ML18036B220

LER 93-001-00:on 930228,unplanned Actuation of ESF Occurred When 3 DGs Automatically Fast Started.Caused by Inappropriate Personnel Action.Licensee Will Replace Damaged CAS Logic Cable & Will Submit Followup rept.W/930329 Ltr

ML18036B220
Person / Time
Site:	Browns Ferry
Issue date:	03/29/1993
From:	Austin S, Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-001-03, LER-93-1-3, NUDOCS 9304020323
Download: ML18036B220 (16)

Text

ACCEI ERA ED DOCUMENT DISTRIBUTION SYSTEM REGUL. RY INFORMATION DISTRIBUTI SYSTEM (RIDS)

ACCESSION NBR..9304020323 DOC.DATE.-93/03/29 NOTARIZED..NO DOCKET ¹ FACIL:50-296 Browns Ferry Nuclear Power Station, Unit 3, Tennessee 05000296 AUTH. NAME AUTHOR AFFILIATION AUSTIN,S.W.. Tennessee Valley Authority ZERINGUE,O.J. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 93-001-00:on 930228,an unplanned actuation of ESF occurred when 3 DGs automatically fast started. Caused by inappropriate personnel action. Licensee will replace damaged CAS logic cable & will submit followup rept.W/930329 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR t ENCL TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

i SIZE:

NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL lD CODE/NAME LTTR ENCL D PD2-4 1 1 HEBDON,F 1 1 WILLIAMS,J. 1 1 D INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DE/EELB 1 1 NRR/DE/EMEB 1 1 NRR/DORS/OEAB 1 1 NRR/DRCH/HHFBHE 1 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 1 NRR/DRIL/RPEB 1 1 NRR/DRSS/PRPB 2 2 NRR DISA SPLB 1 1 NRR/DSSA/SRXB 1 1 E~ILM 02 1 1 RES/DSIR/EIB 1 1 RGN2 FILE Ol 1 1 EXTERNAL'G&G BRYCE F J ~ H 2 2 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC POORE,W. 1 1 NUDOCS FULL TXT 1 1 D

D D

NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 504-2065) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 32 ENCL 32

II I~

I

Tennessee vatley,Atttttonty post office Box 2000 Decatv'tatyatna 35609-2000 O. J. Ike" Zeringue vicv i Io'oi' < ~ otyn,lby'4, ty e v BAR 29 1993 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

Dear Sir:

TVA BROWNS FERRY NUCLEAR PLANT (BFN) UNITS 1, 2, AND 3 DOCKET NOS. 50-259, 260, AND 296 FACILITY OPERATING LICENSE DPR-33, 52, AND 68 LICENSEE EVENT REPORT LER 50-296/93001 The enclosed report provides detai'ls concerning an unexpected auto-start of the Unit 3 diesel generators.

This report is submitted in accordance with 10 CFR 50.73(a)(2)(iv).

Sincerely, J. Zeringue Enclosure cc: See page 2 nanna~

9304020323 930329 PDR S

ADOCK 05000296 PDR P/ I

2 t U.S. Nucl'ear Regulatory Commission

~N 29 Bgg 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, P.O. Box 637 Athens, Alabama 35609-2000 Regional Administrator U.S. Nucle'ar Regulatory Commission Region II 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323 Thierry M. Ross U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852

I~

NRC Form 366 . NUCLEAR REGULATORY COHMISSION Approved OHB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

FACILITY NAME (1)

Brwn Frr TITLE (4) Unexpected N 1 rPl n BFN Auto-Start of Unit ni 3 Diesel Generators.

2'0F IDOCKET NUHBER (2) I PA E 0

EVENT DAY 5 LER NUMBER 6 REP RT DATE 7 THER FACILITIE INV LVED 8 I I I, I I SEQUENTIAL I I REVI SION I I I I FACILITY NAMES )DOCKET NUHBER(S)

HONTH DAY YEAR YEAR NUHBER N MBER MONTH DAY YEAR Br wns F rr ni 1 2 5 I I I I I I I I I I I I 2 2 8 3 0 0 1 0 3 9 9 3 N/A OPERATING [THIS REPORT IS SUBMITTED PURSUANT TO THE RE()UIREHENTS OF 10 CFR $:

HODE Check one or more of the foll win ll 9 N l20 402(b) (20.405(c) ]X )50.73(a)(2)(iv) [73 '1(b)

POWER f (20.405(a)(l)(i) [50.36(c)(1) f (50.73(a)(2)(v) (73.71(c)

LEVEL )20.405(a)(l)(ii) (50.36(c)(2) ) (50.73(a)(2)(vii) ]OTHER (Specify in 10 0 0 0 (20.405(a)(l)(iii) (50.73(a)(2)(i)(B)/ /50.73(a)(2)(viii)(A) / Abstract below and in (20.405(a)(1)(iv) /50.73(a)(2)(ii) f /50.73(a)(2)(viii)(B) [ Text, NRC Form 366A) 20.4 5 a 1 v 0.73 a 2 iii .7 2 x LICENSEE CONTACT FOR THIS LER 12 NAME TELEPH NE N MBER i AREA CODE Steven W. Aus in om liance En ineer 2 0 5 7 2 9 - 2 0 7 '0 C HPLETE ONE LINE FOR EACH COMPONENT FAILURE DES RIBED IN THIS REPORT 1 I I I IREPORTABLEI I I

'I I IREPORTABLEI CAUSE SYSTEM COMPONENT MANUFACTURER TO NPRD CAUSE SY TEH COMPONENT MAN FACTURER TO NPRDS SUPPLEMENTAL REPORT EXPECTED 14 EXPECTED I NTH DAY YEAR I I SUBHI S SION I I I YES If e om 1 EXPECTED UBMI I N DATE X NO DATE 1 ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

On February 28, 1993, at 1243 hours0.0144 days <br />0.345 hours <br />0.00206 weeks <br />4.729615e-4 months <br /> an unplanned actuation of an Engineered Safeguard Feature occurred when Emergency Diesel Generators (EDG) 3A, 3B, 3C and 3D automatically fast started, accelerated to full speed and rated voltage. The EDGs remained running and, because no undervoltage signal existed, did not tie onto their respective 4kV shutdown boards.

TVA believes the root cause of this event was an inappropriate personnel action.

Specifically, the cable that connects the Unit 1 accident signal logic initiating relay to Common Accident Start (CAS) circuits in 4kV Shutdown Board 3EC was partially severed. TVA identified an area on the CAS logic cable where a sharp object struck the cable with enough force to sever one conductor and cutting into another thus, shorting the two conductors and causing the EDGs to start.

TVA will replace the damaged CAS logic cable. Furthermore, TVA will continue to investigate the cause of the inappropriate personnel action and if necessary, will submit a followup report.

NRC Form 366(6-89)

il 0 NRC Form 356A .S. NUCLEAR REGULATORY Approved OMB No. 3150-0104 (6-09) COMMISSION'ICENSEE Expires 4/30/92 EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1) IDOCKET NUMBER (2) LER NUMBER PA E I (SEQUENTIAL /'REVISION/ (

Browns Ferry Unit 3 .I YEAR NUMBER NUMBER 2 1 2 F 5 TEXT (If more space is required, use additional NRC Form 366A's) (17)

I. PLANT CONDITIONS Unit 2 is defueled and in the Unit,2 cycle 6 refueling. outage. Units 1 and 3 were shutdown and in a defueled condition.

II. DESCRIPTION OF EVENT A. Event:

On February 28, 1993, at 1243 hours0.0144 days <br />0.345 hours <br />0.00206 weeks <br />4.729615e-4 months <br /> an unplanned actuation of an Engineered Safeguard Feature (ESF) [JE] occurred when Emergency Diesel Generators (EDG) [EJ] 3A, 3B, 3C, and 3D automatically fast started and accelerated to full speed and rated voltage. The EDGs remained running and, because no undervoltage signal existed, did not tie onto their respective 4kV shutdown boards [EB].

At approximately 1255 hours0.0145 days <br />0.349 hours <br />0.00208 weeks <br />4.775275e-4 months <br />, personnel (utility licensed and nonlicensed) were dispatched .to each 4kV shutdown board and the Auxiliary Instrument Room to observe the state of the auto-start logic and Common Accident Start (CAS) [RLY]'ogic relays. No abnormalities were identified by these observations.

At 1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br /> the EDGs were shutdown returning them to standby readiness.

TVA,reports this event in accordance with 10 CFR 50.73(a)(2)(iv), as an event or condition that resulted in manual or automatic actuation of an ESF, including the reactor. protection system.

B. Ino erable Structures Com onents or S stems that Contributed to the Event:

None.

NRC Form 366(6-89)

Il NRC Form 366A Approved OMB No. 3150-0104 (6-89)

Expires 4/30/92 LICENSEE EVENT 'REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1) IDOCKET NUMBER (2) LER NUMBER PAE 3 I I I I SEQUENTIAL I IREVISIONI I I I I Browns Ferry Unit 3 l YEAR N MBER N MBER 000 2 6 3 1 0 0 I I F

I I 5

TEXT (If more space is required, use additional NRC Form 366A's) (17)

C. Dates and A roximate Times of Ma or Occurrences:

February 28, 1993 at 1243 Emergency Diesel Generators 3A, CST 3B, 3C, and 3D fast started-.

February 28, 1993 at 1530 Emergency Diesel Generators 3A, CST 3B, 3C, and 3D were returned to standby readiness.

February 28, 1993 at 1540 TVA makes a four hour CST nonemergency notification to NRC in accordance with 10 CFR 50.72(b)(2)(ii).

D. Other S stems or Seconda Functions Affected:

None.

E. Method of Discove The start of the EDGs was identified by Unit 3 Main Control Room operator when he received alarms indicating EDG start.

F. 0 erator Actions:

None.

G. Safet S stem Res onses:

None.

III. CAUSE OF THE EVENT A. Immediate Cause:

4 The immediate cause of this event was an automatic start of EDGs 3A, 3B, 3C, and 3D. The cable that connects the Unit 1 Common Accident Signal logic initiating relay to CAS circuits in 4kV Shutdown Board 3EC was partially severed between the Unit 1 Auxiliary Instrument Room and 4kV Shutdown Board 3EC. A walkdown of the cable routing identified an area on the cable where a sharp object, struck the cable with enough force to penetrate one conductor and cut into another, thus shorting the two conductors together. This produced the same effect as closing the contacts on the Unit 1 Common Accident Signal logic initiating relay causing the CASB-1 relay to close which ultimately started the EDGs.

NRC Form 366(6-89)

Cl NRC Form 366A 0U.S. NUCLEAR REGUlATORY COHHISSION

~ Approved OHB No. 3150-0104 (6-69) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1) IDOCKET NUMBER (2) LER N MBER PA E I I I I SEQUENTIAL I I REVIS ION I I I I I Browns Ferry Unit 3 l YEAR NUMBER NUMBER I I I I 2 1 4 F TEXT (If more space is required, use additional NRC Form 366A's) (17)

B. Root Cause:

TVA believes the root cause of this event was an inappropriate personnel action. TVA was performing significant work activities related to the Unit 2, Cycle 6 refueling outage in Cable Spreading Room A which was where the damage to the cable was located. These activities involved conduit and cable modifications. TVA believes that it was during these activities the cable damage occurred.

C. Contributin Factors:

None.

IV. ANALYSIS OF THE EVENT The EDGs are the standby AC power system that provide a highly reliable source of power as required for Emergency Core Cooling Systems. The EDGs ensure no single credible event can disable the core standby cooling [BM] functions or their supporting activities.

During the event, all units were defueled and secondary containment was not required. Therefore minimal equipment was required to be operable.

All safety,-related components operated as expected during the event.

Therefore, the safety of the plant, its personnel, and the public was not compromised.

V. CORRECTIVE ACTIONS A. Immediate Corrective Actions:

At the onset of the event, Operations and Technical Support personnel went to each 4kV shutdown board to observe the state of each EDG auto-start relays. From this observation they found that no start signal was present for any of the four EDGs. Personnel then went to the Unit 2 auxiliary instrument room to observe the relays associated with CAS start logic. No deficiencies were identified by this observation. Finally, the CAS logic circuits were checked for presence of grounds and none were identified.

NRC Form 366(6-89)

NRC Form 366A NUCLEAR REGULATORY COHHISSION Approved OHB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT COttTIt<UATION FACILITY NAME (1) IOOCKET NUMBER (2)

I /SEQUEttTIAL / /REVISIOtt/

Browns Ferry Uni t 3 I N M I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

After completion of the initial investigation, TVA initiated a troubleshooting work order that placed inhibiting boots on the CAS relay contact for each of the four EDGs thus preventing unnecessary starts of EDGs. Placement of the inhibiting boots on the CAS relays allows auto-start from the undervoltage and degraded voltage relays. Each EDG was then shut down returning it to standby readiness state, without further complications. Furthermore, utilizing the same work order, TVA installed a brush recorder to monitor the EDG start circuits for possible spurious actuation signals.

t v t t v t

1. TVA will replace the damaged CAS logic cable.

2. TVA will continue to investigate the cause of the inappropriate personnel action and if necessary, will supplement this report.

VI. ADDITIONAL.INFORNATION A.

None.

B. v LER 1 Ev t TVA has previously issued LERs detailing unanticipated starts of the EDGs. In these reports the root cause has been attributed to personnel error, equipment malfunction, or an actual degraded voltage condition.

TVA concluded that the recurrence controls established by these reports was adequate to minimize recurrence.

VII. COMMITMENTS TVA will replace the damaged CAS logic cable. TVA intends to complete this prior to restart of Unit l.

Energy Industry Identification System (EIIS) codes are identified in the text as [XX].

NRC Form 366(6-89)

!5 II, l