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{{#Wiki_filter:ACCELERATED Dl/RIBUTION DEMONSTRATION SYSTEMREGULATORY INFORMATION DISTRIBUTIONSYSTEM(RIDS)ACCESSION NBR:9205010133 DOC.DATE:
{{#Wiki_filter:ACCELERATED Dl/RIBUTION DEMONSTRATION SYSTEM REGULATORY INFORMATION DI STRI BUT ION SYSTEM (RI DS)ACCESSION NBR:9205010133 DOC.DATE: 92/04/24 NOTARIZED:
92/04/24NOTARIZED:
NO FACIL:50-389 St.Lucie Plant, Unit 2, Florida Power&Light Co.AUTH.NAME.AUTHOR AFFILIATION SAGER,D.A.
NOFACIL:50-389 St.LuciePlant,Unit2,FloridaPower&LightCo.AUTH.NAME.AUTHORAFFILIATION SAGER,D.A.
Florida Power&Light Co.RECIP.NAME RECIPIENT AFFILIATION
FloridaPower&LightCo.RECIP.NAME RECIPIENT AFFILIATION
-Document Control Branch (Document Control Desk)DOCKET 05000389
-DocumentControlBranch(Document ControlDesk)DOCKET05000389


==SUBJECT:==
==SUBJECT:==
In-HouseEventRept92-023:on 920421,turbine generator failedtotripduringmanualreactortrip.Rootcauseanalysisstillinprogress.
In-House Event Rept 92-023:on 920421,turbine generator failed to trip during manual reactor trip.Root cause analysis still in progress.Solenoid valves removed&sent to independent lab for analysis..DISTRIBUTION CODE: IE22D COPIES RECEIVED:LTR I ENCL l SIZE: TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.NOTES: RECIPIENT ID CODE/NAME PD2-2 LA NORRIS,J INTERNAL: ACNW AEOD/DOA AEOD/ROAB/DSP NRR/DLPQ/LHFB10 NRR/DOEA/OEAB NRR/DST/SELB 8D~/~S.T PLB8D1 REG FILE 02 FILE 01 EXTERNAL: EG&G BRYCE,J.H NRC PDR NSIC POORE,W.COPIES LTTR ENCL 1 1 1 1 2, 2 1 1 2 2 1 1 1".'1 1 1, 1 1 1 1 1 1 3 3 1 1 1 1 RECIPIENT ID CODE/NAME PD2-2 PD ACRS AEOD/DSP/TPAB NRR/DET/EMEB 7E NRR/DLPQ/LPEB10 NRR/DREP/PRPB11 NRR/DST/SICB8H3 NRR/DST/SRXB 8E RES/DSIR/EIB L ST LOBBY WARD NSIC MURPHY,G.A NUDOCS FULL TXT COPIES LTTR ENCL 1 1 2 2 1 1 1 1 1 1 2 2 1 1 1 1 1'"1 1 1 1 1 1 D D D NOTE TO ALL"RIDS" RECIPIENTS:
Solenoidvalvesremoved&senttoindependent labforanalysis.
PLEASE HELP US TO REDUCE iVASTE!CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT.20079)TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!TOTAL NUMBER OF COPIES REQUIRED: LTTR 32 ENCL 32 D D P.O.Box 128, Ft.Pierce, FL 34954.0128 g g I 4-8Q.L-92-129 U.S.Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.20555'E: St.Lucie Unit 2 Docket No.50-389 Event Date: April 21, 1992 Turbine Tri Failure Please find attached the preliminary internal problem report of our plant event which occurred on April 21, 1992.Pursuant to 10 CFR 50.73 a Licensed Event Report will be submitted within 30 days of the event date.Please contact us if there are any questions about this submittal.
.DISTRIBUTION CODE:IE22DCOPIESRECEIVED:LTR IENCLlSIZE:TITLE:50.73/50.9 LicenseeEventReport(LER),IncidentRpt,etc.NOTES:RECIPIENT IDCODE/NAME PD2-2LANORRIS,JINTERNAL:
Very truly yours, Vice President St.Lucie Plant DAS/JJB/kw cc: Stewart D.Ebneter, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, St.Lucie Plant DAS/PSL 4681-92 5'205010133 5'20424 PDR ADOCK 05000385'PDR an FPL Group company ST.LUCIE PLANT IN HOUSE EVENT REPORT 92-023 TURBINE GENERATOR FAILED TO TRIP FOLLOWING MANUAL REACTOR TRIP UNIT: 2 DATE: APRIL 21, 1992 I.INITIAL PLANT CONDITIONS On April 21, 1992, St.Lucie Unit 2 was shutting down for a scheduled refueling outage.Reactor power was at approximately 12%.I I.EVENT DESCRIPTION A scheduled Reactor-Turbine shutdown was in progress on Unit 2.During the shutdown, power moved to the top of the core as expected.Existing procedural guidance on Axial Shape Index (ASI)was being employed to minimize its affects.When three out of four Local Power Density Pre-Trips on thc Reactor Protection.System came in, the Nuclear Plant Supervisor (NPS)instructed the Reactor Control Operators to manually trip the Unit.A manual reactor trip was initiated, but the turbine did not trip.Several attempts were made to trip the turbine using the Turbine Trip push button with no success and thc Nuclear Watch Engineer tripped the turbine from the front standard.I I I.EVENT SEQUENCE St.Lucie Unit 2 was performing a scheduled reactor shutdown for refueling purposes.During the plant shutdown ASI approached its upper (negative) limit.Coordination at controlling ASI within limits and maintaining reactor coolant temperature due to Xenon building in became more difficult.
