ML20206D457

Safety Evaluation Supporting Amend 124 to License NPF-42

ML20206D457
Person / Time
Site:	Wolf Creek
Issue date:	04/27/1999
From:	NRC (Affiliation Not Assigned)
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NUDOCS 9905040117
Download: ML20206D457 (3)

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UNITED STATES p

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NUCLEAR REGULATORY COMMISSION t

WASHINGTON, D.C. 30ees 4cM 59.....

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 124 TO FACILITY OPERATING LICENSE NO. NPF-42 WOLF CREEK NUCLEAR OPERATING CORPORATION WOLF CREEK GENERATING STAT.lQN DOCKET NO. 50-482

1.0 INTRODUCTION

By letter dated October 23,1998, Wolf Creek Nuclear Operating Corporation (WCNOC, the licensee) requested changes to the Technical Specifications (TS) (Appendix A to Facility Operating License No. NPF-42) for the Wolf Creek Generating Station (WCGS). The proposed changes would revise TS 3/4.5.1, " Emergency Core Cooling Systems - Accumulators," and the applicable Bases. Specifically, the allowed outage time (AOT) or completion time for ACTION b (to restore an inoperable accumulator, if inoperable for reason other than the boron concentration outside of the requirements), would be changed to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> instead of the current time of one hour. This proposal is based on the methodology described in Topical Report WCAP-15049, " Risk-informed Evaluation of an Extension to Accumulator Completion Times," dated August 1998.

The staff has reviewed WCAP-15049 and concluded that the deterministic and probabilistic safety analysis (PSA) results and insights of WCAP-15049 supported the proposed accumulator AOT extension for all Westinghouse plants. Specifically, the staff concluded that because (1) there is no change to the LCO and consequently no cnange to the Chapter 15 Safety Analysis, and (2) this is an extension of an existing condition, the deterministic aspect of this change is acceptable in addition, the staff found that Westinghouse performed a comprehensive risk analysis to support the proposed AOT extension, which indicated that the impact on risk would be small, as defined in risk-informed Regulatory Guides (RG) 1.174, "An Approach for Using Procabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific j

Changes to the Licensing Basis," dated July 1998, and RG 1.177, "An Approach for Plant-l Specific, Risk-Informed Decision Making: Technical Specifications," dated August 1998. The j

staff's approval of WCAP-15049 is contained in a letter dated February 19,1999, to the l

Westinghouse Owners Group.

2.0 EVALUATION 2.1 Deterministic Evaluation The purpose of the emergency core cooling system (ECCS) accumulators is to supply water to the reactor vessel during the blowdown phase of a loss-of-coolant accident (LOCA). The j

accumulators are large volume tanks, filled with borated water and pressurized with nitrogen.

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,O' The cover-pressure is less than that of the reactor coolant system (RCS) so that following an accident, when the RCS pressure decreases below tank pressure, the accumulators inject the borated water into the RCS cold legs.

Currently, the TS allows for one of the four accumulators to be inoperable for one hour (for reasons other than boron concentration not within limits) during MODES 1,2, and in MODE 3 with pressurizer pressure greater than 1000 psig. With one accumulator inoperable, the remaining three accumulators will remain available to mitigate the consequences of a LOCA event. The licensee is requesting to increase the AOT for one accumulator from one hour to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Since the duration of an allowed TS AOT is not an input into the safety analysis (i.e., the

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safety analysis assumes the accumulators are operable), the extension of the AOT to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> has no impact on the safety analysis. Deterministically, there is no difference between a one hour and a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> AOT. Based on the above, the current safety analysis remains valid, and therefore, the change is acceptable.

The difference in the current TS versus the proposed extension is the added risk due to the extension of the AOT.which is reviewed in the following section of this evaluation.

2.2 Risk Evaluation The staff review of WCAP-15049 concluded that the risk analysis performed in support of the change for "all Westinghouse plants" was comprehensive and reasonable, and that the proposed change would result in a small risk increase, as defined in risk-informed RGs 1.174 and 1.177. The risk impact includes core damage frequency and large early release frequency, and it meets the intent of the guidance in the RGs.

The licensee provided an evaluation that demonstrated the applicability of the topical report to WCGS by way of examining key comparable parameters and assumptions used in both the WCGS probabilistic safety analysis (PSA) model and the WCAP evaluation. The staff finds that the WCAP evaluation envelops, or is comparable with, the WCGS case.

Based on the above, the staff concludes that the risk insights and findings support the

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deterministic evaluation of the accumulator AOT extension. Therefore, the changes are acceptable.

In addition, the staff reviewed the proposed change to TS Bases 3/4.5.1, " Emergency Core Cooling Systems - Bases - Accumulators," and found it to be consistent with the proposed TS I

change.

3.0 STATE CONSULTATION

in accordance with the Commission's regulations, the Kansas State official was notified of the proposed issuance of the amendment. The State official had no comments.

.' 4.0. ENVIRONMENTAL CONSIDERATION This amendment changes a requirement with respect to installation or use 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 significant increase in the amounts, and no significant change in the types, of any effluent 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 the amendment involves no significant hazards consideration, and there has been no public comment on such finding (63 FR 64127). Accordingly, the amendment meets 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 amendmeht.

5.0 CONCLUSION

The staff 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 this amendment will not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributors:

S. Brewer I.Jung K. Thomas Date: April 27,1999 S

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