ML19261E420
| ML19261E420 | |
| Person / Time | |
|---|---|
| Site: | Sterling |
| Issue date: | 05/22/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Arthur J ROCHESTER GAS & ELECTRIC CORP. |
| References | |
| NUDOCS 7907060432 | |
| Download: ML19261E420 (1) | |
Text
J UNITED STATES
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KING OF PRUSSIA, PENNSYLVANIA 19406 Docket No. 50-485 Rochester Gas & Electric Corporation ATTN: Mr. J. E. Arthur Chief Engineer 89 East Avenue Rochester, NY 14649 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.
Stacerely, h
e Boyce H. Grier Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months cc w/encls:
C. R. Anderson, Manager, QA Lex K. Larson, Esquire N. A. Petrick, Executive Director, SNUPPS Gerald Charnoff, Esquire 293 299 290neoy33?
UNITED STATES NUCLEAR REGULATORY 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 SYSTE'iS Discussion:
We have received information from Westinghcuse 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 mrcurrent p otection.
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 < 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.
08-50 and -75 breakers are used extensively in PWR's, and some BWR's may also have the same breakers.
Sim!1ar make and model circuit breakers, when used for scram purposes, do not require the overcurrent trip feature ano thus are not of concern.
The end cap crack defect, if severe enough, could result in premature Pipping 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 ed aps were repiced with a new type made of fibre-filled polyester material cal'.d " navy-gray" Prior to the April 1979 report, there have been no reports of suspect " navy-gray" end caps either from scheculed 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
- he 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 stress and low crack propagation probabil
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