ACNWAEOD/DOAAEOD/ROAB/DSP NRR/DLPQ/LHFB10 NRR/DOEA/OEAB NRR/DST/SELB 8D~/~S.TPLB8D1REGFILE02FILE01EXTERNAL:
When reactor power was decreased to about 12%, control rod insertion had no effect on making ASI less negative and three of the four Reactor Protection System Local Power Density pre-trips came in.At this point, the NPS instructed the Reactor Control Operators to manually trip the unit and the manual reactor trip pushbuttons on RTGB (Reactor Turbine Guage Board)204 and RTGB 201 were depressed at 0238 with the turbine trip pushbutton on RTGB 201 being depressed approximately two seconds later;however, the turbine did not trip.Standard Post Trip Actions from Emergency Operating Procedure (EOP)1 were implemented.
EG&GBRYCE,J.H NRCPDRNSICPOORE,W.COPIESLTTRENCL11112,21122111".'111,111111331111RECIPIENT IDCODE/NAME PD2-2PDACRSAEOD/DSP/TPAB NRR/DET/EMEB 7ENRR/DLPQ/LPEB10 NRR/DREP/PRPB11 NRR/DST/SICB8H3 NRR/DST/SRXB 8ERES/DSIR/EIB LSTLOBBYWARDNSICMURPHY,G.A NUDOCSFULLTXTCOPIESLTTRENCL11221111112211111'"111111DDDNOTETOALL"RIDS"RECIPIENTS:
When the turbine trip pushbutton was depressed, thc Governor Valves indicated closed but the Throttle Valves, Reheat Valves, and Intercept Valves indicated open.Auto Stop Oil and the Emergency Trip Header indicated pressures of approximately 100 psi and 2000 psi, respectively.
PLEASEHELPUSTOREDUCEiVASTE!CONTACTTHEDOCUMENTCONTROLDESK,ROOMPl-37(EXT.20079)TOELIMINATE YOURNAMEFROMDISTRIBUTION LISTSFORDOCUMENTS YOUDON'TNEED!TOTALNUMBEROFCOPIESREQUIRED:
The megawatt recorder indicated ninety megawatts.
LTTR32ENCL32DD P.O.Box128,Ft.Pierce,FL34954.0128 ggI4-8Q.L-92-129U.S.NuclearRegulatory Commission Attn:DocumentControlDeskWashington, D.C.20555'E:St.LucieUnit2DocketNo.50-389EventDate:April21,1992TurbineTriFailurePleasefindattachedthepreliminary internalproblemreportofourplanteventwhichoccurredonApril21,1992.Pursuantto10CFR50.73aLicensedEventReportwillbesubmitted within30daysoftheeventdate.Pleasecontactusifthereareanyquestions aboutthissubmittal.
Several morc attempts were made to trip the turbine using the pushbutton, but they were unsuccessful.
Verytrulyyours,VicePresident St.LuciePlantDAS/JJB/kw cc:StewartD.Ebneter,RegionalAdministrator, RegionII,USNRCSeniorResidentInspector, USNRC,St.LuciePlantDAS/PSL4681-925'205010133 5'20424PDRADOCK05000385' PDRanFPLGroupcompany ST.LUCIEPLANTINHOUSEEVENTREPORT92-023TURBINEGENERATOR FAILEDTOTRIPFOLLOWING MANUALREACTORTRIPUNIT:2DATE:APRIL21,1992I.INITIALPLANTCONDITIONS OnApril21,1992,St.LucieUnit2wasshuttingdownforascheduled refueling outage.Reactorpowerwasatapproximately 12%.II.EVENTDESCRIPTION Ascheduled Reactor-Turbine shutdownwasinprogressonUnit2.Duringtheshutdown, powermovedtothetopofthecoreasexpected.
At this point, the Reactor Control Operator opened the Generator output Breakers 8W52 and 8W49, secured the voltage regulator, stopped the Digital Electrohydraulic (DEH)pumps, closed the Main Stcam Isolation Valves (MSIV), and broke condenser vacuum.IHE¹92-023, 4-24-92 SHEET 1 OF 3 III.EVENT SEQUENCE (cont'd)The Assistant Nuclear Plant Supervisor instructed the Nuclear Watch Engineer to trip the turbine from the Front Standard.At 0241 all the turbine valves closed.EOP-2, Reactor Trip Recovery, was then completed wi'th two sets of satisfactory Safety'unction Status Checks, the plant was stabilized, and the Turbine Shutdown Procedure'as re-entered.
