ML17331A933

Forwards Response to GL 93-04, Rod Control Sys Failure & Withdrawal of Rod Control Cluster Assemblies, Summarizing Evaluations & Compensatory Actions Taken in Response to Salem Rod Control Sys Failure Event

ML17331A933
Person / Time
Site:	Cook
Issue date:	08/05/1993
From:	FITZPATRICK E INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
To:	MURLEY T E NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
AEP:NRC:1190, GL-93-04, GL-93-4, NUDOCS 9308120224
Download: ML17331A933 (16)

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ACCEIERATDOCUMENTDISTRIVTlONSYSTEMREGULATINFORMATIONDISTRIBUTIONSTEM(RIDS)ACCESSIONNBR:9308120224DOC.DATE:93/08/05NOTARIZED:YESDOCKETFACIL:50--315DonaldC.CookNuclearPowerPlant,Unit1,IndianaM0500031550-316DonaldC.CookNuclearPowerPlant,Unit2,IndianaM05000316AUTH.NAMEAUTHORAFFILIATIONFITZPATRICK,E.IndianaMichiganPowerCo.(formerlyindianaaMichiganEleRECIP.NAMERECIPIENTAFFILIATIONMURLEY,T.E.DocumentControlBranch(DocumentControlDesk)I

SUBJECT:

ForwardsresponsetoGL93-04,"RodControlSysFailure&Withdrawal.ofRodControlClusterAssemblies,"summarizingevaluationsacompensatoryactionstakeninresponsetoSalemrodcontrolsysfailureevent.DISTRIBUTIONCODE:A030DCOPIESRECEIVED:LTRENCLSIZE:TITLE:GenericLtr-93-04-RodControlSystemFaiure6WithdrawaloRodContINOTES:RECIPIENTIDCODE/NAMEPD3-1PDINTERNAL:NRR/DRCH/HICB-E~ErB-01EXTERNAL:NRCPDRCOPIESLTTRENCL22111111RECIPIENTIDCODE/NAMENRR/DSSA/SRXBCOPIESLTTRENCL11NOTETOALL"RIDS"RECIPIENTS:PLEASEHELPUSTOREDUCEWASTE!CONTACTTHEDOCUMENTCONTROLDESK,ROOMPl-37(EXT.504-2065)TOELIMINATEYOURNAMEFROMDISTRIBUTIONLISTSFORDOCUMENTSYOUDON'TNEED!DTOTALNUMBEROFCOPIESREQUIRED:LTTR6ENCL6 indianaMichigan~PowerCompanyCookNuclearPlantOneCookPlaceBridgrnan,Ml491066164655901DonaldC.CookNuclearPlantUnits1and2DocketNos.50-315and50-316LicenseNos.DPR-58andDPR-74RESPONSETOGENERICLETTER93-04AEP:NRC:1190GL93-04U.S.NuclearRegulatoryCommissionDocumentControlDeskWashington,D.C.20555Attn:T.E.MurleyAugust5,1993

DearDr.Murley:

Pursuanttotherequirementsof10CFR50.54(f),theNRCissuedGenericLetter93-04,"RodControlSystemFailureandWithdrawalofRodControlClusterAssemblies,"onMonday,June21,1993.GenericLetter93-04wasaddressedtoalllicenseeswiththeWestinghouseRodControlSystem(exceptHaddamNeck)foraction,andtoallotherlicenseesforinformation.Thegenericletterrequiresthatwithin45daysfromthedateofthegenericlettereachaddresseeprovideanassessmentofwhetherornotthelicensingbasisforeachfacilityisstillsatisfiedwithregardtotherequirementsforsystemresponsetoasinglefailureintheRodControlSystem(GDC25).Iftheassessment(RequiredResponse1.(a))indicatesthatthelicensingbasisisnotsatisfied,thenthelicenseemustdescribecompensatoryshort-termactionsconsistentwiththeguidelinescontainedinthegenericletter(RequiredResponse1.(b)),andwithin90days/provideaplanandscheduleforlong-termresolution(RequiredResponse2).SubsequentcorrespondencebetweentheWestinghouseOwnersGroupandtheNRCresultedinschedularreliefforRequiredResponse1.(a)(NRCLettertoMr.RogerNewtondatedJuly26,1993).Thisportionoftherequiredactionswillnowbeincludedwiththe90-daylicenseeresponse.IndianaMichiganPowerCompany(IGM)herebysubmitsitsresponsetotheGenericLetterasitappliestoDonaldC.CookNuclearPlantUnits1and2.ThisresponsesummarizestheevaluationsandthecompensatoryactionstakenbyIGMinresponsetotheSalemrodcontrolsystemfailureevent.ItalsoprovidesasummaryofthegenericsafetyanalysisprogramconductedbytheWestinghouseOwnersGroupanditsapplicabilitytoCookNuclearPlant.TheresultsoftheanalysisindicatedthatforCookNuclearPlantUnits1and2,departurefromnucleateboiling(DNB)doesnot9308i20224930805LPDRADOCK050003158PDR3c~/(gS Dr.T.E.MurleyAEP:NRC:1190GL93-04occurfortheirworst-caseasymmetricrodwithdrawal.IBMconsidersthisactiontobecompletewithrespecttothe45-dayrequiredresponsetoGL93-04(asamendedbyJuly26NRClettertoMr.RogerNewton).Thisletterissubmittedpursuantto10CFR50.54(f)and,assuch,anoathstatementisattached.Sincerely,VicePresidentdrAttachmentcc:A.A.Blind-BridgmanJ.R.PadgettG.CharnoffNFEMSectionChiefJ.B.Martin-RegionIIINRCResidentInspector-Bridgman STATEOFMICHIGAN)COUNTYOFBERRIEN)E.E.Fitzpatrick,beingdulysworn,deposesandsaysthatheistheVicePresidentoflicenseeIndianaMichiganPowerCompany,thathehasreadtheforgoingResponsetoGENERICLETTER93-04andknowsthecontentsthereof;andthatsaidcontentsaretruetothebestofhisknowledgeandbelief.Subscribedandsworntobeforemethisdayof19~.NOTARYPUBLICUNDAL80ELCKENofar)rPublic,8errlenCounty,MlN)rCommlsslonExpiresApril1,1996 3g>J308JACNU'lM,gnuo3noisio8,oiMtR~ORbWf,lli~qAcosiqx3no)cd'~pi%

ATTACHMENTTOAEP:NRC:1190RESPONSETONRCGL93-04 AttachmenttoAEP:NRC:1190Page1fComensatorActionsThepurposeofthisdiscussionistoprovidearesponsetothethreeareasofcompensatoryshort-termactionsidentifiedbytheNRC(RequiredResponse1.(b))andanyadditionalcompensatoryactions)udgedtobeappropriate."additionalcautionsormodificationstosurveillanceandpreventivemaintenanceprocedures"Westinghousedidnotmakeanyinitialrecommendationsregardingsurveillanceorpreventivemaintenanceprocedures.BasedontheresponseprovidedinWestinghouseOwnersGroup(WOG)letterOG-93-42,therewasnoperceivedneedtoincreasethefrequencyoftestingonapermanentorgenericbasis.ItisunderstoodthatPSEQGhadcommittedtoatemporaryincreaseintesting,butonlyuntilitwasdemonstratedthattherodcontrolsystemwasoperatingproperlyandwithconfidence.Arecommendationwasmadeforutilitiestoensurethattheirsurveillancetestingwilldemonstraterodcontrolsystemoperabilityandaddressmaintenancetrouble-shooting.Increasedsurveillancetestingiscontrarytothegeneraltrendandphilosophyofsurveillancetestingrelaxationinthatincreasedtestingcan,inandofitself,resultinhigherratesofsystemandcomponentfailures.Therefore,theWOGandWestinghousehaveconcludedthatincreasedfrequenciesinsurveillancetestingisnotrequiredinresponsetotheSalemrodcontrolsystemfailureevent.IAtCookNuclearPlant,duringeachrefuelingoutage,therodcontrolsystemcabinetsarecleanedandinspected.Thecardsarecheckedand,ifnecessary,replaced.Therehavebeennoidentifiedfailureswiththecardsassociatedwiththepreventivemaintenanceactivities.Also,inreviewoftherodcontrolsystemfailurehistoryasrequestedbytheWOG,nologiccabinetcardfailureswerefoundthatcouldhaveledtoaneventlikeSalem's.Thus,itisnotdeemednecessarytomodifyourmethodsofpreventivemaintenanceontherodcontrolsystem.TheprocedureusedatCookNuclearPlanttoperformthe31dayTechnicalSpecificationSurveillancerequiresthereactoroperatortomonitortherodpositionindicators(RPIs)duringthetest.IfarodcontrolsystemfailureeventsuchasSalem'sweretooccur,thereactoroperatorwouldbealertedbytheRPIsincorrecttrackingandwouldimmediatelyhaltrodmovement.Also,thereisconsiderableconfidenceintherodcontrolsystem;thusitisnotconsiderednecessarytoincreaseoursurveillancefrequencyormodifytheprocedure.

AttachmenttoAEP:NRC:1190.Page220"additionaladministrativecontrolsforplantstartupandpoweroperation"AsstatedinGenericLetter93-04,theSalemunitscommittedtostartupbydilution.NeitherWestinghousenortheWOGhasendorsedthisrequirement.Inactualoperation,theoperatorswouldbeawareofabnormalrodmovementandterminateroddemandpriortoeverreachingcriticality.Theoperatorwouldbemanuallycontrollingtherodwithdrawalsuchthatthedetectionofrodmis-steppinginunderoneminutewouldbereasonable.Znfact,asdemonstratedduringtheR.E.Ginnaevent(July1993),abnormalrodmotionwasterminatedafteronlyonestepbothinautomaticandmanualrodcontrol.Thus,theWoGandWestinghousehaveconcludedthatstartupbydilutionisnotrequiredinresponsetotheSalemrodcontrolsystemfailureevent.AtCookNuclearPlant,dilutiontocriticalisusedfortheinitialstartupofanewcycle.Zntheeventofamid-cycleshutdown,thereactorisreturnedtocriticalusingcontrolrods.TheproceduresusedatCookNuclearPlanttoreturnaunittocriticalproviderequirementswhichwouldalertthereactoroperatorofarodcontrolsystemfailureeventsuchasSalem's.Duringshutdownbankwithdrawal,rodmovementisstoppedatleastevery100stepstocollectdataforaninversecountrateratio(ZCRRor1/m)plot.Forwithdrawalofthecontrolbanks,rodmovementisstoppedatleastevery50stepsforthe1/mplotdatacollection.Theentirerodwithdrawalevolutionisperformedwithrodcontrolinmanual,andareactoroperatorverifyingproperrodmovementbymonitoringtheRPZsanddemandcounter.Alsoduringtheevolution,areactoroperatoriscontinuouslymonitoringthesourcerangemonitorsealer/timer.Thisinstrumentwouldhaveasignificantcountrateincreaseifarodcontrolsystemfailureweretooccurthatcouldcausethereactortoreachcriticalconditionsunexpectedly.ThereactoroperatorsatCookNuclearPlantarerigorouslytrainedtoexpectcriticalityatanytimeandhowtorespondifsuchaneventweretooccur.Thus,weareconfidentthatifarodcontrolsystemfailureweretooccur,whichcouldcauseunexpectedcriticality,thereactoroperatorswouldquicklyrecognizeandrespondtotheeventsuchthatexceedinganyfueldesignlimitishighlyunlikely.Anytimethereactoroperatorisrequiredtomoverods,theRPZsanddemandcounteraremonitoredtoverifypropermovement.ZfarodcontrolsystemfailuresuchasSalem'sweretooccur,thereactoroperatorwouldquicklynoticesuchanevent.Also,whenthereactorisaboveapproximately30%power,theroddeviationmonitorisoperableandisausefultooltoalertthereactoroperator

AttachmenttoAEP:NRCx1190Page3ofabnormalrodmovement.Ifarod'sRPIsignalweretodeviatebymorethan112stepsfromitsdemandedposition,anannunciatorwouldalertthereactoroperator.Theroddeviationmonitorispartofourplantprocesscomputer(PPC)softwarewhichhasproventobehighlyreliable.However,ifthePPCorroddeviationmonitoriseverdeclaredinoperable,itsoperabilityisre-establishedbytheComputerScienceDepartment.Furthermore,thePPCcontinuouslymonitorsalloftheinputstotheprogramforvaliditytoensurethatitisoperable.Thus,duringpowermaneuversorsteadystateoperation,thereactoroperatorwillbealertedtoarodcontrolsystemfailurepriortoexceedinganyfueldesignlimit.3~"additionalinstructionsandtrainingtoheighten'operatorawarenessofpotentialrodcontrolsystemfailuresandtoguideoperatorresponseintheeventofarodcontrolsystemmalfunction"-Atvarioustimes,bothWestinghouseandWOGhaverecommendedthatlicenseesprovideadditionaldiscussion,training,standingorders,etc.'oensurethattheiroperatorsareawareofwhattranspiredatSalem.TherecommendationsoftheWestinghouseNSAL,whichwassubsequentlyendorsedbytheWOGviaLetterOG-93-42,recognizethebenefitsofensuringthatplantoperatorsareknowledgeableoftheSalemrodcontrolsystemfailureevent.UponissuanceofNSAL93-007,theCookNuclearPlantSafetyandAssessmentDepartmentreviewedthedocumentandsubsequentlyrecommendedthattheoperatorsreviewit.Shortlyfollowingtherecommendation,thelicensedoperatorswererequiredtoreviewtherodcontrolsystemfailureeventatSalemthroughNSAL93-007.NotethattheseactionsoccurredpriortoreceiptofGenericLetter93-04.Also,theCookNuclearPlantTrainingDepartmentisscheduledtoincludeaniteminthenextOperationalReviewpackage,whichisbasedontheeventsthatoccurredatSalem.TheOperationalReviewpackagematerialistobecoveredduringOperationsRequalificationTrainingPeriod6,whichisscheduledtobeginSeptember20,1993.Furthermore,theSalemrodcontrolsystemfailureisscheduledtobecoveredwithInstrumentationandControlpersonnelaspartoftheircontinuingtrainingprogram.Thus,theCookNuclearPlanthasproactivelyandaggressivelyaddressedtheSalemeventwithitspersonnel.

