ML19256B373
| ML19256B373 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| 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 7906130042 | |
| Download: ML19256B373 (1) | |
Text
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o, l>NITED STATES 8 \\[' ),, gg( 'g NUCLEAR REGULATORY COMMISSION
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o SUITE 202, WALNUT CHE E K l'LAZA WALNUT CREE K, CALIFORNIA 94596 May 22, 1979 Docket flo. 50-133 Pacific Gas and Electric Conpany 77 Beale Street San Francisco, California 94106 Attention:
Mr. Philip A. Crane, Jr.
Assistant General Counsel Gentlemen:
Enclosed is IE Bulletin fio. 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,
'/
R. b.t JacW pi ngelken-e/
Director
Enclosure:
IE Bulletin f'o. 79-11 with Enclosure cc u/ enclosures:
W. Barr, PG&E W. A. Raymond, PG&E E. Weeks, PG&E, Humboldt Bay 7906130042
UtlITED' STATES fiUCLEAR REGULATORY COMMISSI0ft OFFICE OF IflSPECTI0f! AllD EllFORCEf4EllT WASHIllGT0ft, D.C.
20555 May 22, 1979 IE Bulletin flo. 79-11 FAULTY OVERCURRErlT TRIP DEVICE Ill CIRCUIT BREAXERS FOR EllGIflEERED SAFETY SYSTEMS Discussion:
We have received information from Westinghouse and a flRC 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 08-75.
Westinghouse type DB-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 recuire 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 flo. 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 fabrication, have a signific limit, due to the low residual stre DUPLICATE DOCUMENT Entire document Previously entered into system under.
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