ML19316A464

RO 269/78-04:on 780301,two Reactor Bldg Cooling Units Found Inoperable Simultaneously.Caused by Insufficient Installation Procedures Allowing Trip Point to Be Set Too Low.Breaker Reset & Trip Setpoint Increased

ML19316A464
Person / Time
Site:	Oconee
Issue date:	03/15/1978
From:	DUKE POWER CO.
To:
Shared Package
ML19316A461	List: ML19316A460 ML19316A464 ML19316A466
References
RO-269-78-04, RO-269-78-4, NUDOCS 7912110774
Download: ML19316A464 (2)

Text

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. DUKE POWER COMPANY OCONEE UNIT 1 Report Number: RD-269/78-4 Report Date: March 15, 1978 Occurrence Date: March 1, 1978 4' Facility: Oconee Unit 1, Seneca, South Carolina Identification of Occurrence: Two Reactor Building Cooling Units simultaneously inoperable Conditions Prior to occurrence: 100 per cent full power Description of Occurrence:

At 0430 on February 28, 1978 the IC Reactor Building Cooling Unit (RBCU) was taken out-of-service to repair valve LPSW-24. At 1357 the 1B RBCU circuit breaker tripped putting a second RBCU out-of-service. The brea'act was reset to restore the capability of the 1B RBCU to run at low speed. At 1512 the IC RBCU was returned to high speed service following completion of valve repacking. At 1550 the 1B unit was started in low speed to verify its operability. At approximately 0900 on March 2 it was discovered that the instantaneous breaker trip setting for RBCU 13 was too low and was corrected.

Apparent Cause of Occurrence The apparent cause of the breaker failure was insufficient installation procedures which allowed the breaker's instantaneous trip point to be set too low. The breaker is adjusted so that any power surge associated with low speed startup does not trip the breaker since its function is not related to startup current distortions. However, the procedure does not assure that the breaker will not trip when the unit is shifted to high speed. When the set point was readjusted higher the unic achieved high speed without incident.

Additionally, it was not prudent to test the unit with one of the redundant systems already out-of-service for repairs. Normally, this would have been inconsequential but in this case it caused the momentary exceedance of Technical Specification operating limits.

Analysis of Occurrence The simultaneous outage of two RBCU's was in violation of Technical Specification 3.3.1. One RBCU was inoperable due to maintenance, the other's breaker had tripped open. The IB RBCU breaker was reset within about 5 minutes to provide the redundant cooling unit. Both building spray systems were also available. The health and safety of the public were not endangered.

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Corrective Action

- The immediate corrective action was resetting the breaker. Additionally, the instantaneous trip setpoint was increased to an appropriate level..

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