ML20086E782

AO 74-01:on 740124,reactor Scrammed,Resulting from Turbine Trip Causing Automatic Closure of All But One Msiv.Valve 2-80C Failed to Close Due to Failure of Pneumatic Pilot Valve to Actuate.Valve Assembly Returned to Vendor for Insp

ML20086E782
Person / Time
Site:	Vermont Yankee
Issue date:	01/31/1974
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086E784	List: ML20086E782 ML20086E790
References
AO-74-01, AO-74-1, VYV-3158, NUDOCS 8312070518
Download: ML20086E782 (2)

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) VERMONT YANKEE NUCLEAR POWER CORPORATION l .

j SEVENTY SEVEN OROVC STRECT I RUTLAND, VERMONT OG701 j VYV-3158 P. O. BOX 157 VERNON. VERMONT oS354 January 31, 1974 I

N Director \ b 'l A Directorate of Licensing United States Atomic Energy Commission y f bkEb ). '.3 s)

Washington, D.C. 20545 ,.

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REFERENCE:

Operating License DPR-28 d U / ~' ~ ~ ~ ' , 'j Docket No. 50-271 r ce

! Abnormal Occurrence No. A0-74-01 \'\A'-

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Gentlemen: ,Yd2 As defined by Technical Specifications for the Vermont Yankee Nuclear Power Station, Section 6.7.B.1, we are reporting the following i Abnormal Occurrence as A0-74-01.

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! At approximately 2327 on January 24, 1974, while performing a i test associated with the plant startup test program, a reactor scram l occurred as a result of a turbine trip. Subsequent to the scram, a primary containment isolation signal was initiated causing automatic closure of the main steam isolation valves. All valves closed with the exception of valve 2-80C. This condition was determined to be in

] violation of Technical Specifications, Section 1.A.5, in that it i resulted in abnormal degradation of one of the several boundaries which are designed to contain the radioactive materials resulting from l the fission process. The reactor was in a shutdown condition at the

! time of this incident. Following the transient resulting from the

! plant trip, the outboard isolation valve in steam line C (Valve 2-86) i was tagged in the closed position.

Failure of the isolation valve to close was caused by the failure i of the pneumatic pilot valve to actuate. . The pneumatic pilot valve l' assembly was replaced with a spare and valve 2-80C was successfully

, tested on January 26, 1974, at operating temperature. An examination

of the pilot valve assembly revealed that the valve piston was

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sticking in the valve cylinder. 'Luere was no evidence of dirt or j foreign material in the valve; however, there did appear to be some l

evidence of slight rubbing on the cylinder wall.

8312070518 740131 -

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. O O VERMONT YANKEE NtlCLEAR POWER CORPORATION

• Directorate of Licensing January 31, 1974 Page 2 During the review of the incident by the Plant Operations Review Committee, it was noted that the pilot valve assembly to this same .

isolation valve had been replaced in August, 1973, as a result of ,

performing routine maintenance on the Main Steam Isolation Valves.

! The isolation valve was successfully tested at that time. The main steam line isolation valves were again successfully tested at the end of an extended plant outage in November, 1973, prior to plant l startup as part of the touttae surveillance test schedule.

f The pilot valve assembly will be shipped to the vendor for a detailed inspection in an attempt to specifically identify the cause of the pilot valve failure, and furthermore, an investigation with the vendor will be made to determine if a dry lubricant can be used in the valve.

The Plant Operations Review Committee further concluded that all future full closure tests on the thin Steam 1 solation Valves conducted subsequent to maintenance on the valves should be conducted at the elevated temperature that is experienced when the plant is operating.

Due to the special interest recently expressed by the Directorate j of Licensing in the area of MSIV air pilot valve failures, results of vendor laboratory analyses will be forwarded by separate correspondence -

when available. ,

, Very truly yours,

- , VERMONT YANKEE NUCLEAR POWER CORPORATION-1 o't .

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, ,Bradford W. Riley 4

Plant Superintendent WPM /kbd I

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