ML19256B383
| ML19256B383 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 05/22/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Koester G KANSAS GAS & ELECTRIC CO. |
| References | |
| NUDOCS 7906130069 | |
| Download: ML19256B383 (1) | |
Text
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NUCLEAR REGULATORY COMMISSION
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ARLINGTON, TE XAS 76012 May ??
1979 In Reply Refer To:
RIV Docket No.
STN 50-482/IE bulletin No. 79-11 Kansas Gas & Electric Co.
Attn:
Mr. Glenn L. Koester Vice President-Operations Post Office Box 208 Wichita, Kansas 67201 Gentlemen:
Enclosed is IE Bulletin No. 79-11 which requires action by you with regard to your power reactor facility with an operating license or a construction permit.
Should you have questions regarding this Bulletin or the aitions required of you, please contact this office.
Sincerely, o
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Karl V. Seyfri Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months cc: w/ enclosures Messrs.
Nicholas A. Petrick, SNUPPS D. T. McPhee, Kansas City Power and Light Company Gerald Charnoff, Shaw, Pittman, Potts & Trowbridge E. W. Creel, Kansas Gas and Electric Company 7906130069
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT IE Bulletin No. 79-11 Date: May 22, 1979 Page 1 of 2 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 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 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 breake 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 fiber-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 behavior in service. The 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 materials used may have neared the end of their shelf life before use.
It is not believed the end caps, after fabrication, have a significant shelf life limit, due to the low residual stress and low crack propagation probabilities.
Description of Event:
The following information was ob DUPLICATE DOCUMENT April 12, 1979, and a subsequent the licensee.
Ent1're document previously entered into system under:
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ANO 7
No-of pages:
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