ML19261E418
| ML19261E418 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 05/22/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Tallman W PUBLIC SERVICE CO. OF NEW HAMPSHIRE |
| References | |
| NUDOCS 7907060429 | |
| Download: ML19261E418 (1) | |
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't UNITED STATES 8 y ),, r,o,j NUCLEAR REGULATORY COMMISS:
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May 22,1979 Docket Nos. 50-443 50-444 Public Service Company of New Hampshire ATTN:
Mr. W. C. Tallman President 1000 Elm Street Manchester, New Hampshire 03105 Gentlemen:
Enclosed is IE Bulletin 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 by you, please contact this office.
Sincerely, Yh m
Boyce H. Grier Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months cc w/encis:
John D. Haseltine, Project Manager 293 295 m
7 907060 %2Y.
UNITED STATES NUCLEAR REG'JLATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 IE Bulletin No. 79-11 Date:
May 22, 1979 Page 1 of 3 FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR ENGINEERED SAFETY SYSTEMS Discussion:
We have received information from Westingnouse 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 overcurrent 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. Wettinghouse type DB-50 breakers also uce 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 t'le 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 manufacture. 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.1 ave neared the end of their shelf life before use.
IUy_not believed the end caps, after fabrication, have a significant shelf lif '
m" and low crack propagation probabilities.
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