ML17221A601

LER 87-007-01:on 871125,reactor Tripped on Loss of Load Due to Turbine Trip.Caused by Personnel Error.Permanent Magnet Generator & Exciter Bearing Replaced & Exciter Bearing Thermocouple removed.W/880129 Ltr

ML17221A601
Person / Time
Site:	Saint Lucie
Issue date:	01/29/1988
From:	JOHNSON A B, WOODY C O FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
L-88-41, LER-87-007, LER-87-7, NUDOCS 8802020148
Download: ML17221A601 (6)

Text

REGULA,YINFORMATION DISTRIBUTIYSTEM(RIDS)ACCESSION NBR:8802020148 DOC.DATE:88/01/29NOTARIZED:

NOFACIL:50-389St.LuciePlant>Unit2>FloridaPoeer5LightCo.AUTH.NAMEAUTHORAFFILlATION JOHNSON'.

B.FloridaPoeer5LightCo.WOODY.C.O.FloridaPower5LightCo.RECIP.NAMERECIPIENT AFFILIATION DOCKET¹05000389,

SUBJECT:

LER87-007-01:

on871125.reactortrippedonlossofloadduetoturbinetrip.Causedbgpersonnel error.Permanent magnetgenerator 5exciterbearingreplacedZcexciterbearingthermocouple removed.W/880129ltr.DISTRIBUTION CODE:IE22DCOPIESRECEIVED:

LTRENCLSIZE:TITLE:50.73LicenseeEventReport(LER)iIncidentRptietc.NOTES:RECIPIENTIDCODE/NAME PD2-2LATOURIGNYi ECOPIESLTTRENCL1111RECIPIENTIDCODE/NAME PD2-2PDCOPIESLTTRENCL11INTERNAL:

ACRSMICHELSON AEOD/DOAAEOD/DSP/ROAB ARM/DCTS/DAB NRR/DEST/ADS NRR/DEST/ELB NRR/DEST/MEB NRR/DEST/PSB NRR/DEST/SGB NRR/DLPG/GAB NRR/DREP/RAB A)R/SIBREGFILE02IBRGN2FILE01EXTERNAL:

EG5GGROHiMHSTLOBBYWARDNRCPDRNSICMAYSTG11112211011111111111111111155111111ACRSMOELLERAEOD/DSP/NAS AEOD/DSP/TPAB DEDRONRR/DEST/CEB NRR/DEST/ICSB NRR/DEST/MTB NRR/DEST/RSB NRR/DLPG/HFB NRR/DOEA/E*B NRR/DREP/RPB NRR/PMAS/ILRB RESTELFORDiJRES/DRPSDIRFORDBLDGHOY>ALPDR"NSICHARRIS>J2211111111111111111211111111111TOTALNUMBEROFCOPIESREQUIRED:

LTTR46ENCL45

NRCForm3SSA19413lLICENSEEENTREPORT(LER)TEXTCONTINUAIONU.S,NUCLEARREGULATORY COMMISSION APPROVEDOMBNO.3150&104EXPIRES:9/31/BBFACILITYNAMEIIISt.Lucie,Unit2OOCKETNUMBERIllYEARLERNUMBERIBI@~a.SFOVENT/AL NvMErrxo,:REvrsroNiMNVMEllPAGE0)TEXT/ifmoros/rscoisrsr/rr/rsd, rrsosddio'orrs/

H/ICFonrr3////A'/(IT)osooo389'870070102OF04DESCRIPTION OFENTENTEOn25November, 1987,St.LucieUnitTwowasoperating at50percentpowersteadystateinMode1.Theunitwasreturnedtoserviceon23Novemberfollowing arefueling outageandwasholdingat50percentpowerwhilerepairswereinprogressonthe2ASteamGenerator FeedPump(SGFP)(EIIS:SJ) duetoasmallwaterleakthatdeveloped ontheventlineatthepumpcasing.Thereactorwasbeingmaintained inasteadystatecondition withallautomatic controllers placedinautomatic withtheexception oftheControlRodDriveSystem(EIZS:JD) whichwasinOFF.At2331hours,theReactorProtective System(EIZS:JC) initiated areactortriponlossofloadduetoaturbinetrip.Theturbinetrippedonamaingenerator (EIIS:TB) lockout.Thecontrolroomwasalertedwithinformation thatsmokewasseencomingoutoftheMainGenerator Exciter(EZIS:TL).

