ML19317D957

Unusual Event Rept 269/75-04:on 750209,14,& 20,personnel Hatch Interlocks Failed.Caused by Excessive Wear of Gear Teeth & Pawl on Hatch Door.Interlocks Adjusted & Personnel Hatch Returned to Svc.Maint Procedure Written

ML19317D957
Person / Time
Site:	Oconee
Issue date:	03/21/1975
From:	DUKE POWER CO.
To:
Shared Package
ML19317D954	List: ML19317D953 ML19317D957
References
RO-269-75-04, RO-269-75-4, NUDOCS 7912100635
Download: ML19317D957 (2)

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1 DUKE POWER COMPANY ,

N OCONEE UNIT 1 Report No.: UE-269/75-4 Report Date: March 21, 1975 Event Date: February 9, 14, and 20, 1975 Facility: Oconee Unit 1, Seneca, South Carolina Identification of Event: Failure of personnel hatch interlocks Conditions Prior to Event.: Unit in cold shutdown on February 9 and 14, 1975 Unit in hot shutdown on February 20, 1975 Description of Event:

On February 9, 14', and 20, 1975, the Oconee Unit 1 personnel hatch inter-lock mechanism became out of adjustment and resulted in the interlocks being inoperable. Although the inner and outer doors were maintained to provide containment integrity, when required, the interlock mechanism would not have prevented simultaneous opening of both doors. In all instances, the shif t supervisor was notified and corrective maintenance was initiated to repair the interlocks.

Designation of Apparent Cause of Event:

Each door of the personnel hatch has a gear which is rotated by the door handwheel. A pawl mechanism, in conjunction with this gear, creates a ratchet mechanism to prevent rotation of the door handwheel should the opposite door be open. The pawls are raised from or lowered on the gear by motion of the opposite door transmitted through a cable and linkage mechanism. Adjustments of the interlocks consist of adjusting the effective length of the cable and return spriacs such that the pawls will properly engage the gears and create the ratchet mechanism when the opposite door is opened. The apparent cause of this event was excessive wear of the gear teeth and the pawl making the cable length adjustment extremely sensitive.

Analysis of Event:

i The incidents of February 9 and 14, 1975 occurred when the unit was in a i cold shutdown state; hence, containr. ant integrity was not required. The February 20, 1975 incident did occur with the unit in a hot shutdown state; however, containment integrity was maintained and the hatch was restored to operable status within the time limitations specified in Technical l Specification 3.6.i. In addition to personnel present to prevent simultaneous opentag of the doors, a control room alarm also monitors the status of the personnel hatch doors. It is concluded that the health and safety of the public was not affected.

7912100b I

.. . T, CohrectiveAction: ,

The interlocks were adjusted and the personnel hatch returned to service.

A maintenance procedure for adjustment of the interlocks has been written.

Prior to April 1, 1975, a representative of the designer of the hatch will be on site. Subsequently, a periodic surveillance program will be developed and implemented by May 1, 1975. Identification of recommended spare parts will be discussed with the designer's representative and procurement of the necessary parts initiated. In addition, an investigation is in progress to determine the necessity for modifications to the personnel and emergency hatch interlock mechanisms.

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