ML20064N924
| ML20064N924 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 03/28/1994 |
| From: | Marsh W SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9403300178 | |
| Download: ML20064N924 (2) | |
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( 71 d 1 454-4403 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket Nos. 50-361 and 50-362 Safety-Related Setpoint Program San Onofre Nuclear Generating Station Units 2 and 3
Reference:
April 24,1990 letter from F. R. Nandy (SCE) to Document Control Desk (NRC),
Subject:
Docket Nos. 50-361 and 50-362, Electrical Safety System Inspection, San Onofre Nuclear Generating Station, Units 2 and 3 This letter documents the status of the safety-related setpoint program at San Onofre Units 2 and 3.
Following the October 30 through November 30, 1989, Electrical Safety Systems functional Inspection (SSFI) conducted by the NRC, Southern California Edison (SCE) initiated a comprehensive program to reevaluate all safety-related setpoints.
The Units 2 and 3 setpoint program originally identified 101 calculations associated with safety-related setpoints. To date, 94 of_the calculations have been completed. The remainin the Radiation Monitoring Systems (g calculations, which are associated with RMS), have been deferred as part of a program to upgrade the RMS hardware at San Onofre Units 2 and 3.
Setpoint changes resulting from these calculations will be available for use by the completion of the Cycle 9 refueling outage for each unit.
Results of the Safety Related Setpoint Program Evaluation Most of the safety-related setpoint calculations found the setpoints to be conservative, and no corrective action was required. Nonconformance reports were generated in cases where the existing plant setpoints were not conservative with respect to the calculated setpoints.
Of the setpoints which were determined to be non-conservative, most corrective actions involved only revision of the existing setpoints and procedures. Two of the setpoint calculations identified larger than expected instrument uncertainties. These calculations were associated with-the Subcooling Margin Monitor SMM) alarm, and the Open Permissive Interlock (OPI) for the Shutdown Cooling SDC) system suction valves.
Both of the systems were evaluated.and determined to.be operable. SCE is reviewing the benefit of reducing the uncertainty by replacing certain SMM and SDC suction valve OPI transmitters with more accurate instruments.
If SCE concludes this upgrade has enough 9403300178 940328 PDR-ADOCK 05000361 G
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y Docum'nt Control Desk e benefit to plant operation we would plan to install the upgraded equipment by the end of the Cycle 9 refueling outage for each unit.
Radiation Monitoring Systems The safety-related setpoint calculations being deferred are associated with the Radiation Monitoring Systems (RMS) for the Containment Purge Isolation System, Control Room Isolation Tystem, and Fuel Handling Isolation System.
These calculations will addres; the monitor loop, sample loop, and, if appropriate, a heat tracing loop.
These RMS instruments are currently expected to be replaced by the completion of the Cycle 9 refueling outage for each unit. Specific setpoint calculations consistent with the setpoint program will be performed for the new RMS instruments.
The RMS associated setpoint calculations involve the isolation of vatilation systems in raponse to detection of a high radiation level.
The RMS has been specifically analyzed in recent calculations (although not necessarily setpoint calculations) which demonstrated that considerable margins exist either in the dose assessment inalysis or in the monitor setpoint.
These margins are concluded to be 1 de enough to compensate for any setpoint and loop accuracy uncertainties that may exist. Therefore, deferral of these calculations will not have a significant adverse effect on system safety function.
If you would like any additional information on the safety-related setpoint program, please let me know.
Sincerely, ib?. he i
cc:
K. E. Perkins, Jr., Acting Regional Administrator, NRC Region V J. A. Sloan, NRC Senior Resident Inspector, San Onofre Units 2 & 3 M. B. Fields, NRC Project Manager, San Onofre Units 2 and 3 l
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