ML19340B059
| ML19340B059 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities, Zion  |
| Issue date: | 02/28/1973 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Brian Lee COMMONWEALTH EDISON CO. |
| References | |
| NUDOCS 8010170769 | |
| Download: ML19340B059 (1) | |
Text
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t UNITED STATES
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ATOMIC ENERGY COMMISSION
'.L DIRECTOR ATE OF REGULATORY OPER ATIONS 4
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799 ROOSEVELT ROAO (312) d58 2560 GLEN ELLYN. ILLINOIS 6o137 February 28, 1973 Docket No. M Cetnonwealth Edison Company 50-237 A"iTN : Mr. Byren Lee, Jr.
50-249 Assistant to the President 50-254 P. O. Box 767 50-265 Chicago, Illinois 60690 50-295 50-304 Centlemen:
The attached Directorate of Regulatory Operations Bulletin No. 73-1,
" Faulty Overcurrent Trip Delay Device in Circuit Dreakers for Engineered Safety Systema", is sent to you to provida you with information ve received frem the Wisconsin Electric Power Company and the Rochester Gas and Electric Corporation concerning the Point Beach and Ginna pressurized l
This infor=ation may relate to the design, water reactor facilities.
fabrication and performance of certain equipment at your facilities.
Action requested on your part is identified in Section B of the Bulletin.
in writing, The infomation requested should be provided to this office, within forty-five days of your receipt of this letcar.
Should you have any questions concerning this natter, we vill te pleased to discuss then with you.
Sinceroly yours, Boyce H. Crier Regional Director
Attachment:
R0 Bulletin No. 73-1 bec: RO Files j
DR Central Files PDR Local PDR OGC, Beth, P-506A R. Renfrow, OGC (2)
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February 28, 1973 Directorate of Regulatory Operations Bulletin 73-1 a
FAULTY OVERCURRENT TRIP DELAY DEVICE IN CIRCUIT BREAKERS FOR ENGINEERED SAFETY SYSTEMS 1
We have received information from two licensees relating to the failure of circuit breakers in engineered safety systems. These circuit breakers, Westinghouse Models DB-25, DB-50 and DB-75, are used extensively at both PWR and BWR facilities. These failures, which could negate' operation of engineered safety system components, were attributed to faulty overcurrent trip delay devices.
- Westinghouse has formulated an on-site testing program to determine if the time delay devices are faulty and is i
developing a new end cap for the dashpot used in the time delay devices.
Similar make and model circuit breakers, when used for scram purposes, do not require the overcurrent trip feature and, therefore, are not included in this problem. Pertinent details relcting to this problem are contained in Section A below. Action requested by this Bulletin is contained in Section B.
A.
Description of Circumstances Plant A I
During the performance of the routine monthly surveillance test of the Safety Injection System, the pump motor tripped as it approached operating speed. A second attempt to start the pump produced the same result.
The cause of the pump trip was attributed to malfunc~
tion of an overcurrent trip device. This device, which has an adjustable time delay, tripped out the pump motor on starting current because of leakage in the time delay dashpot.
Subsequent examination of the dashpot disclosed a crack in the end cap of the air chamber.
The crack permitted air to leak into the chamber at an excessiva rate, reducing the time delay from approximately 45 seconds to 5 seconds. Testing of similar model breakers equipped with the overcurrent trip delay feature revealed four additional units with low trip delay times caused by cracks in the end caps.
Approximately 25 circuit breakers of the type described are utiliced to energize components of engineered safety feature systems at this facility.
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. Plant B A 480 volt AC bus circuit breaker tripped open when the auxiliary building supply and exhaust fans were started simultaneously. The cause of the failure was attributed to a crack in the end cap of i
the time delay dashpot in the overcurrent trip device. The trip delay unit and the circuit breaker in question are sinilar to the units which failed at Plant A.
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The cracks found in the end caps of the time delay dashpots are considered a common mode of failure.
3.
Action Recuested of the Licensee It is requested that you determine whether safety related (Class IE) l circuit breakers of the described make and models utilizing over-current trip time delay features are installed, or will be installed, l
at your facilities and provide this office with your findings.
If the subject breakers are installed, please include in your response a description and the results of your program to determine i
if you have any faulty overcurrent trip time delay devices installed and the scheduled completica date of your corrective actions.
For j
facilities currently under construction please inform us of your plans to assure that the appropriate modification has been incorporated I
in all safety related circuit breakers of the type described that have been or will be installed at your facility.
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