05000285/LER-1980-015-03, /03L-0:on 800710,during Insp,Noted That Trip Unit Setpoints on C Channel Had Become Positive Rather than Negative.Caused by Failure of 15-volt Power Supply for Trip Unit 4.Unit Calibr

/03L-0:on 800710,during Insp,Noted That Trip Unit Setpoints on C Channel Had Become Positive Rather than Negative.Caused by Failure of 15-volt Power Supply for Trip Unit 4.Unit Calibr

ML19330C340
Person / Time
Site:	Fort Calhoun
Issue date:	07/18/1980
From:	Core M OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19330C339	List: 05000285/LER-1980-015, Forwards LER 80-015/03L-0 05000285/LER-1980-015-03, /03L-0:on 800710,during Insp,Noted That Trip Unit Setpoints on C Channel Had Become Positive Rather than Negative.Caused by Failure of 15-volt Power Supply for Trip Unit 4.Unit Calibr
References
LER-80-015-03L, LER-80-15-3L, NUDOCS 8008080260
Download: ML19330C340 (4)

LER-1980-015, /03L-0:on 800710,during Insp,Noted That Trip Unit Setpoints on C Channel Had Become Positive Rather than Negative.Caused by Failure of 15-volt Power Supply for Trip Unit 4.Unit Calibr

Event date:
Report date:
2851980015R03 - NRC Website

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63 61 DOCKET NUMBER 68 69 EVENT QATE 74 75 REPORT DATE 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h l o 12 l l 0uring routine inspection, it was noted that tric unit setooints on "C"

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trip unit 4 (Steam Generator Level) had oecome positive rather than necative.

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o,3, i o ;,i i tenance order 6430 was written to investigate and repair the problem. The RPS was I

1oi5i i mmediately placed in a two-out-of-three logic to trip mode. Technical Specification I i

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was replaced, the trip unit calibrated and the channel functionallv tested usine the I

il i,i jappropriate surveillance test, ST-RPS-6, F.2.

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LER No.80-015 Omaha Public Power. District Fort Calhoun Station Unit No.1 Docket No. 05000285.

ATTACHitENT NO. 1

Safety Analysis

The setpoints on trip unit 4 had gone to the positive state due to the

- loss of the -15 volt power supply. The RPS was only slightly degraded as the other. three channels were-operable and witnin specifications at tne time of failure. At no time would the RPS have failed to perform its intended function, that is, to trip the reactor by dropping the control rods into the core.

When-the RPS was placed in two-out-of-three logic, any two channels that agreed on an incongruity would have tripped the reactor.

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LER.No.80-015 Omaha -Public Power District Fort Calhoun Station Unit No.1

- Docket No. 05000285 ATTACHMENT NO. 2

Corrective Action

The results of troubleshooting proved that the + 15 volt power supply, Power Mate Part No. DRA15.750/15.750, had Tost the -15 volt side. ' The power supply was replaced in kind and the trip unit was recalibrated using the appropriate calibration procedure, CP-RPS-2. The unit was then functionally tested using the appropriate surveillance test ST-RPS-6, F.2..

Any reoccurring failure will be detected by sur-veillance testing. No further corrective action is anticipated.

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. LER No.80-015 Omaha Public Power District Fort Calhoun Station Unit No.1 Docket No. 05000285 ATTACHMENT NO. 3 Failure Data t

This is the second reportable failure of its kind at the Fort Calhoun 4

Station.

See LER 23-23.

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