ML20203P605
| ML20203P605 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 04/18/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20203P601 | List: |
| References | |
| TAC-60716, TAC-60717, NUDOCS 8605070521 | |
| Download: ML20203P605 (3) | |
Text
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SAFETY EVALUATION SUPPORTING ISSUANCE OF AMEhDMENT NO. 45 TO NPF-10 AND AMENDMENT NO. 34 TO NPF-15 SAN ON0FRE NUCLEAR GENERATING STATION, UNITS 2 & 3 DOCKET NOS. 50-361 AND 50-362
1.0 INTRODUCTION
Southern California Edison Company (SCE), on behalf of itself and the other licensees, San Diego Gas and Electric Company, The City of Riverside, California, and The City of Anaheim, California, has submitted several applications for license amendments for San Onofre Nuclear Generating Station (SONGS), Units 2 end 3.
One such request, Proposed Change PCN-3, is evaluated herein. This change revises Technical Specification (TS) 3/4.9.8.1 and 3/4.9.8.2 to allow-the shutdown cooling system (SDCS) flow rate to be as low as 2200 gpm, rather that the previous minimum of 4000 gpm.
2.0 EVALUATION OF CHANGE The NRC staff has evaluated the proposed changes and has concluded that they are acceptable. The staff's evaluation is given below.
Technical Specifications 4.9.8.1 and 4.9.8.2, which pertain to Mode 6, currently require, among other things that the licensee verify at least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> that at least one shutdown cooling train is in operation and circulating reactor coolant at a flow rate of greater than or equal to 4000 gpm during refueling operations. Vortexing has been observed in the suction of the SOCS when the water level in the reactor coolant system was reduced to mid-loop. The requirement of a flow rate of greater than or equal to 4000 gpm during refueling operations can cause vortexing in the suction to the SOCS when the water level in the reactor coolant system is reduced to mid-loop. SCE states that the minimum ficw requirement of 4000 gpm for Mode 6 can delay inspec-ting and/or repairing the steam generators and reactor coolant pumps since these activities require a reduced water level in the reactor e
coolant system, and it is more efficient to perform these activities during Mode 6.
The purpose of the minimum flow requirements in TS 3/4.9.8 are given in the bases for this section, which states that the purpose is to ensure "that (1) sufficient cooling capacity is available to remove decay heat and maintain the water in the reactor pressure vessel below 140 F as required during the REFUELING MODE, and (2) sufficient coolant circulation is maintained through the reactor core to minimize the effects of a boron dilution incident and prevent boron stratification."
8605070521 860418 DR ADOCK 05000361 PDR
In regards to cooling capacity, SCE stated in letters dated January 24, 1986 and April 11, 1986 that an analysis had been performed that shows that a minimum SDCS flow rate of 2200 gpm is sufficient to maintain RCS temperature below 140 F while ir. the refueling mode.
In a subsequent meeting on April 16, 1986, SCE provided the staff with more detailed information regarding the bases for the proposed minimum SDCS flow rate of 2200 gpm. This information is contained in a letter from M.0.
Medford to G.W. Knighton, dated April 16, 1986. SCE's analysis includes estimates of the SDCS flow required to maintain the water in the reactor pressure vessel below 140 F for three different periods of time after shutdown. The analysis is based on the heat generation rates from radio-active decay of fission products in a Proposed American Nuclear Society Standard
" Decay Energy Release Rates Following Shutdown of Uranium-Fueled Thermal Reactors," and on standard heat transfer models. The assumptions used in the analysis lead to conservative estimates of the minimum flow requirements. The staff has reviewed SCE's analysis and concludes that the proposed minimum flow requirement for operation of the SDCS during refueling operations will ensure that there is sufficient cooling capacity to remove decay heat and maintain the water in the reactor pressure vessel below 140*F as required during the refueling mode. The lower minimum SDCS flow rate of 2200 gpm will also reduce the potential for vortexing in the SDCS.
In regards to the effects of a boron dilution incident, SCE has analyzed the effects of a boron dilution incident for a partially drained reactor coolant system during refueling operation. This analysis is contained in chapter 7.4.4, "CVCS Malfunction (Inadvertent Boron Dilution)," of the SONGS Unit 2, Cycle 3 Reload Analysis Report. The analysis is based on the models described in Chapter 15.4.1.4 of the Final Safety Analysis Report (FSAR) which contains a detailed analysis of a boron dilution event during cold shutdown. The NRC staff's Standard Review Plan (Chapter 15.4.6) lists the acceptance criteria for analysis of a boron dilution incident. This criteria includes a minimum time interval of 30 minutes for operator action to terminate the transient. With the reduced minimum flow rate, the estimated time to lose the minimum shutdown margin still meets the criterion to terminate the event.
With respect to boron stratification, the FSAR analysis of a boron dilution incident during cold shutdown was based on an SDCS flow of 2200 gpm with only one charging pump available (44 gpm) for Mode 6.
This results in an SDCS flow to charging pump flow ratio of about 50.
In regards to boron stratification, the FSAR analysis still bounds the present analysis for a minimum SDCS flow of 2200 gpm for Mode 6.
We conclude that with the proposed changes to the TS, San Onofre 2 and 3 will continue to meet the regulatory guidance and requirements of Chapter 15.4.6 of the Standard Review Plan.
In summary, we have reviewed the proposed changes to TS 3/4.9.8 for San Onofre Units 2 and 3, and SCE's supporting analysis. The proposed changes would reduce the minimum flow requirement for operation of the shutdown cooling system during refueling operations from 4000 gpm to
-2200 gpm. As discussed in the preceding paragraphs, we find that the proposed changes are acceptable, and meet the applicable regulatory
_ guidance and requirements.
3.0 CONTACT WITH STATE OFFICIAL The NRC staff has ac, vised the Chief of the Radiological Health Branch,' State Department of Health Services, State of California, of the proposed determination of no significant hazards consideration. No comments were received.
4.0 ENVIRONMENTAL CONSIDERATION
These amendments involve changes in the installation or use of facility components located within the restricted area. The staff has determined that the amendments involve no significant increase in the amounts of any effluents that may be released offsite and that there is no significant increase in individual or cumulative occupation radiation exposure. The Commission has previously issued proposed findings that the amendments involve no significant hazards consideration, and there has been no public coment on such findings.
Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR Sec. 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need to be prepared in connection with the issuance of these amendments.
5.0 CONCLUSION
Based upon our evaluation of the proposed changes to the San Onofre Units 2 and 3 Technical Specifications, we have concluded that:
there is reasonable assurance that the health and safety of the public will not be endangered by operation ir the proposed manner, and such activities will be conducted in compliance with the Commission's regulations and the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public. We, therefore, conclude that the proposed changes are acceptable, and are hereby incorporated into the San Onofre 2 and 3 Technical Specifications.
Dated:
APR 181986 i
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