ML20058F615

Safety Evaluation Supporting Amends 56 & 50 to Licenses DPR-42 & DPR-60,respectively

ML20058F615
Person / Time
Site:	Prairie Island
Issue date:	07/16/1982
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20058F614	List: ML20058F605 ML20058F615 ML20058F630
References
NUDOCS 8208020056
Download: ML20058F615 (5)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION j

RELATED TO AMENDMENT NO. 56 TO FACILITY OPERATING LICENSE NO. DPR-42 AND AMENDfENT NO. 50 TO FACILITY OPERATING LICENSE NO. DPR-60 l

NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNIT NOS. 1 AND 2 DOCKET NOS. 50-282 AND 50-306 1

Introduction By letter dated June 14,1982 (Ref.1), Northern States Power Company made application to amend the Technical Specifications for Prairie Island Nuclear Generating Plant Units 1 and 2, in order to continue the current Cycle 7 operation of Ilnit I to higher fuel exposure. The change involves an exposure-dependent power peaking factor limit now contained in the Technical Specific-ations. The limit is currently defined over a range of 0 to 41,850 mwd /MtU peak pellet exposure.. The change would expand the range of burnups over which the limit is defined to accommodate anticipated exposures in Prairie Island.

2 Evalua tion We have examined the supporting document (Ref. 2) for this request, which describes a LOCA reanalysis by Exxon. Most of the methods employed have been previously reviewed and approved by the staff and are therefore acceptable for this application. Three exceptions to this general conclusions are (1) cladding swelling and rupture behavior, (2) improved neutronics input, and (3) application of analytical nethods at high burnup.

The first issue concerns cladding swelling and rupture models employed in ECCS analyses. This issue was identified in November of 1979, at which time the NRC requested (Ref. 3) an assessment of the impact of revised cladding swelling and rupture models (Ref. 4) on the safety analysis of all operating light

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ter reactors. Northern States Power Company responded (Ref. 5) to this

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j request by stating that the Prairie Island analysis continued to demonstrate j

compliance with 10 CFR 50.46 with the revised cladding models. For the pro-1 posed Technical Specification change, which required a reanalysis of the ECCS performance, the licer.see has stated (Ref. 6) that the acceptance criteria of 10 CFR 50.46 continue to be met with the revised cladding swelling and rupture model s.

The first issue has thus been adequately addressed.

i The second issue concerns those changes to the ECCS analysis which result in extending the break point in F to higher burnups. This extension was g

unexpected because the original and revised ECCS analyses rely on essentially the same models. Exxon's description (Ref. 2) of the analysis performed states that the extension is due to the benefit of improved neutronics input to the model. Specifically, these refinements were made to the input moderator densit'y reactivity and the U-238 capture / fission ratio used in the analysis.

These improvements to the LOCA model input have been accepted for other applic-ations (e.g., D.C. Cook, Kewaunee) and we continue to find them acceptable for Prairie Island.

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The third issue involves the application of analytical methods at high burnup, where the models may not have been verified. There are several related limiting l

curves referenced in this evaluation. The first is the normalized exposure f

dependent function, BU (E ), currently in the Prairie Island Technical Specific-j ations. As stated previously, this curve is defined for peak pellet exposures up to 41,850 mwd /Mtu. A second curve, obtained by extrapolating the existing j

l Technical Specification limit to 47,000 mwd /MtU, is currently being administra-

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tively adhered to by the licensee until the amendment is approved. A third l

curve, generated by Exxon Nuclear Company (Ref. 2) to supplement the anendment request, is also defined for peak pellet exposures up to 47,000 mwd /MtV. A fourth curve, proposed by the licensee as part of this submittal, is defined l

for peak pellet exposures up to 50,000 mwd /HtU. For exposures at which all curves are defined (e.g., 40,000 mwd /MtU), they are not necessarily identical.

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. l The F limit developed by Exxon (Ref. -2) for this submittal (the third curve)

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g has been determined for peak pellet exposures of up to 47,000 mwd /MtU. Assuming a peaking factor of 1.3, this exposure corresponds to a batch average discharge burnup of 36,000 mwd /Mtu. We note that batch average discharge burnups of 35,700 and 36,100 mwd /MtU have been achieved for Unit 1 Cycle 5 and Unit 2 Cycle 3 fuel, respectively. An exposure dependent function, as required for the Prairie Island Technical Specificrtiens, is shown in Figure 1.

This exposure dependent functicn is based on the third curve rather than the fourth Analyses to support further extensions of this function were not curve.

submitted by the licensee.

3 Conclusions We have examined the licensee's request for an extension of the exposure-dependent power peaking factor at Prairie Island Unit Nos. I and 2.

The licensee's proposed Figure TS.3.10-7 allows a peak pellet exposure to 50,000 mwd /Mtu. However, our review is based on the licensee's documen-tation supporting operation to 47,000 mwd /Mtu. On this basis we find the proposed change acceptable for'both Units to a peak pellet exposure l

of 47,000 mwd /MtU, as shown in the revised Figure TS 3.10-7.

The revision to the Figure TS 3.10-7 was discussed with and agreed to by the licensee.

Environmental Consideration We have determined that the amendments do not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that the amendments l

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involve an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR 551.5(d)(4), that an

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environmental impact statement or negative declaration and environ-mental impact appraisal need not be prepared in connection with the issuance of these amendments.

Conclusion We have concluded, based on the considerations discussed above, that:

(1) because the amendments do not involve a significant increase in the probability or consequences of an accident previously evaluated, do not create the possibility of an accident of i type different from any evaluated previously, and do not involve a significant reduction in a margin of safety, the amendments do not involve a significant hazards considerction, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of the amendments will not be inimical to t'he common defense and security or to the health and safety of the public.

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REFERENCES 1.

D. Musolf (NSP) letter to the Director, Office of Nuclear Reactor 4

Regulation (NRC) on " License Amendment Request", dated June 14, 1982.

2.

"LOCA ECCS Limiting Break and Exposure Sensitivity Analysis for ENC XN1 and XN2 Reloads at Prairie Island Unit I with 5 Percent Steam Generator Tubes Plugged Using ENC WREM IIA PWR Evaluation Model,"

Exxon Nuclear Cor.pany Report XN-NF-81-06 dated February 6,1981 and transmitted by D. Musoif (NSP) letter to the Director, Office of Nuclear Reactor Regulation (NRC) dated June 15, 1982.

3.

D. G. Eisenhut (NRC) letter to All Operating iWis dated November 9, 1979.

4.

D. A. Fowers and R. O. Meyer, " Cladding Swelling and Rupture Models for LOCA Analysis," U.S. Neelea' Regulatory Comnission Draft Report NUREG-0630, November 1979.

4 5.

L. O. Hayer (NSP) letter to Director, Office of Nuclear Reactor l

Regulation (NRC) dated Jar.uary 8, 1980.

4 6.

D. Musolf (NSP) letter to the Director, Office of Nuclear Reactor l

Regulatf or. (NRC) dated July 7,1982.

i 7.

M. J. Ades, " Qualification of Exxon Nuclear Fuel for Extended Burnup,"

Exxon Nuclear Company Report XN-NF-82-06, March 1982.

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