ML19290B694

Final Deficiency Rept 79-08 Re Failure of solid-state Trip Devices in Low Voltage Power Circuit Breaker.Caused by Defective Assembly of Printed Circuit Boards Supplied by Gould-Brown Boveri Switchgear Div

ML19290B694
Person / Time
Site:	Grand Gulf
Issue date:	11/02/1979
From:	MISSISSIPPI POWER & LIGHT CO.
To:
Shared Package
ML19290B690	List: ML19290B689 ML19290B694
References
NUDOCS 7912130532
Download: ML19290B694 (2)

Text

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FINAL REPORT FOR REPORTABLE DEFICIENCY NO. 79/08 AS DEFINED IN 10 CFR 50.55(e)

I. Description of Deficiency:

Solid-state trip devices on the 480 Volt Load Centers failed to operate properly during a system functional test. The 480 Volt Load Centers were manufactured and supplied by Gould-Brown Boveri, Switchgear Division for Units 1 & 2. Investigation revealed that the problem in the solid-state trip devices was due to inadequate or incomplete soldering on printed circuit board leads.

II. Safety I=clications:

The 480 Volt Load Centers control the electrical functions of various systems determined to be safety related. Hence, failure of an intri-cate component in a safety related system to function properly during an unplanned event or prior to a planned event could adversely af fect the safety of operations of the nuclear power plant.

III. Corrective Ac tion Taken The supplier investigation has determined that the cause of the problem was due to an operator error during the assembly of printed circuit boards.

The extent of the problem was further determined, from manuf acturing records, to be limited to a three-day period during which a soldering operation was inadvertently omitted. The operator was replaced for other reasons. All 480 Volt Load Centers received at the Grand Gulf Nuclear Station for Units 1 and 2 have been examined for the problem. -

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A total of 12 trip units were found with poor soldering joints on the circuit boards. These trip units except for one that was re-turned to the supplier in the "as-found" condition, were reworked to correct the soldering on the printed circuit board joints and the retests of the units were satisfactory.

The supplier has initiated corrective action to establish an auto-matic soldering operation to replace the manual soldering operation.

This has been accomplished to the extent possible. However, not all models can be processed in this manner. Hence, the supplier has committed to inspect all soldering leads. This inspection will also be required on those items processed by the automatic soldering pro-cess. The supplier's investigation also included an examination of un-delivered units for this soldering problem in which none were found. The source of the problem was found to exist only on those units assembled during a three day pericd. Details of this corrective action are summarized in Bechtel thnagement Corrective Actica Report, GGNS-48 and will be available for your review at the GGNS construction site.

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