ML19270G455

Revised 790510 Final Deficiency Rept Re Control Loop Bistable Failure on Loss of Power.Revision Specifies That Wiring Diagrams for Bistable Have Been Corrected & Physical Wiring Will Be Corrected

ML19270G455
Person / Time
Site:	Sequoyah
Issue date:	05/31/1979
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML19270G451	List: ML19270G450 ML19270G455
References
NCR-MEB-79-10, NUDOCS 7906080281
Download: ML19270G455 (1)

Text

,9 h ENCLOSURE SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 CONTROL LOOP BISTABLES FAIL TO UNDESIRABLE POSITION ON LOSS OF POWER NCR MEB 79-10 REVISED FINAL REPORT Description of Deficiency Bistable contacts in the auxiliary control loops of the pressurized power relief valves were found to fail in an undesirable position on loss of control power. The problem was found during preoperational testing of the unit 1 facility auxiliary control room controls and was due to an error in the wiring of the bistable. The problem does not exist in the main control room instrumentation.

The wiring of the pressurizer auxiliary spray valves and the pressurizer backup heater bistables was also in question.

Safety Implications Had the deficiency gone uncorrected, the air-operated pressurizer power relief valve, given loss of control power to the valve bistables, would fail open. This would result in depressurization of the reactor coolant system. Inadvertent lifting of a pressurizer relief valve is evaluated as a fault of moderate frequency in Section 15.2 of the Sequoyah Final Safety Analysis Report.

The control loop wiring for the pressurizer auxiliary spray valve and the pressurizer backup heater bistables was evaluated and has been deter-mined to be correct.

Corrective Action The wiring diagram for the pressurizer relief valve bistables has been corrected such that the bistables will fail open on loss of control power.

This ensures that the valves will fail in their preferred closed position.

The wiring corrections for each unit will be performed before its respective fuel load date. Upon examination of all other control loops in the auxiliary _

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control room controls for similar configurations, no discrepancies were found.

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