ML13330B345
| ML13330B345 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/06/1988 |
| From: | Medford M SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| GL-83-28, HLWR, TAC-53148, NUDOCS 8807120071 | |
| Download: ML13330B345 (3) | |
Text
- 0 Southem California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 M. O. MEDFORD TELEPHONE MANAGER OF NUCLEAR ENGINEERING July 6, 1988 (818) 302-1749 AND LICENSING U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Generic Letter 83-28 Item 4.2 - Testing of Reactor Trip Breakers San Onofre Nuclear Generating Station Unit 1 By letter dated March 15, 1988 you requested additional information required to complete your review of Item 4.2 of Generic Letter 83-28. This request was made subsequent to SCE's submittal dated June 3, 1987 which provided SCE's position and rationale that response time testing and trending of the undervoltage trip attachment (UVTA) of the reactor trip breakers (RTBs) at San Onofre Unit 1 is not necessary. Your response to this submittal requests SCE to evaluate the possibility of design changes that would permit response time testing of the reactor trip breakers using only the UVTA in the "as-found" condition during preplanned shutdowns of the unit, where the advance notice of the shutdown is sufficient to set up necessary equipment.
SCE provided detailed descriptions of the RTB configuration at San Onofre Unit 1 in our letters dated June 3, 1987 and November 13, 1987.
To briefly summarize, San Onofre Unit 1 utilizes two Westinghouse DB-50 breakers in series. Tripping of one breaker will provide a reactor trip. Due to space considerations it is not economically feasible to install bypass breakers.
The economics associated with installation of bypass breakers was discussed in our November 13, 1987 letter. The cost associated with relocation of the existing breakers and the purchase and installation of two bypass breakers is estimated to be $2.5 to $3.0 million. Thus, on-line testing is not currently possible or cost effective to provide. Based on the two breakers in series configuration, obtaining an as-found UVTA response time measurement would require a planned trip of the breaker during a controlled shutdown and thus tripping the reactor. The configuration required to perform this task is described below.
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Document Control Desk
-2 In order to integrate the test equipment with the breakers, it would require use of spare contacts or jumper cables. As previously indicated in our November 13, 1987 letter, very limited space is available near the breaker cabinets. Consequently there is no permanent location available for the test equipment. Therefore, the test equipment would be configured in a temporary location adjacent to the breaker cabinets in the walk aisle.
Once configured, coordination between the operator in the control room and the technicians at the breaker location would have to be established as the shutdown begins. In order to obtain the desired response time it will be necessary to locally trip the breakers.
Notwithstanding SCE's position that response time testing is not necessary to accurately detect breaker degradation (see the discussion in SCE's letter dated June 3, 1987) the testing configuration described above is undesirable and could have a detrimental impact on plant safety. SCE's primary concern is in attempting to integrate temporary test equipment to the reactor trip breakers while the plant is operating. Any misoperation of the test equipment or improper installation could result in tripping of the plant. SCE believes the consequences of an unnecessary or premature reactor trip greatly outweigh the benefit of having a response time data point.
Another concern is that performance of response time testing in the as-found configuration would require tripping of the breakers at the breaker cabinets.
This is necessary to accurately establish the time of initiation and opening of the breakers.
SCE has identified two problems associated with conducting the test in this manner. A feasible method to locally initiate concurrent trip signals to both breakers at exactly the same time has not been determined. If the trip signals are not initiated concurrently then the measured response time of the lagging breaker will not be representative of an actual response time of that breaker. Secondly, locally tripping the breakers is not the normal method of shutting down the plant. Insertion of the reactor control rods and tripping of the breakers are critical operations during plant shutdown. Tripping of the breakers from any location other than the control room is undesirable. Without proper communication with the control room premature tripping could occur resulting in an unnecessary plant transient.
Finally, SCE believes the cost associated with modifications to the breakers to install contacts specifically for response time testing would not be cost beneficial. A detailed engineering evaluation to provide additional contacts has not been performed, however it is estimated to cost in excess of $100,000 per breaker to install the contacts. In consideration of the demonstrated reliability of the RTB's and success of the RTB maintenance and testing programs, the cost associated with providing response time testing will not have a measurable effect on overall plant safety.
Document Control Desk
-3 Based on the information provided above, design changes to permit the above testing are technically feasible. SCE, however, believes the incremental benefit in RTB reliability gained by response time testing is greatly outweighed by 1) the increased probability of inadvertent reactor trips due to the required test configuration and the need to trip the breakers outside the control room, 2) the inability to obtain representative data in the event of inadvertent trips and nonconcurrent trip signals, and 3) the effort associated with modification of the breakers for integration of the test equipment without jumper cables. It is also noted that in the event of unplanned shutdowns or inadvertent trips between data points the cycling of the RTB's may impact the comparison of previous and subsequent trips. SCE believes that implementation of reactor trip breaker response time testing in the as-found configuration would provide little benefit in the ability to detect degradation of function. For this reason, it is SCE's position that response time testing of the reactor trip breakers should not be implemented at San Onofre Unit 1. In view of these considerations, SCE strongly urges the NRC to carefully evaluate the detriments associated with implementing as-found response time testing at San Onofre Unit 1.
If you have any questions or require additional information please let me know.
Very truly yours, cc: J. B. Martin, Regional Administrator, NRC Region V F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3