BVY-98-121, Submits Test Results of Accumulator Added to Valve V10-26A, Per GL 95-07, Pressure Locking & Thermal Binding of Safety- Related Power-Operated Gate Valves

Submits Test Results of Accumulator Added to Valve V10-26A, Per GL 95-07, Pressure Locking & Thermal Binding of Safety- Related Power-Operated Gate Valves

ML20236X924
Person / Time
Site:	Vermont Yankee
Issue date:	08/04/1998
From:	Leach D VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BVY-98-121, GL-95-07, GL-95-7, NUDOCS 9808110031
Download: ML20236X924 (2)

Text

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. i VERMONT YANKEE i y NUCLEAR POWER CORPORATION 185 Old Ferry Road, Brattleboro, VT 05301-7002 August 4,1998 (802) 257 5271 4 BVY 98-121 I

I United States Nuclear Regulatory Commission (

1 ATTN: Dc4cument Control Desk Washington,DC 20555  ;

References:

Letter, VYNPC to USNRC, BVY 98-11, dated January 23,1998 l

(a) l (b) Letter, USNRC to VYNPC, NVY 97-168, dated November 24,1997 (c) Generic Letter 95-07," Pressure Locking and Thermal Binding of 1 Safety-Related Power-Operated Gate Valves", dated August 17,1995 l

Subject:

Vermont Yankee Nuclear Power Station License Number DPR-28 (Docket 50-271)

Test Results of Accumulator Added to Valve V10-26A  ;

Reference (a), in providing our response to the request for additional information in Reference (b),

dealing with Generic Letter (GL) 95-07 [ Reference (c)], indicated that a pressure locking test was to {

be performed, during the 1998 Refueling Outage, on a modification to Motor Operated Valve (MOV) V10-26A. During a subsequent telephone conversation on February 19,1998, between ,

Messrs. Chris Hansen, Joe Lynch, Mike Metell, Gautam Sen and Ray Ashley (Vermont Yankee), i and Kahtan Jabbour and Steve Tingen (NRC), we committed to provide the results of the pressure- l locking test on Valve V10-26A. This letter provides that infonnatic n.

l MOV V10-26A, which performs a safety function during the Drywell Spray Mode of RHR Operation,is a 12-inch,300-pound double-disk gate valve manufactured by Anchor Darling. During our work associated with GL 95--07, it was postulated that this valve could be subject to pressure l locking caused by sudden piping depressurization and heat-up of water in the bonnet (from a temperature increase in a branch line). A design change w as implemented to V10-26A that involved installation of an accumulator, the purpose of which was to limit bonnet pressure so as to alleviate postulated pressure locking that would prevent the valve from opening. The accumulator was conservatively designed to allow sufficient opening thrust margin with a bonnet pressure 50 psig higher than the upstream pressure.

The pressure locking test was conducted on May 1,1998, under an approved Special Test Procedure.

. The purpose of the test was to conGrm that the modified valve would open with a pressure 50 psig higher in the bonnet than in the upstream piping. The test was conducted using water at pressures expected to conservatively envelop design basis conditions. During the test, the accumulator was confirmed to be pre-charged to within the procedurally controlled acceptable range that was calculated for all analyzed ambient temperatures. During performance of the test, the bonnet was to i be pressurized to 382 psig with upstream pressure at 332 psig (i.e.,50 psig less than honnet pressure), and with a downstream pressure of 0 psig. However, while the test was being perfomied, I i

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BVY 98-121 Page 2 of 2 the bonnet would not hold pressure because ofleakage, from the bonnet through the disk area, to the downstream piping. Since the bonnet differential pressure could not be maintained, even for a very -l short period of time (i.e., it could not establish a pressure locking condition), the test was terminated.

Vermont Yankee's assessment, given the test result, is that modified Valve V10-26A is not susceptible to pressure locking conditions. From a systems standpoint, the leakage rate is  ;

insignificant and does not interfere with the valve being able to perform its intended safety function.

However, the leakage is sufficient to prevent maintaining a higher pressure in the bonnet that would be a precursor to a pressure locking condition. It is to be noted that this valve successfully passed 10CFR Part 50, Appendix J leakage tests in the opposite flow direction to that in this pressure locking test.

The accumulator on Valve V10-26A, previously installed by design change and procedurally maintained, assures valve operability absent any future decrease in seat leakage.

If you have any questions regarding this matter, please contact this office.

Sincerely, VER T hKEE NUCLEAR POWER CORPORATION L

Do each Vi resident, Engineering cc USNRC Region I Administrator USNRC Project Manager-VYNPS f USNRC Resident inspector-VYNPS  !

Vermont Department of Public Service L

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