ML19246A797
| ML19246A797 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 05/22/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Clayton F ALABAMA POWER CO. |
| References | |
| NUDOCS 7907060352 | |
| Download: ML19246A797 (1) | |
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'o, UNITED STATES j
NUCLEAR REGULATORY COMMISSION r
REGION 11 gg
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101 M ARIETTA ST., N.W., SUITE 3100 jy,
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ATLANTA, GEORGI A 30303 MAY 2 21979 In Reply Refer To:
RII:JPO C 50-364 c_ _
Alabarna Power Cotapacy AITN:
F. L. Clayton, Jr.
Senior Vice President P. O. Box 2641 Birmingham, AL 35291 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 or a construction permit.
Should you have questions regarding this Bulletin or the actions required of you, please contact this office.
Sincerely, A
t uvw q James P. O'Reilly Dire tor
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months o
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n, 7907060 3fp
MAY 2 z 1979 Alabama Power Company cc w/ enc 1:
A. R. Barton Executive Vice President Post Office Box 2641 Birmingham, Alabama 35291 C. Biddinger, Jr.
Manager-Corporate Quality Assurance Post Office Box 2641 Birmingham, Alabama 35291 R. E. Hollands, Jr.
QA Supervisor Post Office Box U Ashford, Alabama 36312 JUi
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT 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 f ailure of a circuit breaker in an engineered safety system of a nuclear power plant. This circuit breaker had a defect in one of its th ee time delay dashpc,ts which resulted in a reduced time delay for over-current protection. The defect was a small hairline crack in the end cap of Further investigation by this licent ee disclosed that 7 out of the dashpot.
17 spara daahpot end caps and 2 non-engineered safety feature breakers also had similar defects. The circuit breaker is a Vestinghouse 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 BWR'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 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 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 to the April 1979 report, there have been no reports of suspect " navy-gray" The and caps either fron scheduled testing or unusual behavior in service.
manuf acturer of the " navy-gray" and caps believes the crack defects may be linked to a raw material batch probica. 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 residual stress and low crack propagation probabilities.
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