ML20077N990
| ML20077N990 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/12/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20077N988 | List: |
| References | |
| NUDOCS 9108150186 | |
| Download: ML20077N990 (4) | |
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. UNITED STATES 1i NUCLEAR REGULATORY COMMISSION
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED'T0- AMENDMENT NO.97 TO~ FACILITY OPERATING LICENSE NO. NPF-10 AND ~~ AMENDMENT NO. 86 -TO -FACILITY OPERATING LICENSE NO. NPF-15
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SOUTHERN CALIFORNIA EDISON COMPANY SAN DIEGO GAS AND ELECTRIC COMPANY THE CITY OF RIVERSIDE, CALIFORNIA,
.THE CITY OF ANAHEIM, CALIFORNIA SAN-0NOFRE NUCLEAR GENERATlHG STATION, UNIT NOS. 2 AND 3 DOCKET NOS. 50-361 AND 50-362
1.0 INTRODUCTION
By letters-dated April 15, 1991 and supplemented May 7,1991, Southern California Edison Company, et al., (SCE or the licensee) submitted a request for changes' to
' the Technical Specifications -(TS) for San Onofre Nuclear Generating Station, Unit Nos. 2 and 3.
The licensee requested amendments to remove the shutdown cooling system (SDC) auto-closure interlock ( ACI) surveillance requirement on
- TS 3/4.5.4.2, "ECCS System - Tavg Greater Than-or Equal to 350*F."
Removal of i
the interlock is consistent with the: recommendation in Generic Letter (GL) 88-17, " Loss of Decay Heat Removal," which will enhance plant _ safety during mid, loop operations..
The proposed changes will remove the ACI and strengthen administrative procedures.
Over the past several years, there has been increased effort to improve the -
reliability-of-.the shutdown cooling-system (SDCS) in-pressurized water reactors.
It was recognized that ACIs on suction isolation valves of the SDCS have been a frequent cause of loss of SDCS events. - The present-Technical Specification
-requires surveillance of-the AC1.
The proposed changes would delete this requirement but retain the surveillance of the Open Permissive Interlock (OPI).
Testing of _ the SDCS isolation valves p(osition alarms has been added to the Updated Final' Saf ety Analysis' Report. UFSAR).
2.0 EVALUATION The staff __ review of this issue has focused on the effect that the proposed change = has-on the Event V (intersystem LOCA outside of containment) sequence l
and.on the availability' of the SDCS. We have reviewed the licensee's PRA
- analysis of the Event. V_ sequence. We have reviewed and approved the removal of the ACI for_ several other-plants. Most of the plants for which ACI removal has been approved did not have the alarm on the SDCS isolation valve position.
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- Thus, they were renoving the ACI and adding the alarm as well as administrative controls.
San Onofre already had the alarm.
Combustion Ergineering performed the evaluation of the removal of the ACI as a means to imrrove shutdown cooling for San Onofre Units 2 and 3.
The evaluation addresses the seven guidelines for ACI removal reconnended by the NRC in a memorandum f rom Brian Sheron dated January 28, 1985.
1.
The means available to minimize Event V concerns.
San Onofre Units 2 and 3 have a double barrier between the RCS and the SDC sy stem.
Procedural controls, training, alarms and the OPI minimize the potential that the the double barrier will not be available.
2.
Alarms to notify the operator that SDCS suction valves are mispositioned.
Visual and audible alarms are provided in the main control room to inform the operator that any of the SDC system suction valves are not fully closed when e RCS pressure is above the SDC system pressure setpoint.
The alarms will be tested at each refueling to ensure reliability and are designed to alert the operator upon alarm circuit failure.
3.
Verification of the adequacy of relief valve capacity.
Original design calculations to ensure that relief devices in the SDCS suction lines has adequate capacity to prevent overpressurization of the SDCS have been reviewed to confirm-that ACI was not credited in the selection of limiting events or mitigation of the resulting transients.
4 Means other than ACI to ensure that both isolation valves are closed.
The proposed modification uses alarms, position indication, procedures, and training to ensure that the double barrier is established upon heatup.
5.
Assurance that the OPI is not affected by the change.
The OPI. function will be maintained in its present form.
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6.
Assurance that valve position indication will remain available in the control room af ter the change.
The proposed change does not affect the existing valve position indication-in the control room.
The position indication is -independent of the alarms.
7.
Assessment of the effect of ACI removal on SDCS availability and LTOP.
CE performed an analysis on the impact of removing the ACI from the SDCS.
The analysis was performed to determine the change in Interfacing System LOCA (ISLOCA) frequency, the change in DSCS unavailability and the impact on mitigating Low Temperature Overpressure Protection (LTOP) events due to removal of the ACI.
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lSLOCA Results The results indicate no change in the ISLOCA probability when the ACI is remov ed.
(If the valve position alarm had not existed previously there would have been an approximately 13% decrease in the probability).
b.
SDCS Unavailability Results With the removal of the ACI the SDCS unavailability changes from 5.05E-02 to 3.07E-02.
This change represents a 39% decrease in unavailability during refueling, c.
Mitigating LTOP Events San Onofre Units 2_and 3 employ six inch valves in the SDCS with sufficient capacity to mitigate LTOP events that may occur during shutdown cooling operations.
Because these valves are located downstream of the inside containment SDCS suction valves, inadvertent closure of the SDCS valves by ACI will isolate the relief valves and eliminate protection of the RCS piping if an LTOP event occurs.
Since the removal of the ACI decreases the unavailability of the SDCS, the number of inadvertent closures of the SDCS-decreases and the availability of the relief valves (for LTOP protection) increases.
Conclusions The ACI was originally provided to guard against an operator error, namely failure to isolate the SDC system from the RCS prior to raising the RCS pressure above the design pressure of the SDC system. The SDC system relief valve will prevent any transient pressure from exceeding the isolation valve ACI setpoint.
The existing alarm in the control room for each valve warns the operators if the RCS pressure is greater than the valve setpoint and any of the SDC system suction isolation valves are not fully closed.
The potential of an inadvertent closure of the SDC system isolation valves during SDC system operation due to the ACI circuit detracts from plant safety. Thus the SDC system relief valve and the -alarm allow for the removal of the ACI without a negative impact on plant safety.
- The staff finds that the removal of the ACI produces a safety benefit in the SDCS availability and no change in the ISLOCA frequency.
Thus the total impact is a _ safety benefit and is acceptable. Therefore, the staff finds the proposed change to the San Onofre Nuclear Generating Station, Unit Nos. 2 and 3, Technical Specifications to be acceptable.
3.0=-STATE CONSULTATION In accordance with the Commission's regulations, the California State official was notified of the proposed issuance of the. amendment. The State official had no comments.
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4.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to the installation or use of a f acility component located within the restricted area as defined in 10 CFI' Part 20 or a change to a surveillance requirement. The NRC staff has determined that the amendnents involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released off site, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration a been no public comment on such finding (56 FR 20046). Accordingly,nd there has the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
Margaret S. Chatterton Lawrence E. Kokajko Date: August 12, 1991
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