RBG-34-499, Revised Ro:From 901005-06,two 42X Relays in Div 1 Standby Cooling Tower Fans Experienced Failures,Rendering Fans Inoperable.Caused by Cracked Coils on Relays & Low Coil Resistance.Relays Replaced & Ventilation Sys Redesigned

Revised Ro:From 901005-06,two 42X Relays in Div 1 Standby Cooling Tower Fans Experienced Failures,Rendering Fans Inoperable.Caused by Cracked Coils on Relays & Low Coil Resistance.Relays Replaced & Ventilation Sys Redesigned

ML20066J690
Person / Time
Site:	River Bend
Issue date:	02/15/1991
From:	Odell W GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RBG-34-499, NUDOCS 9102260346
Download: ML20066J690 (4)

Text

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4 G ULF SIVATES UTILITIEEs COMPANY

,x o u s o ,.u m remn , v:, x v ns: a uuss i n Afij & ; ID{ 6(sl (.h (.. KH J4 f f't.bi Febntary 15, 1991 RBG- 34,499 File Nos. G9.5, G9.25.1.3 U. S. Nuclear Ibgulatory Ccunission Docunent Control Desk Washington, D. C. 20555 Genticunon:

River Band Station - Unit 1 Docket No. 50-458 Please find enclosed Revision 1 to an Infonctional Report concerning nultiple relay failures in the standby cooling tower fans at River Bend Station - Unit 1. This report is mdsnitted to infonn the NIC of these failures and docunnnt GSU's investigation and corrective actions.

Since ly, f/ ~

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s W. II. Odell Manager-oversight River Bend Nuclear GIrup te N '28,(b,!y lAE/PDG G/DCil/i!AK Wht.[$Kil/ ch cc: U. S. Nuclear Regulatory Ccnmission 611 Ryan Plaza Drive, suite 1000 Arlington, TX 76011 NRC Resident Inspector Post Office Box 1051 St. Francisville, lA 70775 INPO Records Center 1100 Circle 75 Parkway Atlanta, GA 30339-3064 Mr. C. R. Oberg /

Public Utility Ccanission of 'Ibxas //

7800 Shoal Creek Blvd., Suite 400 North fl Austin, TX 78757 I.. pI Sf n 9102260346 910215 ./gg,/, \\

PDR ADOCK 05000458 i S PDR /e

4 INrf0D0LTICN During a 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> tine pericd frun 10/05/90 to 10/06/90, with the unit in Operational Condition 5 (Refueling), two 42X relays (*RLY*) in Division I standby cooling tcur fans ( *rM * ) 1Sh?*IW10 and 1ShT*1HIS experienced failures, rendering the fans inoperative. The 42X relays are used in the j starting circuits of the fans. The results of those failures were that control rcan indication for each of the fans was lost due to blown control fuses. Shortly thereafter, two additional relays, a 62TX and a 62VX (*62*),

in the tirer circuits of the Division Il fans (* FAN *) IShP*INIT and 1ShP*IW1V were also found to be inoperative. The failurus of um 62TX and 62VX relays disabled the zwote operation of these fans fzun the control rcan. However, the fans remained operable locally frun notor control center (Kr) ( *bCC* ) 1 DIS *1MCC16B.

The 42X relays (*RLY*) and the 62TX and 62VX relays (*62*) are all Gould J10 relays. A failure analysis perforned by Wyle Laboratories concluded that the environnental conditions to which the relays were subjected was the nest likely cause of the relay failures.

INVFSTICATICN An inspection of the failed re*;ays revealed the follcuing observations:

. The coils of the relays were cracked, and the coils had been swelled.

. The coils exhibited a burned odor.

. Three relays had low coil resistance.

. One relay open-circuited.

Iow coil resistance is indicative of shorted windings. This and tin other observations are evidence of overheating.

Ib11owing the event, resistance neasurerents were taken on all of the zumaining J10 relays in the starting circuits of the standby cooling tc w r fans. The resistance values were all found to be within allowable limits.

The failure analysis by Wyle Iaboratories concluded that the nest likely cause of failure was the environnental conditions to which the relays were subjected. The standby cooling tower fans are installed in notor-control-centers (MCC's) located in the standby cooling tcher pump rocxn. The temperatures in this rcan typically drop below 40 degrees Fahrenheit during winter nonths when the outside ambient temperature is sufficiently low. Prior to this event, the environment was not properly controlled to naintain rcan temperatures consistent with the specified service conditions of the relays. Deposure of Gould J10 relays to low tanperatures can result in danage to the coil encapsulant. This condition can prevent insertion of the relay arnature into the coils, thus creating a binding condition. This binding condition can causn the coil to draw an inrush of current for a longer time period than nc,naal for relay operation, resulting in shorted windings due to overheating of the coil.

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Noto D.at ti 9re are ntnerous Gould J10 relays in the plant whe w the tcrtperature ariance retains within the specified limits. A review of other plant areas wrere Gould J10 relays are used was perfonxxl to identify where similar tcstperature conditions might exict and none were identified. GSU concludes that Gould J10 relays do not represent a generic safety concern as the failure node descrited atove is limitcd to relays subjected to 1cwr tmperatures than specified by the vendor.

03RmerION /CTION The failed relays have been replaced with new J10 mlays. As stated in the investigation aection of this report , GSU inspected and took resistance readings on all of the failed relays and found evidence of overheating.

Ibsistance neasurenents wre also ted:en on the relays in the starting circuits that did not fail. Thom was no evidence of degeneration of the non-falled relays.

The daily log report, Operations Section Procedure (OSP)-0012 was revised to require temperature nonitoring of the Sirr punp rocrns and switchgear romis .

In the event that the tenperature readings are below 40 degrees F, the procedure requires that Lucign Engineering be contacted. This would be follcwd by corrective neasures to elevate the rocra tenperatures.

7he ultinnte resolution of the ventilation problems in the SICT pump room and electrical switchgear romis includes the following:

. Podesign of the ventilation system to assure that tenperatures can be naintained above 40 degrees F. This is to be cutpletcd by November 1, 1991.

. The use of infra-red tenperature nonitoring (thentographic) in the preventive naintenance program for the relays.

FMTlY ASSES 9ENT At the tire of the fan failures, the plant was in Operational Condition 5 (Refueling), seven days following shutdcun. The standby cooling tcwr

(*BS*) was being utilized to renove decay heat as nornal service water was rot available. The fan failures resulted in Division I being inoperable, since 'Ibchnical Specification 3.7.1.2 requires all fans to be in operation, llowever, since both inoperable fans (* FAN *) were in the sanu cell (2-50%

capacity cells per division), a ntinimum of 50% cooling capacity frcrn Division I was available. In addition, Division II was operational at the tinn with pcwr being supplied from offsite. Mequate cooling was therefore available during the period the fans wre inoperable to naintain the plait in a safe shutdown condition.

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She relays in the starting circuits of tie starxiby cooling tower fans atu continuously energized while operating. The Division I fans operated for 21 days, prior to being secured, withaut additional failures of J10 rela) t; Ba&d on these factors and the corrective actions taken to date, tr.

concludes that the non-fallod J10 relays in the starting circuits are capable of continued service. In addition, there is .no generic cafety concern rajarding the J10 relays. She failures descrilxxl in this report  ;

kere due to the tenperature corx11tions to which the relays were subjected.

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