ML19256B401
| ML19256B401 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 05/22/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Burstein S WISCONSIN ELECTRIC POWER CO. |
| References | |
| NUDOCS 7906130120 | |
| Download: ML19256B401 (1) | |
Text
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MAY 2 21979 Docket No. 50-266 Docket No. 50-301 Wisconsin Electric Power Company ATTN:
Mr. Sol Burstein Executive Vice President Power Plants 231 West Michigan Milwaukee, WI 53201 Gentlemen:
Enclosed is IE Bulletin No. 79-11 which requires action by you with regard to your power reactor facilities 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, Q.wd /d q, A-f fJames G. Keppler Director
Enclosure:
IE Bulletin No. 79-11 cc w/ encl:
Mr. G. A. Reed, Plant Manager Central Files Director, NRR/DPH Director, NRR/ DOR C. M. Tremmel, ORB /h1R PDR Local PDR NSIC TIC Sandra A. Bast, Lakeshore Citizens for Safe Energy 7906130120
t U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT REGION III May 22, 1979 IE Bulletin No. 79-11 FAULTY OVERCURFINT TRIP DEVIC" IN CIRCUIT BREAKERS FOR ENGIhTERED 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 and 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 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 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 ingr'difnt materials used may have neared the end of their shelf life before us..
It is not believed the end caps, after fabrication, have a significant shelf life limit, due t on probabilities.
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