ML19246A795
| ML19246A795 | |
| Person / Time | |
|---|---|
| Site: | Atlantic Nuclear Power Plant  |
| Issue date: | 05/22/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Collier A OFFSHORE POWER SYSTEMS (SUBS. OF WESTINGHOUSE ELECTRI |
| References | |
| NUDOCS 7907060350 | |
| Download: ML19246A795 (1) | |
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+f oq[og UNITED ST ATES NUCLEAR REGUL ATORY COMMISSION
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MAY 2 1979 rai3 In Reply Refer To:
RII:JP0 Ge7D Offshore Power Systems Attn:
Mr. A. R. Collier, President 8000 Arlington Expressway P. O. "ax 8000 Jacksonville, Florida 32211 Gentimen:
Enclosed is IE Bulletin 79-11 which requires action by you with regard to your power reactor f acility(ies) with an operating license or a construction permit.
Should you have questions regarding this Bulletin or tr.e actions required of you, please contact this office.
Sincerely.
v h
4 ames P. O'Reilly J
Director Enclosutes:
1.
List of IE Bulletins Issued in Last Twelve Months
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICr,OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 May 22, 1979 IE Bulletin No. 79-11 FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR D1GINEERED SAFETY SYSTEFJ Discussion:
We have received inf ormation from Westinghouse and an NRC licensee relating to the potential f ailure of a circuit breaker in an engineered safety system of a nuclear power plant. Th's circuit breaker had a def ect in one of '.s three time delay dashpots which resulted in a reduced ti~e delay for over-The defect was a small hairline crack in the end cap of current protection.
Further investigation by this licensee disclosed that 7 out of the dashpot.
17 spare dashpct end caps and 2 non-engineered safety feature breakers also The circuit breaker is a Westinghouse type DB-75.
had similar defects.
Westinghouse type DB-50 breakers also use the same type of dashpot and end DB-50 and -75 breakers a n used extensively in PWR's, and some BWR's cap.
may also have the same breakers.
Similar make and model circuit breakers, when used for scram purposes, do not The end cap require the overcurrent trip f eature and thus are not of concern.
crack defect, if severe enough, could result in pre =ature cripping of the circuit breaker because of insufficient time delay in overcurrent protection, i.e., the motor starting (inrush) current could cause the breaker to trip inadvertently and thus prevent the motor start.
The defects reported by the licensee in April 1979, occurred in the replacement end caps which were provided to solve the problem described in IE Bulletin The subject of Bulletin 73-1 was end capt made of a black phenolic 73-1.
As a result of that Bulletin, the black end caps were repleced with material.
a new type made of fibre-filled polyester material called " navy-gray".
Prior to the April 1979 report, there have been no reports of suspect " navy-gray" The end caps either from scheduled testing or unusual behavior in service.
manufacturer of the " navy-gray" end caps believes the crack defects may be linked to a raw material batch problem. That is, the molding ingredientIt is materials used may have neared the end of their shelf life before use.
not believed the end caps, after fabrication, have a significant shelf life due to the low restdual stress and low crack propagation probabilities.
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