ML19317F171

Abnormal Occurrence Rept AO-287/75-11:on 750807,Control Rod Drive Breaker 10 Failed to Trip.Caused by Breaker Maladjustment.Break Cleaned,Lubricated & Adjusted

ML19317F171
Person / Time
Site:	Oconee
Issue date:	08/21/1975
From:	DUKE POWER CO.
To:
Shared Package
ML19317F167	List: ML19317F166 ML19317F171
References
NUDOCS 8001080889
Download: ML19317F171 (2)

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• ]. 'T Duke Power Company Oconee Unit 3 Report No.: A0-287/75-11 Report Date: August 21, 1975 Occurrence Date: August 7, 1975 Facility: Oconee Unit 3 Seneca, South Carolina Identification of Occurrence: Failure of Control Rod Drive AC Breaker 10 Conditions Prior to Occurrence: Unit at Full Power Description of Occurrence:

On August 7, 1975, during periodic instrument surveillance of the Reactor Protective System Channel A, Control Rod Drive (CRD) breaker 10 failed to trip. Subsequent attempts to trip the breaker were successful and, upon inspection, no visible indication of any problem was found. Redundant trip breakers were then individually tested to verify their operability.

A program to verify the operability of CRD breaker 10 was developed which

, required the breaker be trip tested on 10 consecutive days- During two of these tests, CRD breaker 10 failed to trip on the first attempt. The -

breaker was subsequently inspected and repaired at the vendor's repair facility and returned to Oconee for reinstallation. Subsequent tests verified the operability of the breaker.

Designation of Apparent Cause of Occurrence:

The apparent cause of this occurrence was a mal-adjustment of CRD breaker 10.

Upon inspection of the breaker at the vendor's repair facility, no problem was found. The breaker was cleaned, lubricated, adjusted, and bench tested fifty times with no failures.

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Analysis of Occurrence:

The Reactor Protective System utilizes four separate and redundant channels which actuate four independent control rod drive breaker groups. Actuation of any two of the four protective chsanels will initiate a reactor trip.

Although CRD breaker 10 failed to trip, had a reactor trip been required, the redundant channels would have actuated to trip the reactor. It is concluded that the health and safety of the public was not affected.

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Corrective Action The breaker was cleaned, lubricated, adjusted and then returned to service.

The monthly surveillance test of CRD breakers is considered adequate to detect random breaker failures of this type.

Failure Data:

The CRD AC breakers are General Electric Company type AK-2A-25-1. No previous failures of these breakers have been experienced at Oconee.

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