ML20086E677

AO 74-05:on 740304,LPCI Loop a Valve V10-25A Failed to Open When Control Switch Placed in Open Position.Caused by Burned Out Valve Motor.Motor Replaced

ML20086E677
Person / Time
Site:	Vermont Yankee
Issue date:	03/11/1974
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086E684	List: ML20086E677 ML20086E696
References
AO-74-05, AO-74-5, VYV-3187, NUDOCS 8312070482
Download: ML20086E677 (2)

Text

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REFERENCE:

Operating License DPR-28 /

Docket No. 50-271 D /37[. {yI -* {f/

Abnormal Occurrence No. A0-74-05 ,

Gentlemen:

As defined by Technical Specifications for the Vermont Yankee Nuclear Power Station, Section 6.7.B.1, we are reporting the following Ak.ae =1 Aaa..**nnea oc AA-7/. 0%,

At approximately 2130 on March 4, 1974, while performing routine surveillance testing on the Low Pressure Coolant Injection System (LPCI),

Loop A, valve V10-25A failed to open when the control switch was placed in the open position. It was determined that this condition was in violation of Technical Specifications, Section 1.0.A.4 in that it could have prevented the performance of the intended safety function of an engineered safety feature system. The valve was manually opened immediately and the system injection line upstream normally open valve V10-27A was closed. Since this valve will open in response to a LPCI automatic initiation signal, the subsystem was considered operable. The reactor was operating at approximately 78% power at the time of this incident.

Subsequent investigation revealed that the notor on valve V10-25A had burned out. It was replaced and valve operability was demonstrated by 1520 on March 5, 1974.

The cause of the valve failure was considered to be a direct result of operating the LPCI system in the shutdown cooling mode from February 23, 1974 until February 25, 1974, which subjected the associated components to system temperature. When shutdown cooling was terminated, valve V10-25A was returned to its normally closed LPCI condition. At this time, the valve internals would have exhibited temperatures relative to its most recent operating mode. Contraction of the valve and the piping system i

ensued as temperature was reduced to an ambient condition. When the routine surveillance test on valve V10-25A was performed on March 4,, 1974, l' the forces required to open the valve, due to contraction, were grpager than those which could be. supplied by the valve operator. }g \

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Directorate of Licensing March 11, 1974 Page 2 On two previous occasions, submitted as Abnormal Occurrences 73-03 and 73-12, incidents occurred relative to valve V10-25A. It was felt that those failures were due to high differential pressure across the valve disc which exceeded the design capability of the valve operator. Additional investigation indicates that prior to both incidente the LPCI system had been operated in the shutdown cooling mode. As a result of this, it seems probable that all three incidents are a direct result of contraction of valve internals.

The Plant Operations Review Committee reviewed the incident and concurred that the probabic cause van as stated above. To preclude repetition of this incident, plant operating procedures will he modified to require closing valve V10-27A, or its counterpart in Loop B if shutdown cooling was operated using this loop, after termination ef shutdown cooling. After twelve hours, valve V10-25A will be cycled, and following this action, both valves will be returned to their normal system configuration.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION Q\

B.W. Riley Plant Superintendent WFC/kbd 9

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