ML19210D677

LER 79-138/01T-0:on 791108,Westinghouse Identified Potential Failure in Circuit Reactor Trip Breaker for P-4 Permissive W/Engineered Safety Features Actuation.Caused by Design Failure.Reanalysis in Progress

ML19210D677
Person / Time
Site:	North Anna
Issue date:	11/21/1979
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19210D670	List: ML19210D668 ML19210D677 ML19210D687
References
LER-79-138-01T, LER-79-138-1T, NUDOCS 7911270446
Download: ML19210D677 (2)

Text

NRCgFORM 366 U.S. NUCLEAR REGULATORY COMMISSION (7 7M d LICENSEE EVENT REPORT CONTROL BLOCK: l l l l l l l (PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION) 1 6 lo lt l l Vl Al N A l S l 141 lgl 15 0 l 0 l- l 0 l 0 l 0 l 0 l0 l- l0 l0 LICENSE NUMdhR 25 l@l 26 4lLICENSE 1l 1lTYPE li 1l@l JO l

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? 8 60 61 DOCKET NUMBER 68 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h o 2 l On November 8,19 79, Westinghouse inf ormed Vepco that it had identified an undetectablel o 3 g failure which potentially could exist in a circuit associated with ESF actuation. TheI o 4 circuit af fected is the Reactor Trip Breaker auxiliary contacts for the P-4 permissive I loisl lwhich provides an interlock to enable or defeat the capability to manually reset and l 0 l6 l l block safety injection. Present testing of the SSPS does not check the operation of l o l 7 ] I these P-4 contacts, therefore a potential failure would be undetected. The health andI o g safety of the general public were not affected by this event. Reportable pursuant to I 80 7 8 9 1*D. D*V.1*d.l.

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Virginia Electric and Power Company North Anna Power Station, Unit #1

Attachment:

Page 1 of 1 Docket No. 50-338 Report No. LER 79-138/01T-0 Description of Event On November 8,1979, Westinghouse informed Vepco that an undetectable failure in the Engineered Safety Features Actuation System had been identified.

Because present testing of the Solid State Protection System (SSPS) does not check the operation of the Reactor Trip Breaker auxiliary contacts for the P-4 permissive, a potential failure of the P-4 contacts would not be detected and the automatic initiation of safety injection could be prevented.

Probable Consequences of Occurrence The P-4 permissive provides an interlock in the Engineered Safety Features Actuation System to enable or defeat, depending on the status of the Reactor Trip Breakers, the capability to manually reset and block safety injection.

If the P-4 contacts fail to close when the reactor trip. breakers open, the normal mode of resetting and blocking SI could be prevented. If the contacts fall to open when the breakers are closed, the consequences are such that following a previous initiation of SI and manual reset and block, the block of SI would remain following the reset of the reactor trip breakers, when the plant would return to power. An annunciator is available in the control room to check the correct function of the P-4 pes issive; however, illuminated control board windows are not permitted by IEEE Standards as an acceptable means of detection because the components are not saf ety grade. The health and safety of the general public were not affected by this event. Unit 2 has the same design and is similarly affected.

Cause of Occurrence This undetectable failure is apparently the result of a design error by Westing-house.

Immediate Corrective Action Westinghouse has provided procedures for testing the P-4 contacts with the unit shutdown and with the 2 nit at power. Both test schemes are presently being evaluated.

Scheduled Corrective Action Appropriate procedures will be changed to incorporate the testing of the P-4 contacts on a periodic basis.

Actions Taken to Prevent Recurrence No further actions are required.

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