ML20084N866

AO 50-249/75-35:on 750821,circuit Breaker 152-3403 Failed to Trip During Breaker Trip Test.Caused by Failure of Trip Coil.Breaker Replaced

ML20084N866
Person / Time
Site:	Dresden
Issue date:	08/29/1975
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084N869	List: ML20084N866 ML20084N874
References
562-75, NUDOCS 8306090098
Download: ML20084N866 (2)

Text

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Commonalth Edis:n

' h) h " ,One First f Jsal Ptara Chicago. Hhnois

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V k [G%# J Address Rep!y to: Post Offree Box 767 .

Ns' Chicago, Illinois 60690 BBS Ltr. #562-75 Dresden Nuclear Power Station R. R. in Morris, Illinois 60450f._

t ,g August 29, 1975 i e,

,g Mr. James G. Keppler, Regional Director E- A e y .-

j Directorate of Regulatory Operation-Region III D' 2 10 -

U. S. Nuclear Regulatory Co:=ission - $b^ y(vi'd 7[

799 Roosevelt Road Y Glen Ellyn,' Illinois 60137 c. ( ]g as

SUBJECT:

REPCRT OF AO:0RV3.L CCCURRE:CE PER SECTICN 6.6.A OF THE CICIIC SPECIFICATI'::!S FAILUitE OF CIRCUIT ERFWER 152-3403

References:

1) Regulatory Guide 1.16 Rev. 1 Appendix A

2) Notification of Region III of U. S. Nuclear Regulatory Comission Telephone: H. Kister, 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br /> on August 21, 1975 Telegram: J. Keppler, 1510 hours0.0175 days <br />0.419 hours <br />0.0025 weeks <br />5.74555e-4 months <br /> on August 21, 1975

3) Drawing Nu=ber 12E-3344 ,

Report Number 50-249/75-35 Report Date: August 29, 1975 ~

Occurrence Date: August 21, 1975 Facility: Dresden Nuclear Power Station, Morris, Illinois IDD7fIPICATION OF OCCU"J1 DICE Circuit breaker 152-3403 failed to trip (open) during a breaker trip test.

Circuit breaker 152-3403 isolates bus 34 in the event of loss of off-site power.

CONDITIONS PRIOR TO OCCC RBsCE Unit-3 was in the shutdown mode. The Dnergency Core Cooling System (EECS) functional test was in progress.

go '.2 DESCRIPTION OF OCCURRD:CE i

l At 0200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br /> on August 21, 1975, bus 34 was de-energized for the ECCS test.

The Operational Analysis Department conducted the breaker trip test on the breakers of bus 34 while the bus was de-energized. As the trip coil of Y -) l breaker 152-3430 was energized, the coil burned out before tripping the breaker. l 8306090098 750829 DR ADOCK 05000249 9511 PDR LOPY SENT REGION _ f/L , 3

f Mr. Jam { .'Kapplcr August 29,1975 1 DESIGNATION OF APPAREI;T CAUSE OF CCCURRECE (Component Failure)

The failure of the trip coil caused the breaker to remain closed. Evamination ghowed the trip latching mechanism and other breaker components to be completely serviceable. The coil failure prevented the trip latch from releasing the spring-loaded breaker.

ANtl,YSIS OF OCCURRE;CE 1

Circuit breaker 152-3403 is located in series with breaker 152-3432 on bus 34-1.

Had it become neccseary to isolate bus 34-1 from bus 34 because of emergency conditions, both breakers would have received tripping signals. Since the redundant breaker en bus 34-1 was always operable, there was no threat of inadvert-cntly overloading the diesel generator. Consequently, plant personnel and the public were not jeopardized by this occurrence.

CORREETIVE ACTICN To return normal feed to bus 34-1, breaker 152-3403 was replaced with an identical breaker used in the circulcting vater pump 3C compartz::ent. The trip coil of breaker 152-3403 was replaced, and the breaker was successfully tripped several times.

FAILURE DATA Ko previously reported coil failure in this type of breaker has occurred at Dresden. The air circuit breaker is a General Electric Magne Blast breaker, type AMI 4.76-250, rated at 4KV anc 1200 amps. ,

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