ML13330B202
| ML13330B202 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/04/1987 |
| From: | Medford M SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| TAC-67952, NUDOCS 8705110297 | |
| Download: ML13330B202 (2) | |
Text
Southern California Edison Company P. 0.
BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 M.O.MEDFORD TELEPHONE MANAGER OF NUCLEAR ENGINEERING (818) 302-1749 AND LICENSING May 4, 1987 U. S. Nuclear Regulatory Commission Attention:
Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Operating Basis Earthquake San Onofre Nuclear Generating Station Unit 1 SCE initiated the seismic reevaluation of San Onofre Unit 1 in the early 1970's. When the NRC established the Systematic Evaluation Program (SEP) in 1977, SCE's seismic reevaluation program was incorporated into the SEP. The ground motion that was found to be appropriate by the NRC for the SEP seismic reevaluation of San Onofre Unit 1 was.67g with a modified Housner response spectrum.
One aspect of seismic reviews performed within the context of the SEP, is that they were limited to an earthquake level consistent with a Design Basis Earthquake (DBE) or Safe Shutdown Earthquake (SSE).
There were no reviews or evaluations performed for an Operating Basis Earthquake (OBE).
For San Onofre Unit 1, the seismic evaluations were performed for the DBE type event, the
.67g modified Housner earthquake. These evaluations included seismic analyses, instructure response spectra and appropriate design calculations.
No evaluations were performed for a smaller OBE type earthquake.
Based on the SEP seismic evaluations, SCE has demonstrated that San Onofre Unit 1 is capable of withstanding an earthquake up to and including the 0.67g modified Housner event. Any modifications made to the plant in the future will need to maintain this same level of protection. Therefore, the existing
.67g seismic analyses will be reviewed and updated if necessary. However, since there were no seismic analyses performed for an OBE, there would be no corresponding OBE analyses to be reviewed or updated, nor would there be any requirement to perform new OBE analyses.
Consistent with the above, it is our intention to perform seismic analyses for only the.67g modified Housner earthquake for all future design modifications which require seismic review. No OBE analyses will be performed.
8705110297 870504 PDR ADOCK 05000206 P
PDRI
Southern California Edison Company Document Control Desk 2 -
May 4, 1987 In light of the above situation relative to an OBE at San Onofre Unit 1, SCE will adopt the following procedures. The Abnormal Operating Instruction for earthquakes at San Onofre Unit I specifies that in the event of an earthquake, the reactor will be tripped upon any Control Room indication of any system or component failure or at the discretion of the Control Operator or SRO Operations Supervisor. This procedure will be modified such that if it is subsequently determined by evaluation of the free-field strong motion accelerograph located at San Onofre that the earthquake ground motion exceeded
.25g at the plant, independent of whether the unit was already tripped, a controlled shutdown and cooldown will be initiated to establish cold shutdown as permitted by conditions in the plant. Prior to resuming operations, SCE will demonstrate that no functional damage has occurred to those features necessary for continued operation without undue risk to the health and safety of the public. It should be noted that this procedure will specify an earthquake level (.25g) which is less than half the.67g DBE level.
If you have any questions or require additional information, please let me know.
Very truly yours, cc: R. F. Dudley, NRR Project Manager, San Onofre Unit 1
- 3. B. Martin, Regional Administrator, NRC Region V F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3