ML19261D610

LER 79-034/01T-0 on 790530:diesel Generator Failed to Start During Operability Test.Caused by Failure to Engage of Lower Air Start Bendix Gear.Gear Aligment Will Be Checked After Diesel Generator Tests

ML19261D610
Person / Time
Site:	Dresden
Issue date:	06/12/1979
From:	Chan J COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19261D609	List: ML19261D608 ML19261D610
References
LER-79-034-01T, LER-79-34-1T, NUDOCS 7906200371
Download: ML19261D610 (2)

Text

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. LICE.NSEE EVENT REPORT i i

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8 bu 61 DOCKET NUMBER 66 6J EVENT DATE REPORT DATE EVENT DESCRIPTION AND PROCABLE CONSEQUENCES O'o o 2 lon 5/24/79 with Units 2 and 3 in steady state operation, U 2/3 DG failed to start l g ,

, g during operability test subsequent to finding a LPCI injection valve inoperable. On y o ,,  ; 5/30/79, similar event occurred when D 2/3 DG failed to start during operability test g g g ,after D2 DG was declared inop. U3 DG was immediately proven operable. Shutdown of g g g ;U2 was initiated immediately. Safety significance minimized since offsite power was g g ,

available at all times.  ;

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, , lpast. Mod. in progress to install multiple air start attempt circuitry, y 3 ,,  ; In interim, gear alignment will be checked af ter every test of 2/3 DG. g i 8 9 80 oTHER STATUS DIS OV RY DISCOVERY DF, SCRIPT lClgl Operability test atter b STA  % POWE R 1 5 l E lg 0 l 9 l 9 lgl U3 at 99% l Failure [

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. r ATTACRMENT TO LICENSEE EVENT REPORT 79-034/0lT-0 COMMONUEALTH EDISON COMPANY (C'JE)

DRESDEN UNIT ILDRS2 DOCKET # 050-237 .

On 5/24/79 with both Units 2 and 3 in steady state operation, the U 2/3 D/G failed to start during a test to prove operability subs _quent to finding a LPCI injection valve inoperable. It was observed that the lower bendix gear butted tooth to tooth with the ring gear le failed to engage. A second start immediately following the failure was suc-cessful. Tests performed by maintenance personnel could not repeat the gear abutment. However, on 5/30/79, a similar event occurred when U2/3 D/G failed to start during an opera 5111ty test follcwing a fail- ,

ure of the U2 D/G to properly shutdown (R.O. #79-37/03L-0). U3 was immediately proven operable and an orderly shutdown of Unit 2 commenced.

The safety significance of this event was minimized since offsite power was available at all times.

Both events were caused by the failure to engage of the lower air start bendix gear. Following the first failure on 5/24/79, 2/3 D/G was successfully started three times. The failure could not be duplicated.

After the second failure, the lower air start motor was replaced. It was taken apart and inspected, but no abnormality could be found.

Failures of these motors to engage has occurred in the past.

As a result of these earlier failures the station contacted the vendor to seek a corrective action to prevent recurrence of the air start motors failing to engage.

As a result of that investigation, a modification is pending to the air start circuitry to add a multiple start feature.

The modified system will function by making several attempts at air start motor engagement, before the starting sequence is locked out. The present system only allows one attempt before the start cir-cuitry locks out on " Failure To Start". Installation of the modifi-cation will be completed as soon as all parts are available. The frequency of operability testing for the 2/3 DG has been increased to weekly for one month to assure proper operation. In addition, after each start of the diesel for surveillance testing and until the air start modification is complete, proper alignment of the air start pinions is being verified in accordance with an approved station procedure. .

2286 128 .

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