05000395/LER-1991-001, :on 910219,missed Surveillance for Axial Flux Difference.Caused by Personnel Error.Review Made of Two Computer Generated Alarms Required by Tech Spec & Software Changes Made to Eliminate Synchronization

:on 910219,missed Surveillance for Axial Flux Difference.Caused by Personnel Error.Review Made of Two Computer Generated Alarms Required by Tech Spec & Software Changes Made to Eliminate Synchronization

ML20070Q281
Person / Time
Site:	Summer
Issue date:	03/22/1991
From:	Higgins W, Skolds J SOUTH CAROLINA ELECTRIC & GAS CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-001, LER-91-1, NUDOCS 9103280305
Download: ML20070Q281 (4)

LER-1991-001, on 910219,missed Surveillance for Axial Flux Difference.Caused by Personnel Error.Review Made of Two Computer Generated Alarms Required by Tech Spec & Software Changes Made to Eliminate Synchronization

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(1)
3951991001R00 - NRC Website

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Document Control Desk V. S. Nuclear Regulatory Commission Washington, DC 20555 Gentlemen:

Subject:

VIRGIL C. SUMMER NUCLEAR STATION DOCKET NO. 50/395 OPERATING LICENSE NO. NPF-12 LER 91-001 (ON0 910010)

Attached is Licensee Event Report No.91-001 for the Virgil C. Summer Nuclear Station. This report is submitted pursuant to the requirements of 10CFR50.73(a)(2)(1).

Should there be any questions, please call us at your convenience.

Very truly yours, Tdd /

John L. Skolds DCH:JLS:lcd Attachment c:

0. W. Dixon Jr. (w/o Attachment)

J. W. Flitter R. R. Mahan (w/o Attachment)

L. J. Montondo R. J. White NRC Resident Inspector S. O. Ebneter J. B. Knotts Jr.

G. F. Wunder INP0 Records Center General Managers ANI Library C. A. Price Marsh & McLennan G. J. Taylor NSRC F. H. Zander RTS (0N0 910010)

T. L. Matlosz File (818.05 & 818.07)

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-. e,.,,-,, ~..,nei On February 19, 1991, at approximately 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br />, a computer generated " COMPUTER DELTA FLUX LIMIT EXCEEDED" alarm actuated on the Main Control Board (MCB).

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operators, using indications on the MCB and the Nuclear Instrumentation System, verified that the actual Axial Flux Difference was within Technical Specification (TS) limits. Nuclear Computer Services was called to investigate the discrepancy between the MCB indication and the computer generated alarm.

The computer engineer arrived in the control room and cleared the alarm, but failed to determine that tne computer program that generates the alarm was not running, thereby leaving the alarm cleared but inoperable. With the alarm cleared, the operators considered the alarm operable and did not pursue the compensatory surveillance. On February 21, 1991, at approximately 0820 hours0.00949 days <br />0.228 hours <br />0.00136 weeks <br />3.1201e-4 months <br />, a review of the computer printout showed that the p Ngram that actuates the delta flux alarm had not been running since 1203 hourt on February

19. Since the compensatory surveillance had not been performed, th'.5 represented a missed surveillance. The program and alarm were returned to operation, and delta flux was verifieil to be within the TS limits.

As a result of this event, the Annunciator Response Procedures (ARP) for the delta flux alarm and the computer failure alarm were changed. Also, Computer Services has implemented computer program changes to improve the quality and the reliability of the computer generated nlues for delta flux.

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Westinghouse - Pressurized Water Reactor l

EQUIPMENT 10ENTIFICATION:

l Integrated Plant Computer System (IEEE-ID) l IDENTIFICATION OF EVENT:

An incorrect determination of the status of a computer generated annunciator resulted in continued operation without performing a compensatory surveillance requirement.

EVENT DATE AND TIME:

I Event - February 19, 1991, at 1203 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.577415e-4 months <br />.

