ML20044E400
| ML20044E400 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/13/1993 |
| From: | Fields M Office of Nuclear Reactor Regulation |
| To: | Quay T Office of Nuclear Reactor Regulation |
| References | |
| GL-88-20, NUDOCS 9305240304 | |
| Download: ML20044E400 (3) | |
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UNITED STATES
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May 13,1993 Docket Nos. 50-361 and 50-362 MEMORANDUM FOR:
Theodore R. Quay, Director Project Directorate Y Division of Reactor Projects III/IV/V FROM:
Mel B. Fields, Project Manager Project Directorate V Division of Reactor Projects III/IV/V
SUBJECT:
INDIVIDUAL PLANT EXAMINATION FOR SAN ON0FRE 2 AND 3 Southern California Edison (SCE) has submitted its Individual Plant Examination (IPE) for San Onofre Nuclear Generating Station (SONGS), Units 2 and 3 by letter dated April 29, 1993.
SCE has stated that the IPE utilized PRA methodology in accordance with that described in NUREG/CR-2300, NUREG/CR-2815, NUREG-IISO, NUREG-1335 appendixes, and Generic Letter 88-20 and its supplements.
The IPE includes a Level I (Front-end) analysis of core damage frequencies and a Level II (Back-end) analysis of phenomena affecting containment behavior and the release of radionuclides to the environment.
This report addresses internally initiated events including internal flooding, but not internal fires, per the guidance provided in Generic Letter 88-20.
The external events, such as earthquakes, external floods, tornadoes, internal fire, and other external hazards, will be evaluated as part of the Individual Plant Examination for External Events (IPEEE). The IPEEE is scheduled for submittal no later than June 1, 1995.
The annual core damage frequency (CDF) due to internal initiating events at Units 2 and 3 was calculated to be approximately 3.0E-5.
The loss of offsite power initiating event, which included the station blackout sequences, was the largest contribution to CDF at a fraction of 26%. The initiating event ~ of a transient with power conversion system initially available was next at 15% of CDF, and the combined contribution of large, medium, and small LOCA initiating events was 35% of 00F.
The conditional containment failure probability was calculated to be approximately 16% per core damage event. The most likely mode of release from the containment is a late overpressure failure whose conditional probability is 9.4%.
Containment bypass, with a conditional probability of 6.7%, is the next most likely mode of fission product release. Of these bypass sequences 70% are attributable to steam generator tube rupture, and the remaining 30%
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- F attributable to' interfacing system LOCAs. Finally, failure of the containment to isolate is expected to occur with a conditional probability of 0.1% per core damage event.
In the course of preparing the IPE, preliminary calculations performed by the licensee indicated the possibility of a severe accident vulnerability asscciated with potentially inadequate annunciation of high ambient temperature in inverter / distribution rooms. Without further detailed analysis, the licensee installed high temperature alarms in these rooms (four rooms at each unit). The impact of this plant modification was roughly estimated to be a factor of three reduction in overall core damage ~ frequency.
The results reported in the IPE reflect plant risk with the temperature alarus installed. The licensee concludes in their IPE that no additional.
modifications to either plant design or procedures are warranted.
Mel B. Fields, Project Manager Project Directorate V Division of Reactor Projects III/IV/V cc:
T. Murley F. Miraglia J. Partlow W. Russell J. Roe M. Virgilio A. Thadani J. Richardson G. Bagchi W. Beckner i
D. Wheeler R. Dube E. Chow W. Minners J. Flack R. Hernan l
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Theodore R. Quay May 13, 1993
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attributable to interfacing system LOCAs.
Finally, failure of the containment to-isolate is expected to occur with a conditional probability of 0.1% per j
core damage event.
i In the course of preparing the IPE, preliminary calculations performed by the
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licensee indicated the possibility of k vere accident vulnerability associated with potentially inadequate anr,unciaticr. of high ambient temperature in inverter / distribution rooms. Without further detailed i
analysis, the licensee installed high temperature alarms in these rooms (four rooms at each unit). The impact of this plant modification was roughly estimated to be a factor of three reduction in overall core damage frequency.
The results reported in the IPE ' reflect plant risk with the temperature alarms installed. The licensee concludes in their IPE that no additional modifications to either plant design or procedures are warranted.
Original signed by Mel B. Fields, Project Manager Project Directorate V Division of Reactor Projects III/IV/V cc:
T. Murley F. Miraglia J. Partlow W. Russell J. Roe M. Virgilio A. Thadani J. Richardson G. Bagchi W. Beckner D. Wheeler R. Dube E. Chow W. Minners J. Flack R. Hernan DISTRIBUTION Docket File NRC & Local PDRs TQuay DFoster MFields OGC, 15B18 ACRS (10), P315 KPerkins, RV PDV Reading File-0FFICE PDV/LA PDV/PM PDV/D.-
NAME DFoster M -d MFiddsilh TQuay DATE I/M/93 T /d /93 5 /i)/93 0FFICIAL RECORD COPY DOCUMENT NAME: SOIPE.MEM e
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