AttachmenttoAEP:NRC:1190Page4SummaoftheGenericSafetAnalsisProramIntroductionAspartoftheWestinghouseOwnersGroupinitiative,theWOGAnalysissubcommitteeisworkingonagenericapproachtodemonstratethatforallWestinghouseplantsthereisnosafetysignificanceforanasymmetricRCCAwithdrawal.ThepurposeoftheprogramistoanalyzeaseriesofasymmetricrodwithdrawalcasesfrombothsubcriticalandpowerconditionstodemonstratethatDNBdoesnotoccur.ThecurrentWestinghouseanalysismethodologyforthebankwithdrawalatpowerandfromsubcriticalusespoint-kineticsandonedimensionalkineticstransientmodels,respectively;Thesemodelsuseconservativeconstantreactivityfeedbackassumptionswhichresultinanoverlyconservativepredictionofthecoreresponsefortheseevents.Athree-dimensionalspatialkinetics/systemstransientcode(LOFT5/SPNOVA)isbeingusedtoshowthatthelocalizedpowerpeakingisnotassevereascurrentcodespredict.The3-Dtransientanalysisapproachusesarepresentativestandard4-LoopWestinghouseplantwithconservativereactivityassumptions.Limitingasymmetricrodwithdrawalstatepoints(i.e.,conditionsassociatedwiththelimitingtimeinthetransient)areestablishedforthereferenceplantwhichcanbeappliedtoallWestinghouseplants.Differencesinplantdesignsareaddressedbyusingconservativeadjustmentfactorstomakeaplant-specificDNBassessment.DescriptionofAsymmetricRodWithdrawalTheaccidentalwithdrawalofoneormoreRCCAsfromthecoreisassumedtooccurwhichresultsinanincreaseinthecorepowerlevelandthereactorcoolanttemperatureandpressure.Ifthereactivityworthofthewithdrawnrodsissufficient,thereactorpowerand/ortemperaturemayincreasetothepointthatthetransientisautomaticallyterminatedbyareactortriponaHighNeutronFluxorOver-TemperatureDelta-T(OTDT)protectionsignal.Ifthereactivityincreaseissmall,thereactorpowerwillreachapeakvalueandthendecreaseduetothenegativefeedbackeffectcausedbythemoderatortemperaturerise.TheaccidentalwithdrawalofabankorbanksofRCCAsinthenormaloverlapmodeisatransientwhichisspecificallyconsideredinplantsafetyanalysisreports.TheconsequencesofabankwithdrawalaccidentmeetConditionIIcriteria(noDNB).If,however,itisassumedthatlessthanafullgrouporbankofcontrolrodsiswithdrawn,andtheserodsarenotsymmetricallylocatedaroundthecore,thiscancausea"tilt"inthecoreradialpowerdistribution.The"tilt"couldresultinaradialpowerdistributionpeakingfactorwhichismoreseverethanisnormallyconsideredintheplant AttachmenttoAEP:NRC:1190Page5safetyanalysisreport,andthereforecausealossofDNBmargin.Duetotheimperfectmixingofthefluidexitingthecorebeforeitentersthehotlegsofthereactorcoolantloops,therecanbeanimbalanceinthelooptemperatures,andthereforeinthemeasuredvaluesofT-avganddelta-T,whichareusedintheOTDTprotectionsystemforthecore.Theradialpower"tilt"mayalsoaffecttheexcoredetectorsignalsusedfortheHighNeutronFluxtrip.Theaxialoffset(AO)intheregionofthecorewheretherodsarewithdrawnmaybecomemorepositivethantheremainderofthecore,whichcanresultinanadditionalDNBpenalty.MethodsTheLOFT5computercodeisusedtocalculatetheplanttransientresponsetoanasymmetricrodwithdrawal.TheLOFT5codeisacombinationofanadvancedversionoftheLOFT4code(Reference1),whichhasbeenusedformanyyearsbyWestinghouseintheanalysisoftheRCSbehaviortoplanttransientsandaccidents,andtheadvancednodalcodeSPNOVA(Reference2).LOFT5usesafull-coremodel,consistingof193fuelassemblieswithonenodeperassemblyradiallyand20axialnodes.Several"hot"rodsarespecifiedwithdifferentinputmultipliersonthehotrodpowerstosimulatetheeffectofplantswithdifferent:initialFaHvalues.A"hot"rodrepresentsthefuelrodwiththehighestFaHintheassembly,andiscalculatedbySPNOVAwithinLOFT5.DNBRsarecalculatedforeachhotrodwithinLOFT5withasimplifiedDNB-evaluationmodelusingtheWRB-1correlation.TheDNBRsresultingfromtheLOFT5calculationsareusedforcomparisonpurposes.AmoredetailedDNBRanalysisisdoneatthelimitingtransientstatepointsfromLOFTSusingTHZNC-ZV(Reference3)andtheRevisedThermalDesignProcedure(RTDP).RTDPappliestoallWestinghouseplants,maximizesDNBRmargins,isapprovedbytheNRC,andislicensedforanumberofWestinghouseplants.TheLOFT5-calculatedDNBRsareconservativelylowwhencomparedtotheTHING-IVresults.AssumptionsTheinitialpowerlevelschosenfortheperformanceofbankandmultipleRCCAwithdrawalcasesare100%,60%,10%andhotzeropower(HZP).ThesepowerlevelsarethesamepowersconsideredintheRCCABankWithdrawalatPowerandBankWithdrawalfromSubcriticaleventspresentedintheplantSafetyAnalysisReports.Theplant,inaccordancewithRTDP,isassumedtobeoperatingatnominalconditionsforeachpowerlevelexamined.Therefore,uncertaintieswillnotaffecttheresultsoftheLOFTStransientanalyses.Fortheat-powercases,allreactorcoolantpumpsareassumedtobeinoperation.Forthehotzeropowercase