Existingprocedural guidanceonAxialShapeIndex(ASI)wasbeingemployedtominimizeitsaffects.WhenthreeoutoffourLocalPowerDensityPre-Trips onthcReactorProtection
I V.EVENT EVALUATION A)PLANT RESPONSE The plant response to this event was as expected with the exception of the failure of the turbine to trip.Upon the reactor trip signal, the four Control Element Drive Mechanism (CEDM)Bus undervoltage relays should de-energize.
.Systemcamein,theNuclearPlantSupervisor (NPS)instructed theReactorControlOperators tomanuallytriptheUnit.Amanualreactortripwasinitiated, buttheturbinedidnottrip.SeveralattemptsweremadetotriptheturbineusingtheTurbineTrippushbuttonwithnosuccessandthcNuclearWatchEngineertrippedtheturbinefromthefrontstandard.
This should energize (open)the 20 ET solenoid valve and drain the electro-hydraulic fluid from the emergency trip header (Sec attachment
III.EVENTSEQUENCESt.LucieUnit2wasperforming ascheduled reactorshutdownforrefueling purposes.
¹I).The 20 AST trip solenoid coil should simultaneously energize, pull down the mechanical trip lever, and dump the auto stop oil header.Decreasing auto stop oil pressure allows the Interface valve to open and dump the electo-hydraulic fluid emergency trip header.When auto stop oil pressure decreases to 45 psi, pressure switches 63-1 AST and 63-2 AST should lock in, actuating a generator primary lockout which trips the generator output breakers.The same result should be obtained when attempting to trip the turbine via the Turbine Trip Pushbutton.
DuringtheplantshutdownASIapproached itsupper(negative) limit.Coordination atcontrolling ASIwithinlimitsandmaintaining reactorcoolanttemperature duetoXenonbuildinginbecamemoredifficult.
A multi-discipline team is investigating to determine why the turbine failed to trip when the trip signals were initiated.
Whenreactorpowerwasdecreased toabout12%,controlrodinsertion hadnoeffectonmakingASIlessnegativeandthreeofthefourReactorProtection SystemLocalPowerDensitypre-tripscamein.Atthispoint,theNPSinstructed theReactorControlOperators tomanuallytriptheunitandthemanualreactortrippushbuttons onRTGB(ReactorTurbineGuageBoard)204andRTGB201weredepressed at0238withtheturbinetrippushbutton onRTGB201beingdepressed approximately twosecondslater;however,theturbinedidnottrip.StandardPostTripActionsfromEmergency Operating Procedure (EOP)1wereimplemented.
B)SAFETY SIGNIFICANCE The plant response to this event is bounded by section 15.1.5 of the PSL Unit 2 Final Safety Analysis Report (FSAR),"Increased Heat Removal by the Secondary System"as further described below..12%Power Trip, No Operator Action Scenario.MSIV's auto close at 600 psig.Cooldown terminated.
Whentheturbinetrippushbutton wasdepressed, thcGovernorValvesindicated closedbuttheThrottleValves,ReheatValves,andIntercept Valvesindicated open.AutoStopOilandtheEmergency TripHeaderindicated pressures ofapproximately 100psiand2000psi,respectively.
Core decay heat released via Main Steam Safety Valves (MSSV)Cooldown rate bounded by limiting FSAR cooldown event.100%Power Trip, No Operator Action Scenario.Possible Safety Injection Actuation-Signal (SIAS)but no actual injection.
Themegawattrecorderindicated ninetymegawatts.
Automatic MSIV closure after 66 seconds.Fuels RETRAN analysis validates that no core damage will occur.100%Power Trip with multiple FSAR Chapter 15 Accident Scenario.Operators trained on the simulator for multiple failure events beyond design basis.Excess stcam demand events are simulated and procedurally addressed by the EOP's.IHE¹92-023, 4-24-92 SHEET 2 OF 3 IV.EVENT EVALUATION (cont'd)C)ROOT CAUSEANALYSIS A multi-discipline Turbine Investigation Team is performing a root cause analysis of this event.A Letter of Instruction, 2-LOI-T-67,"Evaluation of Turbine Solenoid Trip Function," was written to evaluate the operation of the turbine manual and automatic trip functions.
