ML19256B385
| ML19256B385 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 05/22/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Gary R TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| References | |
| NUDOCS 7906130073 | |
| Download: ML19256B385 (1) | |
Text
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NUCLEAR REGULATORY COMMISSION GD
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% ' $a" [ob. : [f HEGION IV S'A G11 RYAN PLAZA DRIVE, SulTE 1000
,D ARLINGTON, TEXAS 76012 May 22, 1979 In Reply Refer To:
RIV Docket Nos.
50-445/IE Bulletin No. 79-11 50-446/IE Bulletin No. 79-11 Texas Utilities Generating Company ATTN:
Mr. R. J. Gary, Executive Vice President and General Manager 2001 Bryan Tower Dallas, Texas 75201 Gentlemen:
Enclosed is IE Balletin No. 79-11 which requires action by you with regard to your power reactor facilities with an operating license or a construction permit.
snould you have questions regarding this Bulletin or the actions required of you, please contact this office.
Sincerely, m
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<f Kar V. Seyfrf#
Director Faclosures :
1.
List of IE Bulletins issued in Last Twelve Months 7906130073
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 Ih 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 extensivaly in PWR's and some BWR's may also have the same breakers.
Similar make and model circuit breakers, when used for e cram 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 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 in8redient 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 obta April 12, 1979, and a subsequent m DUPLICATE DOCUMENT the licensee.
Entire document previously entered into system under:
ANO 790 No. of pages: