ML19256B386
| ML19256B386 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 05/22/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Dolan J AMERICAN ELECTRIC POWER CO., INC. |
| References | |
| NUDOCS 7906130079 | |
| Download: ML19256B386 (1) | |
Text
G7JC p aa8Co UNITED STATES g
))3 ys 6
NUCLEAR REGULATORY COMMISSION y
37([
REGION lil o
T. * ' ~ ju j 799 ROOSEVELT RO AD
'g yfg cLEN ELLYN. ILUNOl$ Got37 MAY 2 21979 Docket No. 50-315 Docket No. 50-316 American Electric Power Service Corporation Indiana and Michigan Power Company ATTN:
Mr. John E. Dolan Vice Chairman Engineering and Construction 2 Broadway New York, hT 10004 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, hee fi bs VJames G. Kep er Director
Enclosure:
IE Bulletin No. 79-11 cc w/ enc 1:
Mr. D. V. Shaller, Plant Manager Central Files Director, NRR/DPM Director, NRR/ DOR PDR Local PDR NSIC TIC Ronald Callen, Michigan Public Service Commission Citizens for a Better Environment 7906130079
U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT REGION III May 22, 1979 IE Bulletin No. 79-11 FAULTY OVERCURRENT TRIP DEVICE IN CIRCUIT BREAKERS FOR ENGINEERID 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 protectian. 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 scra= 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 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 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, brication, have a significant shelf life limit, due to the low residual mummmmmmmmmme DUPLICATE DOCUMENT Entire document previously entered into system under:
^uo 73@6eVo&M6~~
No. of pages:
h