ML20086E813

AO 73-35:on 731219,MSIV Relay 5A-K3C Failed to Energize During Monthly MSIV Functional Test.Caused by Limit Switch Actuating Arm Being in Wrong Position.Arm Manually Reset

ML20086E813
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	12/26/1973
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086E820	List: ML20086E813 ML20086E826
References
AO-73-35, VYV-3108, NUDOCS 8312070528
Download: ML20086E813 (2)

Text

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• &z VERMONT YANKEE NUCLEAR POwun CORPORATION SCVCNTY GCVCN OROVE STRCCT RUTLANn, VERMONT 05701 REPLY TO:

VYV-3108 P.O. BOX 157 VERNON VCRMONT c5354 December 26, 1973 G

• Director

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Directorate of Licensing \\-

United States Atomic Energy Commission 9~

RECElWD Washington, D.C. 20545 -

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REFERENCE:

Operating License DPR-28 g Docket No. 50-271 pg#od WA5""# #

Abnormal Occurrence No. A0-73-35

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to Gentlemen:

As defined by Technical Specifications for the Vermont Yankee Nuclear Power Station, Section 6.7.B.1, we are reporting the following abnut ual Gecut ience os A0 -73 35.

On December 19, 1973, at 1330, during conduct of the monthly Main Steam Line Isolation Valve functional test as referenced in Technical Specifications, Table 4.1.1, valve V2-86C was exercised and cycled to the closed position. This was verified when the valve " closed" limit switch caused Reactor Protection System relay SA-K3C to deenergize. When the valve returned to the open position, it was noted that relay 5A-K3C failed to energize as it should have with an open valve condition. Operating personnel, attempting to determine the cause, discovered the limit switch actuating arm to be in a position indicating valve closure. The actuating arm was manually reset and the associated ralay was immediately energized. This action restored the Reactor Protection System logic to its normal operating condition. Valve V2-86C was cycled again and all valve limit switches were verified to be functioning properly. The reactor was operating at approximately 687. power at the time of this incident.

The Plant Operations Review Committee (PORC), meeting to review the incident, noted this to be the first instance of this nature relative to Main Steam Isolation Valve limit switches. Considering this and the fact that all limit switches operated properly during the valve retest, i the incident was determined to be an isolated case of 1nstrument

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_ Directorate of Licensing December 26, 1973 Page 2 malfunction and an increase in the monthly surveillance frequency was deemed unnecessary. In addition, it was ascertained that this condition would not have compromised the safe operation of the Reactor Protection System in that the system is a normally energized configuration of logic. Failure of this particular limit switch to reset would have maintained its associated relay in a deenergized or more conservative state.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION S.\ia. O B.W. Riley C T Plant Superintendent UFC/kbd i

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