ML20043A661

LER 90-004-00:on 900416,diesel Generator 2A Speed Oscillated Prior to Maint Teardown.Caused by Component Failure.Resistors Replaced & Placed on 3-yr Replacement frequency.W/900516 Ltr

ML20043A661
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-90-004-08, LER-90-4-8, NUDOCS 9005220372
Download: ML20043A661 (5)

Text

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T Commonwealth ECoon Braidwood Nucizir Powst St: tion

• • 'o Route #1. Box 04 Braceville, Illinois 60407 Telephone 81$/458 2801 May 16,1990 BW/90-0525 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

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.

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

Very truly yours, rd )

R. E. Querlo Station Manager Braidwood Nuclear Station .

REQ /JDW/jfe (7126z)

Enclosure:

Licensee Event Report No. 90-004-00 cc: NRC Region 111 Administrator NRC Resident inspector INPO Record Center CECO Distribution List p

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DEVIATION REPORT DVR NO.

• 20 - 2 - 30 - 010

_ $1A UNIT YEAR NO. Form Rev 2.0.

PARLLl T11LE OF DEVIATION OCCURRED 2A DG Erratic Operation AU

_ . . DAIL Tl!4E

$Y$1EM AlllCIED PLANT STATUS AT llML OF EVEN1 TESTING 2A DG H0DE 6 POWER (%) D WORK REQUE$T NO. l1l l l DESCRIPTION OF EVENT At 0315 the 2A DG was **.arted for a four hour run prior to a maintenance teardown. At 0316 the 2A DG began to oscillate from 300-600 RPMs after reaching rated speed and voltage. The 2A DG was then shutdown. When the 2A DG was shutdown no cooldown cycle occurred. Tech $taff was called out to investigate.

P01LN11 ALLY $1GNIFICANT EVENT PER N$D DIRECTIVE A-07 YES N0 I I LL_l 10CFR50.72 NRC RED PHONE l l

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_teRI_Ll OPERATING ENGINEER'S COMMENTS Unit was in Mode 6 - Diesel was not being considered operable for Emergency Doron injection, machine was being run to take Hot Web Deflection measurements just prior to being taken 00$ for 18 month overhaul.

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93 50.73(a)(?)(iv) 6 _ 20.402(b) _ 20.a05(c) _ __ 73.7)(b)

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

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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 t+eed of 600 RPM.' Shortly after startup the DG speed began oscillating between 300 and 600 RPM. 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. This resistor had failed on the IB DG several weeks earlier. Byron Station, which has four DGs that are identical to Braidwood DGs, had experienced a f ailure 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 started for its monthly operability run.' The DG had successfully completed the test. DG speed had remained constant at 600 RPM - At 2118 the 2A DG was de'lared c operable. The root cause of the event was component:

failure. The resistor in the governor power-dropping resistor board f ailed creating an open circuit. An evaluation of the f ailure 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 thrse year replacement f requency. The resistor is being evaluated for 10CFR part 21 applicability.

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, LICENSEE EV[1l1 REPORT (LER) TEXT CONTINUATION Fore Rev 2.L FACILITY NAME,(1). DOCKET NUMBER (2) LER NUMBER (6) Page (3) ,

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A. PLANT CONDITIONS PRIOR TO EVENT:

Unit: Braidwood 2: Event Date: 04/16/90; Event T'**: 0315; Mode: 6 - Refueling; Rx Power: 0%; <

RC$ (AD) Temperature / Pressure: Ambient / Atmospheric  ;

D. DESCRIPi!ON OF EVENT: .

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

At 0315 on April 16,1990 the 2A Diesel Generator (DG) (D;) was started to perfonn a four hour warm up run in preparation for its scheduled 18 month maintenance inspection. The 2A DG started normally and achieved rated '

speed of 600 RPH and normal voltage of about 4.16 KV. Shortly af ter startup the 2A DG speed began oscillating - i between 300 and 600 RPH. The 2A DG was immediately shut down.

t At 0913 it was identified that the cause of the speed oscillations was a failure 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 Braidwood's DGs, had I cxperienced a failure of this resistor also. This event was screened for reportability. Based on the failures superienced at Braidwood and Byron it was determined that a four hour non-emergency report was appropriate pursuant to 10CFR50.72(b)(2)(iii)(A).

Th) appropriate NRC notification via the LNS phone system was made at 1220.

At 1607 the EA DG was started for a maintenance test. The DG successfully completed the test DG Speed remained constant et 600 RPH.

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 D6 had successfully completed the test. DG speed remained constant at 600 RPH. ,

t At 2118, f ollowing the completion of the reviews of the test run data and the work package, the 2A DG was declared cperable.

This event is belng reported pursuant 'to 10CFR50.73(a)(2)(v)(A)-any event or condition that alone could have i prevented the fulfillment of the safety function of structures or systems that are needed to shutdown the reactor

• I and maintain it in a safe shutdown condition.

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TEKT Energy Industry Identification System (E!!$) codes are identified in the text as (XX) l' C. CAU$E OF EVENT:

L.

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 ceross the remaining resistor increased resulting in insufficient power supply to the governor. An evaluation of the f ailure mode of the resistor was conducted by $ argent and Lundy Engineers. Based on the r:sults of this evaluation it has been concluded that the cause was simple long term heat fatigue.

D. $AFETY ANALY$l$:

This event had no effect on the safety of.the plant or the public. . The 2B DG was operqble 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 Saf ety.

Injection there would still be no effect. The redundancy of the safety system design provides for full Saf t shutdown capability f rom a single ESF bus. The diversity of the electrical distribution system provides for powering an ESF bus from its System Auxiliary Transformer, its own Diesel Generator, or its corresponding '

nprosite 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:

Both power dropping resistors in the 2A, IA and 18'0G were replaced. These resistors had been replaced on April 4, 1990 for the 2B DG.

r These resistors have been placed on a replacement f requency of three years in accordance with the recopenendations of the Engineering evaluation.

l l The resistor is being evaluated for 10CFR part 21 appitcability. This action is being tracked to completion by action item 457-200-90-01001.

-F. PREVIOU$ OCCURRENCES:

There have been no previous similar reported occurrences at Draidwood Station.

G. COMPONENT fAltURE DATA:

Manufacturer Nomenclature Model Number / MFG part. Number

' pacific Resistor 100CH300 ohm 70wattresisthr l

Note: This item supplied as part of the Woodward Governor Model 2301.

3011:(0$1090)/4