ML19210B392
| ML19210B392 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/21/1973 |
| From: | John Miller METROPOLITAN EDISON CO. |
| To: | |
| Shared Package | |
| ML19210B391 | List: |
| References | |
| NUDOCS 7911070714 | |
| Download: ML19210B392 (1) | |
Text
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METROPOLITAN EDISON COMPANY
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POST OFFICE BOX 542 RE ADING. PENNSYLVANI A 19603 TELEPHONE 215 - 929-360; September 21, 1973 a
9 t g Dr. D. F. Knuth, Director Directorate of Regulatory Operations United States Atomic Energy Commission
,ashington, D. C.
20545 W
Subject:
Three Mile Island Nuclear Station Unit 1 Suppression Diode Failure in a 480 Volt Breaker Docket No. 50-289
Dear Dr. Knuth:
You were notified on August 24, 1973, of a situation which could be considered reportable under 10CFR50.55(e)(1)(iv), " Conditions of Construction Permits". This situation relates to an are suppression diode failure in a 480 volt breaker.
DESCRIPTION OF INCIDENT During checkout of 480 volt breakers by Startup electricians, it was found that some breakers would not close after being tripped. The problem con-cerned Westinghouse 480 volt model DB-25 and DB-50 breakers, which are elec-trically operated.
CORRECTIVE ACTION Investigation revealed the affected breakers have diodes connected across the closing coil, trip coil, and anti-pump relay. During breaker opera-tion, these diodes can be exposed to voltage spikes in excess of their break-down voltage which can result in their shorting out.
The consequence of this failure is that the breaker, once tripped, will not reclose on its next required cycle. The failure does not affect the ability of the breaker to trip.
A design change was initiated to replace the Westinghouse IN 3405 diodes with GE type 6RS20AP10B2 thyrectors which are not subject to this problem.
Very truly yours, 1584 344
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l, J. < "
,J. G. Miller brh Vice President cc:Mr. H. M. Dieckamp 7911070 7/
Mr. J. P. O'Reilly Mr. W. A. Verrochi