05000346/LER-1982-068-03, /03L-0:on 821220,core Imbalance Vs Core Power Limit Computer Alarm C963 Inoperable.Caused by Mistake in Alarm Subroutine.Alarm Statement Corrected So Limits & Value for Imbalance Scaled Same

/03L-0:on 821220,core Imbalance Vs Core Power Limit Computer Alarm C963 Inoperable.Caused by Mistake in Alarm Subroutine.Alarm Statement Corrected So Limits & Value for Imbalance Scaled Same

ML20028E958
Person / Time
Site:	Davis Besse
Issue date:	01/19/1983
From:	Tabbert J TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20028E954	List: 05000346/LER-1982-068, Forwards LER 82-068/03L-0 05000346/LER-1982-068-03, /03L-0:on 821220,core Imbalance Vs Core Power Limit Computer Alarm C963 Inoperable.Caused by Mistake in Alarm Subroutine.Alarm Statement Corrected So Limits & Value for Imbalance Scaled Same
References
LER-82-068-03L, LER-82-68-3L, NUDOCS 8301280299
Download: ML20028E958 (2)

LER-1982-068, /03L-0:on 821220,core Imbalance Vs Core Power Limit Computer Alarm C963 Inoperable.Caused by Mistake in Alarm Subroutine.Alarm Statement Corrected So Limits & Value for Imbalance Scaled Same

Event date:
Report date:
3461982068R03 - NRC Website

text

NRCIOkM 366 U.S. NUCLEAR REGULATC~;Y COMMISSION (7-77)

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8 60 61 DOCKET NUMBER 68 69 EVENT DATE 74 75 REPORT DATE 80 EVENT DESCRIPTION AND PROB ABLE CONSEQUENCES h l (NP-33-82-87) on 12/20/82, it was determined that the Core Imbalance vs. Core Power l

O 2 10 l a I l Limit Computec Alarm, C963, was inoperable. This invoked Tech Spec Surveillance Re-l 1014l lquirement 4.2.1 which requires increased surveillance of the axial power imbalance l

lwith the computer alarm inoperable. There was no danger to the health and safety of l.

o 3 Ithe public or station personnel. The function of computer alarm C963 is to assure thel O s l 0 l 7 l l operator that imbalance is maintained within its limits. With C963 inoperable, only l

l O 1a ] l increased surveillance is required.

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l N1 33 34 35 36 37 40 48 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h IiI0llThe cause was a mistake in the alarm subroutine. The value for imbalance was in deci-l l mal form and was being compared to the limit which was in a percent form. On 12/20/82l i i l

lapproximately 30 minutes after the problem was discovered, the alarm statement was l

,,,7, lcorrected so that the limits and the value for imbalance were scaled the same. Other l i a l computer alarms which are used to reduce surveillance requirements were verified to be; i 4 operable. 80 7

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-82-87 DATE OF EVENT: December 20, 1982 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:

Computer Alarm C963, Core Imbalance vs.

Core Power Limit was discovered to be inoperable Conditions Prior to Occurrence: The unit was in Mode 1, with Power (MWT) = 2740 and Load (Gross MWE) = 923 Description of Occurrence: During the running of Surveillance Test ST 5033.03, Incore Instrument Channel Calibration, the computer alarm C963 could not be alarmed by the method. described in the procedure. At first it was thought that the test method was incorrect. After an investigation of the software, it was found on December 20, 1982 that the value for imbalance was in decimal form whereas the limits were in a' percent form j

(i.e., the value for imbalance was a factor of 100 smaller than the limits). Therefore, the alarm was inoperable.

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l As per Technical Specification Surveillance Requirement 4.2.1, if the alarm is inoperable, increased surveillance was required.

Designation of Apparent Cause of Occurrence: The cause of the event was due to a software mistake in the alarm subroutine.

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Analysis of Occurrence: There was no danger to the health and safety of the public or station personnel. The function of computer alarm C963 is to assurc the operators that imbalance is maintained within its limits.

With the computer alarm C963 inoperable, only increased surveillance is l

required. During the time computer alarm C963 was inoperable, the plant did not experience any adverse conditions. Also imbalance was checked once per shift with no indications of the value to be outside the limits.

Also, imbalance is monitored by the Reactor Protection System (flux-aflux-flow) which was not exceeded.

Corrective Action

Approximately one half hour after the problem was discovered, a Station Programmer, under the direction of a Technical l

Services Engineer, changed the alarm statement for the computer alarm C963 so that the limits and the value for imbalance were scaled the same.

Babcock and Wilcox was notified, and they are producing a Software Change l

Notice (SCN).

Other computer alarms which are used to reduce surveillance requirements l

were verified to be operable. Also, these computer alarms will be func-tionally tested when Technical Specifications require program changes.

In l

(

the future, these computer alarms will be qualitatively checked for operability on a shift basis.

Failure Data: There have been no previous occurrences.

LER #82-068