ML18038A937

LER 94-006-00:on 940831,received Alarms That Indicated Loss of Unit 2 ECCS Instrumentation.Caused by Random Failure of ECCS Division I,Atu Inverter.Atu Inverter Was Replaced by Replacing Shorted SCR.W/940929 Ltr

ML18038A937
Person / Time
Site:	Browns Ferry
Issue date:	09/29/1994
From:	HSIEH C S, MACHON R D TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-006-03, LER-94-6-3, NUDOCS 9410050054
Download: ML18038A937 (18)

Text

j.mj.~ms'i'Y l ACCELERATED RIDS PROCESSING)

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)'CCESSION NBR:9410050054 DOC.DATE: 94/09/29 NOTARIZED:

NO DOCKET FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 050002'60 AUTH.NAME AUTHOR AFFILIATION HSIEH,C.S.

Tennessee Valley Authority MACHON,R.D.

'ennessee Valley Authority RECIP-NAME RECIPIENT AFFILIATION

SUBJECT:

LER 94-006-00:on 940831,received alarms that indicated loss of Unit 2 ECCS instrumentation.

Caused by random failure of ECCS division I, ATU inverter.ATU inverter was replaced by replacing shorted SCR.W/940929 ltr.DISTRIBUTION CODE: IE22T COPIES RECEIVED-LTR ENCL SIZE: TITLE: 50.73/50.9 Licensee Event Report (LER), ncident Rpt, etc.NOTES: RECIPIENT ID CODE/NAME PD2-4-PD COPIES RECIPIENT LTTR ENCL ID CODE/NAME 1 1 WILLIAMS,J.

COPIES LTTR ENCL 1 1 INTERNAL: ACRS AEOD/SPD/RRAB NRR/DE/EELB NRR/DORS/OEAB NRR/DRCH/HICB NRR/DRSS/PRPB NRR/DSSA/SRXB RES/DSIR/EIB 1 1 1 1 1 1 1 1 1 1 2 2 1 1 1 1 QO~ROAB/=DS~

FIXATE CENTER/D EMEB NRR/DRCH/HHFB NRR/DRCH/HOLB NRR/DSSA/SPLB NRR/PMAS/IRCB-E RGN2 FILE 01 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 EXTERNAL'EG&G BRYCE i J H NOAC MURPHY,G.A NRC PDR 2 2 L ST LOBBY WARD 1 1 NOAC POORE,W.1 1 NUDOCS FULL TXT 1 1 1 1 1 1 NOTE TO ALL RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE iVASTE!CONTACI'THE DOCL'MENT CONTROL DESK.ROOKI Pl-37 (EXT.504-2083)TO ELDIINATE YOI.'R BLAME PRO~I DISTRIBUTION LISTS I'OR DOCL'MENTS YOU DON"I'L'ED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF-COPIES REQUIRED: LTTR 27 ENCL 27 4>f I Tennessee Vattey Avthorlty.,Post Office Box 2000.Decatur, Atabama 35609-2000 R.D.(Rick)Machon Vice President, Browns Feny Mtctear Rant September 29, 1994 U.S.Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C.20555'

Dear Sir:

10 CFR 50.73 BROWNS FERRY NUCLEAR PLANT (BFN)-UNITS 1g 2p AND 3-DOCKET NOS~50-259~50-260'ND 296-FACILITY OPERATING LICENSE DPR-33~52@AND 68-LICENSEE EVENT REPORT 50-260/94006 The enclosed report provides details concerning a loss of instrumentation input logic for the plant's Division I Emergency Core Cooling System caused by a fault (i.e., short)in the Analog Trip Unit inverter silicon controlled rectifier.

The inverter supply breaker tripped as a result of the short.The.report is submitted pursuant to 10 CFR 50.73(a)(2)(i)(B), and 50.73(a)(2)(vii).

Section VII of the enclosure describes the.commitment made in this report.Sincerely, Site ce President Enclosure cc: See page 2 9410050054 94092'st PDR'DOCK 05000260 S PDR 4l U.S.,Nuclear Regulatory Commission Page 2 September 29, 1994 cc,(Enclosure):

INPO Records'Center Suite 1500 1100 Circle 75 Parkway Atlanta, Georgia 30339 Paul Krippner.American Nuclear Insurers Town Center, Suite 300S: 29 South Main Street West Hartford, Connecticut 06107 ,NRC Resident Inspector Browns Ferry Nuclear Plant.Route 12, Box 637 Athens, Alabama 35611 Regional Administrator U.S.Nuclear Regulatory Commission Region II 101 Marietta Street,-NW, Suite 2900 Atlanta, Georgia 30323 Mr.J.F,.Williams, Project Manager U.S.Nuclear Regulatory Commission

'One White Flint, North 11555 Rockville Pike Rockville, Maryland'20852 4l 1'I I NRC FORM 366 ,(5-92)U.S.NUCLEAR REGULATORY C(NIIISSION APPROVED BY (X(B NO.3150-0104 EXPIRES 5/31/95 LICENSEE EVENT REPORT (LER)(See reverse, for required number of digits/characters for each block)EST IHATED BURDEN PER RESPONSE TO COHPLY WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS.FORWARD COHHENTS REGARDING BURDEN ESTIMATE TO THE INFORHATION AND RECORDS MANAGEMENT BRANCH (HNBB 7714), U.S.NUCLEAR REGULATORY COHMISSIQN, WASHINGTON, DC 20555-0001 AND TO THE PAPERWORK REDUCTION PROJECT (3140.0104), OFFICE OF MANAGEHENT AND BUDGET WASHINGTON DC 20503.FACILITY NAHE (1)Browns Ferr Nuclear Plant BFN Unit 2 DOCKET NINGIER (2)05000260 PAGE (3)1 OF 6 TITLE (4)Entry into Technical Specification 1.C.1 due to a loss of Emergency Core Cooling System Division I instrumentation from a short in the Analog Trip Unit Inverter EVEN DATE 5 LER NINBER 6 REPORT DATE 7 OTHER FACILITIES INVOLVED 8 HONTH DAY YEAR 08 31'4 YEAR 94 SEQUENTIAL HUHBER 006 REVISION NUMBER 00 09 29 MOHTH DAY YEAR 94 FACILITY NAHE N/A FACILITY NAME'N/A DOCKET NUHBER DOCKET NUMBER OPERATING ,MCDE (9)N THIS REPORT IS SUBMITTED PURSUANT 20.402(b)-

e 11 TO THE REQUIREMENTS OF 10 CFR: Check one or mor 20.C05(c)73.71(b)50.73(a)(2)(iv)

POWER LEVEL (10)93 20.405(a)(1)(i) 20.405(a)(1)(ii) 20.405(a)(1)(iii) 20.405(a)(1)(iv)

'0.405(a)(1>(v) 50.36(c)(1) 50.36(c)(2) 50.73(a)(2)(i)(B) 50.73(a)(2)(ii) 50.73(a)(2)(iii)

LICENSEE CONTACT FOR THIS LER 12 50.73(a>(2)(v) 50.73(a)(2)(vii) 50.73(a)(2)(viii)(A) 50'3(a)(2)(viii)(B) 50.73(a)(2)(x) 73.71(c)OTHER (Specify in Abstract below and in Text, NRC Form 366A NAHE Clare S.Hsieh, Compliance Engineer TELEPHONE HUHBER (Include Area Code)(205)729-2635 4 C(NPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 13 CAUSE STSTEH X AD SCR A080 COHPONENT MANUFACTURER REPORTABLE TO NPRDS N CAUSE SYSTEH COMPONENT MANUFACTURER REPORTABLE TO NPRDS X AD.INVT N431 SUPPLEMENTAL REPORT EXPECTED 1C YES (I f yes,-conpiete.

EXPECTED SUBHISSION DATE)~X NO EXPECTED SUBMISSION DATE (15)HONTH DAY YEAR ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)(16)On August 31, 1994, at 1248 hours0.0144 days <br />0.347 hours <br />0.00206 weeks <br />4.74864e-4 months <br /> CDT, at approximately 93 percent power, control room operators received alarms that indicated a loss of Unit 2, Division I Emergency Core Cooling Systems (ECCS)instrumentation.

The operators declared Division I of ECCS instrumentation inoperable and entered Technical Specification (TS)1.C.1 (i.e., Standard TS 3.0.3)which requires that the UIIit be placed in Hot Standby within six hours and Cold Shutdown within 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.Troubleshooting determined that the event was initiated from a shorted Silicon Controlled Rectifier (SCR)in the ECCS Division I, Analog Trip Unit (ATU)inveiter.The short caused the inverter supply breaker to trip, which resulted in a loss of power to the inverter and loss of input logic signals from the affected systems to the control room instrumentation.

TVA determined the root cause to be a random failure of the, inverter.Contributing to the event is the ECCS ATU design which lends itself to the loss of an entire ECCS division from a single component failure.The ATU inverter was repaired by replacing the shorted SCR, and a search of previous similar events has not found any other incidents with the same root cause.TVA will evaluate the present design on the ECCS ATU power distribution to determine if design enhancements can be made.NRC FORM (-)

NRC FORH 366A (5-92)U.S.NUCLEAR REGULATORY CQNIISS ION LICENSEE EVENT REPORT TEXT CONTINUATION APPROVED BY (NS NO.3150-0104 EXPIRES.5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY UITH THIS INFORMATION COLLECTION REOUEST: 50.0 NRS.FORUARD COMHENTS REGARDING BURDEH ESTIMATE TO THE INFORMATION AND RECORDS MANAGEHENT BRANCH (HNBB 7714), U.S.NUCLEAR REGULATORY COMHISSION, NASNINGTON, DC 20555-0001, AND TO THE PAPERlJORK REDUCTION PROJECT (3150 0104), OFFICE OF MANAGEHENT AND BUDGET, NASHINGTON DC 20503 FACILITY NAKE (1)DOCKET NlÃBER (2)LER NWSER (6)YEAR, SEQUENTIAL REVISION NUHBER NUMBER PAGE (3)Browns Ferry Unit 2 05000260 94 006 00 2 of 6 TEXT If more s ce is r uired use edd tionsl co ies of NRC Form 366A (17)Z~PLANT CONDZTIONS Unit 2 was in end-of-cycle coastdown at approximately 93 percent power (3080 megawatts thermal).Units 1 and 3 were shutdown and defueled.ZI.DESCRIPTION OF EVENT A.Events On August 31, 1994, at 1248 hours0.0144 days <br />0.347 hours <br />0.00206 weeks <br />4.74864e-4 months <br /> Central Daylight Time (CDT), the Unit 2 Control Room operators received alarms that indicated a loss of Division I Instrumentation for the plant's Emergency Core Cooling System (ECCS).High Pressure Coolant Injection (HPCI)and Reactor Core Isolation Cooling (RCZC)steam flow, reactor level and pressure, and drywell pressure input signals were lost to the instrumentation logic for the following ECCS subsystems:

~HPCI[BJ]~RCIC[BN]~Core Spray (CS), Division I[BG]~Anticipated Transient Without Scram (ATWS), Division.I[JC]~Residual Heat Removal (RHR), Division I[BO]~Automatic Depressurization System (ADS),,Division I[JC]Additionally, instrumentation which operates the suppression pool to Reactor Building Vacuum Breakers[VB]was rendered inoperable.

ECCS Division ZZ instrumentation remained operable and was available for initiation of both divisions of the affected systems with the exception of RCIC, which had also lost power to its flow controller.

The event did not require plant operators to take any actions other than initiation of troubleshooting activities.

Plant operators declared the subsystems or division of subsystems inoperable.

Because there was no single TS (Technical Specifications)

Limiting Conditions for Operation (LCO)which enveloped the event, plant operators entered TS 1.C.1 (i.e., Standard TS 3.0.3).TS 1.C.l requires the unit be placed in Hot Standby within six hours and Cold Shutdown within 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

Il Qi NRC FORM 366A (5-92)U.S.NUCLEAR REGULATORY LXSIIISSION LICENSEE EVENT REPORT TEXT CONTINUATION APPROVED BY (NS NO 5150-0104 EXPIRES 5/31/95 ESTIMATED BURDEH PER RESPONSE TO COMPLY IJITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS.FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT SRANCH (MHBB 7714), U.S.NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001, AHD TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON DC 20503 FACILITY NiULE (1)Browne Ferry Unit 2 DOCKET NLNLSER (2)05000260 TEAR 94 LER NLNBER (6)SEQUEN1'IAL NUMBER 006 REVISION NUMBER 00 PAGE (3)3 of 6 TEXT If more s ce is r uired use sdditionaL co ies of NRC Form 3 66A (17)Troubleshooting of the ECCS Division I Instrumentation logic determined that the event was initi.ated from a short in the ECCS Division I, Analog Trip Unit (ATU)inverter Silicon Controlled

'ectifier (SCR).The short caused the inverter supply breaker to trip, resulting in a loss of power supply to the ATU inverter and loss of input logic signals from the affected systems to the control room instrumentation.

TVA repaired the inverter by replacing the shorted SCR and declared the associated instruments and systems operable at 1350 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.13675e-4 months <br /> on August 31, 1994.TS 1.C.1 was exited before having to initiate actions required to achieve Hot Standby.TVA determined this event to be reportable pursuant to 10 CFR 50.73(a),(2)(i)(B) as a condition prohibited by TS due to entry into TS 1.C.l.Additionally, this event is reportable in accordance with 10 CFR 50.73(a)(2)(vii) as any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems.B.Zno erable Structures Com onents or S stems that, Contributed to the Event!None.C.Dates and A roximate Times of Ma or Occurrences:

August 31, 1994 at 1248 CDT Division I ECCS Instrumentation was lost due to a short in the ATU inverter SCRI LCO 1.C.1 was entered.1336 CDT 1350 CDT The ATU inverter was repaired;Division I ECCS ATU inverter was reeneigized.

Associated instruments and systems were declared operable;LCO 1.C.1 was exited.

NRC FORH 366A (5-92)U.S NUCLEAR REGULATORY CQIII SS I ON LICENSEE EVENT REPORT TEXT CONTINUATION APPROVED BY (HBI" NO.3150-0104 EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE TO COHPLY llITH THIS INFORHATIOII COLLECTION REQUEST: 50.0 HRS~FORWARD COHHENTS REGARDING BURDEN'ESTIHATE TO THE INFORNATION AND RECORDS HANAGEHEHT BRANCH (HNBB 7714), U.S.'NUCLEAR REGULATORY COHHISSION, WASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF NANAGEHEHT AND'BUDGET,'WASHINGTON, DC 20503 FACILITY NAHE (1)DOCKET NINBER (2)LER NLSSER (6)YEAR SEQUEHT IAL REVI SI OH HUNGER HUNGER PAGE (3)Browns Ferry Unit 2 05000260 94 006 00 4 of 6 TEXT If more s ce is r ired use additions(co ies of NRC Form 366A (17)DE Other S stems or Seconda Functions Affected'one.

E.Method of Discove This event was immediately discovered at 1248 hours0.0144 days <br />0.347 hours <br />0.00206 weeks <br />4.74864e-4 months <br /> on August 31, 1994, when control room alarms indicated ECCS Division I instrumentation problems.Primary among the alarms received was the ECCS ATU Trouble Alarm.F.0 erator Actions: There were no TS safety system initiations required of control room operators.

The steps taken to identify the problem and initiate maintenance actions were appropriate.

0.Safet S stem Res onses: None.ZIZZ CAUSE OF THE EVENT A.Immediate Cause: The immediate cause of the event was due to a short in the SCR of the ECCS Division I, ATU.inverter.

B.Root Cause:.'TVA determined that the root cause was a random failure of the ECCS Division I, ATU inverter.The short in the ATU inverter SCR caused the inverter supply breaker to trip.C.Contributin Factors: The design of the ECCS ATU power supply system lends itself to the loss of an entire division of ECCS instrumentation from a single component failure.,Each ECCS ATU power distribution panel is fed from a 250 VDC reactor motor-operated-valve board through an ATU inverter to two 24 VDC redundant power supplies.This inverter is a single failure point.The loss of an ATU inverter results in the loss of an entire division of ECCS instrumentation.

i(i V NRC FORM 366A (5-92)U.S.NUCLEAR REGULATORY C(HBIISSIOH LICENSEE EVENT.REPORT TEXT CONTINUATZON APPROVED BY (NS NO.3150-0104 EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY llITH THIS INFORMATION'OLLECTION REQUEST: 50.0 HRS.FORHARD COMMENTS REGARDIHG BURDEH ESTIMATE TO THE INFORMATION AHD RECORDS MANAGEMENT BRANCH (MHBB 7714), U.S.NUCLEAR REGULATORY COMMISSION/

NASHINGTON, DC 20555-0001, AND TO THE PAPERNORK REDUCTION'ROJECT (3150-0104), OFFICE OF MANAGEMENT AHD BUDGET, HASHINGTON, DC 20503 FACILITY NAME (1)DOCKET NLBIBER (2)YEAR LER IRNBER (6)SEQUENTIAL

'EVISION NUMBER NUMBER PAGE (3)Browns Ferry Uni.t 2 05000260 94 006 00 5 of 6 TEXT If more s ce>s r uired use additions(co ies of HRC Form 3 66A (17)IV.ANALYSIS OF THE EVENT This event did not result in any plant transient described in the BFN FS&, Chapter 14 accident analyses nor did it adversely affect the health and safety of plant personnel or the public.The short in the ECCS'Division I, ATU inverter SCR caused the inverter supply breaker to trip, resulting in a loss of power supply to the inverter and loss of RCIC and HPCI steam flow, reactor level and pressure, and drywell pressure input signals from the HPCI, RCIC, CS, RHRg ATWS~ADS, and vacuum breakers to their respective i.nstrumentati.on logic systems.However, Division ZI instruments remained operable during the event and were available to Control Room operators for initiation of both divisions.

The rel'iabi.lity and redundancy of the controls and instrumentation for the ECCS ensure that no failure of a single initiating sensor would either prevent or falsely start the initiation of these cooling systems.Additionally, no single control failure prevents the combined cooling systems from providing the core with adequate cooling.V.CORRECTIVE ACTIONS A.Immediate Corrective Actions: TVA repaired the ECCS Division I, ATU inverter by replacing the shorted SCR in the inverter.B.Corrective Actions ta Prevent Recurrencel A search of TVA trending databases has not found any other previous SCR failures.Thus, TVA considers this failure to be a random event.Preventive Maintenance (PM)inspections are currently performed on the ATU inverter in accordance with vendor recommended guidelines.

These PM inspecti:ons include calibration of the meters, cleaning of the inverter internals, maintenance of the circuit breakers, insulation testing of the transformer and inductor coi.ls, and visual inspections of the inverter components.

Additionally, the electrolytic capacitors of the inverter are replaced periodically.

Since this event affected an entire division of ECCS instrumentation from the loss of an ATU inverter, TVA will evaluate the present design of the ECCS ATU power distribution to determine i.f design enhancements can be made.

l C 4l gi L II/~~,

NRC FAtH 3t4h (5-92)U.S.NUCLEAR REGULATORY CDIIISSION LICENSEE EVENT REPORT TEXT CONTINUATZON APPROVED BY (HEI NO.3150-0104 EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE TO COHPLY MITH THIS INFORMATION COLLECTIOH RE(tUEST: 50.0 HRS.FORNARD COHHEHTS REGARDING BURDEH EST IHATE TO THE IHFORHATI OH AND RECORDS HANAGEHENT BRANCH (HNBB 7714), U.S.NUCLEAR REGULATORY COHHISSIOH, llASHINGTOH, DC 20555-0001, AND TO THE PAPERNORK REDUCTION PROJECT (3150 0104)~OFFICE OF HANAGENEHT AND BUDGET~'WASHINGTOH DC 20503 FACILITY NAHE (1)'Browns Ferry Unit 2 DOCKET NIHIBER (2)05000260 LER NIMBER (6)YEAR SEQUENTIAL REVI SIOH NUHBER HUNGER 006 00 94 PACE (3)6 of 6 TEXT If more s ce is r ired use edditionet co ies of NRC Form 366A (17)VIE ADDITIONAL INFORMATION Ar Failed Com onentsI~SCR, 1 kV, 68 Amp, 15 microsecond, Part No.TD42F1000, Manufactured by AEG-Telefunken

~ATU Znverter, Part No.6841310, Manufactured by HDR Power Systems, Znc.B.Previous LERs on Similar Events: TVA has reviewed previous BFN LERs to determine if similar events have occurred.There have been previous LERs involving the loss of an ECCS ATU inverter (i e~LERs 260/83028 260/83034@

260/94001).

However, none of the previous LERs resulted from a shorted SCR.VII.Commitments

+A will evaluate the present design on the ECCS ATU power distribution to determine if design enhancements can be made.This evaluation will be completed by November 30, 1994.Energy Industry Identification, System (EIIS)system and component codes are identified in the text with brackets (e.g., (XX]).

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