ML18036A380

LER 91-016-00:on 910819,unplanned ESF Actuation Occurred. Caused by Blown Fuse Due to Failed Relay in PCIS Circuitry. Failed Relay Coil & Cleared Fuse Replaced & PCIS Signal reset.W/910918 Ltr

ML18036A380
Person / Time
Site:	Browns Ferry
Issue date:	09/18/1991
From:	Ridgell E, Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-016-01, LER-91-16-1, NUDOCS 9109240391
Download: ML18036A380 (12)

Text

ACCELERATED DI TBJBUTION DEMONS TION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9109240391 DOC DATE: 91/09/18 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 R

SUBJECT:

'.LER 91-016-00:on 910918,unplanned ESF actuation occurred.

Caused by blown fuse due to failed relay in PCIS circuitry.

Corrective actions:failed relay coil & cleared fuse replaced D

& PCIS signal reset.W/910918 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 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 S AEOD/DOA 1 1 AEOD/DS P/TPAB 1 1 AEOD/ROAS/DSP 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 1 1 NRR/DST/SRXB 8E 1 1 1 1 RES/DSIR/EIB 1 1 RGN2 F GE 01 1 1 EXTERNAL: EG&G 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 NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE O':XSTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM PI-37 (EXT. 20079) TO'ELIMINATEYOUR NAME FROiil DISTRIBUTION LISTS FOR DOCUiv!ENTS YOU DON'T NEED!

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

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Tennessee valley Authority, post ottice Box 2000. Decatur.'Atabaina 35609 O. J. 'Ike'eringue Vice President. Browns Ferry Operations SEP i 8 lQQ3 U-ST Nuclear Regulatory Commission ATTN: Document Control Desk Mashington, D.C. 20555 Dear Sir-TVA BROMNS FERRY NUCL'EAR PLANT (BFN)'NIT 2' .

DOCKET NO. 50-260 FACILITY OPERATING LICENSE DPR-52 LICENSEE 'EVENT REPORT LER-50-260/91016 The enclosed report provides details concerning an unplanned Engineered Safety Feature actuation due to a blown fuse caused by a failed xelay-This report is submitted in accordance with 10 CFR 50.73(a)(2)(iv).

Very truly yours, TENNESSEE VALLEY AUTHORITY Enclosure cc- see page 2

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U.S. Nuclear Regulatory 'Commission SEP i 8 1991 cc (Enclosure):

INFO 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'0852

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A

NRC (6-89)

Form 366 FACILITY NAME (1)

U. LEAR REGULATORY LICENSEE EVENT REPORT (LER)

~ISSION t Approved OMB No. 3150-0104 Expires 4/30/92

)DOCKET NUMBER (2)

Brw Fr i TITLE (4) n n i F r VNT Y I I I I SE()UENTIAL IREVISIONI I I I FACILITY NAMES IDOCKET NUMBER(S) 0 Y Y Y B N I I I 'I 09 I 189l I I I I 1 1 OPERATING (THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR $ :

MODE I I r b f 1 N I20.402(b) (20.405(c) (50 '3(a)(2)(iv) )73.71(b)

I20.405(a)( l)(i) 150 w'OWER I I 36(c)(1) )50.73(a)(2)(v) (73.71(c)

LEVEL I )20.405(a)( l)(ii) ISO 36(c)(2) (50.73(a)(2)(vii) (OTHER (Specify in 1 (20.405(a)( l)(iii) I l50.73(a)(2)(i) (50.73(a)(2)(viii)(A) Abstract below and in (20.405(a)( 1)(iv) [50.73(a)(2)(ii) (50.73(a)(2)(viii)(B) I Text, NRC Form 366A) 4 v 11 N NTA T F NAME I AREA CODE I rl M. id 1 m li n Li i n N N F AH MP N I I I IREPORTABLEI I I I I IREPORTABLEI T M PNNT MANF T T 0 A YT P T N T T NP

' I' I I I I I I I I I I I I I I PP iT P T 0 4 I I SUBMISSION I I I

~YES f ml P TD 8 I NDT ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

On August 19, 1991 at 1335 hours0.0155 days <br />0.371 hours <br />0.00221 weeks <br />5.079675e-4 months <br />, during Unit 2 normal operations at 100 percent power (3290 megawatts thermal)., -a blown fuse in the Primary Containment Isolation System (PCIS) logic circuitry resulted in .unplanned actuations of various engineered safety features. This included isolation of the Radwaste system drywell floor drain isolation valve,, the drywell equipment drain sump isolation valve, and the Core Spray system suppression pool drain valve. In addition, the Main Steam system main steam line inboard drain valve and the Traversing Incore Probe system isolation valves would have isolated. However, they were isolated, at the time of this event.

The root cause of thi;s event was the failure of a General Electric (GE) type CR120A relay in the PCIS circuitry due to a faulted coil.

