ML19256B444
| ML19256B444 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 05/22/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Proffitt W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| References | |
| NUDOCS 7907110127 | |
| Download: ML19256B444 (2) | |
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k UNITED STATES 8 ',,,
NUCLEAR REGULATORY COMMISSION
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E REGION 11 4
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A TL ANTA, GEORGI A 30303 In Reply Refer To:
RII;JPD 50-339' '- s 50-404 i
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Virginia Electric and Power Company ATTN:
W. L. Proffitt Senior Vice President, Power P. O. Box 26666 Richmond, VA 23261 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.
A t
M\\/ W q James P. O'Reilly Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months 5
835 158 20evuolz7
MAY 2 21979 Virginia Electric and Power Company cc w/ encl:
W. R. Cartwright, Station Manager Post Office Box 402 Mineral, Virginia 23117 P. G. Pe r ry Senior Resident Engineer Post Office Box 38 Mineral, Virginia 23117 O
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, 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 from 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 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 BWR's cap.
may also have 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 premature 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 problem described in IE Bulletin 73-1.
The subject of Bulletin 73-1 was end caps made of a black phenolic naterial. 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 and caps either from scheduled testing or unusual behavior in service.
manufacturer of the " navy-gray" and 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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