ML20206J916
| ML20206J916 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 03/31/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20206J852 | List: |
| References | |
| NUDOCS 8704160209 | |
| Download: ML20206J916 (3) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 61 TO FACILITY OPERATING LICENSE NO. NPF-12 SOUTH CAROLINA ELECTRIC A GAS COMPANY SOUTH CAPOLINA PUBLIC SERVICE AtlTHORITY VIRGIL C. StfMMER NflCLEAR STATION, UNIT NO. 1 DOCKET NO. 50-395 INTRODUCTION By letter dated December 11, 1986, South Carolina Electric and Gas (the licensee) made application to amend the Technical Specifications of the Virgil C. Summer Nuclear Station. The proposed amendment would increase the required boron concentration in the refueling water storage tank (RWST) and the accumulators. The changes are necessary to assure that the reactor will remain sub-critical in cold shutdown following a LOCA when higher enrichment fuel is used fer anticipated longer fuel cycles.
EVALUATION The proposed amendment increases the minimum allowable value of boron concentrations in the emergency core cooling system (ECCS) accumulators to 2200 ppm and in the RWST to 2300 ppm. The maximum allowable value is 7500 ppm for both systems.
This increase has implications for the analysis of several non-LOCA events and for the system chemistry (through the mechanism of pH change in the post accident containment). The licensee has addressed these concerns in the submittal.
1.
Non-LOCA Safety Analyses The only non-LOCA events which are affected by the increased boron concentration are those for which the safety in.iection system (SIS) is actuated. Each of these events has been examined to determine the effect of increased boron concentration. The results show that the increased boron concentration has a generally helpful effect on the event and in no case does it have a hamful effect.
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LOCA Analysis i
The small break LOCA analysis makes no assumption about the boron concentration in the ECCS water (shutdown is achieved and maintained by control rods). Thus, the increased boron concentration has no effect on the small break LOCA analysis.
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, t During the initial portion of the large break LOCA analysis subcriticality is maintained by voids in the core and the increased boron concentration has no effect on this portion of the analysis. Since the peak clad temperature occurs during this portion of the event there is no effect on the results of the LOCA analysis.
For post LOCA shutdown no credit is taken for control rods in the Summer analysis. Thus, the boron in the ECCS water is relied upon to maintain shutdown. The ECCS water, when mixed with other sources (reactor coolant water, etc.) must produce a boron concentration sufficient to maintain the reactor in a shutdown state. The adequacy of the increased concentration to achieve this goal will be addressed for each reload.
A potential problem of boron precipitation due to concentration of boron in the liquid occurs as a result of steaming produced by decay heat in the core.
Conservative analysis of this effect by the licensee produced the conclusion that the initial switch to hot leg injection should occur at 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> finstead of the present 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) and that altentation between hot and cold leg in,iection should subsequently occur every 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> (instead of the present 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />). The emeroency procedures for the Sunner Plant will be altered to reflect the new times.
3.
Other Considerations Increasing the ECCS boron concentration reduces the pH of the containment spray and recirculating core coolant solutions. The reduction in pH can lead to reduction of the iodine spray removal coefficient and decontamination factor (DF), increase the rate of hydrogen production due to zinc corrosion and increase the potential for chloride induced stress corrosion cracking of stainless steel. These effects have been examined by the licensee with the following results.
The minimum calculated pH resulting from the increased boron concentration does not reduce the iodine spray removal coefficient or DF below that assumed in the FSAR. This is acceptable.
Examination of zine corrosion rate data shows that the corrosion rate for the minimum pH resulting from the increased boron concentration (7.81 is less than that assumed in the FSAR. This is acceptable. Corrosion of other materials (e.g., aluminum) decreases montonically with decreasing pH.
The pH value of 7.8 is greater than the minimum value recommended by the vendor in order to minimize chloride stress corrosion cracking of stainless steel and is acceptable. Other equipment has been qualified at high pH values to maximize effects. The reduced pH will have a positive effect for other equipment qualification.
4.
Finding Based on the review described above, the NRC staff concludes that the proposed Technical Specification changes, which implement an increase in the boron concentration of the ECCS water, are acceptable.
, f ENVIRONMENTAL CONSIDERATION This amendment involves a chance in the installation of a facility component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendment involves no sionificant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public connent on such finding. Accordingly, this anendment meets the eligibility criteria for catecorical exclusion set forth in 10CFRSection51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection i
with the issuance of this amendment.
CONCLUSION We have concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endanoered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Dated:
March 31, 1987 Principal Contributors:
J.B. Hopkins, Pro.iect Directorate #2, DPLA W.L. Brooks, Reactor Systems Branch, DPLA
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