wasexposedtohydrogenburnconditions, including cables,pressuretransmitters, solenoidvalves,amotoroperatedvalve,limitswitches, afanmotor,resistance temperature detectors, hydrogenigniters, andcontainment penetrations.

Allbutafewequipment specimens operatednormallyduringandafteralltests;andallcablespassedpose-test electrical checks.

ATTACHMENT TOAEP'NRC:0500Y PAGE10HydrogenBurnThermalEffectonEquipment Inthesequenceanalyses, thehighinitialignitioncriteriainthevariousregionsallowsthemaximumamountofhydrogentoreturntothelowercontainment volumes.Thiswillmaximizethehydrogenburninginthelowervolumes,whichwillmaximizethethermalloadonequipment inthosevolumes.Itwasshownabovethatthehydrogentobereturnedtothelowercompartment islimitedtothelowerflammability limitintheuppercontainment.

However,inallbutthelossofCCWcase,thehighuppercontainment ignitioncriterion forcestheburningtobeintheannularregionsurrounding thelowercompartment, whichmaximizes theheatflowintothelowercompartment.

InthelossofCCWcase,thebulkofthisburningoccursintheuppercontainment.

Asimple,thinsteel(1/4")heatstructure wasaddedtotheMAAPmodeltorepresent apieceofequipment.

Thepeaktemperature ofthisheatstructure wasusedasanindicator ofthemostsevereconditions inthelowercompartment forfurtheranalysis.

ThelargebreakLOCAbasecasewasfoundtobelimitingforthermalresponse, sincethehydrogenburnsinthatregionoccurredshortlyafterblowdownwhentheequipment isstillquitehot.ThisistrueeventhoughthesmallbreakLOCAcasepredicted overtwicetheamountofhydrogentoburninthelowercompartment.

Toensurethelimitingloadsontheequipment wereobtained, twovariations ofthelargebreakLOCAcasewereanalyzed.

First,twoinsteadofonecontainment airrecirculation fanswereassumedtobeoperating.

Thisisshowntonotsignificantly affectthehydrogenburncharacteristics andlocations; thebasecaselargeLOCAwasfoundtoremainlimiting.

Thesecondvariation ofthelargebreakLOCAcasewastousecoreparameters representative ofUnit2insteadofUnit1.Unit1wasoriginally chosensinceitcontainsmorezirconium thanUnit2.Unit2,however,.

operatesata5Xhigherpower.Inaddition, thefuelrodarrayinUnit,2is17x17insteadof15xl5,withagreatersurfaceareaforzirconium oxidation.

TheUnit2sensitivity caseresultsinaslightlygreaterpeakhydrogengeneration rateatreflood,andaslightlygreaterpeakequipment temperature inthelowercompartment.

Athirdsensitivity withapotential interesttoequipment thermalresponseistheCEQfanfailurecase.Althoughfanfailureisnotexpectedasdiscussed below,itwastheintentofthissensitivity todetermine whethersurvivalofthecontainment airrecirculation (CEQ)fanwasnecessary toobtain,acceptable equipment ATTACHMENT TOAEP:NRC:0500Y PAGE11survivability results.ThelossofCCWsequenceprovidesthegreatestchallenge tothefans,sothatbasecasewasmodifiedtoassumeCEQfanfailureatthetimeofthefirstburnintheuppercontainment.

Thelowercirculation flowhastheeffectofincreasing thehydrogenconcentration exitingtheicecondenser, wheremostofthehydrogenburningnowoccurs.TheimpactoftheCEQfanfailurewasfoundtohavenoeffectofthepeakequipment temperature inthelowercompartment.

AthermalmodelofaFoxboropressuretransmitter wasdeveloped toobtainthetemperature responseofthetransmitter internals.

Theexternalconditions forthisheattransfercalculation werecalculated bytheMAAPcodeforthelimitingsequenceforthermalresponse, theUnit2largebreakLOCA.Theanalysisdetermined thetemperature ofthepressuretransmitter cover,theairinsidethecover,andthesurfaceoftheelectronics insidethecover.Theresultsindicatethattheelectronics temperature isnotexpectedtoexceed200'F.TheNTSexperimental measurements oftheelectronics ofaFoxboropressuretransmitter reached246'F,andcontinued tofunction.

Therefore, essential equipment isconcluded tosurvivethethermalenvironment causedbyhydrogenburningundertherulesof10CFR50.44(c)(3)(iv)(A).

Containment AirRecirculation FanTheassumption ofthehighignitioncriterion of8Xhydrogenconcentration attheicecondenser outletduetofog'ginghasasignificant impactontheevaluation ofthesurvivability ofContainment AirRecirculation fans.Givenamoremoderatefoggingignitionpenaltyattheicecondenser outlet,.significant burningwouldbeexpectedthere.Asdescribed above,theignitioncriterion of8Xincludessignificant conservatism intheestimation ofthefogconcentrations attheicecondenser outlet.Asaresultofhydrogenburningintheupperplenum,insufficient hydrogenwouldbeexpectedtobuildupintheuppercontainment tosupportaglobalburnonabestestimatebasis.Aglobalburnisaburnthatpropagates throughalargefractionofavolume,consuming asignificant fractionofthehydrogen.