Severalmorcattemptsweremadetotriptheturbineusingthepushbutton, buttheywereunsuccessful.
Deficiencies identified are noted below.Root cause analysis is still in progress.D)DEFICIENCIES IDENTIFIED Testing of thc 20 ET Trip solenoid, 20 AST solenoid valve, and the 20 OPC 1 and 2 solenoid valves was performed in accordance with 2-LOI-T-67.
Atthispoint,theReactorControlOperatoropenedtheGenerator outputBreakers8W52and8W49,securedthevoltageregulator, stoppedtheDigitalElectrohydraulic (DEH)pumps,closedtheMainStcamIsolation Valves(MSIV),andbrokecondenser vacuum.IHE¹92-023,4-24-92SHEET1OF3 III.EVENTSEQUENCE(cont'd)TheAssistant NuclearPlantSupervisor instructed theNuclearWatchEngineertotriptheturbinefromtheFrontStandard.
The results of this evaluation are as follows: 1)20 ET Solenoid valve Thc original solenoid valve was removed to prescrvc the"as found" condition of the valve.A new solenoid valve was installed and tested satisfactorily.
At0241alltheturbinevalvesclosed.EOP-2,ReactorTripRecovery, wasthencompleted wi'thtwosetsofsatisfactory Safety'unctionStatusChecks,theplantwasstabilized, andtheTurbineShutdownProcedure'as re-entered.
This verified the 20 ET electrical circuits did not contribute to the failures.2)20 AST Trip Solenoid The solenoid was tested numerous times with two of thc tests indicative of intermittent circuit problems.A loose connection was found on relay 62 ASTX/pin 6.This connection is in the circuit for all 20 AST trip functions.
IV.EVENTEVALUATION A)PLANTRESPONSETheplantresponsetothiseventwasasexpectedwiththeexception ofthefailureoftheturbinetotrip.Uponthereactortripsignal,thefourControlElementDriveMechanism (CEDM)Busundervoltage relaysshouldde-energize.
Further troubleshooting is continuing.
Thisshouldenergize(open)the20ETsolenoidvalveanddraintheelectro-hydraulic fluidfromtheemergency tripheader(Secattachment
3)20 OPC 1 and 2 Solenoid Valves One OPC soleniod valve was removed prior to testing for potential failure mode analysis.Testing of one original and onc replacement OPC solenoid valve indicated acceptable operation of the OPC circuits.V.CORRECTIVE ACTIONS 1.The original 20 ET, 20 OPC-1 and 20 OPC-2 Solenoid valves have been removed and were sent to an independent laboratory for analysis.2.Maintenance is continuing to investigate thc root cause of the intermittent electrical problems of thc 20 AST Trip Solenoid.The circuits of the 20 ET and 20 OPC 1 and 2 Solenoids are also being evaluated to ensure similar problems do not exist.3.Nuclear Fuels is evaluating additional guidance for ASI control at the end of core life.4.Operations is evaluating additional guidance for EOP-1,"Standard Post Trip Actions", on actions to take for a reactor trip with no subsequent turbine trip.IHE¹92-023, 4-24-92 SHEET 3 OF 3 e WESTINGHOUSE ELECTRO-HYDRAULIC CONTROL SYSTEM AND AUTO-STOP OIL SYSTEM~esatttt Trtvt tvvaalra lS CO P L 5'7~\rt act tt vatvt tvt altar w aavt awa T Jtrt tvt at taa w wwat alar TTLTa g Z~~4 la~stasttw~s las ILW Tat Tt tas ttw Savtr g EMERGENCY TRIPS I I I I I I I I 3 I I I l I I I l I I I I I l I I I I I I I l I I twaatwr I~~QO g7~Ttawtaa~a I I~tsttataca'vaLva AUTO STOP OIL PRESSURE SWITCHES (3)~ace vaLTC~v a atra t a t ala I~t Lava~I~avt 1.LOW AUTO-STOP OIL PRESSURE (2/3)2.REACTOR TRIP ('I)3.MANUAL TRIP 4.HI-Hl LEVEL IN ANY S/G SOLENOID TRIPS 1.REACTOR TRIP (A)2.ELECTRICAL OVERSPEED~3.LOW EH FLUID PRESSURE 4.MANUAL 5.ETC.vaccw tav Lao aa a.OL~tatta tat/2o-i OPc Qo-2 opg 0 ro asf 0 I tat~tL Ovsaaaaa tva OVERSPEED PROTECTION CONTROLLER 103K OF NORMAL SPEED 2.GENERATOR OUTPUT BREAKERS OPEN ABOVE A PRESET POWER LEVEL 3.CHANGE IN GENERATOR OUTPUT AND TURBINE INLET PRESSURE AVIO IIOPOILSY5ICII}}
¹I).The20ASTtripsolenoidcoilshouldsimultaneously
: energize, pulldownthemechanical triplever,anddumptheautostopoilheader.Decreasing autostopoilpressureallowstheInterface valvetoopenanddumptheelecto-hydraulic fluidemergency tripheader.Whenautostopoilpressuredecreases to45psi,pressureswitches63-1ASTand63-2ASTshouldlockin,actuating agenerator primarylockoutwhichtripsthegenerator outputbreakers.
Thesameresultshouldbeobtainedwhenattempting totriptheturbineviatheTurbineTripPushbutton.
Amulti-discipline teamisinvestigating todetermine whytheturbinefailedtotripwhenthetripsignalswereinitiated.
B)SAFETYSIGNIFICANCE Theplantresponsetothiseventisboundedbysection15.1.5ofthePSLUnit2FinalSafetyAnalysisReport(FSAR),"Increased HeatRemovalbytheSecondary System"as furtherdescribed below..12%PowerTrip,NoOperatorActionScenario.
MSIV'sautocloseat600psig.Cooldownterminated.
CoredecayheatreleasedviaMainSteamSafetyValves(MSSV)CooldownrateboundedbylimitingFSARcooldownevent.100%PowerTrip,NoOperatorActionScenario.
PossibleSafetyInjection Actuation-Signal (SIAS)butnoactualinjection.
Automatic MSIVclosureafter66seconds.FuelsRETRANanalysisvalidates thatnocoredamagewilloccur.100%PowerTripwithmultipleFSARChapter15AccidentScenario.
Operators trainedonthesimulator formultiplefailureeventsbeyonddesignbasis.Excessstcamdemandeventsaresimulated andprocedurally addressed bytheEOP's.IHE¹92-023,4-24-92SHEET2OF3 IV.EVENTEVALUATION (cont'd)C)ROOTCAUSEANALYSIS Amulti-discipline TurbineInvestigation Teamisperforming arootcauseanalysisofthisevent.ALetterofInstruction, 2-LOI-T-67, "Evaluation ofTurbineSolenoidTripFunction,"
waswrittentoevaluatetheoperation oftheturbinemanualandautomatic tripfunctions.
Deficiencies identified arenotedbelow.Rootcauseanalysisisstillinprogress.
D)DEFICIENCIES IDENTIFIED Testingofthc20ETTripsolenoid, 20ASTsolenoidvalve,andthe20OPC1and2solenoidvalveswasperformed inaccordance with2-LOI-T-67.
Theresultsofthisevaluation areasfollows:1)20ETSolenoidvalveThcoriginalsolenoidvalvewasremovedtoprescrvcthe"asfound"condition ofthevalve.Anewsolenoidvalvewasinstalled andtestedsatisfactorily.
Thisverifiedthe20ETelectrical circuitsdidnotcontribute tothefailures.
2)20ASTTripSolenoidThesolenoidwastestednumeroustimeswithtwoofthctestsindicative ofintermittent circuitproblems.
Alooseconnection wasfoundonrelay62ASTX/pin6.Thisconnection isinthecircuitforall20ASTtripfunctions.
Furthertroubleshooting iscontinuing.
3)20OPC1and2SolenoidValvesOneOPCsoleniodvalvewasremovedpriortotestingforpotential failuremodeanalysis.
Testingofoneoriginalandoncreplacement OPCsolenoidvalveindicated acceptable operation oftheOPCcircuits.
V.CORRECTIVE ACTIONS1.Theoriginal20ET,20OPC-1and20OPC-2Solenoidvalveshavebeenremovedandweresenttoanindependent laboratory foranalysis.
2.Maintenance iscontinuing toinvestigate thcrootcauseoftheintermittent electrical problemsofthc20ASTTripSolenoid.
Thecircuitsofthe20ETand20OPC1and2Solenoids arealsobeingevaluated toensuresimilarproblemsdonotexist.3.NuclearFuelsisevaluating additional guidanceforASIcontrolattheendofcorelife.4.Operations isevaluating additional guidanceforEOP-1,"Standard PostTripActions",
onactionstotakeforareactortripwithnosubsequent turbinetrip.IHE¹92-023,4-24-92SHEET3OF3 eWESTINGHOUSE ELECTRO-HYDRAULIC CONTROLSYSTEMANDAUTO-STOP OILSYSTEM~esattttTrtvttvvaalralSCOPL5'7~\rtactttvatvttvtaltarwaavtawaTJtrttvtattaawwwatalarTTLTagZ~~4la~stasttw~slasILWTatTttasttwSavtrgEMERGENCY TRIPSIIIIIIII3IIIlIIIlIIIIIlIIIIIIIlIItwaatwrI~~QOg7~Ttawtaa~aII~tsttataca'vaLva AUTOSTOPOILPRESSURESWITCHES(3)~acevaLTC~vaatratatalaI~tLava~I~avt1.LOWAUTO-STOP OILPRESSURE(2/3)2.REACTORTRIP('I)3.MANUALTRIP4.HI-HlLEVELINANYS/GSOLENOIDTRIPS1.REACTORTRIP(A)2.ELECTRICAL OVERSPEED
~3.LOWEHFLUIDPRESSURE4.MANUAL5.ETC.vaccwtavLaoaaa.OL~tattatat/2o-iOPcQo-2opg0roasf0Itat~tLOvsaaaaatvaOVERSPEED PROTECTION CONTROLLER 103KOFNORMALSPEED2.GENERATOR OUTPUTBREAKERSOPENABOVEAPRESETPOWERLEVEL3.CHANGEINGENERATOR OUTPUTANDTURBINEINLETPRESSUREAVIOIIOPOILSY5ICII}}

Revision as of 17:17, 7 July 2018

In-House Event Rept 92-023:on 920421,turbine Generator Failed to Trip During Manual Reactor Trip.Root Cause Analysis Still in Progress.Solenoid Valves Removed & Sent to Independent Lab for Analysis
ML17227A402
Person / Time
Site: Saint Lucie NextEra Energy icon.png
Issue date: 04/24/1992
From: SAGER D A
FLORIDA POWER & LIGHT CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
92-023, 92-23, L-92-129, NUDOCS 9205010133
Download: ML17227A402 (6)


Text

ACCELERATED Dl/RIBUTION DEMONSTRATION SYSTEM REGULATORY INFORMATION DI STRI BUT ION SYSTEM (RI DS)ACCESSION NBR:9205010133 DOC.DATE: 92/04/24 NOTARIZED:

NO FACIL:50-389 St.Lucie Plant, Unit 2, Florida Power&Light Co.AUTH.NAME.AUTHOR AFFILIATION SAGER,D.A.

Florida Power&Light Co.RECIP.NAME RECIPIENT AFFILIATION

-Document Control Branch (Document Control Desk)DOCKET 05000389

SUBJECT:

In-House Event Rept 92-023:on 920421,turbine generator failed to trip during manual reactor trip.Root cause analysis still in progress.Solenoid valves removed&sent to independent lab for analysis..DISTRIBUTION CODE: IE22D COPIES RECEIVED:LTR I ENCL l SIZE: TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.NOTES: RECIPIENT ID CODE/NAME PD2-2 LA NORRIS,J INTERNAL: ACNW AEOD/DOA AEOD/ROAB/DSP NRR/DLPQ/LHFB10 NRR/DOEA/OEAB NRR/DST/SELB 8D~/~S.T PLB8D1 REG FILE 02 FILE 01 EXTERNAL: EG&G BRYCE,J.H NRC PDR NSIC POORE,W.COPIES LTTR ENCL 1 1 1 1 2, 2 1 1 2 2 1 1 1".'1 1 1, 1 1 1 1 1 1 3 3 1 1 1 1 RECIPIENT ID CODE/NAME PD2-2 PD ACRS AEOD/DSP/TPAB NRR/DET/EMEB 7E NRR/DLPQ/LPEB10 NRR/DREP/PRPB11 NRR/DST/SICB8H3 NRR/DST/SRXB 8E RES/DSIR/EIB L ST LOBBY WARD NSIC MURPHY,G.A NUDOCS FULL TXT COPIES LTTR ENCL 1 1 2 2 1 1 1 1 1 1 2 2 1 1 1 1 1'"1 1 1 1 1 1 D D D NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE iVASTE!CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT.20079)TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!TOTAL NUMBER OF COPIES REQUIRED: LTTR 32 ENCL 32 D D P.O.Box 128, Ft.Pierce, FL 34954.0128 g g I 4-8Q.L-92-129 U.S.Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.20555'E: St.Lucie Unit 2 Docket No.50-389 Event Date: April 21, 1992 Turbine Tri Failure Please find attached the preliminary internal problem report of our plant event which occurred on April 21, 1992.Pursuant to 10 CFR 50.73 a Licensed Event Report will be submitted within 30 days of the event date.Please contact us if there are any questions about this submittal.

