ML19330C372

LER 80-013/03L-0:on 800707,during Normal Power Operation, Noted That Channel a Dc Sequencer SI-1 Had de-energized on-auto Light.Caused by Sequencer Circuitry Failure Due to Faulty Relay

ML19330C372
Person / Time
Site:	Fort Calhoun
Issue date:	07/08/1980
From:	Mueller R OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19330C368	List: ML19330C367 ML19330C372
References
LER-80-013-03L, LER-80-13-3L, NUDOCS 8008080292
Download: ML19330C372 (4)

Text

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QATE EVENT DESCRIPTION AND PROB ABLE CONSEQUENCES h I o ! 21 I During norma? cover operation it was noted that Channel A DC secuencer SI-l had a l Ic tal 1 de-energized "on-auto" light associated with AC-3A,or the safeguards equipment sup-l 1o la l I plied from Bus 133B. The AC sequencer for channel A related safeguards equipment l l cts} l remained operable throughout the event as were the channel B AC & DC sequencers. l l 0 461 1 The safeeuards loads from all 480 volt ecuipment, ex :ent 1B3B associated equipment I loi7l l (which is AC-3A oniv) remained operable from the DC channel A sequencer SI-1. I I

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h i1 ie l l The contact of a General Electric CR120A. 125 VDC relav. which upon closure sucolies!

L1 j,; ] l oover to the Channel "A" DC secuencer circuitrv associated with Bus 133B was fetmes 1 4 ii i:l l to be hanging-ue/bindina due to the celcon contact arm retainer. The retainer was 1 4 1i13i l properlv adiusted and the relav was restored to procer operability as well as the l

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LER'No.80-013 Omaha Public Power District i

Fort Calhoun Sta?. ion Unit No. 1 Docket No. 05000285

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ATTACHMENT NO. 1 Safety Analvsis

.. The Engineered Safeguards system is so designed that no single failure can jeopardize enough safeguards equipment to prevent the safe shutdown of the plant if required.

The Sequencer System is designed to provide systematic loading of' i safeguards motors in the event of a safeguards initiation signal. 'This system is comprised of DC and AC sequencers for both Channels "A'.' and '

"B" of the safeguards system. During the time that the Channel "A" DC sequencer circuitry associated with bus 1B3B equipment was inoperable (due to a faulty contact of a GE CR120A relay), the. channel "A" AC sequencer and the channel "B" AC and DC sequencers were operable. If, required, AC-3A could have been started manually via operator action.

If accident conditions caused the need for AC-3A to be sequenced onto bus 1B3B, 'it would have been accomplished by means of Channel "A" AC i sequencer circuitry.

.Though the safeguards equipment tied to the Channel "A" DC se- l i

quencer from the 480 volt bus 1B3B was operable from the AC sequencer.

only, the remaining safeguards loads tied to the sequencers from all remaining 480 volt buses were operable from both the AC and DC sequencers during this event. Since the normal plant alignment calls for the 1B3B-4B 480, volt bus to be. fed from the bus lA4/ Diesel D2 side, (i.e. breaker ,

-BT-1B3B is open and BT-134B is closed), the only equipment associated with sequencer circuitry on bus 1B3B is AC-3A.

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LER No.80-013 Omaha Public Power District Fort Calhcun Station Unit No. 1-Docket No. 05000285 ATTACHMENT NO. 2 Corrective Action The cause of the sequencer circuitry failure was traced to a faulty relay (52XXA/1338). The reason for the relay failure was tra:ed to a binding Celcon contact arm retainer unit which was located on the relay.

The contact arm retainer was adjusted so that contact binding in the relay would be elininated. Subsequently, the relay, as well as the associated sequencer circuitry, was tested and found to be operating as designed. No further action corresponding to this relay f ailure is required.

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LOR No.80-013 Omana.Public Power District Fort Calhoun Station Unit No. 1-

. Docket No. 05000285 ATTACHMENT NO. 3 Failure Data ,

This is the second failure of this type at the Fort Calhoun Station.

The first failure of a DC sequencer due to a faulty GE CR120A relay is documented in I.ER 79-011.

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