ML19261E387
| ML19261E387 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/22/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| NUDOCS 7907060392 | |
| Download: ML19261E387 (1) | |
Text
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i UNITED STATES
- [$cfj NUCLEAR REGULATORY COMMISSION NN (3.Wcr.h, [5 REGION 1 2
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May 22,1979 Docket Nos. 50-336 50-245 50-423 Northeast Nuclear Energy Company ATTN:
Mr. W. G. Counsil Vice President - Nuclear Engineering and Operations P. O. Box 270 Hartford, Connecticut 06101 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, Boyce H. Grier
' Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months cc w/encls:
K. W. Gray, Construction Quality Assurance Lead H. R. Nims, D.irector of Nuclear Projects J. F. 0peka, Station Superintendent D. G. Diedrick, Manager of Quality Assurance J. R. Himmelwright, Licensing Safeguards Engineer A. Z. Roisman, Natural Resources Defense Council 790706034L
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UNITED STATES NUCLEAR REGULATORY COMMISSION 0FFICE 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 D1scussion:
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 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 DB-75. Westinghouse type D8-50 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 prerrature 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 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 significant shelf life limit, due to the low residual strys and low crack propagation proba R ~
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