ML20043B803

LER 90-019-00:on 900425,RWCU Sys Isolation & ESF Actuation Occurred After Completion of Channel Check of Riley Temp Trip Unit.Caused by Unit Exceeding Differential Temp Setpoint of 46 F.Unit replaced.W/900524 Ltr

ML20043B803
Person / Time
Site:	River Bend
Issue date:	05/24/1990
From:	England L, Odell W GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-019, RBG-32898, NUDOCS 9005310311
Download: ML20043B803 (4)

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GULF- STATX?S UTILITIES COMPANY ~

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AF11 A COOF bod 035 0094 346 865) p i

e May 24 ,1990 'fi RBG- 32898 File Nos. G9.5, G9.25.1.3 i i

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. U.S. Nuclear Regulatory Cantnission Document Control Desk 4 Washington, D.C. 20555 s

. Gentlenen: e River Bend Station - Unit 1 I Docket No. 50-458 i Please find enclosed Licensee Event Report No.90-019 for River Bend Station - Unit 1. This report- is being subnitted-pursuant to 10CFR50.73.  ;

Sincerely, j

)W.. Odell i

Manager-Oversight ,

River Bend Nuclear Group j TSC/pg TFPhE/

cc: U.S. Nuclear Regulatory Ccmnission >

611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 NRC Resident Inspector ,

P.O. Box 1051 '

St. Francisville, IA 70775 l

g. INPO Records Center 7' ~ 1100 Circle 75 Parkway a Atlanta, GA 30339-3064 l

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LICENSEE EVENT REPORT (LER) 'a's 8 7' "

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1. ACittTV NAMI 11) DOCKlf NUMBER (24 PAGE (3i RIVER BEND STATION

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o is j o lo j o l41518 i l0Fl013 Reactor Water Cleanup Systen Isolation Occurred due .to a Riley s

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COMPLif t ONE LINI FOR ( ACM COMPONINT F AILURE DESCRISED IN THIS REPORT (13 RE$QRTA (i '5 CAUS$ $YST E M COMPONE NT "$Fjc, U$t Svt i PONENT

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B IlJ TlDISi l l J Yes l l l l l- l l SUPPLEMENT AL REPORT E XPECTED 114) l MONT M DAV YEAR SUO Mi$$ ION 485 III ver toke.ete iM94CTED $vgMrs$tCh CA TEI NO l l l AS$TR ACT t& amer to f 400 speces 4 e . vooro.emerev Meeen sve spece rvoeweetswa s,nes/ tiet At 0055 on '04/25/90 with reactor at 100 percent power (Operational Condition 1), a reactor water cleanup (RWCU) system isolation occurred. The engineered safety feature actuation occurred shortly after the completion of a channel check of Riley- temperature -trip units and was determined to be caused by a faulty Riley temperature trip unit. The faulty unit was replaced and the RWCU system returned to service at 1202 on the same day.

The trip . unit monitors RWCU valve nest room for system leakage by monitoring inlet and outlet air temperature, and trips if the temperature exceeds a setpoint of 46 degrees Fahrenheit dffferential

( F). Readingg obtained before and after replacing the faulty trip unit were 19 F. During the retest, to verify the calibration of the trip channel, measurement madg directly across thermocouple leads with test equipment indicated 19 F . All readings obtained indicated that i the RWCU valve nest room differential temperature was at all times within acceptable range. l There was no impact on the safe operation of the plant or the health i and safety of the public since no leakage actually occurred.

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EXPtRES 4/31/W

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- REPORTED CONDITION At 0055 on 04/25/90, with the reactor at 100 percent -power n (Operational Condition 1), and shortly after completion of channel check of Riley temperature trip units, Riley trip unit 1E31*N615A tripped. As a result, the reactor water cleanup (RWCU) system (*CE*)

-isolated. The trip unit monitors RWCU valve nest room inlet and

~ outlet air temperature agd trips if the' differential-temperature exceeds a setpoint of 46 F. The isolation of the RWCU system a constitutes an engineered safety feature (ESP) actuation. Therefore,.

this event is . reportable under 10CFR50.73 (a) (2) (iv) .

k INVESTIGATION

= Subsequent to the isolation, the unit was observed to trip and reset four times without operator intervention. Since the RWCU system was

isolated due to the first trip and the isolation logic was not reset, the subsequent trips did not cause any further system isolation.

m L The faulty. unit was replaced under prompt Maintenance Work Order (MWO)

R056532. An 18 month channel calibration surveillance test procedure (STP) and a monthly functional check STP were performed successfully to verify the calibration and trip function of the replacement module.

The RWCU system was placed back into service at 1202 the same day. No additional RWCU isolations have occurred since the replacement.

During the time that the RWCU system was isolated, the reactor water quality was monitored periodically and was determined to be within limits.

I Regdings obtained before and after replacing the faulty trip unit.were

_ 19 F. During the retest STP performance to verify the calibration of the trip channel, measurement made directly across thermocouple leads with test equipment indicated 19 F. All readings obtained indicated that the RWCU valve nest room differential temperature was within acceptable range and that the faulty trip unit was the root cause of this event.

A review of earlier LER submittals revealed that LER 85-037 (dated 12/17/85) was a similar RWCU isolation. It was also due to a defective trip unit. A review of' condition report history indicated the one failure in 1985. This failure rate is not considered excessive since a review of the Nuclear Plant Reliability Data System Report showed only six units were replaced system wide where this one root cause of failure was identified.

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01 0 01 3 0' 0l3 vent a- . ..ae , mm,nn CORRECTIVE ACTION The faulty trip unit was replaced and the new unit was calibrated and ~

functionally checked before returning to service. An 18 month calibration STP and a monthly functional check STP are periodically performed, the frequencies of STP performance appear appropriate.

Therefore, no further corrective action is required.

SAFETY ASSESSMENT The Riley temperature trip unit detects' leaks in the RWCU valve nest

-room in order to isolate the system and prevent the loss of reactor-coolant. The trip unit failed safe since RWCU was isolated. There was no leakage; therefore, there was no impact on the safe operation of the plant or the health and safety of the public.

NOTE: Energy Industry Identification System Codes are identified in the text as (*XX*).

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