As a result of previous events, TVA -committed to replacing the GE type CR120A relays used in. normally energized, safety-related applications on Unit 2 ~r'gg the Unit 2.,

Cycle 6 refueling outage. As a result of this event, TVA will accelerate the

, replacement of .some of the relay coils. Specifi'cally, the relay coils in applications where a relay failure could result in a plant shutdown will be replaced ygj~tg the Unit 2, Cycle 6 refueling outage.

NRC Form 366(6-89)

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NRC Form 366A (6-89)

U.S. LEAR REGULATORY CONNISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION t Approved OMB No. 3150-0104 Expires 4/30/92 FACILITY NANE (1) IOOCKET NUNBER (2)

I. I I I SEQUENTIAL I IREVISIONI I I I I Browns Ferry Unit 2 I I I I I If more is required, use additional Form 366A's) (17)

TEXT (

t'space t NRC On August 19, 1991 at 1335 hours0.0155 days <br />0.371 hours <br />0.00221 weeks <br />5.079675e-4 months <br />, during Unit 2 normal operations at 100 percent power (3290 megawatts thermal), a fuse in the Primary Containment Isolation System (PCIS) [JM] cleared resulting in the actuation of Engineered Safety Features (ESF)

[JE]. The ESF actuations, a PCIS group 2 isolation, included closure of the Radwaste [WD] system drywell floor drain isolation valve, the drywell equipment drain sump isolation valve, and the Core Spray [BM] system suppression pool drain valve. In addition, a PCIS group,8 isolation signal was transmitted. This signal would have resulted in the closure of the Main Steam [SB] syste'm main steam line inboard drain valve and the Traversing Incore Probe (TIP) [IG] system isolation valves. However, these valves were isolated during the event.

The cleared fuse was the result of a failed relay coil (General Electric type CR120A). The relay was replaced and on August 19, 1991 at approximately 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br />, the PCIS logic was reset and the affected systems were realigned to their normal configuration.

In accordance with 10 CFR 50.73(a)(2)(iv), TVA reports this unplanned ESF actuation.

AL E EN The PCIS isolates various systems related to the primary containment when accident conditions are sensed in order to limit inventory loss from the reactor vessel, and prevent the release of radioactive materials in excess of specified limits. The systems involved in this event are desi'gned to remove leakage from the drywell equipment, the general drywell area, and to isolate the suppression pool. The main steam line inboard drain line isolation valve and the TIP system isolation valves were out of service at this time and were in the closed position.

The PCIS logic is designed such that actuations/isolations occur on a loss of logic power. The clearing of the fuse resulted in a loss of logic power and plant systems responded properly and were placed in their safe configurations. Therefore, this event had no safety significance.

Qm v nt The root cause of this event was an unexpected failure of a PCIS relay due to a faulted coil'. The faulted coil caused a short to ground which resulted in a blown fuse in the PCIS logic circuitry. The relay coil failed due .to thermal aging.

Vendor information indicates that the service life for a normally-energized coil on a CR120A relay is on the order of 15-20 years. The BFN Unit 2 coils are now approaching an average service life of 15 years.

NRC Form 366(6-89)

Ci

NR C Form 366A U.S. EAR REGULATORY COMMISSION Approved'OMB No. 3150- 0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAHE (1) IOOCKET NUHBER (2)

I, /SEQUENTIAL J

)REVISIONS Browns Ferry Unit 2 I I I I I F

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

'v t Initial corrective actions included the replacement of the failed relay coil and the cleared fuse. Also, the PCIS'ignal was. reset and the affected plant equipment was realigned.

Previously identified corrective actions included replacing the relay coils in GE type CR120A relays used in normally energized, safety-related applications on Unit 2. The replacement would be performed during the Cycle 6 refueling outage for Unit 2. This corrective action was identified in Licensee Event Reports (LER) 260/91001 and 260/91005.

Additional corrective actions will include accelerating the replacement schedule of some of the CR120A relay coils. Specifically, in applications where failure of these coils would have a high probability of causing a plant shutdown. The relays which meet this criteria are the PCIS group 6 relays which isolate the main steam

'tunnel cooling system; these relay coils will be replaced prior to the Unit 2, Cycle 6 refueling outage.

P ev'm' v nt Several previous LER events have occurred due to a failure of GE type CR120A relays. These events include the following LERs: 296/87006, 260/86013, 259/85024, 259/85011, 260/91001, and 260/91005. As noted above, LER 260/91001 and 260/91005 determined the relay failures to be a result of a faulted relay coil and committed to replace the normally energized, safety-related relay coils on Unit 2 during the Cycle 6 refueling outage.

mmitm t TVA will replace relay coils in GE type CR120A relays associated with the isol'ation of the main steam tunnel cooling system prior to March 30, 1992.

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

NRC Form 366(6-89)

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