RBG-33961, Informational Rept:During 901005-06,two 42X Relays in Div I Standby Cooling Tower Fans Experienced Failures Resulting in Loss of Control Room Indication.Caused by Overheating.Relays Replaced W/New J10 Relays.Addl Actions Will Follow Analys

Informational Rept:During 901005-06,two 42X Relays in Div I Standby Cooling Tower Fans Experienced Failures Resulting in Loss of Control Room Indication.Caused by Overheating.Relays Replaced W/New J10 Relays.Addl Actions Will Follow Analysi

ML20065K129
Person / Time
Site:	River Bend
Issue date:	11/07/1990
From:	Odell W GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RBG-33961, NUDOCS 9011150225
Download: ML20065K129 (3)

Text

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O GULF STATES UTILETIES COMPANY fUV4 h El ND $1 ATION POST OFFICE ItoX 220 ET f 4 Anti $vlut. Lottis>AN A 7077%

arf A CODE SO4 63b 9794 346 9651 Novtsnber 7 , 1990 RDG- 33961 File Nos. G9.5, G9.25.1.3 U.S. Nuclear Regulatory Ctmnission Dccunent Control Desk Washington, D.C. 20555 Genticrtent i

River Bend Station - Unit 1 Docket No. 50-458 Please find' enclosed an Infonrational Report concerning nultiple relay failures in the standby cooling tower fans at iuver Bend Station - Unit 1. This report ir subnittcd to infonn the NRC of these failures and docunent .GSU's investigation and corrective actions.

Sincoruly,

. 1. 11 (

Manager-Oversight River Bend Nuclear Group IN}t$ & W.!

IAE/PDG/g(/DCil/HNK/jt DET cc: U.S. Nuclear Regulatory Ctmnissian

~'611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 NRC Resident Inspector P.O. Box 1051 St. Francisville, IA 70775 INFO Recortis Center 1100 Circle 75 Parkway Atlanta, CA 30339-3064 Mr. C. R. Oberty Public Utility Ctmnission of Texas 7800 Shoal Creek Blvd., Suite 400 North Austin, TX 78757 p]jl150225901107

[.' 79 1 s anckOsooge r5aa  !

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'. INm0DUCTIG4 i

During a 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> tine period frm 10/05/90 to 10/06/90, with the unit in Operational Cbndition 5 (Refueling), two 42X relays ( *RLY*) in Division I standby cooling tower fans (* FAN *) IShP*IN10 and ISh?*I'NIS experienced failurus. The 42X relays are used in the starting '

circuits of the fans. The results of those failures were that control roam indication for each of the fans was lost due to blown contml

• fures. Shortly thereafter, two additional relays, a 62TX and a 62VX '

(*62*), in the tiner circuits of the Division II fans (*FN4*)

IShT*FNIT and ISh?*FNIV were also found to be inoperative. The failures of the 62TX and 62VX relays disabled the renote operation of these fans fmn the control mczn. Ilowever, the fans rmained operable

. locally fmn notor control center (MOC) (*MCC*) 1FJIS*110C16B.

7he 42X relays (*RLY*) and the 62TX and 62VX relays (*62*) are all Gould J10 relays. Inspection of the failed relays indicates that they  :

overheated. 7he failed relays have been shipped offsite for falhuv  !

analysis. A supplemental report will be sultnitted by February 15, '

1991 to provide the results of the faihuu analysis and additional corrective actions, if required.

IWESTICATION An inspection of the failed relays revealed the following observations:

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

swelled.

. The coils exhibited a burned odor.

. Three relays had low coil msistance.

. One relay open-circuited.

Iow coil resistance is indicative of shorted windings. This and the '

other observations are evidence of overheating. GSU has shipped 2 of tho' 4 failed relays to Wyle Laboratories in !!antsville, Alabana for root cause analysis. A supplenental report will be issue <1 by February 15, 1991 to provide the results of the failure analysis.

Fbilowing the event, resistance neasurements were taken on all of the rcnaining J10 miays in the starting circuits of the standby cooling tower- fans. The resistance values were all found to be within allowable limits.

• 4 00RRBCTIVE ACTION The failed relays have been replaced with new J10 relays. GSU continues to evaluate the node of failum. Additional corrective actions, if required, will be taken following the failure analyLis.

As stated in the investigation section of this report, GSU has inspected and taken resistance readings on all of the failed relays and has found evidence of overheating. Resistance masumments were also taken on the relays in the starting circuits that did not fail.

%cre was no evidence of degeneration of the non-failed relays.

SAFmY Amane At the tim of the fan failures, the plant was in Operational condition 5_ (Refueling) , 7 days following shutdown. The standby cooling tower (*BS*) was being utilized to rmove decay heat as normal service water was not available. The fan failures resulted in Division I being inoperable, since hchnical Specification 3.7.1.2 requires all fans to be in operation. Ilowever, since both inoperable fans (* FAN *) weru in the sam cell (2 -

50% capacity cells per division), a minimum - of 50% cooling capacity flun Division I was available. In addition, Division II was operational at the time with power being supplied fzun offsite. Adequate cooling was therefore availabic during the period the fans were inoperable to maintain the plant in a safo shutdown condition.

We relays in the starting circuits of the standby cooling tower fans are continuously energized while operating. We Division I fans operated for 21 days, prior to being secured, without additional failures of J10 relays. Based on the continucus operation of the Division I fans for 21 days and the results of tie resistance measuremnts of the non-failed relays, GSU concludes that the non-failed J10 Irlays in the starting circuits are capable of continued operation.

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

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