05000458/LER-1985-029, :on 851031,isolation of Div 1 RWCU Sys Occurred Causing Closing of Four Outboard Isolation Valves.Caused by Spurious Opening of Contacts on Riley Temp Modules.Mods to Temp Modules to Reduce Transient Susceptibility Begun

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:on 851031,isolation of Div 1 RWCU Sys Occurred Causing Closing of Four Outboard Isolation Valves.Caused by Spurious Opening of Contacts on Riley Temp Modules.Mods to Temp Modules to Reduce Transient Susceptibility Begun
ML20137X109
Person / Time
Site: River Bend 
Issue date: 11/30/1985
From: Bysfield G
GULF STATES UTILITIES CO.
To:
Shared Package
ML20137X056 List:
References
LER-85-029, LER-85-29, NUDOCS 8512100413
Download: ML20137X109 (3)
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LER-1985-029, on 851031,isolation of Div 1 RWCU Sys Occurred Causing Closing of Four Outboard Isolation Valves.Caused by Spurious Opening of Contacts on Riley Temp Modules.Mods to Temp Modules to Reduce Transient Susceptibility Begun
Event date:
Report date:
4581985029R00 - NRC Website
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At 0630 on 10/31/85 while in operational condition 2 (startup), an isolation of Division I neactor Water Cleanup nyntom occurred resulting in cloning of the four outboard isolation valves.

The isolation was attributed to a spurious opening of contactn on Itiloy temperaturo modules.

These modulos have boon reported to generato inadvertent trips as a result of trannient conditionn.

The trannients waro probably generated by the Itonctor Water. Cleanup inolation bypann timor relay which in in closo proximity of the temperature modulon.

The Itiley temperaturo modulon are being modified to reduce tranniont susceptibility.

Plant nafety wan not compromined and the health and safety of the public was not affocted.

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g At 0630 on 10/31/85 while in operational condition 2 (startup) an unexpected Division I Reactor Water Cleanup (RWCU) isolation signal occurred which closed the four outboard isolation valves 1G33*F004, F034, F039 and F054.

The isolation signal was generated when relay B2111-K172 was de-energized for approximately 0.2 seconds as indicated by the Emergency Response Information System (ERIS).

Alarm 2370 in control room panel lill 3-P 6 80 was illuminated which e

indicates that one of four temperature modules manufactured by U.S.

Riley Corporation tripped.

These are E31-N616A and E31-N624A Division I in panel 11113

  • P 6 3 2 and E31-N616B and E31-N624B Division II in panel 11113
  • P 6 4 2.

The isolation occurred in Division I.

Therefore, either E31-N616A or E31-N624A had an inadvertent trip.

Filey temperature modules have been reported to generate inadvertent trips as a result of trannient conditionn (reference LER 85-009).

The trannients for thin particular inadvertent trip are hypothesized to have been generated by the RWCU isolation bypass timer relay.

This relay is energi: ed by high dif ferential flow between three flow transmitters.

On the day of thin occurrence there was a high number of closures by this relay (audible average about 1-3 per minute).

Thin relay being in close pro >:imity to the temperature modulen, in the mont probable cause of the trannient (see LEll 8S-030).

In an attempt to minimize the probability of inadvertent trips, the Hiley temperaturo modulen are being modified (FDDR LDI-3640) to reduce their nunceptibility to trannients.

This work in ocheduled to be complete by Pobruary 1, 1986. Plant nafety won not compromised and the henith and nafety of the public wan not affected.

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continued operation of the plant prior to modification of these j

temperature modules will not affect safe operation of the plant and will have no impact on the health and safety of the public, because these valves actuate (close) in a safe direction.

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