ML19319B785

RO NP-33-77-55:on 770815,main Steam Line 2 Isolation Valve MS100 Closed Due to Control Air Leak.Caused by Instrument Air Moisture Trap Failure at Plastic Bowl Threads.Valve Closure Investigated & Moisture Traps Removed by 770817

ML19319B785
Person / Time
Site:	Davis Besse
Issue date:	09/09/1977
From:	Batch S, Lingenfelter J TOLEDO EDISON CO.
To:
Shared Package
ML19319B687	List: ML19319B686 ML19319B785
References
NUDOCS 8001270253
Download: ML19319B785 (2)

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. TOLEDO EDISCN COMPANY C/ DAVIS-3 ESSE UNIT ONE NUCLEAR POWER STATION SUPPLEMENTAL INFORMATION FOR LER NP-33-77-55 DATE OF EVENT: August 15, 1977 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Main Steam Isolation Valve MS100 failing closed due to control air leak.

Conditions Prior to Occurrence: The plant was in Mode 3, with Power (MWT) = 0 and Load (MWE) = 0.

Description of Occurrence: At 1315 hours0.0152 days <br />0.365 hours <br />0.00217 weeks <br />5.003575e-4 months <br /> on August 15, 1977, Main Steam Line 2 Isolation Valve MS100 closed due to a control air leak. This placed the station in the Action Statement of Technical Specification 3.7.1.5 which requires both Main Steam Isolation Valves to be operable in Mode 3, Hot Standby.

Main Steam Isolation valve MS100 was declared inoperable and left in the closed position. Station Instrument and Control personnel were notified of the failure.

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Desiunation of Apoarent Cause of Occurrence: The investigation by Instrument and Control personnel found that the valve operator instrument air coisture trap had f ailed it the plastic bowl threads. This component failure caused a loss of instru-ment air to the valve-which closes (fails safe) without air pressure acting on the operator.

Analysis of Occurrence: The purpose of the Main Steam Isolation Valves is to iso-late the affected steam generator in the event of a main steam line break down-stream of the isolation valve. Since the main steam isolation valve failed closed and remained closed, no threat to the health ande. safety of the public or to station personnel occurred.

Corrective Action: Maintenance Work Order 77-1695 wa_s writ, ten to investigate the main steam isolation valve closure and repair as needed. It was decided the moisture traps were not needed and should be removed on both main steam isolation e.. es.

This work was completed on August 17, 1977. Facility Change Request 77-231 was initiated for written approval of the moisture trap.

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'/- Failure Data: No previous similar events have occurred.

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