TheAssistant NuclearPlantSupervisor (ANPS)instructed theTurbineOperator(TO)tocheckforrubsontherotatingcomponents oftheturbine-generator.

TheTOreportedevidenceofturbine-generator rubstothecontrolroomandtheANPSinstructed theReactorControlRoomOperators (RCOs)toopenthevacuumbreakersonthemaincondenser (EIZS:SG) toaidinslowingdowntheturbine.Afireteamwasassembled andstationed withfirefightingequipment atthevicinityofthemaingenerator exciter.Therewerenoreportsofanactualfire.Thetripwasanuncomplicated tripandallsystemsfunctioned normally.

TheSteamBypassControlSystem(SBCS)(EIIS:JI) operatedtoreduceprimaryaveragetemperature (T-avg)tothezeropercentpowersetpointof532degreesF.Auxiliary feedwater (EIZS:BA) wasinitiated manuallytocontrolthesteamgenerator (S/G)levelforReactorCoolantSystem(RCS)(EIZSEAB) heatremoval.Thestandardposttripactionswerecompleted andtheunitwasimmediately stabilized inHotStandby,Mode3.NRCFORM316A19831 NRCForm3ddA(983)LICENSEENTREPORT(LER)TEXTCONTINUONV.S.NUCLEARREGULATORY COMMISSION APPROVEOOMSNO.3150MI(HEXP!RES:8/3(188FACILITYNAME(I)DOCKETNUMBER(3)LERNVMSER(8)PACE(3)St.Lucie,Unit2TERT(Ilmoro<<>>oobror)rrr'rod, Ir>>odds'onel NRCFarm3ddl3I()T)osoooYEAR@gSEQUENTIAL NUMtR007REVISIONNUMER0103OF04CAUSEOFTBBEVENTSTheimmediate causeofthemaingenerator lockoutwaslossofthegenerator field.Thelossoffieldwascausedbydestruction oftheexciterPermanent MagnetGenerator (PMG)thatoccurredwhentheexciterbearingfailedallowingthePMGarmaturetorubonthePMGstator.Furtherinvestigation intothefailureoftheexciterbearingindicated thatagroundwascausedbyacompleted electrical circuitbetweentheexciterbearingandtheexciterbase.Thiscompleted electrical circuitbypassedtheinsulation betweenthebearingpedestalandtheexciterbase.Thegroundwascausedbyanimproperinstallation ofaninstrument cable(EIIS:IT).

Theinstrument cableprovidestheterminalconnection fromthethermocouple oftheN9exciterbearinghousingtoitsterminalbox,whichprovidesremotetemperature indication inthecontrolroom.Theas-foundcondition oftheinstrument cableindicated thatthebraidedwirecableshieldwasnotproperlypositioned intheclamp;therefore, agrounddeveloped attheexciterbearing.Examination oftheexciterbearingrevealedpittingmarksonthebearingsurface,characteristic ofcurrentflowingacrossthebearingjournaltothebearingpad,whichresultedinthebearingfailure.Theimproperarrangement oftheinstrument cablecannotbeconclusively identified asawiringerrorduringtheinstallation ofthenewmaingenerator exciter.ThePMGandtheinstrument cableweremeggeredtodetectforpossiblegroundsandtheresultswereacceptable.

Ithasbeenpostulated thatoneoftwocircumstances mayhaveoccurred:

1)theinstrument cablewasinstalled correctly withthebraidedwireshieldintheclampwhenitwasmeggered; thenatsomelaterdate,theinstrument cablewasaccidently steppedoncausingthecableshieldtobecomeseparated fromtheclamp;or2)theinstrument cable,beingclampedincorrectly tothepedestal, hadnotyetbeenconnected totheterminalboxwhenthemeggertestwasperformed.

