ML18033B652

LER 91-001-00:on 910201,unplanned Actuation of ESF Occurred Due to Deenergization of Reactor Protection Sys Bus 3A. Caused by Tripping of Reactor Protection Sys Circuit Protector 3A2.Protector replaced.W/910301 Ltr

ML18033B652
Person / Time
Site:	Browns Ferry
Issue date:	03/01/1991
From:	Bynum J, Hsieh C TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-001-04, LER-91-1-4, NUDOCS 9103110026
Download: ML18033B652 (12)

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j REGULATORY INFORMATION -DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:,9103110026 DOC. DATE: 91/03/01 NOTARIZED: NO DOCKET ¹ FACIL:50-296 Browns Ferry Nuclear Power Station, Unit 3, Tennessee 05000296 AUTH. NAME AUTHOR AFFILIATION HSIEH, C S. Tennessee Valley Authority BYNUM,J.R. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 91-001-00:on 910201,unplanned actuation of ESF occurred due to deenergization of reactor protection sys bus 3A.

Caused by tripping of reactor protection sys circuit protector 3A2.Protector replaced.W/910301 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR 5 TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

ENCL SIZE:

NOTES:1 Copy each to: S. Black,B.WILSON 05000296 RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL KREBS,M. 1 1 HEBDON,F 1' ROSS,T. 1 1 INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 2' NRR/DET/ECMB 9H 1 1 AEOD/ROAB/DSP'RR/DET/EMEB 7E, 1 1 NRR/DLPQ/LHFBll 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB 8D 1 1 NRR/DST/SICB 7E 1 1 1 1 NRR/DST/SRXB 8E 1 1 1 1 RES/DSIR/EIB 1 1 RGN2 FILE'1 1 1 EXTERNAL EG&G BRYCE g J ~ H 3 3 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MAYS,G 1 1 NSIC MURPHY,G.A 1 1 NUDOCS FULL TXT 1 1 NOTES 5 5 NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE ~VASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079), TO ELIMINATEYOUR NAME FROiVI DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

FULL 'TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 38 ENCL 38

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Tennessee Vaitey Avthority, 1101 Market Street, Chattanooga. Tennessee 37402 Joseph R. Bynum

'Vice President, hltrctear Operations MAR '0 i 1Q9l U.S. Nuclear Regulatory Commission ATTN: Document Control 'Desk Washington, D.C. 20555

Dear Sir:

TVA BROWNS FERRY NUCLEAR PLANT (BFN) 'UNIT 3 DOCKET NO. 50-'96 FACILITY OPERATING LICENSE DPR-68 REPORTABLE OCCURRENCE REPORT BFRO-50-296/91001 The enclosed report provides details concerning the deenergization of a reactor protection system bus caused by failure of an -overvoltage voltage monitor. This report is submitted in accordance with 10 .CFR 50.73(a)(2)(iv).

Very truly yours, TENNESSEE VALLEY AUTHORITY R. Bynum Enclosure cc: see page 2 910311OVZC Y108Vl PDR ADOCK 05Q00296 S . PDR

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2 U.S. Nuclear Regulatory Commission MAR Oi >ss>

cc (Encclosure):

INPO Records Center

'Suite 1500 1100 Circle 75 Parkway Atlai>ta, Georgia 30339 NRC Resident Inspector, BFN Regional Administration U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region II 101 Mar'ietta Street, Su'ite 2900 Atlanta, Georgia 30323 Thierry M. Ross U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockvil'le Pike Rockville, Maryland 20852

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(6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

FACILITY NAME (1) w 1 lDOCKET NUMBER (2) l~gf~

TITLE (4) Deenergization of reactor protection system bus by normal supply circuit protector operations caused v

I I I I I SE()UEttTIAL IREVISIONI I I I FACILITY NAMES IDOCKET NUMBER(S) w

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0 OPERATING lTHIS REPORT IS SUBMITTED PURSUAtiT TO THE REQUIREMENTS OF 10 CFR It:

MODE l~l50.73(a) (2) (iv) '73.71(b)

POWER I l20.405(a) (1) (i) l50.36(c) (1) l50.73(a)(2)(v) l73.71(c)

LEVEL I l20.405(a)( 1)(ii) '50.36(c)(2) l50.73(a)(2)(vii) lOTHER (Specify in l20.405(a)( 1)(iii) l l50.73(a)(2)(i) l50.73(a)(2)(viii)(A) l Abstract below and in l20.405(a)( l)(iv) ( l50.73(a)(2)(ii) l50.73(a)(2)(viii)(B) l Text, NRC Form 366A) l AREA CODE l

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IREPORTABLEI I I I I SUBHISSION I I I m D ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

At 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br /> on February 1, 1991, an unplanned actuation of engineered safety features (ESFs) occurred on Browns Ferry Unit 3. The actuations occurred because Unit 3 reactor protection system (RPS) bus 3A was deenergized. ESFs affected by this event include standby gas treatment system, control room emergency ventilation system, and Unit 3 primary containment isolation system. The actuated plant systems responded as expected to the loss of the RPS bus.