Very truly yours, Vice President St.Lucie Plant DAS/JJB/kw cc: Stewart D.Ebneter, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, St.Lucie Plant DAS/PSL 4681-92 5'205010133 5'20424 PDR ADOCK 05000385'PDR an FPL Group company ST.LUCIE PLANT IN HOUSE EVENT REPORT 92-023 TURBINE GENERATOR FAILED TO TRIP FOLLOWING MANUAL REACTOR TRIP UNIT: 2 DATE: APRIL 21, 1992 I.INITIAL PLANT CONDITIONS On April 21, 1992, St.Lucie Unit 2 was shutting down for a scheduled refueling outage.Reactor power was at approximately 12%.I I.EVENT DESCRIPTION A scheduled Reactor-Turbine shutdown was in progress on Unit 2.During the shutdown, power moved to the top of the core as expected.Existing procedural guidance on Axial Shape Index (ASI)was being employed to minimize its affects.When three out of four Local Power Density Pre-Trips on thc Reactor Protection.System came in, the Nuclear Plant Supervisor (NPS)instructed the Reactor Control Operators to manually trip the Unit.A manual reactor trip was initiated, but the turbine did not trip.Several attempts were made to trip the turbine using the Turbine Trip push button with no success and thc Nuclear Watch Engineer tripped the turbine from the front standard.I I I.EVENT SEQUENCE St.Lucie Unit 2 was performing a scheduled reactor shutdown for refueling purposes.During the plant shutdown ASI approached its upper (negative) limit.Coordination at controlling ASI within limits and maintaining reactor coolant temperature due to Xenon building in became more difficult.

When reactor power was decreased to about 12%, control rod insertion had no effect on making ASI less negative and three of the four Reactor Protection System Local Power Density pre-trips came in.At this point, the NPS instructed the Reactor Control Operators to manually trip the unit and the manual reactor trip pushbuttons on RTGB (Reactor Turbine Guage Board)204 and RTGB 201 were depressed at 0238 with the turbine trip pushbutton on RTGB 201 being depressed approximately two seconds later;however, the turbine did not trip.Standard Post Trip Actions from Emergency Operating Procedure (EOP)1 were implemented.

When the turbine trip pushbutton was depressed, thc Governor Valves indicated closed but the Throttle Valves, Reheat Valves, and Intercept Valves indicated open.Auto Stop Oil and the Emergency Trip Header indicated pressures of approximately 100 psi and 2000 psi, respectively.

The megawatt recorder indicated ninety megawatts.

Several morc attempts were made to trip the turbine using the pushbutton, but they were unsuccessful.

At this point, the Reactor Control Operator opened the Generator output Breakers 8W52 and 8W49, secured the voltage regulator, stopped the Digital Electrohydraulic (DEH)pumps, closed the Main Stcam Isolation Valves (MSIV), and broke condenser vacuum.IHE¹92-023, 4-24-92 SHEET 1 OF 3 III.EVENT SEQUENCE (cont'd)The Assistant Nuclear Plant Supervisor instructed the Nuclear Watch Engineer to trip the turbine from the Front Standard.At 0241 all the turbine valves closed.EOP-2, Reactor Trip Recovery, was then completed wi'th two sets of satisfactory Safety'unction Status Checks, the plant was stabilized, and the Turbine Shutdown Procedure'as re-entered.

I V.EVENT EVALUATION A)PLANT RESPONSE The plant response to this event was as expected with the exception of the failure of the turbine to trip.Upon the reactor trip signal, the four Control Element Drive Mechanism (CEDM)Bus undervoltage relays should de-energize.

This should energize (open)the 20 ET solenoid valve and drain the electro-hydraulic fluid from the emergency trip header (Sec attachment

¹I).The 20 AST trip solenoid coil should simultaneously energize, pull down the mechanical trip lever, and dump the auto stop oil header.Decreasing auto stop oil pressure allows the Interface valve to open and dump the electo-hydraulic fluid emergency trip header.When auto stop oil pressure decreases to 45 psi, pressure switches 63-1 AST and 63-2 AST should lock in, actuating a generator primary lockout which trips the generator output breakers.The same result should be obtained when attempting to trip the turbine via the Turbine Trip Pushbutton.

A multi-discipline team is investigating to determine why the turbine failed to trip when the trip signals were initiated.

B)SAFETY SIGNIFICANCE The plant response to this event is bounded by section 15.1.5 of the PSL Unit 2 Final Safety Analysis Report (FSAR),"Increased Heat Removal by the Secondary System"as further described below..12%Power Trip, No Operator Action Scenario.MSIV's auto close at 600 psig.Cooldown terminated.

Core decay heat released via Main Steam Safety Valves (MSSV)Cooldown rate bounded by limiting FSAR cooldown event.100%Power Trip, No Operator Action Scenario.Possible Safety Injection Actuation-Signal (SIAS)but no actual injection.

Automatic MSIV closure after 66 seconds.Fuels RETRAN analysis validates that no core damage will occur.100%Power Trip with multiple FSAR Chapter 15 Accident Scenario.Operators trained on the simulator for multiple failure events beyond design basis.Excess stcam demand events are simulated and procedurally addressed by the EOP's.IHE¹92-023, 4-24-92 SHEET 2 OF 3 IV.EVENT EVALUATION (cont'd)C)ROOT CAUSEANALYSIS A multi-discipline Turbine Investigation Team is performing a root cause analysis of this event.A Letter of Instruction, 2-LOI-T-67,"Evaluation of Turbine Solenoid Trip Function," was written to evaluate the operation of the turbine manual and automatic trip functions.

Deficiencies identified are noted below.Root cause analysis is still in progress.D)DEFICIENCIES IDENTIFIED Testing of thc 20 ET Trip solenoid, 20 AST solenoid valve, and the 20 OPC 1 and 2 solenoid valves was performed in accordance with 2-LOI-T-67.

The results of this evaluation are as follows: 1)20 ET Solenoid valve Thc original solenoid valve was removed to prescrvc the"as found" condition of the valve.A new solenoid valve was installed and tested satisfactorily.

This verified the 20 ET electrical circuits did not contribute to the failures.2)20 AST Trip Solenoid The solenoid was tested numerous times with two of thc tests indicative of intermittent circuit problems.A loose connection was found on relay 62 ASTX/pin 6.This connection is in the circuit for all 20 AST trip functions.

Further troubleshooting is continuing.

3)20 OPC 1 and 2 Solenoid Valves One OPC soleniod valve was removed prior to testing for potential failure mode analysis.Testing of one original and onc replacement OPC solenoid valve indicated acceptable operation of the OPC circuits.V.CORRECTIVE ACTIONS 1.The original 20 ET, 20 OPC-1 and 20 OPC-2 Solenoid valves have been removed and were sent to an independent laboratory for analysis.2.Maintenance is continuing to investigate thc root cause of the intermittent electrical problems of thc 20 AST Trip Solenoid.The circuits of the 20 ET and 20 OPC 1 and 2 Solenoids are also being evaluated to ensure similar problems do not exist.3.Nuclear Fuels is evaluating additional guidance for ASI control at the end of core life.4.Operations is evaluating additional guidance for EOP-1,"Standard Post Trip Actions", on actions to take for a reactor trip with no subsequent turbine trip.IHE¹92-023, 4-24-92 SHEET 3 OF 3 e WESTINGHOUSE ELECTRO-HYDRAULIC CONTROL SYSTEM AND AUTO-STOP OIL SYSTEM~esatttt Trtvt tvvaalra lS CO P L 5'7~\rt act tt vatvt tvt altar w aavt awa T Jtrt tvt at taa w wwat alar TTLTa g Z~~4 la~stasttw~s las ILW Tat Tt tas ttw Savtr g EMERGENCY TRIPS I I I I I I I I 3 I I I l I I I l I I I I I l I I I I I I I l I I twaatwr I~~QO g7~Ttawtaa~a I I~tsttataca'vaLva AUTO STOP OIL PRESSURE SWITCHES (3)~ace vaLTC~v a atra t a t ala I~t Lava~I~avt 1.LOW AUTO-STOP OIL PRESSURE (2/3)2.REACTOR TRIP ('I)3.MANUAL TRIP 4.HI-Hl LEVEL IN ANY S/G SOLENOID TRIPS 1.REACTOR TRIP (A)2.ELECTRICAL OVERSPEED~3.LOW EH FLUID PRESSURE 4.MANUAL 5.ETC.vaccw tav Lao aa a.OL~tatta tat/2o-i OPc Qo-2 opg 0 ro asf 0 I tat~tL Ovsaaaaa tva OVERSPEED PROTECTION CONTROLLER 103K OF NORMAL SPEED 2.GENERATOR OUTPUT BREAKERS OPEN ABOVE A PRESET POWER LEVEL 3.CHANGE IN GENERATOR OUTPUT AND TURBINE INLET PRESSURE AVIO IIOPOILSY5ICII