ML20004B111

LER 81-005/03L-0:on 810423,dc Sequencer Timers AC-3A (Component Cooling Water Pump) & AC-102A (Raw Water Pump) Failed to Time Out within Prescribed Limit.Cause Unknown Mechanisms Satisfactorily Inspected

ML20004B111
Person / Time
Site:	Fort Calhoun
Issue date:	05/06/1981
From:	Mueller R OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20004B106	List: ML20004B105 ML20004B111
References
LER-81-005-03L, LER-81-5-3L, NUDOCS 8105270253
Download: ML20004B111 (4)

Text

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HEFORT D ATE EVENT DESCRIPTION AND PRO 9 ABLE cO*2 SEQUENCES h I o 12 l l While operatJng at approximately 45% power and performing surveillance test ST-ESF-2,i

!ojal l Section F.1 (the monthly DC sequencer timer test), timers AC-3A (Component Cooling Wat$r lo ia j [ Pump) and AC-10A (Raw Water Pump) failed to time out within their prescribed limit. I jotaJ lDuring the time of the failure, the AC se'quencer timers which activate AC-3A and AC-104 I o I a l I we. e operable and available if needed. In addition, all sequencer timers, both AC andl l o ! ; l l DC (from both "A" and "B" safeguards trains) feeding redundant Component Cooling Waterl jc{si l Pumps and Raw Water Pumps were available and operable if needed. {

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7 LER No.81-005 Omaha Public Power District Fort Calhoun Station Unit No. 1

• Docket No. 05000285 ATTACHMENT NO. 1 Safety Analysis The Fort Calhcun Station Unit No. 1 is designed such that no single failure can prevent the safe shutdown of the plant. The failure of DC sequencer, Sl-1, would not have prevented the complete and proper load-ing of essential safeguards equipment should the need have arisen.

It is the intention of surveillance test ST-ESF-2 (F.1) to test the operation of "A" safeguards channel sequencer circuitry associated with sequencer Sl-1. Sequencer-S1-1 and S2-1 are " prime signal" DC powered sequencers fed from the "A" and "B" safeguards logic channels, respectively.

(Each of the safeguards channels also has an AC sequencer, Sequencer S2-1 being the channel "B1" sequencer electrically powered from the Channel "A" safeguards panel, and Sequencer S2-2 being the channel "Al" sequencer electrically powered from the "B" safeguards channel.) As part of the SI-ESF-2 (F.1) surveillance test, the derived signal cutoffs switch for the "Al" channel is turned to the "off" position, thereby eliminating the secondary sequencer S2-2 from operating. The primary sequencer associated with the "A" channel circuitry (sequencer Sl-1) is being tested and therefore all isolation switches for Sl-1 circuitry are in the "off" position. (This "off" position allows for the Sl-1 sequencer timers to be operated without any actual breakers / equipment being loaded or sequenced onto the bus.)

During the time when the S1-1 and S2-2 sequencers were inoperable, due to testing via ST-ESF-2 (F.1), the redundant "B" channel primary signal DC sequencer, S2-1, as well as the "Bl" secondary AC sequencer, S1-2, were operable and fully capable of sequencing the appropriate safeguards loads to either "A" or "B" trains - the "A" train equipment being loaded by sequencer S1-2 and the "B" train equipment being loaded by the sequencer S2 should the need have arisen.

1 LER No. 31-005--

Omaha Public Power District Fort Calhoun Station Unit No. 1 -

Docket No. 05000285 ATTACHMENT NO. 2 Corrective Action Two sequencer timers associated with Sequencer Sl-1, AC-3ALand AC-10A did not. time out within their prescribed time limits during.the initial run of surveillance test ST-ESF-2 (F.1). The timers were subsequently retested in.an effort to duplicate the problem identified above. However, upon retest, the timers timed out within their. pre-scribed / designed limits. The timers were retested a second time and again they timed out properly and within prescribed limits. The DC sequencer timer mechanisms were inspected to ensure cleanliness and to ensure that no abnormalities existed which could have detracted from satisfactory operation of the timers. No abnormalities or cleanliness related problems were observed. Since the computer printout is the only means used, per the surveillance test section,.of timing the timers /

simulated breaker closures, the appropriate personnel were questioned as-to the validity of specific computer points during the time the test was run. The results of this investigation again proved no apparent com-puter problem or abnormalities relating to the surveillance test.

It is therefore concluded that timers AC-3A and AC-10A of sequencer Sl-1 initially failed to time out within prescribed limits due to unknown causes.

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LER No.81-005 -

Omaha Public Power District Fort Calhoun Station Unit No.1 Docket No. 05000285 ATTACIDENT NO. 3 Failure Data Although there have been numerous instances of AC sequencer timers failing to " time out" within prescribed limits, this is the first failure involving a DC sequencer timer.

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