05000457/LER-1990-004

LER 90-004-00:on 900416,diesel Generator 2A Speed Oscillations Occurred Due to Defective Resistor.Caused by Failure of One Dropping Resistor in Governor Unit.Resistors replaced.W/900516 Ltr

ML20055C556
Person / Time
Site:	Braidwood
Issue date:	05/14/1990
From:	Grzemski J, Querio R COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BW-90-0525, BW-90-525, LER-90-005-08, LER-90-5-8, NUDOCS 9005250049
Download: ML20055C556 (4)

LER-2090-004,

Event date:
Report date:
4572090004R00 - NRC Website

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May 16,1990 BW/90-0525 - 1 l

U.' S, Nuclear Regulatory Commission ,

' Document Control Desk '

Washington; D.C. 20555

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Dear Sir:

The enclosed Licensee Event Report from Braldwood Generating Station is being transmitted to you in accordance with the requirements of -

10CFR50.73(a)(2)(v) which requires a 30-day written report.

T This report is number 90-004-00; Docket No. 50-457.  !

Very truly yours,

f&s, a R. E.' Querto -

Station Manager ,

Braldwood Nuclear Station L ,

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Enclosure:

Licensee Event Report No. 90-004-00 .

I cc: NRC Region 111 Administrator ,

NRC Resident inspector INPO Record Center  ;

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'2A DieselJeneLLt.9r Speed Oscillations due_in_alefective Resister.  !

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__Q I 4 11 6 91 0 91 0 0l014 Q_l 0 0l5 . Il 4 91 0- 01510101Ol l i THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10CFR OP N M I EI N 1 n2 W H0DE (9) 6 20.402(b) _ 20.405(c) _ 50.73(a)(2)(iv) _._. 73.7)(b)

POWER __ 20.405(a)(1)(1) ___ 50.36(c)(1) L 50.73(a)(2)(v) _._ 73.71(c)

LEVEL. , , ._ 20.405(a)(1)(li) _ 50.36(c)(2) __ 50.73(a)(2)(vil) ___ Other (Specify j (10) J_lj) 1 0- __ 20.405(a)(1)(iii) ._ 50.73(a)(2)(1) _. 50.73(a)(2)(viii)(A) in Abstract

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LICENSEE CQHIACT FOR THIS LER (121 Name. TEf,Ef11QMEJV!101R AREA CODE jin GrtemLki . Tech Staf f Io.g. Ext. 2M2 8l115 415181 -l 2Le.llL1 COMPLETE ONE LINE FOR EA_CH_COM 0 FAILURE DESCRISID IN THlilEPORT (13)

CAUSE- SYSTEM COMPONENT MANUFAC- REPORTABLE CAUSE SYSTEM COMPONENT HANUFAC- REPORTABLE TUB 18__ TO NPRD$ TURER TO NPRDS j

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._lY31 (If veb tQmplele_EKEECIED..SW_MISS104.DAJE.) 1 ABSTRACT (Limit to 1400 spaces, i.e, approximately fifteen single-space typewritten lines) (16)

At 0315 on April 16,1990 the 2A Diesel Generator (DG) was started to perform a four hour warm up run. The  !

DG started normally and achieved rated speed of 600 RPM. Shortly af ter startup the DG speed began  ;

escillating between 300 and 600 RPM. The 2A DG was immediately shut down. At 0913 it was identified that th3 cause of the speed oscillattuns was a failure of one of the dropping resistors in the Governor Unit. The rssistor was replaced. This resistor had f ailed on the IB DG severcl weeks earlier. Byron Station, which has four DGs that are identical to Braidwood DGs, had experienced a failure of this resistor also. At 1607 the 2A DG was started for a maintenance test, DG speed remained constant at 600 RPM. At 1653 the 2A DG was  !

sttrted for its monthly operability run. The DG had successfully completed the test. DG speed had remained constant at 600 RPH. At 2118 the 2A DG was declared operable. The root cause of the event was component failure, fhe resistor in the governor power-dropping resistor board failed creating an open circuit. An evaluation of the failure mode of the resistor was conducted. It has been concluded that the cause was simple long term heat fatigue. The resistors have been replaced on all DGs at the station, and placed on a three year replacement frequency. The resistor is being evaluated for 10CFR part 21 applicability.

