ML19246A806
| ML19246A806 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 05/22/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Mary Johnson SOUTH CAROLINA ELECTRIC & GAS CO. |
| References | |
| NUDOCS 7907060362 | |
| Download: ML19246A806 (1) | |
Text
MAY 2.1979 thmRECe 3
p UNITED STATES f
NUCLEAR REGULATORY COMMISSION
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101 M ARIETT A ST., N W., SUIT E 3100 ATL ANT A GEORGI A 30303
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hiAY 2 21979 In Reply Refer To:
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South Carolina Electric and Gas Company Attn:
Mr. M. C. Johnson, Vice President and Group Executive - Special Services and Purchasing P. O. Box 764 Colu=bia, 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.
regarding this Bulletin or the actions required of Should you have questione you, please contact this office.
Sincerely, 4 a=es P. O'Reilly J
Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months T, p "_;
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7907060 % 2
MAY r : 1979 South Carolina Electric and Gas Company cc w/ encl:
T. B. Conners, Jr.
Conners, Moore and Corbe r 1747 Pennsylvania Avenue, N.W.
Washington, D.C.
20006 A. A. Smith Quality Assurance Post Office Box 8 Jen>>csville, South Carolina 29065 O. S. Bradbam, Manager Nuclear Operations Post Office Box 8 Jenkinsville, South Carolina 29065
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASP.INGTON, D.C.
20555 May 22, 1979 IE Bulletin No. 79-11 FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR ENGINEERED SAFETY SYSTEMS Discussion:
We have received information f rom Westinghouse and an NRC licensee relating to the potential failure 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 time delay for over-current protection. The defect was a small hairline crack in the end cap of the dashpot. Further investigation by this licensee disclosed that 7 out of 17 spare dashpot end caps and 2 non-engineered safety feature breakers also bad similar defects. The circuit breaker is a Westinghouse type DB-75.
Vestinghouse 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 BWR's cap.
may also ha-the same breakers.
Similar make and model circuit breakers, when used for scram purposes, do not require the overcurrent trip feature and thus are not of concern. The end cap 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 (iurush) 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 thst Bulletin, the black end caps were replaced with a new type cade of fibre-filled polyester material cc.lled " navy-gray".
Prior to the April 19/9 report, there have been no reports of suspect " navy-gray" The and 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, af ter f abrication, have a significant shelf lif e limit, due to the low residual stress and low crack propagation probabilities.
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