ML20210B737

Safety Evaluation Supporting Amends 223 & 204 to Licenses DPR-70 & DPR-75,respectively

ML20210B737
Person / Time
Site:	Salem
Issue date:	07/21/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20210B730	List: ML20210B727 ML20210B737
References
NUDOCS 9907230218
Download: ML20210B737 (4)

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-pq UNITED STATE 3

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-NUCLEAR REGULATORY ';OMMISSION C

WASHINGTON, D.C. 20555 0001 h

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS. 223 AND 204 TO FACILITY OPERATING LICENSE NOS. DPR-70 AND DPR-75 PUBLIC SERVICE ELECTRIC & GAS COMPANY PHISDELPHIA ELECTRIC COMPANY -

DELMARVA POWER AND LIGHT COMPANY ATLANTIC CITY ELECTRIC COMPANY I

SALEM NUCLEAR GENERATING STATION. UNIT NOS.1 AND 2 DOCKET NOS. 50-272 AND 50-311

1.0 INTRODUCTION

By letter dated February 2,1999, as supplemented on April 26,1999, the Public Service Electric & Gas Company (the licensee) cubmitted a request for changes to the Salem Nuclear Generating Station, Unit Nos.1 and 2, Technical Specifications (TSs). The requested changes

' would increase the limit for the uranium-235 (U-235) enrichment of new (unirradiated) fuel stored in the new fuel storago racks. The proposed changes would allow for the storage of fuel

with a maximum nominal enrichment of 5.0 weight percent (w/o) U-235, with a tolerance of I

+0.05 w/o, in the new fuel storage racks! The U.S. Nuclear Regulatory Commission (NRC) staff previously approved the storage of fuel assemblies with maximum enrichments of 5.0 w/o U-235 in the Salem spent fuel storage racks. The requested changes would also allow the use of equivalent criticality control to that provided by the current TS requirement of 2.35 milligrams L

of Boron-10 per linear inch loading in the integral Fuel Burnable Absorber pins. Plant operation using the higher enriched fuel will be demonstrated to be acceptable by the cycle-specific reload safety evaluation performed prior to.each fuel loading. The April 26,1999, letter

provided clarifying information that did not change the initial proposed no significant hazards consideration determination.

2.0 EVALUATION 2.11 Background New (fresh) fuel is normally stored dry in the new fuel racks. However, to meet the criteria stated in Section 9.1.1, "New Fuel Storage," of the NRC Standard Review Plan (SRP), k,n must not exceed 0;95 with the racks fully loaded with fuel of the highest anticipated reactivity and flooded with unborated water. Furthermore, k n must be no greater than 0.98 under low-density o

- (optimum moderation) conditions. The maximum calculated reactivity must include a margin for I

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\\ l uncertainties in reactivity calculations and in manufacturing tolerances such that the true k,n will not exceed these limits at a 95% probability, with a 95% confidence (95/95) level.

2.2 Evaluation The licensee performed its analysis of the reactivity effects of fuel storage in the new fuel l

storage racks with the NITAWL, XSDRNPM, and KENO Va methodologies using the 227

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energy group neutron cross section library generated from ENDF/B-V data. The analytical methods and models used in the reactivity analysis are widely used for the analysis of fuel rack j

reactivity and have been benchmarked against results from numerous critical experiments.

j These experiments simulste the Salem storage racks as realistically as possible with respect to l

parameters important to reactivity such as enrichment, assembly spacing, and moderator properties. The NRC has concluded that the analysis methods used are acceptable and capable of predicting the reactivity of the Salem new fuel storage rack with a high degree of confidenco.

The fuel assembly parameters used in the criticality analysis are based on the Westinghouse 17x17 Vantage 5H (V5H) fuel assembly design. However, with the simplifying assumptions

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employed (no grids, sleeves, axial blankets, etc.), the analysis is also appropriate for Westinghouse 17x17 Vantage + and Performance + assembly types. No credit was taken for any natural enrichment axial blankets, fission product buildup, spacer grids or spacer sleeves,

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or burnable absorbers. The NRC staff finds that these are conservative assumptions and are acceptable.

For the full density moderation analysis, the moderator was assumed to be pure water at a density of 1.0 gm/cc. All fuel rods contain uranium oxide (UO ) at a U-235 enrichment of j

2 4.65 w/o (nominal) and 4.70 w/o (maximum) over the entire length of each rod without integral fuel burnable absorbers (IFBAs). The calculated k,n included a method bias determined from benchmark critical comparisons, a 95/95 uncertainty in the method bias, and 95/95 uncertainties arising from consideration of mechanical and material thickness tolerances. The maximum calculated k,n was 0.9324. Since k,n is less than 0.95, including uncertainties at a 95/95 probability / confidence level, the NRC staff's acceptance criterion for precluding criticality is met under full density water flooding conditions for storage of Westinghouse 17x17 fuel assemblies with nominal enrichments up to 4.65 w/o U-235.

