ML19263C500

LER 79-017/01T-0 on 790212:during Axial Power Distribution Monitoring Sys Failure on 790206,FQ Survey Computer Program Could Not Monitor Axial Power Distribution.Caused by Incorrect Power Inputs from Process Computer

ML19263C500
Person / Time
Site:	North Anna
Issue date:	02/20/1979
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19263C497	List: ML19263C496 ML19263C500
References
LER-79-017-01T, LER-79-17-1T, NUDOCS 7902260355
Download: ML19263C500 (2)

Text

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14 7S HEPORT DATE 80 7 8 LU 61 DOCKE T NUYBEH EVENT DESCRIPTION AND PROBADLE CONSEQUENCES h o 2 [ On 2-12-79, it was discovered thal _during_an_axiitl_ power _distributico monitorinq l g i system failure, on 2-6-79, the FQ Survey Computer Program was not capable of moni- l 0 4 toring the axial power distribution, as required by T.S. 4.2.6.1, 1 O s gljiseventisreportableasperT.S.6.9.1.8.i.

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33_ 3 36 31 40 41 44 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h l: lOI The cause of the event was that a power level of anproximately 86 ; was inputed to the l li li l l FQ Survey Program by the Plant Process Computer while the actual nower level was 97 ' I

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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 79-017/0lT-0 Description of Event:

On 2-12-79, it was discovered that the FQ Survey Computer Progra:a was not capable of monitoring the Axial Power Distribution during an Axial Povier Distribution Monitoring System failure on 2-6-79. This is contrary to T.S. 4.2.6.1. This event is reportable as per T.S. 6.9.1.8.i.

Probable Consequences of Occurrence:

The limit on axial power distribution ensures that FQ will be controlled and monitored on a more exact basis through use of the APDMS or the incore moveable detectors when operating above 95% of Rated Thermal Power.

Comparison of the APDMS results after the system was restored to the results before the system failed, showed that the peak FQ values and % margins between peak and limit values had not changed during the APDMS failure. There was no change in power level or any rod movement that would change the core power configuration during the eight hours when the APDMS was not available.

As a result, the safe operation of the plant was not affected and the public health and safety was not endangered.

Cause of Occurrence:

The cause of the event was that a false power level was inputed into the FQ Survey Program from the plant process computer.

On 1-24-79, the process computer failed and after being restored, a computer constant was changed in the process computer's thermal power calcula-tion by an unknown mechanism.

As a result, a power level of approximately 86% was inputed into the FQ Survey Program. Since the FQ limit changes with power level, the Survey program was incapable of calculating the correct % margins between the actual FQ values and the FQ limit. The program was able to correctly calculate the actual FQ value.

Immediate Corrective Action:

The correct computer constant was entered into the process computer resulting in the correct power level inputed into the FQ Survey Program.

Scheduled Corrective Action:

No further corrective action was required.

Actions Taken to Prevent Recurrences:

A program to monitor constants after restoration of the computer following a failure is currently under investigation.