ML19317F499

RO 270/76-08:on 760723,simultaneous Loss of 2A Reactor Bldg Cooling Unit & Spray Train Occurred.Caused by Tripped 2XS1 Load Ctr Feeder Breaker.Preventive Maint Procedure Being Written

ML19317F499
Person / Time
Site:	Oconee
Issue date:	08/09/1976
From:	DUKE POWER CO.
To:
Shared Package
ML19317F496	List: ML19317F495 ML19317F499
References
RO-270-76-08, RO-270-76-8, NUDOCS 8001140728
Download: ML19317F499 (2)

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DUKE POWER COMPANY OCONEE UNIT 2

- Report No.: R0-270/76-8 Report Date: August 9, 1976 Occurrence Date: July 23, 1976 Facility: Oconee Unit 2, Seneca, South Carolina Identification of Occurrence: Simultaneous loss of 2A Reactor Building cooling unit and 2A Reactor Building spray train due to tripped load center breaker Coaditions Prior to Occurrence: 100 percent full power Description of Occurrence:

On July 23, 1976 following a startup of the 2A Reactor Building Unit (RBCU),

the RBCU discharge dampers failed to open resulting in an overload and subsequent trip of the 2XS1 motor control center feeder breaker. This load center supplies power to one train of ES equipment which was disabled when the breaker tripped. Valve 2BS-1 was included in this equipment,and therefore, one of the two redundant Reactor Building spray trains was disabled at the same time 2A RBCU was out of service. This condition existed for approximately 21 minutes until motor control center 2XS1 was returned to service.

Apparent Cause of Occurrence:

This occurrence resulted from mechanical binding of electrical contacts in the 2A RBCU motor starter. This malfunction prevented the discharge dampers from opening during startup of the cooling unit and also prevented the unit from tripping due to the resulting overload condition. Consequently, the 2XS1 supply breaker overloaded and tripped, disabling one train of .ES equipment.

Analysis of Occurrence:

This occurrence resulted in the loss of one train of Reactor Building spray and one Reactor Building cooling unit, and additional ES equipment receiving power via motor' control center 2XS1, for a period of approximately 21 minutes until the motor control center could be returned to service. During this period, redundant ES 2quipment was operable. It is, therefore, felt that. due to the operability of redundant ES trains and the brief ' interval over which this incident c; curred, that there was little reduction in any safety margins. -It is thus concluded that this occurrence did not adversely affect the health and safety of the public.

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. . t 2-Corrective' Action:

A preventive maintenance procedure is presently being written to assure that

-RBCU motor ' starters are periodically cleaned and lubricated. This action should prevent further occurrences.resulting from mechanical binding of motor starter ' contacts.

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