ML19246A798
| ML19246A798 | |
| Person / Time | |
|---|---|
| Site: | Catawba, Perkins, Cherokee  |
| Issue date: | 05/22/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Dail L DUKE POWER CO. |
| References | |
| NUDOCS 7907060353 | |
| Download: ML19246A798 (1) | |
Text
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'o UNITED ST ATES NUCLEAR REGULATORY COMMISSION 8'
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E REGION 11
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i it '*ARIETT A ST., N W., $UITE 3100 o,
ATLANTA, GEORGIA 30303
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TI R #1 MAY 2 r 1979 In Reply Refer To:
RII:JPO 50-413 u5_0-414 5 R 88, 50-489 N (JiO-490,'550-491~~
50-492, 50-493 Duke Power Company Attn:
Mr. L. C. Dail, Vice President Des?gn Engineering P. O. Box 33189 Charlotte, North Carolina 28242 Gentlemen:
Enclosed is IE Bulletin 79-11 which requires action by you with regard to your power reactor f acility(ies) with an operating license -)r a construction permit.
Should you have questions regarding this Bulletin or t~.te actions required of you, please contact this office.
Sincerely,
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%a TV 4,.y James P. O'Reill/
g4 Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months 30 1%
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197C)
. Duke Power Company cc w/ enc 1:
D. G. Beam, Project Manager Post office Box 223 Clover, South Carolina 29710 J. T. Moore, Project Manager Post office Box 422 Gaffney, South Carolina 29340 l
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UNITED STATES NUCLEAR REGULATORY C0rEISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 May 22, 1979 IE Bulletin No. 79-11 FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKErl; FOR ENGINEEFID SAFETY SYSTEMS Discussion:
We have received information froe 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-The defect was a small hairline crack in the end cap of current protection.
Further investigation by this licensee disclosed that 7 out of the dashpot.
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 ^creakers also use the same type -f dashpot and end DB-50 and -75 breakers are used extensively in PWh's, and some BWR's cap.
may also have the same breakers.
Similar make and model circuit breakers, m a used for scrar purposes, dc y t The end cap require the overcurrent trip feature and thus are not of cracern.
crack defect, if severe enough, could result in pre =ature tripping of the circuit breaker because of insuf ficient tine delay in ov.:rcurrent 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 The subject of Bulletin 73-1 was end caps made of a black phennlic 73-1.
As a result of that Bulletin, the black end caps were replaced with material.
a new type made of fibre-filled polyester material called " navy-gray".
Prior there have been no reports of suspect " navy-gray" to the April 1979 report, The end caps either from scheduled testing or unusual behavior in service.
manuf acturer of the " navy-gray" end caps believes the crack lefects uy be linked to a raw material batch problem. That is, the molding ingredientIt is materirls used may have neared the end of their shelf life before use.
not believed the end caps, after fabrication, have a significant shelf life due to the low residual stress and low crack propaEstion probabilities.
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