ML19246A805
| ML19246A805 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 05/22/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Stampley N MISSISSIPPI POWER & LIGHT CO. |
| References | |
| NUDOCS 7907060361 | |
| Download: ML19246A805 (1) | |
Text
/pa ss o 'of UNITED ST ATES v
NUCLEAR REGULATORY COMMISSION l'
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101 MARif TT A ST., N.W, SulT E 3100
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ATLANTA, GEORGI A 30303 MAY 2 21973 In Reply Refer To:
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C50 416, 50-417 Mississippi Power and Light Company Attn:
Mr. Norris L. Stampley Vice President of Production P. O. Box 1640 Jacksen, Mississippi 39205 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 of you, please contact this office.
Sincerely, Y
tr 4 ames P. O'Reilly J
Director Enclosuces:
1.
List of IE Bullecins Issued in Last Twelve Months
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f/AY 2 ' 1979 Mississippi Power and Light Company cc w/ encl:
C. K. McCoy Plant Manager Post Office Box 756 Port Gibson, Mississippi 39150 k
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMEh7 WASHINGTON, D.C.
20555 May 22, 1979 IE Bulletin No. 79-11 FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR ENGINEERED 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 dashpets 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 PWR'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 are not of concern.
The end cap crack defect, if severe enovsh, could result in pre =ature tripping of the circuit breaker because of insuf ficient 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 proble= described in IE Bulletin 73-1.
The subject of Bulletin 73-1 was end esps made of a black phenolic material. As a result of that Bulletin, the black end capa 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 end caps either from scheduled testing or unusual behavior in service.
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 It is materials used may have neared the end of their shelf life before use.
not believed the end caps, after fabrication, have a significant shelf life limit, due to the low residuaLstress and low crack propagation probabilities.
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