ML18036A483

LER 91-019-00:on 911208,unexpected Loss of One of Offsite Power Supplies Occurred.Caused by Fuse Failure.Util Will Investigate Spurious Tripping of Trinity 1 Line During Event & Correct Identified deficiencies.W/920107 Ltr

ML18036A483
Person / Time
Site:	Browns Ferry
Issue date:	01/07/1992
From:	Ridgell E, Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-019-01, LER-91-19-1, NUDOCS 9201130145
Download: ML18036A483 (16)

Text

ACCELERATED DIGBUTION DEMONSTRATION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9201130145 DOC.DATE: 92/01/07 NOTARIZED: NO DOCKET FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH. NAME AUTHOR AFFILIATION RIDGELL,E.M.. Tennessee Valley Authority ZERINGUE,O.J., Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 91-019-00:on 911208,unexpected loss of one of offsite power supplies occurred'.Caused by fuse failure. Util will D investigate spurious tripping of Trinity 1 line during event

& correct identified deficiencies.W/920107 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

NOTES:

RECIPIENT COPIES RECIPIENT. COPIES D ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL SANDERS,M. 1 1 HEBDON,F 1 1 D ROSS,T. 1 1 INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DS P 2 2 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB, 7E 1 1 NRR/DLPQ/LHFB10 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/SICB8H3 1 1 NR~RD~ST SPLB8D1 1 1 NRR/DST/SRXB 8E 1 1 EG FIL 02 1 1 RES/DSIR/EIB 1. 1 R FILE 01 1 1 EXTERNAL: EGGG BRYCE,J.H 3 3 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:

S

~

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

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 33 ENCL 33

Tennessee vatfey Authority. post office Box 2000. or cotta. Araharna 3s609 JAN OV l992 O. J. 'Ike'eringue Vce President, Browns Ferry Operations U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

Dear Sir:

TVA BROWNS FERRY NUCLEAR PLANT (BFN) UNIT 2 DOCKET NOo 50-260 FACILITY OPERATING LICENSE DPR-52 LICENSEE EVENT REPORT LER-50-260/91019 The enclosed report provides details concerning an automatic reactor scram following a turbine trip. The turbine .trip was a result of an unexpected and unforeseen fuse failure. This report is submitted in ac'cordance with 10 CFR 50.73(a)(2)(iv).

Sincerely, 0 J. Zeringue Enclosure cc: see page 2

r201 1u0r.4 a 9 01 v 7 PDR ADOCK 0'5000260 pV t- DR

U.S. Nuclear Regulatory Commission JAN 07 1992 cc (Enclosure):

INPO Records Center Suite 1500 1100 Circle 75 .Parkway Atlanta, Georgia 30339 NRC Resident Inspector, BFN Regional Administrator U.S. Nuclear 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

0>

NRC. Form 366 U. LEAR 'REGULATORY COt%GSSION Approved'MB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT 'REPORT (LER)

FACILITY.NAME (1) IDOCKET NUMBER'(2) I w

TITLE (4) m 1 r 11 wi Tr W w T

[SE{)UENTIAL ) [REVISION) ] ( f FACILITY NAMES lDOCKET NUHBER(S)

I I I I I I I I I I I 0 10 792 OPERATING I I THIS REPORT IS SUBHITTED PURSUANT TO THE REQUIREHENTS OF 10 CFR g:

MODE I I w'

I20.402(b') I l20.405(c) [M(50.73(a)(2)(iv) I73.71(b)

POWER I (20.405(a)(1)(i) ) )50.36(c)( 1) )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 (20.405(a)( 1)(iii) ( )50.73(a)(2)(i) )50.73(a)(2)(viii)(A) Abstract below and in

[20.405(a)(l)(iv) f )50.73(a)(2)(ii) (50.73(a)(2)(viii)(B) Text, NRC Form 366A) v TA T F NAME i AREA CODE R A MP N 1 I IREPORTABLEI I I I IREPORTABLEI Y TH NT N P D I I P EXPECTED i I [ SUBMISSION I I l 1 P 0 B I TE N ABSTRACT (L'imit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

On December 8, 1991 at 2320 CST, Browns Ferry Unit 2 automatically scrammed from approximately 80 percent power following a turbine trip. In addition, during this event, an unexpected loss of one of the offsite power supplies occurred.

The root cause of this event was .an unexpected'nd unforeseen fuse (Gould-Shawmut) failure.

TVA has replac'ed the existing 500kV Bus Potential Transformer secondary fuses to minimize the possibilit'y of spurious relay operations.

TVA will evaluate reconfiguring the existing plant design to eliminate the.

possibility that the loss of the relaying potential from a single bus will result in the loss of the generating unit. In addition, TVA will investigate the spurious trip of Trinity line 1 line during this event and correct any identified deficienc'ies.

