ML19256B372
| ML19256B372 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 05/22/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Crane P PACIFIC GAS & ELECTRIC CO. |
| References | |
| NUDOCS 7906130041 | |
| Download: ML19256B372 (1) | |
Text
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NUCLEAR REGULATORY COMMISSION
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- e,,,e" WALNUT CR E E K, CALIFORNI A 94596 May 22,1979 Docket Hos. 50-275 50-323 Pacific Gas and Electric Company 77 Beale Street San Francisco, California 94106 Attention: Mr. Philip A. Crane, Jr.
Assistant General Counsel Gentlemen:
Enclosed is IE Bulletin No. 79-11 which requires action by you with regard to your power reactor facility (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,
/)/(( LEY F,.
ngelken
' /'
Director
Enclosure:
IE Bulletin No. 79-11 with Enclosure cc w/ enclosures:
W. A. Raymond, PG&E J. D. Worthington, PG&E R. Ramsay, Diablo Canyon 7906130041
UNITED ~ STATES flVCLEAR REGULATORY COMMISSION OFFICE OF IflSPECTIO!! A!!D EllFORCEMEllT WASHIflGT0ft, D.C.
20555 May 22, 1979 IE Bulletin !!o. 79-11 FAULTY OVERCURREllT TRIP DEVICE Ill CIRCUIT BREAKERS FOR Ef!GINEERED SAFETY SYSTEMS Discussion:
We have received information from Westinghouse and a fiRC 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 08-50 breakers also use the same type of dashpot and end cap.
DB-50 and -75 breakers are used extensively in PWR's, and some BWR's 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 No. 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" end caps either from scheduled testing or unusual behavior in service. The 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 materials used may have neared the end of their sh not believed the end caps, after fat limit, due to the low residual stres DUPLICATE DOCUMENT Entire document previously entered into system under:
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