Discovery - February 21, 1991, at 0820 hours0.00949 days <br />0.228 hours <br />0.00136 weeks <br />3.1201e-4 months <br />.

I REPORT DATE:

i March 22, 1991

CONDITIONS PRIOR TO EVENT

Mode 1, 99% reactor power

DESCRIPTION OF EVENT

On February 19, 1991, at 1203 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.577415e-4 months <br />, the control room. received a " COMPUTER DELTA FLUX LIMIT EXCEEDE0" alarm and an " INTEGRATED PLANT COMPUTER SYSTEM (IPCS)

FAILURE" alarm. Both alarms are computer generated. The IPCS failure alarm cleared shortly after its annunciation, but the delta flux alarm remained.

The i

l operators immediately verified that the delta flux meters on the main control board (MCB) indicated that Technical Specification (TS) limits were being complied with.

They then utilized the Annunciator Response Procedure (ARP) for the delta flux alarm and verified that delta flux was within TS limits by using the Nuclear Instrumentation System, MCB, and rod position indications. Since no reason for the alarm could be found, a computer engineer was contacted at 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br />. Also, preparations were initiated to perform a surveillance that is required when'the delta flux alarm is inoperable.

At approximately 1315 hour0.0152 days <br />0.365 hours <br />0.00217 weeks <br />5.003575e-4 months <br />s--before the surveillance was-initiated--the computer engineer cleared the alarm and determined l

that the alarm was operable, using the computer-indication which appeared normal and compared closely to the MCB indicators. No further action was taken by the operators.-

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--..- m m m, e On February 21, 1991, at 0820 hours0.00949 days <br />0.228 hours <br />0.00136 weeks <br />3.1201e-4 months <br />, a reactor engineer notified the control room that the computer had stopped updating the delta flux value at 1203 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.577415e-4 months <br /> on February 19, 1991. A computer engineer was contacted again; he discovered that the computer program which calculates delta flux and compares it to acceptable limits had failed, but the color of the displayed value of delta flux was not affected (most program failures will change the color of the displayed value to magenta).

The program was restarted at 0830 hours0.00961 days <br />0.231 hours <br />0.00137 weeks <br />3.15815e-4 months <br />, and operations verified that the alarm was returned to operable status. The failure to perform surveillance requirement (SR) 4.2.1.1.b during the period that the alarm was inoperable represented a condition prohibited by Technical Specifications per 10CFR50.73.a.2.1.B.

CAUSE OF EVENT

The surveillance was missed due to personnel error in interpreting-the misleading computer indication and the failure to verify the status of the program for the delta flux alarm.

The delta flux program failed due to the calculation of a negative time interval j

that resulted from a daily synchronization of the IPCS. internal clock with the national time standard, i

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ANALYSIS OF EVENT

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The oscillations of delta flux were known to be within TS' limits at the initiation of the event. Also, no transients ar oporational actions that could significantly affect the value of delta flux occurred during the period-that the' delta flux alarm was inoperable. Therefore, the failure of the alarm had_no adverse affects or safety consequences with respect to_the plant.

IMMEDIATE CORRECTIVE-ACT!0NS:

- Immediately upon the alarm actuation and again at the discovery that the alarm was-inoperable,. delta flux indications:on the nuclear instrumentation system and MCB were verified to.be within TS limits. Upon discovery that-the alarm was inoperable, a computer _ engineer was contacted and'the alarm was restored.

ADDITIONAL CORRECTIVE ACTIONS

- 1.

A review was made of the two computer generated alarms that are required by TS (delta flux alarm and rod deviation alarm). As a result,-the ARPs for both of

- these_ alarms were revised to include steps that verify the computer program status of the associated alarm.

2.

Software _ changes have been made to eliminate the daily synchronization of-_the computer clock with the national time. standard and.to improve the detection of_.

prcgram failures.

PRIOR OCCURRENCES:

None.

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