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' A. PLANT CONDITIONS PRIOR TO EVENT: [

' Unit: . Braidwood 2;

, Event Date: 04/16/90; Event Time: 0315;-

Mode: 6 - Refueling; Rx Power: 0%;

RCS (AB) Temperature / Pressure: Ambient / Atmospheric

B.. DESCRIPTION ~0F EVENT

' Th;re were no systems or.cumponents inoperable at the beginning of the event which contributed to the severity of -

th) event.

At 0315 on April '16i 1990 the 2A Diesel Generator (DG) (EK) was started to perform a four hour warm up run in-pr paration for its scheduled 18 month maintenance inspection.- The 2A DG started normally and achieved rated speed of 600 RPH and nonnal voltage of about 4.16 KV. Shortly af ter startup the 2A DG speed began oscillating between 300 and 600 RPH, The 2A DG was immediately shut down.

At 0913 it was identified that the cause of the speed oscillations was a f ailure of one of the dropping resistors -

in the Governor Unit. The resistor was replaced. The equivalent resistor on the IB DG had failed several weeks earlier during maintenance. Byron Station, which has four DGs that are identical to Draldwood's DGs, had -

experienced a failure of this resistor also. This event was screened for reportability. Based on the failures sxperienced at Braidwood and Byron _ lt was determined that a four hour non-emergency report was' appropriate pursuant to 10CFR50'72(b)(2)(lii)(A). .

The appropriate NRC notification via the ENS phone system was made at 1220.

1 At 1607 the 2A DG was started for a maintenance test. The DG successfully completed the test. DG speed remained constant at 600 RPM.

At 1615 the 2A DG was shut down.

At 1653 the 2A DG was started for its monthly operability run.

- At 1819 the 2A DG was shut down. The DG had successfully completed the test. DG speed remained constant at 600 RPH.

At 2118, following the completion of the reviews of the test run data and the work package, the 2A DG was declared

=op;rable.

This event is being reported pursuant to 10CrR50.73(a)(2)(v)(A)-an) event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to shutdown the reactor and maintain it in a safe shutdown condition.

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LC2CAUSEOFEVENT:

The root cause of the event was component failure. The resistor in the governor power-dropping resistor board failed open. The f ailed resistor is one of 2 resistors in parallel on the positive lead of the governor's DC power _ supply. With one of the resistors f ailed, creating an 'open circuit, the voltage drop across the remaining resistor increased resulting in insuf ficient power supply to the governor. An b =cvaluation of the failure mode of the resistor was conducted by Sargent and Lundy Engineers. Based on the results of this evaluation it has been concluded that the cause was simple long term heat fatigue.

D .' SAFETY ANALYSISI This event'had no effect on the safety of the plant or the public. The 2B DG was operable and available throughout the event. Only 1 DG is required in Mode 6.

Under the worst case conditions of this f ailure occurring af ter a valid initiating signal. following a Safety  !

Injection there would still be no effect. The redundancy of the safety system design provides for full safe I shutdown capability from a single ESF bus. The diversity of the electrical distribution system provides for powering an EST bus f rom its System Auxiliary Transformer, its own Diesel Generator, or its corresponding ;  !

opposite Unit ESF bus which is capable.of being powered from its Diesel Generator or System Auxiliary Transformer. This is enveloped in section.8 of the Updated Final Safety Analysis Report.

E. CORRECTIVE ACTIONS:

B:th power dropping resistors in the 2A, lA and IB DG were replaced. These resistors had been replaced on April 4, 1990 for the 2B DG.

> These resistors have been'placed on a replacement frequency of three years in accordance with the reconmiendations of the Engineering evaluation.

Thr resistor is being evaluated for 10CFR part 21 applicability. This' action is being tracked to completion *

by action item 457-200-90-01001.

F. PREVIOUS OCCURRENCES:

Th2re have been no previous similar reported occurrences at Braidwood Station.

G. COMPONENT FAILURE DATA:

Manufacturer Nomenclature Model Number / MFG Part Number 'I i

Pacific Resistor 100 CH 300 ohm 70 watt resistor Note: This item supplied as part of the Woodward Governor Model 2301.

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'3011m(0$1090)/4 '

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