ML18036B167

LER 93-001-00:on 930124,RCIC Sys Declared Inoperable When Outboard Steam Line Isolation Valve Discovered Closed.Caused by Failure of RWCU Isolation Valve Bonnet Pressure Seal Ring.Rwcu Valve repaired.W/930223 Ltr

ML18036B167
Person / Time
Site:	Browns Ferry
Issue date:	02/23/1993
From:	Austin S, Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-001-01, LER-93-1-1, NUDOCS 9303020006
Download: ML18036B167 (18)

Text

" UTION SYSTEM ACCELERA. DOCVMENT DIST REGULAT INFORMATION'ISTRIBUT10 YSTEM (RIDS:)

i ACCESSION'BR:9303020006 DOC.DATE: 93/02/23 NOTARIZED: NO DOCKET ¹

-.~l FACIL:50-)60 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH.NIMS AUTHOR AFFILIATION AUSTIN,S.W. Tennessee Valley Authority ZERINGUE,O.J. Tennessee Valley Authority RECIP.NAME' RECIPIENT AFFILIATION,

SUBJECT:

LER 93-001-00:on 930124,RCIC sys declared inoperable when outboard steam line isolation:-',valve discovered closed. Caused by failure of RWCU isolation"~valve bonnet pressure seal ring.RWCU valve repaired.W/930223 ltr.

if' DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

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

NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID'ODE/NAME , LTTR ENCL SANDERS,M. 1 1 HEBDON,F 1 1 ROSS,T. 1 1 INTERNAL: ACNW 2 2 ACRS 2 2

~ AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1

AEOD/ROAB/DSP 2'1 2 NRR/DE/EELB 1 1 NRR/DE/EMEB 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 SPLB 1 1 NRR/DSSA/SRXB 1 1 EG F E 02 1 1 RES/DSIR/EIB 1 1

)

RGN2 FILE 01 1 1 EXTERNAL EG&G BRYCEg J ~ H 2 2 v',"' 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 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 p p~L/

TOTAL NUMBER OF COPIES REQUIRED: LTTR 32 ENCL 32

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Tennessee valley AU'.rrority, post 0:rce Box 2000. Decatur, Ataoanta 35609-2000 O. J. "Ike" Zeringue Vrce PresidentBrowns Ferry Nocrear Ptant FEB 23 1993 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Mashington, D.C. 20555

Dear Sir:

TVA BROGANS 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 50-260/93001 4 The enclosed report provides details concerning an inoperable Reactor Core Isolation Cooling System due to a ground fault in the 250 Volt DC power system.

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

Sincerely, (t:jj~,d/r'j~ig'.r J. Zeringue Enclosure cc: See page 2 Og06

303020006 PDR 8

ADOCK 930223 05000260 /JgiI'I PDR

U.S. Nuclear Regulatory Commission FES 2 3 ]99i cc (Enclosure):

INFO Records C'enter 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 Brovns Ferry Nuclear Plant Route 12, P.O. Box 637 Athens, Alabama 35609-2000 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 NUCLEAR REGULATORY COtRISSION

. Approved OMB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

FACILITY NAHE (1) rr N n BF

[DOCKET NUHBER (2) )~P 1

~~

TITLE .(4) Inoperable Reactor Core Isolation System Due To Ground Fault in the 250 Volt DC Power System.

NT 0 Y N B T V IREVISIONI FACILITY NAHES IDOCKET NUHBER(S)

I SEQUENTIAL I

=

I I I I I I I NTH 0 Y Y Y T Y 1

I, 4 I I I I I I I 0 22'393 I I I I OPERATING I ITHIS REPORT IS SUBHITTED PURSUANT TO THE REQUIREHENTS OF 10 CFR 5:

h w' NODE I I I20.402(b) )20.405(c) ] [50.73(a)(2)(iv) I73.71(b)

POWER I I l20 405(a)( l)(i) [50.36(c)( 1) ))( (50.73(a)(2)(v) I l73 71(c)

LEVEL I )20.405(a)( l)(ii) (50.36(c)(2) J

)50.73(a)(2)(vii) )OTHER (Specify in

)50.73(a)(2)(i)(B)) (50.73(a)(2)(viii)(A) Abstract below and in

[20 '05(a)( 1)(iv) (50.73(a)(2)(ii) f ]50.73(a)(2)(viii)(B) Text, NRC Form 366A)

.4 1 v .7 ill N E N H N N NAHE I AREA CODE I i m 1'P in r T N A P 1NTF R 0 IREPORTABLEI I I I I IREPORTABLEI I I PNN A Y T H H N 1 N F I I I I I I F V V I I I I P TA P T P T 0 14 I I SUBHISSION I I I m 1 BH N ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

On January 24, 1993, at 2230 hours0.0258 days <br />0.619 hours <br />0.00369 weeks <br />8.48515e-4 months <br /> the Reactor Core Isolation Cooling (RCIC) system was declared inoperable when the outboard steam line isolation valve was discovered closed.

The root cause of this event was failure of a Reactor Water Cleanup (RWCU) isolation valve bonnet pressure seal ring. The ring failed allowing RWCU water to spray filling the local control station for the RCIC outboard steam line isolation valve with water and grounding the local switch.

Corrective actions to prevent recurrence will be removal of the RCIC local control station and associated hand switch, and repair of the RWCU valve involved.

NRC Form 366(6-89)

4l i

~ >

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

TEXT CONTINUATION FACILITY NAME (1) P I J SEQUENTIAL i i REVISION /

Browns Ferry'Unit 2 I. YA MB N I I I I F

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

I. PLANT CONDITIONS Unit 2 was at 2177 megawatts thermal or approximately 66 percent power coasting, down for a scheduled refueling outage. Units 1 and 3 were defueled.

~ II. DESCRIPTION OF EVENT A. ~Ev t:

On January 24, 1993, at 2230 hours0.0258 days <br />0.619 hours <br />0.00369 weeks <br />8.48515e-4 months <br />, the- Reactor Core Isolation Cooling (RCIC) [BN] system was declared inoperable when the outboard steam line isolation valve (FCV) was discovered closed due to a ground on the 250 volt DC [EJ] system. TVA cannot identify -the specific time the isolation valve went closed. However, TVA is aware that the valve was open at 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> on January 24, 1993.

On January 24, 1993, at approximately 0900 hours0.0104 days <br />0.25 hours <br />0.00149 weeks <br />3.4245e-4 months <br /> a ground was identified on the 250 Volt DC system. At approximately 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> the source of the ground was identified as the RCIC outboard steam line isolation valve control circuit. Further investigation revealed that the source of the ground was the local control station [PL'] for the isolation valve which was located inside the Unit 2 steam tunnel. At 2230 hours0.0258 days <br />0.619 hours <br />0.00369 weeks <br />8.48515e-4 months <br />, the RCIC outboard steam isolat'ion valve was found closed. Subsequently, TVA entered two limiting conditions for operation (LCO). The first LCO was entered due to an inoperable RCIC system and a second LCO was entered because of an inoperable containment isolation valve.

On January 26, 1993, at approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, the Unit 2 steam tunnel was entered to inspect the local control station for the RCIC outboard steam line isolation valve. The inspection revealed that water from a Reactor Water Cleanup System (RWCU) [CE] isolation valve [ISV] was spraying onto the local control station and a junction box mounted just above the station. Subsequent inspection of the station revealed standing water in the station. The water was drained from the station and the ground on the 250 Volt DC system cleared. TVA assessed the leaking RWCU valve and the local control station and determined it could be repaired at power. However, TVA determined based on ALARA concerns and since Unit 2 would enter a preplanned shutdown outage January 29, 1993, that it was acceptable for Unit 2 to remain in the LCO until it would be brought to cold shutdown for the outage.

January 29, 1993, as part of the preplanned shutdown for a scheduled

"

On outage, at approximately 1755 hours0.0203 days <br />0.488 hours <br />0.0029 weeks <br />6.677775e-4 months <br />, TVA exited the LCO for inoperable RCIC system when, as part of the shutdown for a planned refueling outage, reactor pressure was brought to less than 150 psig and RCIC was no longer required. The LCO for an inoperable containment isolation valve was exited on January 29, at 2215 hours0.0256 days <br />0.615 hours <br />0.00366 weeks <br />8.428075e-4 months <br /> when the reactor was brought to cold shutdown condition.

NRC Form 366(6-89)

NRC Form 366A U.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3'150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1) IOOCKET NUMBER (2)

I I I I SEQUENTIAL I I REVISIONI I I I I Browns Ferry Unit 2 I Y A N B N M R I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

TVA reports this event in accordance with 10 CFR 50.73(a)(2)(v)(D), as any event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

t t t t t t t t thy B.

~t:

Jane None.

C. x t e January 24, 1993, at 2230 RCIC system is declared CST inoperable due to an inoperable outboard steam isolation valve January 25, 1993, at 0225 TVA makes a four hour CST nonemergency notification to NRC in accordance with 10 CFR 50.72(b)(2)(iii)

January 29, 1993, at 1755 Exited LCO for inoperable RCIC.

CST Reactor pressure had been reduced to less than 150 psig January 29, 1993, at 2215 Exited LCO for inoperable CST containment isolation valve.

Reactor temperature is reduced to less than 212', cold shutdown has been established.

D. th None.

The ground fault was identified by the operator when he had indication that there was a ground on the 250 Volt DC system. The Unit 2 operator noted the outboard steam isolation valve had closed when the main control room valve position lights indicated that the valve was in the closed position.

NRC Form 366(6-89)

II ~ ~

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

TEXT CONTINUATION .

FACILITY NAME (1) iOOCKET. NUMBER (2)

I I I SEQUENTIAL

'I I REVISIONI I I I I I

Browns Ferry Unit 2 I M R I I. I I 035hl 4 F TEXT (If more space is required, use additional NRC Form 366A's) (17) jy'1 F. C If, ~

g None. if) i t t None.

III.

I CAUSE OF THE EVENT The immediate'ause of the event was an electrical ground in a local control station! The local control station for the RCIC system outboard steam isolation valve was found with water in it, which caused a ground in the control switch.

B.

root cause of this event was failure of a RWCU isolation valve bonnet The sealing ring. The ring failure caused RWCU water to fill the local control station for the isolation, valve with water and grounding the local control switch.

C. t t None.

IV. ANALYSIS OF THE EVENT'he RCIC system provides makeup water to the reactor'pon loss of feedwater

[SJ] system flow. During. the event, due to the inoperable outboard steam isol'ation valve, the RCIC system was declared inoperable, and TVA entered 'the LCO for an inoperable RCIC. Technical specifications allowed for continued reactor operation for up to seven days provided the High Pressure Coolant Injection (HPCI) [BG] system was operable. During the period in which RCIC was inoperable, HPCI was operable and't is expected that if called upon, would have performed its required function.

NRC Form 366(6-89)

0 it NRC Form 366A U. UCLEAR 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 I I I SEQUENTIAL I I REVI S ION I I I I I

• Browns Ferry Unit 2 I I I I I TEXT (If more. space is required, use additional NRC Form 366A's) (17)

The RCIC outboard steam isolation valve is designed to isolate the reactor vessel, in order to limit the loss of vessel inventory during certain accident scenarios. The valve automatically closes upon receiving a primary containment isolation signal [JE]. Technical specifications allow continued reactor power operation with an inoperable containment isolation valve as long as within four hours the inoperable valve is restored to operable status or the affected line is isolated by use of at least one deactivated containment isolation valve secured in the isolated position. The motive power to the valve was removed, thus securing it in the closed position.

The local control station for the RCIC outboard isolation valve and the junction box located just above the local control station in the Unit 2 steam tunnel are designed and installed to meet the TVA Environmental Qualification (EQ) program. The EQ program ensures that safety related equipment will function under the harsh environmental conditions of a design basis accident.

The local control station and junction box were designed to withstand a steam environment resulting from a steam line break for up to 100 days following a loss of coolant accident or a high energy line break. However, these components were subjected to a direct spray of water from the RWCU valve. TVA has concluded that the water spray from the valve filled the local control panel with water and grounding the switch.

There were no operator actions or safety system response required for this event. Technical specifications requirements were met during the event.

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

V. CORRECTIVE ACTIONS A. tv t The ground fault was cleared from the 250 Volt DC system when the. water was drained from the local control station. TVA evaluated the working conditions in the steam tunnel and because of 'these conditions and the planned shutdown, scheduled for January 29, 1993, no further immediate actions repair to the, switch were performed.

B. t v t t

1. The local control station and switch for the RCIC outboard steam isolation valve serves no safety function. Therefore, it will be removed.

2. The RWCU isolation valve involved in this event will'e repaired.

NRC Form 366(6-89)

i> 0~

NRC Form 366A U.S. NUCLEAR 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 / i REVISIONS

'rowns Ferry Unit 2 I I I I I F

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

VI. ADDITIONAL INFORMATION A.

The seal ring on the RWCU isolation valve failed.

B.

None.

VII. COMMI3MrNTS

1. The local control station and switch for the RCIC outboard isolation. valve will be removed. This will be completed prior to restart from Unit 2 Cycle 6 outage.

2. The RWCU isolation valve involved in this event will be repaired. This will be completed prior to restart from Unit 2 cycle 6 outage.

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

NRC Form 366(6-89)

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