Afterplacingthemaingenerator backinservice,thegroundshouldhavebeendetectedduringtheperformance oftheweeklygenerator excitergroundcheck.Thepreventative maintenance PlantWorkOrder(PWO)requiresvoltagestobereadacrosstheN9bearingshafttogroundandacrossthe59bearingpedestaltoground.Thedataistobeevaluated toensurenogroundshavedeveloped inthemaingenerator exciter.Earlyrecognition ofthegroundwouldhavepromptedimmediate actiontoremovethemaingenerator fromserviceforthenecessary repairs.Therootcauseoftheeventwasacognitive personnel errorbyautilitymain-tenancesupervisor inmisinterpretation ofthemaingenerator excitergroundvoltagereadings.

Theappropriate procedure wasproperlyfollowed.

However,lackofunderstanding ofthesignificance ofthegenerator excitergroundcheckandinadequate acceptance criteriainthePWOwerecontributing factorsinthepersonnel error.Therewerenounusualcharacteristics oftheworklocationthatdirectlycontributed tothepersonnel error.NRCfORM3ddA(983)

URCForm366A(983)LICENSEENTREPORT(LER)TEXTCONTINUAONU.S.NVCLEARRECULATORY COMMISSION APPROVEDOMBNO.3150WIOiEXPIRES:8/31/88FACILITYNAME(11St.Lucie,Unit2DOCKETNUMBER(2)YEARLERNUMBER(6)SEOUENTIAL NUMBERREVISIONNUMEllPACE(3)TEXT/I/mortt/Mcoitror)rr/rtd.

IhtotdChr/ont/HRC Forrrr36(L('ti(17)p5ppp389870070104OF04ANALYSISOFTHEEVENT:Theeventisreportable under10CFR50.73(a)(2)(iv),

"anyeventorcondition thatresultedinmanualorautomatic actuation ofanyEngineered SafetyFeature,including theReactorProtection System."Thiseventwasobservedtobearoutinereactortriponlossofload.Theresulting transient waswellenveloped bytheSt.LucieUnitII2FinalUpdatedSafetyAnalysisReportsection15.2.1.2"Limiting ReactorCoolantSystemPressureEvent-Isolation ofTurbine(100%power)."AllPlantSafetyFunctions weremetandtherewerenoadditional complications.

Consequently, thehealthandsafetyofthepublicwerenotaffectedbythisevent.CORRECTIVE ACTIONS.1.ThePermanent MagnetGenerator wasreplaced.

2.TheExciterBearingwasreplaced.

3.Anevaluation wasmadeand'theExciterBearingthermocouple wasdetermined tobeunnecessary anditwasremovedtopreventfutureincidents ofthistype.4.Thepreventative maintenance plantworkorderwasrevisedtoadequately definetheacceptance criteriaandtheproperactionswhentheacceptance criteriaarenotmet.5.TrainingwasgiventoallElectrical Maintenance personnel toelaborate ontheimportance ofproperlyevaluating thedataduringperformance oftheweeklygenerator excitergroundcheck.h6.Theplanttraininggroupwillevaluatethisitemtodetermine appropriate trainingrequirements andmethods.ADDITIONAL INFORMATION:

FAILEDCOMPONENT INFORMATION:

Westinghouse ExciterBearing(89bearing)PartI)613F432 GOlPREVIOUSSIMILAREVENTS:SeeLER5389-84-011 forapreviousreactortripduetoexciterbearingfailure.NRCFORM366*(983)

P.O.14000,JUNOBEACH,FL33408.0420 SKNLI5291988L-88-4110CFR50,73U.S.NuclearRegulatory Commission Attn:DocumentControlDeskWashington, D.C.20555,Gentlemen:

Re:St.LucieUnit2DocketNo.50-389Reportable Event:87-07Revision1DateofEvent:November25,1987ReactorTriponLossofLoadCausedbyMainGenerator ExciterBearinFailureDuetoPersonnel ErrorTheattachedLicenseeEventReport(LER)isbeingsubmitted pursuanttotherequirements of10CFR50.73toprovideanupdateonthesubjectevent.Verytrulyyours,C.0.odyExecutive VicePresident COW/GRM/gp Attachment cc:Dr.J.NelsonGrace,RegionalAdministrator, RegionZI,USNRCSeniorResidentInspector, USNRC,St.LuciePlantGRM/022.LER anFPLGroupcompany