ML20141N096

Safety Evaluation Accepting K(Z) Curve & Current Tech Spec Fq Value of 2.32

ML20141N096
Person / Time
Site:	Prairie Island
Issue date:	02/25/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20141N093	List: ML20141N092 ML20141N096
References
NUDOCS 8603030564
Download: ML20141N096 (5)

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,f o, UNITED STATES 3 a NUCLEAR REGULATORY COMMISSION l D ;j WASHINGTON, D. C. 20555 S

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l SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l

RELATED TO THE REQUIREMENTS OF 10 CFR 50.46 l TO FACILITY OPERATING LICENSE NOS. DPR-42 AND 60 l

NORTHERN STATES POWER COMPANY PRAIRIE ISLAND UNITS 1 AND 2 DOCKET h05. 50-282 AND 50-306

1.0 INTRODUCTION

As a result of errors discovered in Exxon LOCA Analyses on March 15, 1985, the staff requested each licensee utilizing Exxon fuel to evaluate the impact of these errors on their plants. The licensee, Northern States Power Company (NSP), for Prairie Island Units 1 and 2 provided its assessment in reference 1. The staff's evaluation of that submittal is contained in reference 2.

In our evaluation, we concluded that application of the Westinghouse derived K(z) curve to the Exxon fuel had not been verified using an ECCS ,

evaluation model wholly in conformance with Appendix K. Thus, we were unable to conclude that the Prairie Island Units 1 and 2 LOCA analyses fully satisfied the requirements of Appendix K.

In order to provide reasonable assurance of compliance to 10 CFR 50.46, the licensee imposed a penalty on the maximum allowable total peaking factor. In reference 3, the licensee committed to reduce the Fq from 2.32 to 2.27. Based upon the imposed Fq penalty, the staff concluded that Prairie Island Units 1 and 2 could be operated without undue risk to the public health and safety. However, we required the licensee to provide within six months an analysis, using an approved ECCS evaluation model, which demonstrated that the K(z) curve assured compliance with 10 CFR 50.46.

The licensee provided the required analyses in references 4 and 5. Based upon these analyses, the licensee has concluded that the Fq penalty is no longer required. This report evaluates the licensee's analyses.

2.0 EVALUATION To confirm the application of the Westinghouse-derived K(z) curve, in the Prairie Island Units 1 and 2 Technical Specifications, to the Exxon fuel, the licensee provided, in reference 4, the results of large break LOCA analyses perfonned by Westinghouse for the Exxon fuel. These analyses were performed using the 1981 Westinghouse large break LOCA evaluation model which has been approved by the staff as meeting the requirements of Appendix K to 10 CFR 50.

8603030564 86022522 DR ADOCK O

Analyses were performed for the limiting break, a double-ended cold leg guillotine break with a discharge coefficient of 0.4, for Prairie Island Units 1 and 2. Three power shapes were investigated which were peaked at 6 ft., 9 ft. and 10.5 ft. The peak power utilized is consistent with that allowed by the Technical Specification K(z) curve. In addition, the analysis was based upon a maximum Fq of 2.32, consistent with the Technical Specifications, and a hot channel enthalpy rise factor, FA of 1.60, which is in excess of the current Technical Specification vaYu,e of 1.55.

In performing these analyses, Westinghouse utilized a new upper internals design package which is scheduled for installation at Prairie Island in the first quarter of 1986. The licensee stated that using the new upper internals package is bounding compared with using the current upper internals.

To model the Exxon fuel, Westinghouse utilized their currently approved -

methodology and fuel performance model. However, to assure that the values obtained were appropriate to the Exxon fuel, Westinghouse adjusted the calculated fuel temperatures and rod internal pressures to be consistent with the previously calculated Exxon limiting values.

The results of the calculations were:

Power Shape Peak Elevation, ft Peak Cladding Temperature, 'F 6.0 2034 F 8.0 1688 F 10.5 1679 F As shown, the chopped cosine power shape, i.e., 6.0 ft. peaked shape, resulted in the limiting clad temperature. Thus, the analysis confirms that analysis of the 6 ft. power shape is sufficient to demonstrate compliance of the K(z) curve to 10 CFR 50.46.

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4 In reference 5, the licensee provided an adjusted peak cladding temperature, for the 6 ft. power shape, which includes the UPI penalty and cross flow penalty. This resulted in a peak cladding temperature of 2129*F, thus satisfying the 2200 F criterion of 10 CFR 50.46.

Based on our review of the licensee's analysis, we have concluded that the analysis demonstrates that the current Prairie Island Units 1 and 2 Technical Specifications assures conformance to 10 CFR 50.46.

Specifically, we find that the analyses have been perfonned with an evaluation model wholly in conformance with Appendix K. We have concluded that the licensee's use of the new upper internals package and the FA $of1.60isconservative. . In addition, we find that the approach utilize to model the Exxon fuel is appropriate and meets the requirements of Appendix K. Thus, the new analyses demonstrate the adequacy of the current K(z) curve.

Accordingly, we have concluded that the imposed Fq penalty is no longer ,

required and can be removed. The_ analysis has demonstrated that operation of Prairie Island Units 1 and 2 with the Technical Specification Fq value of 2.32 poses no undue risk to the public health and safety.

We note that the licensee has stated that they will be requesting an increase to the Technical Specification value of fag to 1.60 in the near future. While the licensee must yet provide the supporting non-LOCA transient evaluations for this potential future request, we find that the LOCA analyses of references 4 and 5 are sufficient to demonstrate compliance to 10 CFR 50.46 for this change for the Exxon fuel.

3.0 CONCLUSION

S We have concluded that the Prairie Island Units 1 and 2 meet the requirements of 10 CFR 50.46. The current Technical Specification Fq value of 2.32, and the associated K(z) curve, are acceptable. The Fq penalty is no longer necessary and can be removed.

4.0 REFERENCES

1. Letter, D. Musolf (NSP) to the Director, NRR (NRC), "K(z) Curve'" ,

March 26, 1985.

2. Letter, H. Thompson, Director NRR to D. Musolf (NSP) transmitting Safety Evaluation, " Prairie Island Units 1 and 2 LOCA Analyses-Impact of Exxon Code Errors," May 6, 1985.

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3. Letter, D. Musolf (NSP) to the Director, NRR (NRC) " Implementation' of a Voluntary Peaking Factor Penalty," April 4,1985.

4. Letter, D. Musolf (NSP) to the Director, NRR (NRC), " Demonstration of the Conformance with the K(z) Curve Existing is the Prairie Island Technical Specifications with the Requirements of 10 CFR 50.46 and Appendix K, " November 4, 1985.

5. Letter, D. Musolf (NSP) to the Director, NRR (NRC), December 18, 1985.

5.0 ACKNOWLEDGEMENT This Safety Evaluation has been prepared by W. Jensen.

DATE: FEB 2 5 7986

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