ML19316A627

LER-78-009/03L-0:on 780627,Control Rod 6,Group 4,found to Have Short in Control Rod Drive Line Stator,Which Would Preclude Normal Power Movement.Caused by moisture-induced Corrosion.Shorted Stator Repaired 780701

ML19316A627
Person / Time
Site:	Oconee
Issue date:	07/28/1978
From:	Ken Wilson DUKE POWER CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19316A626	List: ML19316A625 ML19316A627
References
LER-78-009-03L-02, LER-78-9-3L-2, NUDOCS 8001130144
Download: ML19316A627 (2)

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DUKE POWER COMPANY 1,

OCONEE UNIT 2 Reportabic occurrence: R0-270/78-9 4

Report Date: July 28, 1978 i

occurence Date: June 27, 1978 Facility: Oconee Unit 2, Seneca, South Carolina

! Identification of Occurrence: Control Rod 6 Group 4

Conditions Prior to Occurrence: 100% Full Power Description of Occurrence:

l On June 9, 1978 during a routine inspection, control rod 6 of group 4 was found 1 to have a shorted "A" phase. With this phase shorted, performance of the bi-

[ weekly control rod movement test on this rod would cause the rod to unlatch i and drop into the core. This performance test was due to be performed by J

June 27, 1978 and in an ef fort to prevent unnecessary reduction of power,

, a proposed revision to the Oconee Nuclear Station Technical Specifications was submitted to the NRC on June 22, 1978. This revision would have extended the surveillance interval an additional seven days in order to allow the Unit to be shut down to repair the stator over the July 1, 1978 weekend.

l On June 27, 1978 the NRC/0NRR staff informed Duke that Rod 6 Group 4 should be I considered inoperable pursuant to the Technical Specifications. A temporary

change of Specification 3.5.2.21 was granted, however, to allow full power operation through July 1,1978 with the " inoperable" rod.

On July 1,1978, Unit 2 was shutdown for stator repair. The unit was returned to power operation on July 6, 1978.

f Cause of Occurrence:

l The cause of the rod inoperability was a short in the control rod drive stator.

This short isolated phase A from the stator which would cause rod drop if normal movement was attempted. The short, however, did not inhibit the rod from per-i forming its intended safety function. The bases for the movement specification j is to verify the rod as oeing trippable and' the rod was indeed capable of doing

! so.

Analysis of Occurrence:

l 4 The short precluded normal powered rod movement. However Group 4 was in a fully withdrawn configuration and thus no powered movement was necessary. The j

safety function of the rod in the withdrawn position is to drop on an ES trip i signal. The short in no_way interfered with the rod's ability to perform its function. Thus, this incident caused no adverse ef fect to public health i

and safety.

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Tlo- <ontrol s od dr ive stator was repaired and has performed normally since the orrurrence. Also, until any appropriate clarification can be made to the Technical Specifications, rods will be considered " inoperable" pursuant to the I;HC/0:!RR position expressed in this instance.

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[o l2 l l On June 9,1978 control rod 6 group 4 was found to have a short in the ,

g o 131 l CRD stator which would preclude normal powered movement. The group was l

go y,; ; fully withdrawn so that no hazard resulted from the short. The unit was ,

Io lst I shut down for repair on July 1, 1978. See attached for details. I I

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CAUSE DESCRIPTION AND CCRRECnVE AcrlCNS h li lo l l The short was probably caused by moisture induced corrosion which has t y

occurred previously on all Oconee units. Corrective action was to repair ,

the shorted stator. ,

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