ML19256B382
| ML19256B382 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 05/22/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Eric Turner HOUSTON LIGHTING & POWER CO. |
| References | |
| NUDOCS 7906130067 | |
| Download: ML19256B382 (1) | |
Text
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NUCLEAR REGULATORY COMMISSION
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REGION IV S f.
611 RYAN PLAZA DRIVE,5UITE 1000 h,'%>'
- ...e May 22, 1979 In Reply Refer To:
'RIV Docket Nos. 50-498/IE Bulletin No. 79-11 50-499/IE Bulletin No. 79-11 llouston Lighting & Power Company ATTN:
Mr. E. A. Turner, Vice President Power Plant Construction and Technical Services Post Office Box 1700 liouston, Texas 77001 Gentlemen:
Enclosed is IE Bulletin No. 79-11 which requires action by you with regard to your power reactor facilities 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, Karl V. Seyfrf Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months 7906130067
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 safecy feature breakers also had similar defects.
The circuit breaker is a Westinghouse type DB-75.
Westinghouse type DB-50 Meakers 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 trig, 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 ma te ri a l.
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 1 inked 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, af ter 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.
Entire document previously entered into system under:
ANO No. of pages: