ML17241A404

LER 99-005-00:on 990604,CEA Drop Resulted in Manual Reactor Trip.Caused by Procedural Inadequacies.Procedure Changes Are Planned to Correct Lack of Procedural Guidance for CEA Subgroup Power Switch Replacement.With 990706 Ltr

ML17241A404
Person / Time
Site:	Saint Lucie
Issue date:	07/06/1999
From:	FREHAFER K W, STALL J A FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-99-149, LER-99-005, LER-99-5, NUDOCS 9907120142
Download: ML17241A404 (8)

Text

~CATEGORY10REGULATORYINFORMATIONDISTRIBUTIONSYSTEM(RIDS)ACCESSIONNBR:9907120142DOC.DATE:99/07/06NOTARIZED:NOFACIL:50-389St.LuciePlant,Unit2,FloridaPower&,LightCo.AUTH.NAMEAUTHORAFFILIATIONFREHAFER,K.W.FloridaPower&.LightCo.STALL,J.A.FloridaPower&LightCo.RECIP.NAMERECIPIENTAFFILIATIONDOCKET05000389

SUBJECT:

LER99-005-00:on990604,CEAdropresultedinmanualreactortrip.Causedbyproceduralinadequacies.ProcedurechangesareplannedtocorrectlackofproceduralguidanceforCEAsub-grouppowerswitchreplacement.DISTRIBUTIONCODE:IE22TCOPIESRECEIVED:LTRLENCLISIZE:TITLE:50.73/50.9LicenseeEventReport(LER),IncidentRpt,etc.NOTES:ARECIPIENTIDCODE/NAMELPD2-2PDINTERNAL:ACRSNRR/DZPM/IOLBNRR/DSSA/SPLBRES/DRAA/OERABEXTERNAL:LSTLOBBYWARDNOACPOORE,W.NRCPDRCOPIESLTTRENCL1111111111111111RECIPIENTIDCODE/NAMEGLEAVES,WFILECENTE~RNRR'/DRIP/REXBRES/DET/ERABRGN2PILE01LMZTCOMARSHALLNOACQUEENER,DSNUDOCSFULLTXTCOPIESLTTRENCL11111111111111110DNNOTETOALL"RiDS"RFCIPiEN;S:PLEASEHELPUSTOREDUCEWASTE.TOHAVEYOURNAMEORORGAN:ZATiONREMOVEDFROMDiSTRiBUTiONLISTSORREDUCETHENUMBEROFCOPiESRECE:VE".YOUOFLOURCRGANiZATON,CONTACTTHEDOCUMENTCONTROLDESK(DCD)ONEXTENSION415-2063PULLTEXTCONVERSIONREQUIREDTO.ALNUMBEROFCOPIESREQUIRED:LTTR16ENCL16 FloridaPower&LightCompany,6351S.OceanDrive,JensenBeach,FL34967July6,1999L-99-14910CFR550.73U.S.NuclearRegulatoryCommissionAttn:DocumentControlDeskWashington,D.C.20555Re:St.LucieUnit2DocketNo.50-389ReportableEvent:1999-005-00DateofEvent:June4,1999CEADropsResultinManualReactorTriTheattachedLicenseeEventReport1999-005isbeingsubmittedpursuanttotherequirementsof10CFR$50.73toprovidenotificationofthesubjectevent.Verytrulyyours,J.A.StallVicePresidentSt.LucieNuclearPlantJAS/EJW/KWFAttachmentcc:RegionalAdministrator,USNRC,RegionIISeniorResidentInspector,USNRC,St.LucieNuclearPlant'ir907i20i42990706PDRADOCtr050003898PDRanFPLGroupcompany

,f NRCFORM366(6-1996)LICENSEEEVENTREPORT(LER)(Seereverseforrequirednumberofdigits/charactersforeachblock)Estimatedburdenperresponsetocomplywiththismandatoryhfonnsgoncollectionrequest:50hrs.Reportedlessonslearnedsreincorporatedintolhegcenstngprocessandfedbackloindustry.ForwardcommentsregsngngburdenesbmstelotheRecordsManagementBranch(TWF33),US.RudearReguhtoryCommission,Washington,1)C205554001,andlolhePaperworkRer)octanProject(315041M(,OfficeofManagementsndBudget,Washington,DC20503.IfanInformathncollecgondoesnotdisplayacurrentlyvalidOMBcontrolnumber,theNRCmaynotconductorsponsor,andapersonhrnotrequiredlorespondlo,theInfonnsthncollection.U.S.NUCLEARREGULATORYCOMMISSIONAPPROVEDBYOMBNO.3150.0104EXPIRES06/30/2001FACIUTYNAME(1)St.LucieUnit2DOCKETNUMBER(2)05000389PAGE(3)Page1of4TITLE(4)CEADropsResultinManualReactorTripEVENTDATE(5)DAYYEARLERNUMBER6)REPORTDATE7YEARSEQUENTIALREVISIONMONTHNUMBERNUMBERDAYYEARFACIUTyNAMEOTHERFACILITIESINVOLVED(BIDOCKETNUMBER060419991999-005-000706FACiUTYNAMEDOCKETNUMBEROPERATINGMODE(9)POWERLEVEL(10)04950.73(s)(2)(viii)50.73(e)(2)(x)50.73(a)(2)(i)50.73(e)(2)(ii)50.73(e)(2)(ui)20.2203(e)(2)(v)20.2203(s)(3)(i)20.2203(a)(3)(ii)20.2201(b)20.2203(e)(1)20.2203(e)(2)(i)73.71THISREPORTISSUBMITTEDPURSUANTTOTHEREQUIREMENTSOF10CFR5:(Checkoneormore)(11)20.2203(e)(2)(ii)20.2203(a)(2)(iii)20.2203(s)(2)(iv)20.2203(s)(4)50.36(c)(1)50.36(c)(2)50.73(e)(2)(iv)50.73(s)(2)(v)50.73(e)(2)(vii)OTHERSpecifyinAbstractbeloworlnNACForm366ANAMELICENSEECONTACTFORTHISLER(12)TELEPHONENUMSERtiricrvtroAreeCodatKennethW.Frehafer,LicensingEngineer(561)467-7748COMPLETEONELINEFOREACHCOMPONENTFAILUREDESCRIBEDINTHISREPORT13CAUSESYSTEMCOMPONENTMANUFACTURERAEPOATABLETOEPIXCAUSESYSTEMCOMPONENTMANUFACTURERREPORTABLEToEPIXC490YESDSUPPLEMENTALREPORTEXPECTED(14)YES(Ifyes,completeEXPECTEDSUBMISSIONDATE).XNOEXPECTEDSUBMISSIONDATE(15)MONTHDAYABSTRACT/Limitto1400speces,le.,approximately15single-spacedtypewrittenlines/(16)OnJune4,1999,St.LucieUnit2wasinMode1atapproximately49percentreactorpower.Aneventresponseteamwasintheprocessoftroubleshootingrecentcontrolelementassemblyanomalies.Unit2washeldinreducedpowerpendingtheeventresponseteamtroubleshootingresults.At0313hours,foursubgroup21controlelementassembliesfullyinsertedintothecoreduringreplacementofthesubgroup21powersupply.AUtilitylicensedoperator,thenuclearplantsupervisor,immediatelydirectedamanualreactortrip.TheplantwasstabilizedinMode3forrepairs.Repairswereimplemented,andplantrestartandpowerascensioncommencedonJune11,1999.Thecontrolelementassemblydropeventwascausedbyproceduralinadequaciesthatdidnotrequireverificationoftheproperseatingofapowerswitch.Thisresultedinlossofpowertothecontrolelementassemblieswhentheirsubgroupwastransferredofftheholdbus.Lossofpowertothesubgroup21controlelementassemblieswascorrectedbyreseatingthesubgroup21powerswitch.ProcedurechangesareplannedtocorrectthelackofproceduralguidanceforCEAsubgrouppowerswitchreplacement.Theeventresponseteamconductedothercorrectiveactionsrelatedtotheoriginalcontrolelementassemblyanomalies.NACF0AM366(6-1999)

NRCFORM366A(6-19991LICENSEEEVENTREPORT(LER)TEXTCONTINUATIONU.S.NUCLEARREGULATORYCOMMISSIONFACILITYNAME(1)St.LucieUnit2DOCKETNUMBERI2)05000389LERNUMBERIS)SEQUENTIALREVISIONNUMBERNUMBER1999-005-00PAGE(3)Page2of4TEXT(Ifmorespeceisrequired,useedditionelcopiesofNRCForm366A/(17)DescriptionoftheEventOnJune4,1999,St.LucieUnit2wasinMode1atapproximately49percentreactorpower.Aneventresponseteam(ERT)wasintheprocessofinvestigatingrecentcontrolelementassembly(CEA)[EIIS:AA]events(aCEAdroptwodaysearlierandCEAsspontaneouslytransferringtotheirlowergrippers).Unit2wasbeingheldinreducedpowerpendingtheERTtroubleshootingresults.TheUnit2controlelementdrivemechani.smcontrolsystem(CEDMCS)isdesignedtocontrolthemovementofthe91controlroddrivemechanisms.Eachcontrolrodmechanismhas5coils,whichengagevariousgripperswithintheCEDMmotortocontrolCEAmovement.Undernormalconditions,theuppergrippermaintainstheCEAinitslastposition.Shouldpowerberemovedfromthisgripper,andtheothergrippersnotengagetoprovidemovement,theCEAwilldropintothecore.Powerforthegrippercoilsisprovidedbymotorgenerator(MG)setsthroughthereactortripswitchgear~TheCEDMpowersourceisthreephase240VACandi.sdesi.gnedasafloatingsystemtotoleratesinglegroundconditions.EachCEAsubgrouputilizesapowerswitchthatpxovidesthree-phasepowerforuptofourCEAs.ThepowerswitchiscontrolledbylogictimingboardsandanautomaticCEAtimingmodule(ACTM)whichdecideswhichcoilstofireduringmovementorholdingofeachCEA.TheACTMreceivesinformationastotheenergyprovidedtothecoilthroughaHalleffecttransduceraroundeachcoilpowercable.ShouldtheACTMseethepossibilityofaroddropitwillautomaticallyapplyadditionalpowerortransfertheCEAtothelowergrippertopreventtherodfromdropping.Thisactionisannunciatedinthecontrolroom.Duringtroubleshootingadecisionwasmadetoinstallasparepowerswitch[EIIS:AA:JX]insubgroup21,whichrequiredtheaffectedCEAstobetransferredtothemaintenanceholdbus.Afterthepowerswitchwasreplaced,,thesubgroup21CEAswereremovedfromtheholdbusandtransferredtosubgroup21whilecoiltraceswereobtained.Itwasobservedthatwiththesubgroup21CEAsontheholdbus,thevisicordertracesimprovedandwiththeCEAspoweredbythesubgroupthetraceswerestilldegraded.TheCEAswereplacedbackonthemaintenanceholdbus.Afterfurthertestingandreplacementofalogicboard,subgroup.21wasremovedfromtheholdbusandtransferredtothesubgroup.At0313hours,allfoursubgroup21CEAsfullyinsertedintothecoreupondeenergizationofthemaintenanceholdbus.Thenuclearplantsupervisor(NPS)immediatelydirectedamanualreactortripandentryintoEmergencyOperatingProcedure(EOP)-1,"StandardPostTripActi.ons".AllsafetyfunctionswereverifiedasbeingmaintainedandEOP-2,"ReactorTripRecovery",wasenteredat0323hours.TheplantwasstabilizedinMode3.Thetripwasdeterminedtobeuncomplicatedwiththeexceptionthefollowingissues:DuringtheperformanceofEOP-1,the2Cmainsteamreheater(MSR)temperaturecontrolvalve(TCV)blockvalve[EIIS:SB:V],MV-08-10,wouldnotclose.Inaccordancewithcontingencyactions,theMSRTCVswereclosed.MV-08-10wassubsequentlyde-energizedandmanuallyclosed.~The"A"sidepressurizerheaters[EIIS:AB:PZR1EHTR]werede-energizedduetoalo-lolevelsignalfromthepressurizerlevel"X"channel.However,thesignalwasnotresetwhenpressurizerlevelwasraisedabovethesetpoint.A72-houractionNRCFOIIMSBBA(9-1999)

NRCFORM366A(6.1998)LICENSEEEVENTREPORT(LER)TEXTCONTINUATIONU.S.NUCLEARREGUIATORYCOMMISSIONFACILITYNAME(1)St.LucieUnit2DOCKETNUMBER(2)05000389LERNUMBER(6)SEQUENTIALREVISIONNUMBERNUMBER1999-005-00PAGE(3)Page3of4TEXTIifmorespacoisrequired,useaddidonalcopiesofNRCPerm366AI(17)DescriptionoftheEvent(cont'd)statementwasenteredinaccordancewithTechnicalSpecification3.4.3at0313hoursonJune4,1999,duetohavinglessthantherequirednumberofpressurizerheatersbeingcapableofbeingpoweredfromaClass1Eelectricbus.CauseoftheEventCEAIssuesSubgroup21CEAsspontaneouslytransferringtotheirlowergripperswascausedbynoisegeneratedbythefailureofthesubgroup21powerswitch.Disassemblyofthepowerswitchindicatedashort,whichmost,likelydevelopedovertimebetweena"C"phasesiliconcontrolledrectifier(SCR)(Q125)anodeandground.Measurementsofthepowerswitch"C"phasetogroundindicateashortedconditionanddetailedinspectionoftheSCR'smylarinsulatingwashershowavisiblebreakdownoftheinsulationandanarcpathtoground.Becausethisconditioncontinuedforsometime,inducinghighnoiselevelsintothesystem,variousACTMcardsinterpretedthisabnormalconditionasunfavorableuppergrippervoltage.Asdesigned,theACTMcardstransferredtheCEAstotheirlowergripperstopreventroddrops.Uponreplacementofthesubgroup21powerswitchandthefailedfuseassociatedwithphase"C"thenoisewasnolongerseenonthesubgroup21CEAs.TheJune4,1999roddropeventwascausedbyalackofproceduralguidancethatshouldhaveverifiedthatthereplacementCEAsubgroup21powerswitchwasproperlyseatedduringtroubleshootingactivities.Theimproperseatingofthepowerswitchwasnotapparentbecausetwicebeforethesubgroup21CEAsweresuccessfullytransferredfromtheholdbustothesubgrouppowerswitchandback.Thezewerenoindicationsthatthepowerswitchwasnotproperlyseated,andthatintermittentpowerwasbeingdeliveredtotheCEAs.Eventually,thelatentintermittentelectricalpowerledtothefullinsertionofthesupgroup21CEAswhentheholdbuswasdeenergized.Post-TriIssuesThefailureofthe2CMSRTCVblockvalve,MV-08-10,toclosewascausedbydirtyauxiliarycontactsintheMCCcontrolcircuit.Thefailureofthe"A"sidepressurizerheaterstoresetonrisingpressurizerlevelwascausedbyafaultycrimpedconnectioninFoxboromoduleLC-1110X.AnalysisoftheEventThiseventisreportableunder10CFR50.73(a)(2)(iv)as"anyeventorconditionthatresultedinamanualorautomaticactuationofanyEngineeredSafetyFeature(ESF),includingtheReactorProtectionSystem(RPS)."AnalysisofSafetySignificanceTheCEDMcontrolsystemdoesnotprovi.deanysafetyrelat'edfunctionsandtheidentifiedproblemswouldnothavepreventedtheaffectedrodsfromdroppingintothecoretoshutdownthereactor.Additionally,thedropofaCEAsubgroupisananalyzedevent.Therefore,thecondit'ionsdescribedabovedidnotpresentanoperabilityconcern.Additionally,duringCEAtroubleshootingactiviti.es,apre-evolutiontailboardwasconductedwithOperationstoinstallasparepower'switchinNRCFORM366A(6.1998)

~NRCFORM366A(6-1998)LICENSEEEVENTREPORT(LER)TEXTCONTINUATIONU.S.NUCLEARREGULATORYCOMMISSIONFACILITYNAME('I)St.LucieUnit2DOCKETNUMBER2)05000389LERNUMBER(6)SEQUENTIALREVISIONNUMBERNUMBER1999-005-00PAGE(3)Page4of4TEXT(Ifmorespeceisrequired,useeddi(ionelcopiesofNRCForm366AJ(17)AnalysisofSafetySignificance(cont')subgroup21.Whenallfoursubgroup21CEAsfullyinsertedi,ntothecore,Operationsconfirmedtheroddropindicationandmanuallytrippedthereactorinaccordancewiththepre-evoluti.ontailboard.Basedontheabove,thiseventhadnoimpactonthehealthandsafetyofthepublic.CorrectiveActionsl.AllCEDMCSsubgrouppowerswitcheswereverifiedtohaveproperelectricalandmechanicalcontactunderworkorder(WO)99010204.2.Thesystem(CEAcoils,CEDMpowerdistributionandpowerswitchcomponentsforeachofthe24subgroups)wasverifiedtobefreeofgroundsbyameggerof250Vorgreatertoground.3.Coiltraceswereobtainedduringrodmovementandverifiedtobeofproperwaveform,timing,andthatallphaseswereoperatingsatisfactorily.4.TheauxiliarycontactsforMV-08-10werecleanedunderWO99010433.5.ThepressurizerheatercontrolcircuitrywasrepairedunderWO99010873'.PostmaintenancetestrequirementsazebeingdevelopedforCEAsubgrouppowerswitchesandminimumcheckstobeperformedpriortoremovingaCEAsubgroupfromtheholdbus.7.GuidelinesarebeingdevelopedfortherepairofCEDMCSpowerswitchmodulesincludingproperremovalandinstallation.AdditionalInformationFailedComonentsIdentifiedComponent:Manufacturer:Model:PowerSwitchAssemblyCombustionEngineeringPartNo.35200SimilarEventsNoneNROFOAM3BBA(B.1998)