ML19261E369
| ML19261E369 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 05/22/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| References | |
| NUDOCS 7907060363 | |
| Download: ML19261E369 (1) | |
Text
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UNITED STATES l'
.,gg'1 NUCLEAR REGULATORY COMMISSION REGION 11
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ATLANT A, GEORGI A 30303 g'
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MAY o 1979
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In Reply Refer To:
RII:JPO South Carolina Electric and Gas Conpany Attn:
Mr. T. C. Nichols, Jr.
Vice President and Group Executive Power Production and System Operations P. O. Box 764 Columbia, South Carolina 29218 Gentlemen:
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 the actions required of you, please contact this office.
Sincerely.
d M-A/ W-4 anes P. O'Reilly J
Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFCRCEMENT WASHINGTON, D..C.
20555 May 22, 1979 IE Bulletin No. 79-11 FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR ENGINEEPID SAFETY SYSTEMS Discussion:
We have received information 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. This circuit breaker had a defect in one of its three time delay dashpots which resulted in a reduced tire 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 dashpot end caps and 2 non-engineered safety feature breakers also had similar defects. The circuit breaker is a Westinghouse type DB-75.
Westinghouse type DB-50 breakers also use the same type of dashpot and end DB-50 and -75 breakers are used extensively in PWR's, and some BVR'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 feature and thus are not of concern.
crack defect, if severe enough, could result in pre =ature tripping 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 proble= described in IE Bulletin 73-1.
The subject of Bulletin 73-1 was end caps made of a black phenolic material. As a result of that Bulletin, the black end caps were replaced with 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 ingredient It 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 limit, due to the low residual stress and low crack propagation probabilities.
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