ML19246A769
| ML19246A769 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 05/22/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Short T OMAHA PUBLIC POWER DISTRICT |
| References | |
| NUDOCS 7907060328 | |
| Download: ML19246A769 (1) | |
Text
c#
p UNITED STATES PDR HQ EN'
~ ^
g NUCLEAR REGULATORY COMMISSION G i, ~
- 2 REGION IV I
O,,
[
611 HYAN PLAZA DRIVE, SUITE 1000
'pjg7g ARLINGTON, TE XAS 76012 May 22, 1979 Docket No.
50-285 Omaha Public Power District ATTN:
T. E. Short, Assistant General Manager 1623 Harney Street Omaha, Nebraska 68102 Centlemen:
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 actions required of you, please contact this office.
Sincerely, fh f~
Karl V. Sey rit Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months cc:
R. L. Andrews, Manager
')
Fort Calhoun Station Post Office Box 98 Fort Calhoun, Nebraska 68102
- 29070003 @
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT y-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 potentia] 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 protectiou.
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 ~5.
5 stinghouse type DB-50 breakers also use the same type of dashpot t.nd 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 tued for scram purp< ses, do not require the overcurrent trip feature and thus are not of concern.
The end cap crack tefect, if severe enough, could result in premature trippint of the circuit breaker because of insufficielt 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 tne 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 ewy be linked to a raw material batch problem. That is, the molding ingredient materials used may have neared the e.ad 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 as obtaine DUPLICATE DOCUMENT April 12, 1979, and a subsequent meet the licensee.
-Entire document previously entered 2 $,)
into system under:
QD&
D\\N$
ANO No. of pages:
_ _ _ _ _