ML18037A663

LER 93-002-00:on 931209,emergency Diesel Generator auto- Started as Result of Degraded Voltage Condition on 4 Kv Shutdown Board.Caused by Blown Fuse.Failed Fuse Replaced & SD Board 3EB Circuit replaced.W/940103 Ltr

ML18037A663
Person / Time
Site:	Browns Ferry
Issue date:	01/03/1994
From:	Hsieh C, Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-002-04, LER-93-2-4, NUDOCS 9401210057
Download: ML18037A663 (16)

Text

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RI DS )

ACCESSION NBR:9401210057 DOC.DATE: 94/01/03 NOTARIZED: NO DOCKET 4s FACIL:50-296 Browns Ferry Nuclear Power Stat'ion, Unit 3, Tennessee 05000296 AUTH. NAME AUTHOR'FFILIATION HSIEH,C.S. Tennessee Valley Authority Authority

'ECIPIENTValley ZERINGUE,O.J. Tennessee RECIP.NAME AFFILIATION R"

SUBJECT:

LER 93-002-00:on 931209,emergency diesel generator auto-started as result of degraded voltage condition on 4 kV shutdown board. Caused by blown fuse. Failed fuse replaced D SD board =3EB circuit replaced.W/940103 ltr. &

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR 'NCL SIZE:

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

NOTES: A:

RECIPIENT COPIES RECIPIENT COPIES D ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-4" 1 1 PD2-4-PD 1 1 WILLIAMS,J. 1 1 D INTERNAL'CRS 2 . 2 AEOD/DOA 1 1 S AEOD/DSP/TPAB 1 1 AEOD/ROAB/DS P 2 2 NRR/DE/EELB 1 1 NRR/ DE/EME B 1 1 NRR/DORS/OEAB 1 1 NRR/DRCH/HH F B 1 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 1 NRR/DRIL/RPEB 1' NRR/DRSS/PRPB 2 2 NRR/~SSA/SPLB 1 1 NRR/DSSA/SRXB 1' EG ~XX/ 02 1 1 RES/DSIR/EIB 1 1 GN2 FILE Ol 1 1 EXTERNAL

EG&G BRYCE,J.H 2 2 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC POOREgW 1 1 NUDOCS FULL TXT 1 1 D

D D

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FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 30 ENCL 30

0 41 Tennessee valley Autnonty, post Otfce Box 2000, oecatun Alabama 35609 JAN 03 l994 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

Dear Sir:

TVA BROWNS 'FERRY NUCLEAR PLANT (BFN) UNITS 1, 2, AHD 3 DOCKET,NOS. 50-259, 260, AND 296 FACILITY OPERATING LICENSE DPR-33, 52, AND 68 LICENSEE EVENT REPORT 50-296/93002 The enclosed report provides details concerning an emergency diesel generator that automatically fast started as a result of degraded voltage condition caused by a 'blown fuse.

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

Sincerely, S te Vice Pres dent PAB lE-BFN Enclosure cc: See page 2

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9401210057 940103 PDR ADOCK 05000296 PDR

0 U.S. Huclear Regulatory Commission Page 2 JAi". ".". /Ski cc (Enclosure):

IHPO 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 HRC Resident Inspector Browns Ferry Nuclear Plant Route 12, P.O. Box 637 Athens, Alabama 35609-2000 Regional Administrator U.S. Huclear Regulatory Commission Region II 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323 J. F. Williams U.S. Nuclear Regulatory Commission One White Flint, Horth 11555 Rockville Pike Rockville, Maryland 20852

0 I

HRC Form 366 U S NUCLEAR REGULATORY C(NNISSION Approved OHB No. 3150-0104

'6-89)

Expires 4/30/92 LICENSEE EVENl'EPORl'LER)

FACILITY HAHE (1) lGGGKE> NGNGER (2> [~PAGE 3 Browns Ferr Nuclear Plant BFN Unit 3 050002 9 6 1OF 0 5 TITLE (4) An Emergency Diesel Generator Auto-started as a Result of Degraded Voltage Condition on 4kV Shutdown Caused b a Blown Fuse EVENT DAY 5 LER NUHBER 6 REPORT AT OTH R FACILITIES INVOLVED 8 JSEGUEHTIAL f ]REVISION] ] f ) FACILITY NAMES .IDOCKET NUHBER(S)

HONTH DAY YEAR YEAR NUHBER NUMBER H Y R 0 5 0 0 0 I I I I I I I I I I I 1 2 0 9 9 3 9 3 0 0 2 0 0 0 ~ 0 3 9 4 05000 OPERATIHG I ITHIS REPORT IS SUBHITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 5 NODE Check one r m e of f n 9 N I20.402(b) i20.405(c) , i~(50.73(a)(2)(iv) i73.71(b)

POWER I ]20 ~ 405(a)(1)(i) ]50 36(c)(1)

~

( [50.73(a)(2)(v) i73.71(c)

LEVEL I I 120 '05(a)(1)(ii) i50.36(c)(2) i i50.73(a)(2)(vi I) ]OTHER (Specify in 10 0 l20 ~ 405(a)(1)(iii) I l50.73(a)(2)(i)(B)l ISA 73(a)(2)(viii)(A) Abstract below and in i20.405(a)(1)(iv) I l50.73(a)(2)(ii) ISA 73(a)(2)(viii)(B)

I Text, NRC Form 366A) 20 405 a v 0.

L C SEE ONT CT FOR TNIS LER 1 NAHE TEL PHONE NUHB R Clare S. Hsieh, Compliance Engineer I AREA CODE I 0 7 2 2 6 3 CONP ET ONE NE FOR EAC COMP N NT F R R D M TH S REPORT 3 I I I IREPORTABLEI I

'I I I IREPORTABLEI CAUSE S STEH COMPONENT HANUFACT ER TO NP DS C US Y T H COHP MENT HANUFA URER 0 NPRDS I I I I I I I I I I I X E B F U G 0 8 0 N I I I I I I I I I I I SUPPLEHENTAL REPORT EXPECT 4 I I SUSHI SSIOH I I I YES If es com lete EXPE TED SUBHISS OM DAT NO DATE 15 ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

On December 9, 1993, at 1840 hours0.0213 days <br />0.511 hours <br />0.00304 weeks <br />7.0012e-4 months <br /> CST, Unit 3 Emergency Diesel Generator (EDG) 3B automatically (auto) fast started and tied onto 4kV Shutdown (SD) Board 3EB folloving a transfer of 4kV Unit Board 3A from its alternate power supply to its normal supply. The EDG auto-start was the result of a sensed degraded voltage condition on SD Board 3EB.

(The degraded voltage signal started EDG 3B and tripped all feeder and load breakers on SD Board 3EB.) This event is reportable in accordance vith 10 CFR 50.73(a)(2)(iv) as a condition that resulted in automatic actuation of an engineered safety feature.

The cause of the EDG auto-start was an unexpected and unforeseen failure of a primary potential transformer (PT) fuse on the 3EB SD Board bus. This failure was attributed to random PT fuse fatigue. There were no abnormalities identified in the failed fuse contacts or in the PT winding/circuitry that could have attributed to this fuse failure.

TVA examined the remaining three fuses on the 3EB SD Board PT circuits and found no abnormalities. The failed fuse was replaced. As a precautionary measure, the remaining three PT fuses on the affected SD Board 3EB circuit vere replaced. No further corrective actions are warranted.

NRC Form 366(6-99)

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

TEXT CONTINUATION FACILITY NAHE (1) ,IOOCKET NUHBER <2) GE 3 I I I ISEOUENTIAL I IREVISIONI I I I I BroNns Ferry Unit, 3 'I Y R BER NUHBER I .

I I I 0 2 -- 0 0 0 2 OF 0 5 TEXT ( If more space is required, use additional NRC Form 366A's) (17)

I. PLY COHDITIOHS Unit 2 vas at approximately 100 percent pover (3293 megavatts thermal). Units 1 and 3 vere shutdown and defueled. All Unit 3 4kV Shutdovn (SD) boards and Emergency Diesel Generators (EDG) vere operable and in service..

II 'DESCRIPTIOK OF EVEST

h. Bvent:

On December 9, 1993, at 1840 hours0.0213 days <br />0.511 hours <br />0.00304 weeks <br />7.0012e-4 months <br /> CST, Unit 3 EDG 3B [EK] automatically (auto) fast started and tied onto 4kV SD board 3BB [EB] folloving a transfer of 4kV Unit Board 3A [BB] from its alternate power supply to its

,normal supply. The EDG auto-start vas the result of a sensed degraded voltage condition on SD board 3BB. (The degraded voltage signal from the SD board started BDG 3B and tripped all feeder and load breakers on SD board 3EB.) After BDG 3B reached rated speed and voltage, the closed as expected. At 2035 hours0.0236 days <br />0.565 hours <br />0.00336 weeks <br />7.743175e-4 months <br />, BDG 3B was stopped and an EDG'utput'breaker investigation of this event vas initiated.

This event was initiated vhen vorkers transferred the 4kV Unit Boards from their normal pover supplies to their alternate supplies. It vas following Operations'ransfer of Unit Boards back to their normal supplies that the degraded voltage alarm vas received'nd the EDG started.

During troubleshooting on the potential circuit associated with the 3ED SD board bus, one, of the four primary Potential Transformer (PT) fusee (FU) on the bus was- found blovn. The blown fuse was replaced and the BDG vas started, loaded, and declared operable at 2043 hours0.0236 days <br />0.568 hours <br />0.00338 weeks <br />7.773615e-4 months <br /> on December 10, 1993.

This event is reportable in accordance vith 10 CFR 50.73(a)(2)(iv) due to an unplanned actuation of an Engineered Safety Feature.

B. no crab e Structuree C ents o S eteae that Cont ibuted to the 'Jhvent:

Hone.

NRC Form 366(6-89)

0 0 NRC Form 366A U.S. NUCLEAR REGULATORY COHHISSION Approved OHB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAHE (1) IDOCKET NUHBER (2) N B R 6 PAGE 3 I [SEQUENTIAL J )REVISION(

Brogans Ferry Unit 3 I R HB UHBER I I I I 0 0 0 0 0 0 3 OF 0 5 TEXT (If more space is required, use additional NRC Form 366A!s) (17)

C. Dates and A roximate Times o o Oc encs December 9, 1993 at 1735 CST 4kV Unit Board 3A transferred to its alternate supply.

1840 CST 4kV Unit Board 3A. transferred back to its normal supply. BDB 3B auto fast started.

2035 CST SDG 3B stopped and declared inoperable. Work request initiated to investigate this event.

2041 CST A four-hour nonemergency notification was made to NRC in accordance with 10 CFR 50.72(b)(2)(ii).

December 10, 1993 at 0700 CST A primary PT fuse was found blown.

2043 CST BDG 3B declared operable.

D. Other S stems or Seconda Fane ons f ected:

None.

B. Method of Discove This event was immediately discovered at 1840 hours0.0213 days <br />0.511 hours <br />0.00304 weeks <br />7.0012e-4 months <br /> on December 9, 1993, when the control room alarms indicated a degraded voltage condition and an BDG auto started.

F. 0 erator c ons:

I Operations personnel responded hamediately to the BDG start and the degraded voltage condition. The steps taken to unload the SD board and secure the BDG were appropriate.