NRC Form 366(6-89)

0 NRC Form 366A 'U. CLEAR REGULATORY CONHISSION Approved ONB No. 3150-0104 (6-09) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1) IOOCKET NUMBER (2) B IREVISIONI 'I t

J SEQUENTIAL I.

~~~ l I

l I

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

I. PLANT CONDITIONS Unit 2 was at 80 percent power operations and was slowly increasing power for fuel preconditioning. Units 1 and 3 were shutdown and defueled.

II. DESCRIPTION OF EVENT A. ~t:

On December 8, 1991 at 2320 CST, Browns Ferry Unit 2 automatically scrammed from approximately 80 percent power due to an unexpected fuse failu're.

The failed fuse, manufactured by Gould-Shawmut, was. located on the 500kV Bus 1 Section 1 potential transformer [EL] output and resulted in a loss of restraint potential to the generator backup impedance relay, causing the relay to actuate. The restraint potential is provided to a logic circuit which ratios the potential (voltage) to the current (amperage).

The loss of restraint potential is sensed by the logic circuit as an overcurrent condition, which caused the relay to actuate.

The actuation of the generator backup impedance relay resulted in a trip of the Unit 2 generator breaker and the associated supply breakers. This relay also initiated an exciter field, breaker trip and subsequent turbine trip '[TA]. Following the turbine trip, the Unit 2 'reactor automatically scrammed and all required electrical boards automatically transferred to their alternate power supply, as designed.

Following 'the reactor scram, the control room received indication of a low Reactor'ressure Vessel Level and entered Emergency Operating Instruction of the Primary Containment Isolation System (PCIS) [JN].

As a result of the automatic reactor scram and actuation. of the PCIS, 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 any engineered safety feature, including the reactor protection system.

NRC Form 366(6-89)

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

TEXT CONTINUATION FACILITY NAHE (1)

I-

~~whirr I

is&

I Y A I I SEQUENTIAL P H8 ll (I IREVISIONI I, I I aJ

.l I

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

B. '

t t

'gvggt:

None.

C December 8, 1991 at 2320 CST Failed fuse resulted in generator load rejection, turbine trip, and automatic reactor scram., Operations, received low reactor vessel water level indication, subsequent PCIS actuation and entered the EOI.

2354 CST EOI exited based on the entry conditions no longer existing.

0129 CST TVA provided'our-hour non-emergency report to NRC required by 10 CFR 50.72(b)(2)(ii).

D.. th The incoming plant power line (Trinity line 1) breaker also tripped during this event. This breaker tripped due to actuation of the directional ground Phase B relay .which also receives its restraint potential from the 500kV Bus 1 Section 1 Potential Transformer. This was an unexpected event which had no direct impact on plant safety.

E. th

'This event was immediately known to the control operator upon receiving indication of the turbine trip and subsequent reactor scram.

F.

Operations verified the reactor scram and turbine trip had occurred.

Reactor pressure was controlled by use of the turbine 'bypass valves and reactor- water level was. restored and controlled by use of the reactor feedwater pumps.

NRC Form 366(6-89)

NRC Form 366A U. S. CLEAR REGULATORY COHHISSION Approved OHB No. 3150-0104

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

TEXT CONTINUATION FACILITY NAHE (1) )DOCKET NUHBER (2) B 1 I I I SEQUENTIAL I I REVISIONI I I I I

-I NHB '

~r (If TEXT w r i more space is required, use additional NRC Y

Form 366A's) "(17) 4 I I I G. t t R All expected electrical boards automatically transferred to their alternate power supply following the turbine trip and subsequent loss of their normal power supply.

In addition, the PCIS system actuated following the automatic reactor scram. These actuations included group 2 (shutdown cooling mode of residual heat removal), group 3 (reactor water cleanup), group 6 (ventilation systems), and group 8 (traversing incore probes),. The PCIS actuations,were a result of a low,water level which occurred due to the voids collapsing in the reactor vessel.

III. CAUSE OF THE EVENT A.

The immediate cause of this event was fuse failure.

B- Rua~t ause=

The root cause of this event was an unexpected and unforeseen fuse failure which resulted in a turbine trip and subsequent automatic reactor scram.

C. t ta t None.

IV. ANALYSIS OF THE EVENT A.

The 500kV Bus 1 Section 1 potential transformer provides restraint potential to the generator backup impedance relay. The loss of restraint potential was sensed by the logic circuit as an overcurrent condition which caused the relay to actuate. The actuation of the relay resulted in a turbine trip and subsequent plant scram.

In addition, a'low reactor'ater level condition occurred following the plant scram. This is a. normal occurrence after a pressure transient since the voids in the reactor coolant collapse.

All safety-related piant components operated as expected during the plant scram. The safety. of the plant, its personnel, and the public was not compromised.

NRC Form 366(6-89)

~i NRC Form 366A U. CLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME '(1) IDOCKET NUMBER (2)

I /SEqUENTIAL J

/REVISION/

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

V. CORRECTIVE ACTIONS A.

The existing 500kV Bus Potential Transformer secondary fuses were replaced to minimize the possibili;ty of spurious relay operations due to generic fuse failures.

B. tv '

1. TVA will evaluate reconfiguring the existing design at BFN to eliminate the possibility that the loss of the relaying potential from a single bus will result in the loss of a generating unit.

2. TVA will further investigate the spurious tripping of the Trinity 1 line during this event and correct any identified deficienci'es.

VI. ADDITIONAL INFORMATION None.

B. v None.

VII. tm t

1. TVA will evaluate reconfiguring the existing design at BFN to eliminate the possibility that the loss of the relaying potential from, a single bus will result in the loss of a generating unit. This evaluation will'e completed by February 28, 1992.

2. TVA will further investigate the spurious tripping of the Trinity 1 line during this event and correct any i'dentified deficiencies. This evaluation will be completed by February 28, 1992.

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

NRC Form 366(6-89)

4i 4