ML19256B443
| ML19256B443 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 05/22/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | John Miller GEORGIA POWER CO. |
| References | |
| NUDOCS 7907110105 | |
| Download: ML19256B443 (2) | |
Text
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jo, UNITED STATES Ng
,o NUCLEAR REGULATORY COMMISSION 1,,
M, a
REGION 11 0,
[
101 MARIETT ST., N.W., sutTE 3100 ATLANTA, GEORGI A 30303
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e gy 2 21979 In Reply Refer To:
RII:JPO (MD-425 50-424 Georgia Power Company ATTN:
J. B. Miller, Jr.
Executive Vice President 270 Peachtree Street Atlanta, GA 30303 Centlemen:
Enclosed is IE Dulletin 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.
A t
MV by q James P. O'Reilly Director
Enclosures:
1.
List of IE Bulletics Issued in Last Twelve Months 835 148 7907110L of
MAY 2 21979
. Georgia Power Con:pany cc w/ encl:
K. M. Gillespie Construction Project Manager Post Office Box 282 Waynesboro, Georgia 30830 E. D. Grover QA Site Supervisor Post Office Box 282 Waynesboro, Georgia 30830 836 149
)
.)
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 I
May 22, 1979 IE Bulletin No. 79-11 FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR ENG~IEERED 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 end 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 DB-50 and -75 breakers are used extensively in FWR's, and some BVR's cap.
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 s.re 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" The and caps either from scheduled testing or unusual behavior in service.
manufacturer of the " navy-gray" and caps believes the crack defects may be linked to a raw material batch problem. That is: the molding ingredient It is materials used may have neared the end of their snelf life before use.
not believed the end caps, after fabrication, have a significant shelf life limit, due to the low residual stress and low crack propagation probabilities.
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