ML13333A608
| ML13333A608 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/02/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML13333A605 | List: |
| References | |
| TAC-66405, NUDOCS 8712100019 | |
| Download: ML13333A608 (3) | |
Text
RfkREGj UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 ENCLOSURE 1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO SINGLE ELECTRICAL FAILURES AFFECTING SAFETY RELATED FUNCTION OF ENGINEERED SAFETY FEATURES
.. SOUTHERN CALIFORNIA EDISON COMPANY SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 1 DOCKET NO. 50-206
1.0 INTRODUCTION
On July 30, 1986, a failure of PT-459 occurred at San Onofre Unit 1 which identified a single failure susceptibility of the Reactor Protection System which had not been previously identified. By a letter dated September 23, 1986, NRC requested that the licensee provide a single failure analysis of the Engineered Safety Features (ESF) for San Onofre Unit 1. The results of the licensee's ongoing analysis have identified several additional scenarios where an electrical system single failure can prevent the ESF from performing its function as required for design basis transients and accidents.
On October 7, 1987, the NRC staff was notified of the existence of these newly identified single failure susceptibilities of the ESF. On October 9, 1987, a meeting was held between the licensee and the NRC staff to describe the single failure scenarios and to describe actions being taken to ensure continued safe operation with the identified scenarios.
2.0 EVALUATION On October 16, 1987, the licensee submitted an ESF single failure analysis report for the staff review. The submittal includes a description of the scenarios for which a single failure of an ESF function will result in consequences not bounded by current analyses of record. Each scenerio includes 6712100019 671202 PDR ADOCK 05000206 P
2 a specific justification for continued operation which references a best estimate analysis case and additional operator actions.
In these analyses, credit is taken for realistic plant behavior and existing conditions of moderator temperature coefficient (MTC). The MTC used in the analysis is applicable for core burn-up until December 14, 1987. The licensee stated that prior to that date, additional analysis will be performed or other actions taken to justify further operation.- The submittal also provides a description of the operator actions which have been identified to correct equipment misoperations resulting from the postulated single failures.
Additional manning has been provided to assist the on shift staff in accomplishing the required actions. Training has been conducted to instruct each shift on the conditions and required actions for each affected scenario.
For those scenarios where 5 minute operator actions are required the feedwater control system is in the-manual-mode.--The -operator---action-would consist of- --
isolating the feedwater system by tripping the feedwater pump manually from the control room.
If operator action is required outside the control room, the action would be required to be completed in either 10 or 20 minutes. The licensee has performed a best estimate analysis which verifies that the locations where the local operator actions would be performed are accessible.
An Emergency Event Dedicated Operator (EEDO) has been added to each shift staff with no assigned duties during the event other than necessary mitigating actions. The EEDO has successfully completed special training and examination for coping with the postulated single failures.
The licensee has committed to provide an updated report on the ESF single failure analysis to NRC by November 6, 1987. This report will include a complete description of the methodology used and results obtained to the extent that information regarding design modifications is available.
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3.0 CONCLUSION
Based on our reviews of the plant design and the procedures provided for the operator to mitigate the postulated single failure scenarios, we conclude that the licensee's justification for continued plant operation, until modifications to the affected systems are implemented during the upcoming refueling outage, is.acceptable. -However, the best estimate analyses were performed with an MTC which will be valid only to December 14, 1987. Additional actions or analyses must be submitted for staff evaluation and approval in order to justify continuous-plant-operation after December 14, 1987.