ML19256B380
| ML19256B380 | |
| Person / Time | |
|---|---|
| Site: | Columbia, Washington Public Power Supply System, Satsop  |
| Issue date: | 05/22/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Strand N WASHINGTON PUBLIC POWER SUPPLY SYSTEM |
| References | |
| NUDOCS 7906130054 | |
| Download: ML19256B380 (1) | |
Text
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NUCLEAR REGULATORY COMMISSION
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- e WALNUT CREE K, Calif ORNIA 9459G i,g May 22,1979 Docket flos. 50-E 0 50-397 50-508 50-509 50-513 Washington Public Power Supply System P. O. Box 968 3000 George Washington Way Richland, Washington 99352 E'
Attention: Mr. fl. O. Strand Managing Director Centlemen:
Enclosed is IE Bulletin flo. 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, hN Re[i. ngelken. (
Director
Enclosure:
IE Bulletin fio. 79-11 with Enclosure cc w/ enclosures:
M. E. Witherspoon, WPPSS A. D. Kohler, WilP-2, WPPSS J. P. Thomas, WPPSS W. J. Talbot, WPr'SS G. C. Sorensen, WPPSS 7906130054
UhlTED' STATES fiUCLEAR REGULATORY C0!'.MISSIO:1 0FFICE OF IflSpECTI0ft Arid Ef;FORCEMENT WASHIflGT0h, D.C.
20555 fiay 22,1979 IE Bulletin flo. 79-11 FAULTY OVERCURREllT TRIP DEVICE Ill CIRCUIT BREAKERS FOR Ef GIflEERED SAFETY SYSTEMS Discussion:
We have received information from Westinghouse and a f1RC 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-enqineered 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 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 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" cnd 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,
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