ML13330A757
| ML13330A757 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/02/1979 |
| From: | Head J SOUTHERN CALIFORNIA EDISON CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| NUDOCS 7909100536 | |
| Download: ML13330A757 (2) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE J. T. HEAD, JR.
ROSEMEAD, CALIFORNIA 91770 T
Vl -~ES-DEWT 2352t July 2,
1979
)
U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region V 1993 North CalIFornia Boulevard Suite 202, Walnut Creek Plaza Walnut Creek, California 94596 Attention:
Mr. R. H. Engelken, Director Docket No. 50-206 San--Onofre Unit 1
Dear Sir:
IE Bulletin 79-11 Overcurrent Trip Device in Circuit Breakers for Engineered Safety Systems Reference is made to your correspondence of May 22, 1979, forwarding the subject IE Bulletin. Identified therein was the possibility of the failure of engineered safety system Westinghouse type DB-50 and DB-75 breakers, due to defective dashpot end caps of the overcurrent trip delay devices.
This letter documents the results of our investigation into this matter.
Responses to individual items specified in the Bulletin are listed below.
Item
- 1.
"Determine whether circuit breakers of the above described manufacturer and type with overcurrent trip devices are in safety related Class IE service or in spares at your facilities".
Eleven Westinghouse DB-50 breakers are in service in safety-related electrical power applications at San Onofre Unit 1. Of these breakers, four have the "navy-gray" end caps installed. These four breakers are utilized in D.C. applications which do not involve the starting of large motors.
79O91OO 53G,
USNRC Page 2 Item
- 2.
"If the subject breakers are in service in safety-related systems:
within 30 days, review the existing test data for all overcurrent trip device calibrations since plant startup or since replacement caps were installed and tested in response to Bulletin 73-1, whichever is most recent.
Determine if any delay times are:
(1) outside of the accept ance band; (2) marginally acceptable -
on the low side of the accept ance band; or (3) if any significant change in delay time performance has been observed. These breakers should be retested and end caps replaced as nacessary to assure no loss o safety function".
A review of the most recent existinag test data for all DB-50 breakers was conducted. In all cases the delay times shown by the test results were well within the acceptance band.
Additionally, a visual inspection of the end caps was conducted.
This inspection disclosed no indications of end cap cracking.
Both the review and the inspection were conducted within 30 days of receipt of this Bulletin.
Item
- 3.
"Inspect all end caps in spares for cracks using at least a 3x magni fying glass.
Caps having visible flaws should be discarded or pre vented from use in Class IE applications".
There are no overcurrent trip delay device end caps described in*
IE Bulletin 79-11 in spare parts inventory at San Onofre Unit 1.
Item
- 4.
"Review test procedures and test schedules for all safety-related cir cuit breakers to assure that all such breakers are tested at least each refueling outage to confirm overcurrent time delay protection".
In response to IE Bulletin 79-11, San Onofre Unit 1 procedures are being modified to require testing of circuit breakers to confirm overcurrent time delay protection.
This testing will be performed as a minimum at each refueling outage.
Sincerely, cc:
Director, Office of Inspection & Enforcement, Division of Reactor Operations Inspection