The RPS bus deenergization resulted from the tripping of RPS circuit protector 3A2.

Troubleshooting revealed that the internal voltage monitor (Diversified Electronics UOA-0267) of the circuit protector had failed.

The root cause of this event was a random component failure of the circuit protector overvoltage voltage monitor. The type of voltage monitor that failed in this event had no history of any previous failures.

The faulty component was identified and replaced. TVA has contacted the vendor to arrange for an evaluation of the failed voltage monitor.

NRC, Form 366(6-89)

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'(6-89) Expires 4/30'/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NANE (1)

I ) SEQUENTIAL / i REVISION)

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

At 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br /> on February 1', 1991, an unplanned actuat'ion of engineered safety features (ESFs) occurred on Browns Ferry Unit 3. The,actuations occurred because Unit 3 reactor protection system (RPS), [JC] 'bus 3A was deenergized.

ESFs affected, by this event include standby gas treatment system [BH], control room emergency ventilation system [VI], and Unit 3 primary containment isolation system [JM]. Additional system .actuations that normally would have occurred were removed from service in the performance of a periodic operation instruction.. The actuated plant systems responded as expected to the. loss of the RPS bus.

The RPS bus deenergi'zation. resulted from the tripping of RPS circuit, protector 3A2. (Circuit protector 3Al was found to be operating normally.) The tripping of 3A2 removed the normal power supply, motor generator (MG) set 3A, from RPS bus 3A. 'The RPS bus was reenergized by connecting it,to the alternate power supply, a regulating transformer, and the affected'solations/actuations were reset.

The power output of the MG set was checked for any evidence of power disturbances that would require circuit protector operation. No power

,disturbances were identified nor any abnormalities found upon visual inspecti.on of the circuit protector. However, additional troubleshooting revealed that the internal'oltage monitor (Divers'ified Electronics UOA-0267) of the circuit protector had failed.

All three units were shutdown and defueled at the time of this event. No fuel handling or operations over spent, fuel were in progress. during thi's event. The unplanned actuations of the ESF systems are reportable, in accordance with 10 CFR 50.73(a)(2)(iv).

The systemsaffected during this event are designed to shut down the reactor, contain and process any radioactive releases, and to fulfill their safety functions upon loss of initiation logic power. The systems- responded correctly to the loss of power; therefore, plant safety was not adversely affected. The plant's safe shutdown capabilit'ies would not have been. diminished had the unit been in power operation.

NRC Form 366(6-89)

r, NRC Form 366A U.S. CLEAR REGULATORY CONTISSION Approved ONB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER) 7 EX 1'ONTINUATION FACILITY NAHE (1) (DOCKET NUNBER (2)

I ) SEQUENTIAL ) (REVISION(

I ~umxJ. I I I I r w F 1 TEXT (If more space is required, use additional NRC Form 366A's) (17)

The root cause of this event was a random component fai.lure of the circuit protector overvoltage voltage monitor. The type of voltage monitor that failed in this event had no history of any previous failures.

TVA has contacted the vendor to arrange for an evaluation of the failed voltage monitor. The faulty component was identified and replaced. RPS bus 3A was realigned to its normal power supply, and the affected systems returned to their normal alignments by 2150 hours0.0249 days <br />0.597 hours <br />0.00355 weeks <br />8.18075e-4 months <br /> on February 2, 1991.

In reviewing voltage monitor records of circuit protectors, TVA has had no histoxy of failures of the overvoltage voltage monitor. A search of the NER Network and INPO NPRDS data base did not reveal any industry information on Diversified Electronics voltage monitors.

V Overall component performance of the Diversified Electronics voltage monitors has been acceptable at Browns Ferry. Only one prior in-service failure of a voltage monitor had occurred (June 1988). However, that device was an undervoltage voltage monitor failure, which is normally energized internal relay versus the normally de-energized internal relay in the overvoltage application.

Therefore, TVA believes the failure mode of that device is not consistent with the overvoltage monitor observed symptoms. Nevertheless, in light of surface similarity, TVA is returning the faulty component to the vendor for evaluation.

None.

Energy Industry Identification System (EIIS) Codes are identified in the test as

[xx].

NRC Form 366(6-89)

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