NRC Form 366(6-89)

il 41 V

NRC Form 366A U.S. NUCLEAR REGULATORY CollMISSION Approved ONB Mo. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAKE (1) IDOCKET KUNBER (2) N AGE 3 I )SEDUENTIAL f )REVISION[

Brouns Ferry Unit 3 I YAR N NUMBER 0 0 0 0 0 4 OF 0 TEXT (If more space is required, use edditlonet NRC Form 366A's) (17)

G. Safe S stea R nses Hone III. CAUSE OF THE EVENT The immediate cause of the event was a blown primary PT fuse on the 3EB SD board bus.

B. oot Cause:

The cause of the EDG auto fast start was an unexpected and unforeseen failure of a primary PT fuse on the,3EB'D Board bus. This failure was attributed to random PT fuse fatigue.

Troubleshooting did not identify any abnormalities in the PT fuse contacts or in the PT secondary circuitry/winding that could have caused the fuse to blow. At the time of the event, there were no testing or maintenance activities in progress on the SD boards or the EDGs.

C. Contribut Factors:

None.

IV. ANALYSIS OF THE EVEIT

-.The degraded voltage .sensing logic on 4kV SD board monitors phase-to-phase voltages on the SD board PT secondaries. When one of the four PT fuses failed, a degraded voltage was sensed between the A to B and A to C phase voltage and completed the two-out-of-three degraded voltage logic. This logic completion started EDG 3B, load shed the SD board, and closed the EDG 3B tie breaker as designed. The 4kV SD Board 3EB provides power and control to various emergency loads which primarily support Unit 3 operation. This board also supports Unit 2 operation by providing power to Emergency Equipment Cooling Water (EECW) pump C3. Due to the standing degraded voltage signal in the degraded voltage logic, no SD board load breakers could be closed to provide power and control'o various Unit 3 emergency loads. The loss of the EECW pump had no adverse impact on Unit 2 since there were adequate pumps available to supply the required flows.

NRC Form 366(6-89)

HRC Form 366A U.S. NUCLEAR REGULATORY CONNISSION Approved OHB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT'LER)

TEXT CONTINUATION FACILITY NAHE (1) IDOCKET NUHBER (2) R NUHBER 6 P GE I (SEOUENTIAL ( / REVISION /

BroMns Ferry'Unit 3 I YE R NUHBER NUHBER I I I I 050 0. 6 9 -- 0 -- 0 0 0 5 OF 0 5 TEXT (If more space is required, use additional NRC Form 366A's) (17)

IV. AHALTSIS OF THB EVBIIT (Continued)

Additionally, as noted in the BFH Safety Analysis Report, the loss or degraded condition of a single division power supply is an analyzed event and is fully within the design basis of the plant. Furthermore, this event occurred while Unit 3 was in a shutdown condition with fuel removed from the reactor vessel.

Therefore, plant safety was not adversely affected and the safety of plant personnel 'and the public was not compromised.

V. CORRECTIVB ACTIOHS

h. amediate Co re ve Operators shutdown BDG 3B with a degraded voltage signal, present by opening the BDG 3B logic breaker and tripped the BDG tie breaker.

B. Co re tive t 0 v ce:

After removing the blown fuse, TVA examined the remaining three fuses on the 3BB SD board PT circuits and found no abnormalities. The blown fuse was replaced. As a precautionary measure, the remaining three primary PT fuses on affected 3BB SD board circuit were replaced.

VI. ADDITIOHAL IHFOITIOH

h. Failed Com nents:

This event was caused by a failed fuse manufactured by General Electric (5.5 kV, 0.5 Amp, Type EJ-1).

B. Previous LBRs on S lar ts:

There were seven previous events identified to have random fuse failures (LERs 259/85006, 260/85010, 260/85011, 259/85021, 260/86030, 259/90014, and 260/91019). However, all of these fuses were control type fuses and none of these failures involved primary PT fuses.

VII. CO?IGIlKHTS Hone.

Energy Industry Identification System (EIIS) system and component codes are identified in the text with brackets (e.g., [XX]).

NRC Form 366(6-89)

0 I