ML18036B342

LER 93-002-01:on 930131,MSIV on MSL C Found to Have Leakage in Excess of TS Limit.Caused by Abnormal Wear.Steamline Inboard C MSIV Repaired & Successfully Retested & Other Failed Components Repaired,Modified or Replaced

ML18036B342
Person / Time
Site:	Browns Ferry
Issue date:	06/28/1993
From:	Austin S TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18036B341	List: IR 05000260/1993002 ML18036B340 ML18036B342
References
LER-93-002, LER-93-2, NUDOCS 9307060230
Download: ML18036B342 (10)

Text

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

FACILITY NAHE (1) IDOCKET NUHBER (2) I P r wn rr N 1 TITLE (4) Hain Steam Line Isolation Valves Exceeding Allowable Leakage During Testing.

VN DY' D T I. I I I SEQUENTIAL IREVISIONI I I I FACILITY NAHES IDOCKET NUHBER(S NTH DA N I I I I I I I I I I P 6 2 N 1

OPERATING ITHIS REPORT IS SUBHITTED PURSUANT TO THE REQUIREHENTS OF 10 CFR g:

HODE I- I r I20.402(b) I I20.405(c) I I50.73(a)(2)(iv) I73.71(b)

POWER I I I20.405(a)( 1)(i ) I I50.36(c),( 1) I ISO-73(a)(2)(v) l73 71(c)

LEVEL,I' I20.405(a)(1)(ii) I I50.36(c)(2) I I50.73(a)(2)(vii) IOTHER (Specify in I20.405(a)(l)(iii) I I50.73(a)(2)(i)(B)l I50.73(a)(2)(viii)(A) I Abstract'below and in I20.405(a)(l)(iv) I~I50.73(a)(2)(ii) I I50.73(a)(2)(viii)(B) I Text, NRC Form 366A)

I

.I I AREA coDE I in IREPORTABLEI I I I IREPORTABLEI I I A Y T P N HAN A T NPD P N P I I I I B B I V I I I I I T P EXPECTED I Y I I SUBHISSION I I I Y f m 1 ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

On January 31, 1993, at 1030 hours0.0119 days <br />0.286 hours <br />0.0017 weeks <br />3.91915e-4 months <br /> during performance of local leak rate testing (LLRT), it was determined that the main steam system isolation valves (MSIV) on main steam line "C" were found to have leakage in excess of the technical specification limit of 11.5 standard cubic feet per hour. Additional LLRT resulted in a total as-found maximum path leak rate of 6625 standard cubic feet per hour (SCFH).

The root cause of the unforeseen failure of the "C" Main Steam Line .Inboard Isolation 'Valve was abnormal wear. Upon inspection of the valve, .TVA identified rib guide wear on the bottom guide where the poppet contacts the guide when the valve is in the open position. Because of this wear, the main poppet tilted as the valve traveled to the closed position, failing to contact the seat properly and isolate.

TVA repaired the "C" MSIV valve and successfully retested it. Additionally, TVA repaired, modified, or replaced other failed components. During subsequent retesting, TVA attained a total as left maximum path leakage of 160.1642 SCFH.

NRC Form S'DR 9307060230 930628 PDR 366(6-89)

ADOCK 05000260

II Ol I

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

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

I I I ISEQUENTIAL i iREVISIONt t I I Browns Ferry Unit 2 I I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

I. PLANT CONDITIONS Unit 2 was in cold shutdown for the Unit 2 cycle 6 refueling outage. Units 1 and 3 were defueled.

II 4 DESCRIPTION OF EVENT A. ~Ev t:

On January 31, 1993, at 1030 'hours during performance of local leak rate testing, it was determined that the main steam '[SB] system isolation valves [ISV], on main steam line "C" were found to have leakage in excess of the technical specifications (TS) limit of 11.5 standard cubic feet per hour (SCFH) allowed for a main steam isolation valve (MSIV). Furthermore the leak rate of the -valves exceeded the 655.9 SCFH allowed for total primary containment. The leak rate in steamline "C" was determined to be 1320.26 SCFH. Subsequent evaluation has determined that only the inboard MSIV exceeded the TS leak rate limit.

Additional local leak rate testing (LLRT) performed during the refueling outage resulted in a total as-found maximum path leak rate of 6625 SCFH.

The major contributors to the as-found leak rate were the "C" inboard MSIV and the primary containment ventilation isolation valves [BF], feedwater system [SJ] check valves [CKV],and'ontainment atmospheric dilution system

[BB] solenoid valves.

This event is reportable pursuant to 10 CFR 50.73(a)(2)(ii)(A) as any event or condition that resulted in .the condition of the nuclear plant, including its principal safety barriers, being seriously degraded or the resulted in the nuclear plant being in an unanalyzed condition that significantly compromised plant safety.

B None.

NRC Form 366(6-89)

Ol NRC Form 36GA U. . NUCLEAR REGULATORY COHHISSION Approved OHB No ~ 3150-0104 (6-89) ,

Expires 4/30/92 1.ICENSEE EVENT REPORT (LER)

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

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

C. t A January 31, 1993, at. 1030 Primary containment total leak CST rate is determined to have exceeded acceptance criteria.

January 31, 1993, at 1420 TVA makes a four-hour CST nonemergency notification to NRC in accordance with 10 CFR 50.72(b)(2)(i).

D. th r tern t A t None.

E. Mt v s The leak rate was determined to be unacceptable during performance of the surveillance instruction that determined the amount of leakage through main steam line "C" primary containment isolation valves. Additional leakage was identified through performance of the LLRT program.

CL to t None.

G. t t None.

III. CAUSE OF THE, EVENT A. Imm t The immediate cause of the event was excess leakage in the "C" main steamline. Subsequent evaluation of "C" MSIVs determined that the inboard isolation valve was exhibiting leakage greater than'he TS limit. Failure of the MSIV and other components, placed the plant outside the allowable total as-found maximum path leak rate.

NRC Form 366(6-89)

0 I

NRC Form 366A

{6-89)

U.. NUCLEAR REGULATORY CONNISSION LICENSEE EVENT REPORT (LER) t Approved ONB No. 3150-0104 Expires 4/30/92

, TEXT CONTINUATION FACILITY RANE (1) IDOCKET NUNBER (2) l f t SEQUENTIAL I f REVISION I l l I I Browns Ferry Uni t 2 I I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

B The root cause of the unforeseen failure of the "C" MSIV was abnormal wear. Inspection of the valve identified rib guide wear on the bottom rib where the poppet contacts the guide when the valve is in the open position. Because of 'this wear, the main poppet tilted as the valve traveled to the closed position, thus, prohibiting an adequate seal.

C. tr t None.

XV. AMLYSXS OF THE EVENT Each main steam line has two isolation valves, one on the inside and one on the outside of primary containment. The isolation valves prevent radiation release in excess of 10 CFR 100 guidelines in the event of a steam line break outside primary containment. The valves also 1'imit 'inventory loss during a loss of coolant accident. Technical specifications require that the MSIVs be tested for leakage during each refueling outage. If the leakage rate for any one MSIV exceeds 11.'5 SCFH, TSs require that the valve be repaired and retested. Furthermore, if the total as-found maximum path leak rate is greater than allowed, TSs require that repairs are implemented and that local leakage meets acceptance criteria as demonstrated .by retest.

V- CORRECTIVE ACTXONS tv t None.

B. v TVA repaired the "C" steamline inboard MSIV. and successfully retested it.

Additionally, TVA repaired, modified or replaced other failed components.

During subsequent retesting, TVA attained a total as-left maximum path leakage of 160.1642 SCFH.

NRC Form 366(6-89)

NRC Form 366A (6-89)

U.S. NUCLEAR REGULATORY COHHISSION LICENSEE EVENT REPORT (LER) t Approved OHB No. 3150-0104 Expires 4'/30/92 TEXT CONTINUATION FACILITY NAHE (1) IOOCKET NUMBER (2)

I I I t SEQUENTIAL I lREVISION I I I l t Browns Ferry Uni t 2 I I I I I TEXT (If more space is required, use additional NRC, Form 366A's) (17)

VI. ADDITIONAL INFORMATION The "C" MSIV is manufactured by Atwood and Morrill, Model 20851-H-26.

TVA has previously issued reports detailing multiple failures of MSIVs to

meet the required acceptance criteria. Subsequently, TVA has instituted a MSIV upgrade program. This program has greatly reduced the number of failures. TVA has disassembled and inspected this valve in the past four refueling outages and this is the first instance that noticeable wear has been identified. Therefore, no further actions are required to prevent recurrence.

The Reactor Building Ventilation System containment isolation valves whic have performed poorly during previous local leak rate testing were replaced with an updated design. Other failed components were repaired, replaced, or modified. Thus, TVA concludes this will minimize recurrence of vent valve failure.

VII. COMMITMIKTS None.

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

NRC Form 366(6-89)

Oi f