ML19338E591

LER 80-020/03L-0:on 800905,axial Power Distribution Setpoints on D Channel Discovered Out of Tolerance in Nonconservative Direction.Caused by Dependent Setpoint Selection Switch Failure.Switch Cleaned & Returned to Svc

ML19338E591
Person / Time
Site:	Fort Calhoun
Issue date:	09/08/1980
From:	Core M OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19338E590	List: ML19338E589 ML19338E591
References
LER-80-020-03L, LER-80-20-3L, NUDOCS 8010030418
Download: ML19338E591 (4)

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, EVENT DESCRIPTION AND PROB A8LE CONSEQUENCES h

. l o ! 2, I During normal power operation, it was discovered by ooerator observation that the i t o ia; i Axial Power Distribution (APD) setpoints on 0 channel were out of tolerance in the i ioi4i i non-conservative direction. The other three channels were operable at the time and l lo isi i would have provided a necessary trip of the reactor if necessary. Technical l lo is i i Specification 1.3(8), Table 1.1, item 8, and Figure 1.2 aoplies. l l

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h

,, ioil During trouble shooting, it was discovered that wafer #6, contact #1 of the Flow i Dependent Setpoint Selection Switch, a Grayhill 42136-8-2-5N, was making poor contact l. l

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,,,7i i This poor contact fed a 0% power indication into the APO calculator thus making the i i,,3i ] calculator calculate setpoints for 0% power. The switch was cleaned and returned l i,i,i i to service. i

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LER 80-020 Omaha Public Power District Fort Calhoun Station Unit No.1 Docket No. 05000285 ATTACHMENT NO. 1 Safety Analysis The Reactor Protection System uses a two-out-of-four to trip logic. One channel at a time may be bypassed, placing the system in a two-aut-of-three to trip logic. When the setpoint was found out of tolerance, the system was immediately placed in the two-aut-of-three logic mode. Therefore, the function of the R.P.S. was only slightly degraded as the other three channels were operable during this time and A, B and C channels had setpoints within tolerance. At no time would the R.P.S. have failed to perform its design functions, that is, to safely shutdown the reactor. See attachment 2 for further technical information.

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LER 80-020 Omaha Public Power District Fort Calhoun Station Unit No.1 Docket No. 05000285 ATTACHMENT NO. 2 Corrective Action One of the inputs to the APD calculator is from the flow dependent setpoint selector switch. The switch is normally used in the 4-pump position only and is only moved out of that position to perform surveil-lanc.e on the RPS. The switch on "0" channe' was making poor contact on one contact which fed the APD calculator information that indicated the reactor was at the 0% power setpoints. The switch was cleaned by rotating several times through full travel and returned to 4-pump operation. The applicable portions of the APD surveillance test, ST-RPS-12, F.2, were performed to prove operability of the reactor pro-tective system. No further corrective action is anticipated.

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LER 80-020 Omaha Public l'ower District-Fort Calhot.n Station Unit No.1 Docket No. U5000285 i

ATTACHMENT NO. 3 Failure Data This is the first occurrance of setpoints being out of tolerance due to a selector switch malfunction.

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