Aglobalburninitiated atarelatively highhydrogenconcentration inthisregionhasbeenshownbeforetocausethecollapseoftheContainment AirRecirculation fanhousing[14].However,basedontheevaluation ofcontinuous injection experiments providedbelow,ahydrogenburninducedpressureexcursion sufficient todestroythefansisnotexpected.

IntheMAAPanalysespresented intheAppendix, theinitialpressureriseof10psidwhichaccompanied hydrogenburningintheuppercompartment isduetotheconservatism employedinthe ATTACHMENT TOAEP'NRC:0500Y PAGE12analysis, i.e.,ignitioncriterion of6vol.XHzandtheuseoftheHECTRcodeburncompleteness correlation.

TheHECTRcodeburncompleteness correlation represents anupperboundofscattered burncompleteness testdataofpremixedcombustion inaclosedchamberwithoutcontinuous injection.

IntheNTStestswithcontinuous injection, theobservedpressurerisewasmodestcomparedtothatwithoutinjection.

Theuppercompartment isanopenthrough-flow volumewithcontinuous injection ofhydrogenfromtheupperplenum.Thepressureriseassociated withburningisexpectedtobesmall.Therefore, thehydrogenmodelling combination isoverlyconservative intheprediction ofpressurepulsesfortheCookNuclearPlantuppercontainment region.InsightsgatheredfromtheNTStestssupportthisobservation

[7,15].Althoughpressurepulsesduetohydrogenburningofupto6psidwereobservedinNTScontinuous injection testsatthetimeoffirstignition, thesepressurepulseswereonlyseenforspecialconditions.

Incaseswhereasignificant pressurepulsewasobserved, awideboundarylayerofacombustible mixtureofhydrogengrewuntilitcameincontactwithanigniter.Thepressurepulsewasduetotherapidpropagation ofthehydrogenburnthroughthisboundarylayer.Theboundarylayerwasfedbytheinjection sourceofhydrogenandsteam.Theconfiguration andhydrogeninjection sourceintheCookNuclearPlantuppercontainment differsfromthisscenario.

Thehydrogeninjection sourceintheuppercontainment isdiffusewithamaximumhydrogenconcentration of8X,inertedbyfog.Therateofincreaseinhydrogenconcentration intheuppercompartment isveryslow(40,000cfmfanflowatamaximum8Xconcentration intothe746,000cu.ft.volumeuppercontainment).

Containment sprayinduceduppercompartment flowsareexpectedtobehigh(intherangeofseveralmeters/second

[16]),promoting goodmixing.Noboundarylayerbetweenignitable andnon-ignitable regionsshouldexist,andcombustion shouldinitiateatthelowerflammability limit.Therefore, asignificant pressureproducing deflagration isnotexpectedintheCookNuclearPlantuppercontainment.

Forthisregion,therateofhydrogenburningwillrisetoequalthehydrogenflowrateintouppercontainment.

Therefore, theCEQfansareconcluded tosurvivetheconditions causedbyhydrogenburningundertherulesof10CFR50.44(c)(3)(iv)(A).

Eventhoughthefansarenotexpectedtofailduetoaburnintheuppercontainment, asasensitivity analysisthese'ans wereassumedtofailatthefirstburninuppercontainment.

Sincethissensitivity analysisdoesnotproducemoresevereresultsthanthebasecaseanalyses, itcanbeconcluded thatthedesignfunctionoftheCEQfanswouldhavebeenmet,andthatfailureoftheCEQfanswouldhavebeenacceptable.

ATTACHMENT TOAEP:NRC'0500Y PAGE13Therearetwodesignobjectives forthesefans.First,thefansareintendedtoprovidegoodcirculation ofthesteamreleasedinthelowercontainment throughtheicecondenser toreachuppercontainment.

Thisensuresthattheicecondenser anduppercontainment spraysremovesteameffectively, keepingthecontainment pressuretowithinitsdesignbasisvalueof12psig.However,duetothefactthatthesubjectdegradedcoreaccidentconditions arewellbeyondthedesignbasis,theacceptance criterion forcontainment pressureforthisanalysisisthecontainment ultimatestrengthof36psig.Thesequenceanalyzedshowsthat,evenwithapostulated fanfailure,thepeakcontainment pressureis13.3psig,(28psia)whichiswellbelowthecontainment ultimatestrengthof36psig.TheseconddesignbasisfortheContainment AirRecirculation systemissupportfortheHydrogenSkimmerSystem(HYS)flows.TheHYSdrawsgasesfromthesteamgenerator andpressurizer doghouses andthecontainment domeregiontopreventcombustible concentrations ofhydrogenfromaccumulating inadesignbasisaccident, inwhichasmallpercentage ofthecladdingisassumedtoreactwithsteam.Forthedegradedcoreaccidentsequences, theHYSwouldbegreatlyoverloaded andthiscriteriacannotbemet.Fordegradedcoreaccidents, theDIStakesover,eliminating theneedforHYSoperation.

