ML19242B151

LER 79-089/01T-0 on 790720:discovered Possibility That Process Cards,Types Nmb,Nvp & Ncb,Could Fail,Causing Adverse Effects on Associated Loop Actions.Caused by Faulty Component Layout on Cards.Analysis Performed

ML19242B151
Person / Time
Site:	North Anna
Issue date:	08/02/1979
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19242B146	List: ML19242B145 ML19242B151
References
LER-79-089-01T, LER-79-89-1T, NUDOCS 7908070583
Download: ML19242B151 (2)

Text

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60 61 COCs ET F.L*.t'3 t a tA 63 EVENT D ATE 14 75 AEPOR T D A TE BJ EVENT DESCRIPTION AND PROB ABLE CONsECuENCES h o 2 l On July 20, 1979, Vepco Instrument Deoartment discovered that it is possible for oro- l o 3 cess cards, types NMB, NVP and NCB, to fail causing adverre effects on the associatei l R .q loop actions. Because the f ailures are ei ther in a conserva tive di rection or have l o s [ redundant backuo ?rotec tion, the health and safety of the general public were not l

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Virginia Electric and Power Company At**chment, page 1 of 1 North Anna Power 5tation, Unit #1 Docket No. 50-333 Report No. LER 79-039 /01T-0 Description of Event On July 20, 19 79, the Vepco Instrument Dep..rtment discovered that it is possible for its process cards, types NMD, NVP and. NCB, to f ail causing adverse ef fects on the associated loop actions.

Probable Consecuences of Occurrence The consequences of this event were limited because analysis revealed that all possible f ailures are in the conservative direction with the exception of feedwater flow. The Steam /Feedwater Flow Mismatch in coinciden:e with a Steam Generator Low Water Level trip is not used in the transient and accident analy-ses but is included in the Technical Specifications to insure the functional capability of the specified trip settings and thereby enhance the overall reli-ability of the Reactor ?rotection System. This trip is redundant to the Steam Generator Water Level Low-Low trip. The health and safety of the general public were not af fected by this occurrence. Unit 2 uses identical process cards in its orotection system and is similarly af fected.

Cause The cause for the possib? e card failures is the layout of the components on the cards. Because of this layout, it is possible for ccmponents to short cl..ctric-ally to ground. A similar problem vr.s encountered w.th one lead / lag card in Unit 2's protection system (AT/TAVG circuitry) on June 25, 19 79 .

Immediate Corrective Action The Vepco Instrument Department performed a Process Card Failure Analysis for each card in question to determine the exact ef fects of its failure on pro -

tection loops.

Scheduled Corrective Action The defective process cards will be replaced by newer models with proper component layout when they become available.

Actions Taken To Prevent Recurrente No further actions required.

5!9 359 LER:E2