ML19256B379
| ML19256B379 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 05/22/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| References | |
| NUDOCS 7906130053 | |
| Download: ML19256B379 (1) | |
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WALNUT CHLEK, CALIFORNIA 94596 May 22,1979 Docket No. 50-312 Sacramento Municipal Utility District P. O. Box 15830 Sacramento, California 95813 Attention: Mr. John J. Mattimoe Assistant General Manager Gentlemen:
Enclosed is IE Bulletin No. 79-11 which requires action by you with regard to your power reactor facility (ies) uith 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, s
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'firector
Enclosure:
IE Bulletin No. 79-11 with Enclosure cc w/ enclosures:
R. J. Rodriguez, SMUD L. G. Schwieger, SMUD 790613005a 7906130053
UtlITED' STATES fiUCLEAR REGULATORY COMMISSION OFFICE OF IllSPECTI0il ATID EtiFORCEMENT WASHINGT0fl D.C.
20555 May 22, 1979 IE Bulletin flo. 79-11 FAULTY OVERCURRENT TRIP DEVICE Ill CIRCUIT BREAKERS FOR ENGINEERED SAFETY SYSTEMS Discussion:
We have received information from Westinghouse and a 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 ~;reaker is a Westinghouse type 08-75.
Westinghouse type DB-50 breakers 1so use the same type of dashpot and end cap.
D8-50 and -75 breakers are ; sed 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 shelf life before use.
It is not believed the end caps, after fabr limit, due to the low residual stre DUPLICATE DOCUMENT Entire document previously entered into system under ANO N o.
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