ATTACHMENT TOAEP:NRC:0500Y 5.0REACTORHEADVENTSPAGE14Thereactorheadventswereinstalled intheCookNuclearPlantinresponseto10CFR50.44 (c)(3)(iii) toventahydrogenbubbleinthereactorheadintheeventofadegradedcoreaccidentwithsignificant hydrogengeneration.

ThisheadventisalsousedintheEmergency Operating Procedures toaidinvesseldepressurization afterallothermechanisms havefailed,including boththeprimaryandsecondary poweroperatedreliefvalves.Thereactorheadventventstothelowerlevelofuppercontainment, andassuchisapotential hydrogensourcethatcanbypasstheignitersinthelowercontainment andicecondenser upperplenum.Theprimarypurposefortheheadventistorelievea"hardbubble"afterhydrogengeneration hasoccurred.

Atthistime,itisassumedthatthecoreiscovered,andthathydrogenhasaccumulated inthereactorhead.Sincethecoreiscovered,notimecriteriaexistsforthespeedofventingthisbubble.TheEmergency Operation Procedures directtheoperatortoreadthehydrogenconcentration intheuppercontainment beforeventingthehydrogen, andlimitthetimeofventingsothatacombustible mixtureofhydrogencouldnotaccumulate intheuppercontainment.

Thehydrogencouldthenberemovedbythehydrogenrecombiners.

Sincetheventingprocedure explicitly preventsacombustible mixturefromaccumulating, thisuseofthereactorheadventissupported.

Theseconduseoftheheadventistorelieveprimarysystempressurewhenallotherdepressurization systemfail.Giventhenumberofsystemfailuresneededtoreachthispoint,thisuseisconsidered extremely unlikely.

Theheadventgeometryandflowcharacteristics areverysimilartothecontinuous injection experiments performed atNTS[7,15).Iftheheadventisusedtoaidindepressurizing thecore,amixtureofsteamandhydrogenwillbereleasedatahighflowrateandmomentumtotheuppercontainment.

Forthisconfiguration intheNTSexperiments, aslowapproachtoignitionwasfound,withnosignificant pressurepulsewhenignitionoccurred.

Infact,theonlycaseswheresignificant pressurepulseswereseenintheNTScontinuous injection experiments werethosecaseswithonlybottomigniters.

TheCookNuclearPlantuppercontainment hasignitersbothintheupperdomeoftheuppercontainment andonthesteamgenerator andpressurizer doghousewalls.AsseenintheNTStestswithcontinuous injection ofajetofhydrogenandsteam,ignitionwouldeitherbeatapointwherethejetpassedarelatively lowigniter,orasthehydrogenreachedthetopofthecontainment.

Ineitherevent,ignitionwouldoccurwhilethehydrogenoccupiesarelatively smallportionofthecontainment volume,andapressurepulsesufficient to ATTACHMENT TOAEP:NRC'0500Y PAGE15damageordestroytheCEQfanswouldnotoccur.Therefore, theuseofheadventstodepressurize theprimarysystemintheeventofadegradedcoreaccidentisacceptable.

ATTACHMENT TOAEP'NRC:0500Y

6.0 SUMMARYANDCONCLUSIONS

PAGE16Tomeetthehydrogencontrolrequirements of10CFR50.44,theDistributed IgnitionSyst:emwasinstalled attheCookNuclearPlant.AsrequiredbySection(c)(3)(vi) ofthatregulation, analyseshavebeencompleted tosupportthedesignofthehydrogencontrolsystem.Theanalyseswerebasedontheaccidentsequences identified intheCookNuclearPlantIndividual PlantExamination.

Theseanalysesassumedthatthecorewasrecovered beforethecorebecameseverelydegraded, andthat75Xofthezirconium inthecorereactedwithsteamtogeneratehydrogen.

Thecontainment conditions thatresultedfromthishydrogenburninginthepresenceoftheDistributed IgnitionSystemwasthencalculated.

Theregulation requiresthatthecontainment maintains itsstructural integrity, andthattheequipment necessary tomaintainsafeshutdownandcontainment integrity becapableofperforming theirfunctionduringandafterexposuretotheenvironment createdbythehydrogenburning.Theanalysesshowthatthemaximumpressurepredicted forhydrogenburnconditions isfarlessthantheultimatestructural capability.

Inaddition, themaximumtemperature calculated inimportant equipment isshowntobelessthanthetemperature requiredtothreatenthecapability ofthatequipment.

Therefore, theanalysesshowthatthedesignoftheDistributed IgnitionSystemissufficient tocontrolhydrogenundertherequirements of10CFR50.44.

APPENDIXTOATTACHMENT TOAEP:NRC:0500Y HYDROGENCONTROLPROGRAM(10CFR50.44(c))

FORTHEDONALDC.COOKNUCLEARPLANTSUBMITTAL OFANALYSES

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