ML20246Q077

Safety Evaluation Supporting Proposed Mod to Delete K74B & K74D Relays from Electrical Control Circuitry of MSIV to Resolve Spurious Opening of MSIV on Loss of Reactor Protection Sys Bus a or B

ML20246Q077
Person / Time
Site:	Perry
Issue date:	05/09/1989
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20246Q070	List: ML20246Q066 ML20246Q077
References
NUDOCS 8905220360
Download: ML20246Q077 (2)

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SAFETY EVALUATION BY THE OFFICE 0F NUCLEAR. REACTOR REGULATION M51V ELECTRICAL CONTROL.CIRCUIIRY THE CLEVELAND ELECTRIC ILLUMINATING COMPANY, ET AL.

PEPRY huCLEAR POWER PLANT,. UNIT.NO. 1 DOCKET.h0. 50-440 l INTRODUCTION On January 23, 1988, the Perry Plant experienced a Reactor Protection System (RPS) "B" bus deenergiz6 tion resulting in opening of the inboard Main Steam IsolationValves(MSIV's),eventhoughtheMSIVcontrolswitchremainedinthe closed position. Subsequent investigations verified that this 6nomaly existed for both the RPS A and B busses cno was in 6ccordance with the as-built design.

Therevit$isperformedinconjunctionwiththeHSSSvendor(GE)determinedthat' the spurious opening of the MSIV's was the result of a characteristic of the design which allows a normally energized relay to change open or close status upon loss of power, resulting in an open signal to the MSIV's. The MSIV's, if open, will always close upon loss of both power busses, and upon receipt of an MSlV isolation signal. Furthermore, if an isolation signal'is present, the valves will not reopen upon loss of power ~to either power bus. When there is no isolation signal present and either the outboard or inboard valves have opened on loss of the A or B bus, the v61ves would innediately close upon restoration of power to the bus or upon receipt of an isolation signal. It is only when no isolation signal is present, and power has been lost to'only one RPS bus, that the inboard or the outboard MSIV's will open.

DISCUSSION Each MSIV has an MSIV position switch in the existing logic. The position of the MSIV position switch (SIA) determines whether two relays are energized or deenergized. When the position switch is in the " Closed" position, the K74B relay is' energized. When the position switch is in the " Test" position, the K74D relay is energized. This circuit is powered from the RPS "B" bus. The K74B and D relays will both deenergize on loss of RPS "B" bus no matter what position the MSIV position switch is in. Both relays are also deenergized if the MSIV position switch is in the " Auto" position.

The K74B relay is used in four circuits. Two of the relay cont 6 cts are used in the B and C MSIV Automatic Isolation Logics to allow the isolation logic to be reset following an isolation signal as long as the four associated '

MSIV's are shut (i.e., MSIV position switch in test or auto position).

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,, l The other two K74B relay contacts being used go into the logic circuit for energizing the A and B pilot solenoids for "A" inboard MSIV. Whenever the K74B is acenergized, these relay contacts are closed (six contacts) permitting the pilot solenoids to be energized. When one or both of the two pilot solenoids associeted with an MSIV is energized, the MSIV w!11 open and stay open. The two pilot solenoids receive power from different hPS busses. The loss of the "B" RPS bus with the MSIV position switch in the closed position caused the K74B relay to deenergize, thereby closing the MSIV pilot solenoid logic contacts.

Since one of the two logics was still being powered by an energized RPS bus, ,

this resulted in energizbtion of the associated pilot solenoid and the opening of the respective MSIV.

The proposed modification will delete the K74B and K74D relays from the electrical control circuitry of the MSIV, and instead add contacts of the MSIV position switch into the logics affected. Since the MSIV position switch is not affected by loss of electrical power, the spurious opening of the MSIV due to power loss will be correcteo. -

CONCLUSION The MSIV position switch is not affected by loss of electrical power and thus a loss of electrical power does not result in the spurious opening of the MSIV. The proposed modification to delete the K74B and K740 relays from the electrical control circuitry of the MSIV will resolve the spurious opening of the MSIV on loss of RPS "A" bus or RPS "B" bus , and is, therefore, accepta'le.

u Principal. Contributor: S. Rhow Date: May 9, 1989 l

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