AttachmenttoAEP:NRC:1190Page6(subcriticalevent),only2/4reactorcoolantpumpsareassumedtobeinoperation.A"poormixing"assumptionisusedforthereactorvesselinletandoutletmixingmodel.ResultsAreviewoftheresultspresentedinWCAP-13803(Reference4)indicatesthatfortheasymmetricrodwithdrawalcasesanalyzedwiththeLOFTScode,theDNBdesignbasisismet.AsdemonstratedbytheA-Factorapproach(describedbelow)foraddressingvariouscombinationsofasymmetricrodwithdrawals,thesinglemost-limitingcaseisplant-specificandisafunctionofrodinsertionlimits,rodcontrolpattern,andcoredesign.TheresultsoftheA-FactorapproachalsodemonstratesthatthecasesanalyzedwiththeLOFTScomputercodearesufficientlyconservativeforawiderangeofplantconfigurationsforvariousasymmetricrodwithdrawals.Inaddition,whenthedesignFuHistakenintoaccountontherepresentativeplant,theDNBRcriterionismetfortheat-powercases.AtHZP,aworst-casescenario(3-rodswithdrawnfromthreedifferentbankswhichisnotpossible)showsanon-limitingDNBR.ThisresultisapplicabletoallotherWestinghouseplants.PlantApplicabilityThe3-Dtransientanalysisapproachusesarepresentativestandard4-LoopWestinghouseplantwithboundingreactivityassumptionswithrespecttothecoredesign.Thisresultsinconservativeasymmetricrod(s)withdrawalstatepointsforthevariousasymmetricrodwithdrawalsanalyzed.ThemajorityofthecasesanalyzedeitherdidnotgenerateareactortriporwereterminatedbyaHighNeutronFluxreactortrip.FortheOTDTreactortrip,nocreditisassumedforthef(a,I)penaltyfunction.Thef(~I)penaltyfunctionreducestheOTDTsetpointforhighlyskewedpositiveornegativeaxialpowershapes.Comparedtotheplant-specificOTDTsetpointsincludingcreditforthef(aI)penaltyfunction,thesetpointusedintheLOFTSanalysesisconservative,i.e.,forthosecasesthattrippedonOTDT,aplant-specificOTDTsetpointwiththef(aI)penaltyfunctionwillresultinanearlierreactortripthantheLOFTSsetpoint.ThisensuresthatthestatepointsgeneratedforthosecasesthattriponOTDTareconservativeforallWestinghouseplants.Withrespecttotheneutronicanalyses,anadjustmentfactor("A-Factor")wascalculatedforawiderangeofplanttypesandrodcontrolconfigurations.TheA-factorisdefinedastheratiobetweenthedesignFaHandthechangeinthemaximumtransientFaHfromthesymmetricandasymmetricRCCAwithdrawalcases.Anappropriateandconservativeplant-specificA-FactorwascalculatedandusedtodeterminethecorrespondingDNBRpenaltyorbenefit.Withrespecttothethermal-hydraulicanalyses, AttachmenttoAEPsNRC:1190Page7differencesinplantconditions(includingpowerlevel,RCStemperature,pressure,andflow)areaddressedbysensitivitiesperformedusingTHZNC-IV.ThesesensitivitiesareusedtodetermineadditionalDNBRpenaltiesorbenefits.UncertaintiesintheinitialconditionsareaccountedforintheDNBdesignlimit.Sincethedifferencesinplantdesignsareaccountedforbythead)ustmentapproach,plant-specificDNBRcalculationscanandhavebeengeneratedforallWestinghouseplants.ConclusionUsingthisapproach,thegenericanalysesandtheplant-specificapplicationdemonstratethatforCookNuclearPlantUnits1and2,DNBdoesnotoccurfortheirworst-caseasymmetricrodwithdrawal.

AttachmenttoAEP:NRC:1190Page8ReferencesBurnett,T.W.T.,etal.,"LOFTRANCodeDescription,"WCAP-7907-A,April1984.2~Chao,Y.A.,etal.,"SPNOVA-AMulti-DimensionalStaticandTransientComputerProgramforPWRCoreAnalysis,"WCAP-12394,September1989.3~Friedland,A.J.andS.Ray,"ImprovedTHINCIVModelingforPWRCoreDesign,"WCAP-12330-P,August1989.4~Huegel,D.,etal.,"GenericAssessmentofAsymmetricRodClusterControlAssemblyWithdrawal,"WCAP-13803,August1993.

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