ML20086E460

AO 74-09:in 740625,movements of LPCI Loop Break Detection Logic Differential Pressure Indicating Switches 2-129B & 2-129C Found Sticking,Causing Pointer to Log Input Pressure. Caused by Frequent Switch Actuation

ML20086E460
Person / Time
Site:	Vermont Yankee
Issue date:	07/03/1974
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML20086E468	List: ML20086E460 ML20086E473
References
AO-74-09, AO-74-9, VYV-3318, NUDOCS 8312070317
Download: ML20086E460 (2)

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VERMONT YANKEE NUCLEAR POWER CORPORATION J ScVcNTY ScVcN OROVE STRCCT .

RuTLAxo, VenutoxT osToi l VYV-3318 P. O. BOX 157 VERNON. VERMONT oS354 July 3, 1974 Director 4 $G Directorate of Regulatcry Operations, Region I United States Atomic Energy Commission k&[g e g 631 Park Avenue Z N4 y # (ogL._

King of Prussia, Pennsylvania 19406 g '

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REFERENCE:

Operating Licease DPR-28  %

3 Docket No. 50-271 g 4 Abnormal Occurrence No. A0-74-09 (10 Day Report)

Dear Sir:

As defined by Technical Specifications for the Vermont Yankee Nuclear Power Station, Section 6.7, we are reporting the following Abnormal Occurrence as A0-74-09.

At approximately 1200 on June 25, 1974, plant personnel who were-performing routine instrument surveillance testing on the Riser d/p LPCI Loop Break Detection Logic discovered that the movements of DPIS 2-129B and C were sticking to the extent that the pointer would lag the input pressure by approximately 0.5 psid on increasing and decreasing pressure. This condition was determined to be in violation of Technical Specifications, Section 3.2, Table 3.2.1, in that the requirement for the minimum number of operable trip channels per trip system for the A>B d/p Across Risers trip function was not satisfied. The plant was operating at 80% power at the time of this discovery.

The immediate course of action was to replace switch DPIS 2-129B with an operable spare and to place switch DPIS 2-129C in the tripped condition because of a lack of a second operable spare.

The Plant Operations Review Committee met to review this occurrence on July 2, 1974, and concluded that corrective action taken up to that time was appropriate. It was also concluded that the cause of the mal-function of these two switches was the frequent actuation of the switches caused by cyclic hydraulic fluctuations in the recirculation loops. This had previously been reccgnized as an undesirable situation and an engineer-ing design change which proposed to install snubbers in the instrument lines to these switches to reduce their frequent unnecessary operation was in the final stages of management review when this abnormal occurrence was discovered.

The Plant Operations Review Committee recommended that yhe engideering design change be implemented as soon as possible. '

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~4 8312070317 740703 .

PDR ADOCK 05000271 s N COPY SENT REGION / 3 ,

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, Directorateof(julatoryOperations,RegionI V July,3 3 1,974 Page 2' On July 3, 1974, a new indicating switch was obtained and installed in place of DPIS 2-129C thereby making all of the A>B d/p Across Risers trip channels operable. Final canagement approval has been obtained on the engineering design change and the snubbers will be installed during the week of July 8, 1974.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION

.bd- N B. W. Riley Plant Superintendent WPM /sjp l

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