ML19261E377
| ML19261E377 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 05/22/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Dunn C DUQUESNE LIGHT CO. |
| References | |
| NUDOCS 7907060380 | |
| Download: ML19261E377 (1) | |
Text
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UNITED STATES Db'
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NUCLEAR REGULATOnY COMMISSION 3 @T h / !
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REGION I o
631 PARK AVENut!
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V KING OF PRUSS3, PENNSYLVANIA 19406 9.....g May 22, 1979 Docket No. 50-334 Duquesne Light Company ATTN: Mr. C. N. Dunn Vice President Operations Division 435 Sixth Avenue Pittsburgh, Pennsylvania 15219 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.
Sincerely, Boyce H. Grier Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months cc w/encls:
F. Bissert, Technical Assistant Nuclear R. Washabaugh, OA Manager J. Werling, Station Superintendent G. Moore, General Superintendent, Power Stations Department J. J. Carey, Nuclear Technical Assistant 7 9 0 7 0 6 0 3
,'c, 293 CP;.
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 BREAXERS FOR ENGINEERED SAFETY SYSTEMS Discussion:
We have received information from Westinghouse and an NRC licensee relating to the potential failure of a circuit bre.W in an engineered safety system of a nuclear power plant.
This circuit bre ver had a defect in one of its three time delay dashpots which resulted in a reduced time delay for overcurrent 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 08-50 breakers also use the same type of dashpot and end cap.
DB-50 and -75 breakers are used extensively in PWR's, and some BWR's 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 insuf ficient time delay in overcurrent protaction, 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" end caps either from scheduled testing or unusual be - -
4 ervice.
The manufacturer of the
" navy-gray" end caps believes oppt
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batch problem. That is, the m N
TE Do have neared the end of their shelf life be Entir fabrication, have a significa into d cument
.' Qer ess and low crack propagation pro,
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