ML19317F498

RO 270/76-03:on 760226,dropped Control Rod 5,Group 2 Caused Reactor Quadrant Tilt to Exceed Tech Spec Limits.Caused by Electrical Short in Rod Drive Stator.Stator Replaced

ML19317F498
Person / Time
Site:	Oconee
Issue date:	03/25/1976
From:	DUKE POWER CO.
To:
Shared Package
ML19317F484	List: ML19317F483 ML19317F498
References
RO-270-76-03, RO-270-76-3, NUDOCS 8001140727
Download: ML19317F498 (1)

Text

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O DUKE POWER COMPANY OCONEE UNIT 2 Report No.: R0-270/76-3 Report Date: March 25, 1976 Occurrence Date: February 26, 1976 Facility: Oconee Unit 2, Seneca, South Carolina Identification of Occurrence: Reactor quadrant tilt exceeds Technical Specification Jimits due to a dropped control rod.

Conditions Prior to Occurrence: Unit at 100% full power. ,

Description of Occurrence:

On February 26, 1976, while the Control Rod Exercise Testing was being performed on Oconee Unit 2, Group 2 rod 5 stator electrically shorted, allowing the control rod to drop into the core. In compliance with Oconee Technical Specification 3.5.1.1.1, which requires that reactor power be reduced below 60% when a control rod is declared inoperable, reactor power was immediately reduced to 58%. Within five hours reactor quadrant power tilt had increased above the 9% Technical Specification limit and, in compliance with Technical Specification 3.5.2.4.c, a unit shutdown was initiated. On February 27, 1976, after the unit was shutdown and cooled to 200 F, the stator was replaced.

Apparent Cause of Occurrence This occurrence was apparently caused by an electrical short in the control rod drive stator. The failed stator was an epoxy type stator which has been determined to have a design deficiency in which the epoxy layers covering the stator coils deteriorate after prolonged usage and cause the coils to electri-cally short.

Analysis of Occurrence Actions involving power reduction and later, reactor shutdown, were initiated correctly and promptly in compliance with the above mentioned Technical Specifications. No hydraulic, thermal or linear heat rate limits were exceeded as a result of this incident. The failure mechanism of the control rod drive stators is in the safe direction resulting in a dropped control rod. It is concluded that the health and safety of the public was not affected by this occurrence.

Corrective Action The failed stator was replaced with the latest type design, a varnish bifilar type stator. Presently, there are 35 epoxy type stators installed in the Unit 2 control rod drives. It is currently planned to replace these stators during the next refueling outage in May 1976.

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