For the low density, optimum moderation analysis, a fully loaded rack of fuel assemblies with i

nominal enrichments of 5.0 w/o U-235 (5.05 w/o maximum) was modeled. A method bias determined from benchmark critical experiments, as well as appropriate 95/95 uncertainties, were included for the low density, optimum moderation analysis. The analysis shows that for j

5.05 w/o fuel, the maximum k,n under low density moderation conditions of 0.9120 occurs at 1

0.05 gm/cc water density. Since k,n is less Inan 0.98, including uncertainties at a 95/95 probability / confidence level, the NRC staff's acceptance criterion for prec!uding criticahty under low-density, optimum-moderation conditions, is met.

Storage of fuel assemblies with nominal enrichments greater than 4.65 w/o U 235 is achievable by means of the concept of reactivity equivalencing. This concept is predicated upon the reactivity decrease associated with the addition of IFBAs. IFBAs consist of neutron absorbing J

. material applied as a thin zirconium diboride coating on the outside of the UO fuel pellet. A 2

series of IFBA rod number versus enrichment ordered pairs are generated which all yield the equivalent k n when the fuelis stored in the fresh fuel racks. The minimum Westinghouse o

standard boron loading is assumed as well as the standard IFBA patterns used by Westinghouse. However, since the worth of individual IFBA rods can change depending on position within the assembly, a conservative reactivity margin was included in the development of the IFBA requirement to account for this effect. The IFBA requirements also include a conservatism of approximately 10 percent on the total number of IFBA rods at the 5.0 w/o end (i.e., about 2 extra IFBA rods for a 5.0 w/o fuel assembly) to account for calculational uncertainties. The results indicate that an assembly with an initial U-235 enrichment of 4.65 w/o is equivalent to an assembly initially enriched to 5.0 w/o U-235 containing 24 IFBAs.

I Both satisfy the NRC staff's criterion of k,n no greater than 0.95 in a fully-flooded Salem fresh-fuel storage rack.

The criticality analysis has shown that fresh fuel assemblies with enrichments less than or equal to 4.65 w/o U-235 can be stored in the new fuel storage racks without IFBA rods. Fuel assemblies with enrichments greater than 4.65 but less than 5.0 w/o U-235 must contain a number of IFBA rods (with an equivalent nominal 2.35 mg B-10 per linear inch loading).

However, the current storage restrictions for the spent fuel pool allow unrestricted storage (in the spent fuel pool racks) of unirradiated fuel assemblies with a maximum U-235 enrichment of 4.25 w/o. Unirradiated fuel assemblies with enrichments (E) greater than 4.25 w/o U-235 and less than or equal to 5.0 w/o U-235 must contain IFBA rods with a nominal 2.35 mg B-10 per linear ir,ch loading and a number of IFBA rods equal to or greater than N, where N is given by N = 42.67 (E - 4.25)

Therefore, for consistency with the epent fuel storage requirements % equation will be i

included in the amended TSs for the new fuel storage racks and wil.

.,iude the possibility of having new fuel assemblies which would not satisfy the requirements for unrestricted storage in the spent fuel pool.

2.3 Proposed TS Changes

The licensee proposed the following TS changes. Based on the evaluation presented above, the NRC staff finds these changes to be acceptable.

(1)

TS 5.6.1.1.c is being modified to allow unrestricted storage in the new fuel racks of unirradiated fuel assemblies with enrichments less than or equal to 4.25 w/o U-235 and no IFBA rods.

(2)

TS 5.6.1.1.d is being added to allow storage in the new fuel racks of unirradiated fuel assemblies with enrichments (E) greater than 4.25 w/o U-235 and less than or equal to 5.0 w/o U-235 which contain a minimum number of IFBA rods (N) determined by N =.42.67 (E - 4.25)

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1 2.4 Summary Based on the prcceding review, the NRC staff finds the criticality aspects of the proposed enrichment increase to the Galem new fuel storage racks to be acceptable and to meet the requ' 1ents of General Design Criterion 62 for the preventioit of criticality in fuel storage and handi.. ig.

Although the Salem TSs have been modified to specify the above-mentioned fuel as acceptable for storage in the new fuel racks, evaluations of reload core designs (using any enrichment) will, of course, be performed on a cycle-by-cycle basis as part of the reload safety evaluation process. Each reload design is evaluated to confirm that the cycie core design adheres to the limits that exist in the accident analyses and the TGs to ensure that reactor operation is acceptable.

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3.0 STATE CONSULTATION

in accordance with the Commission's regulations, the New Jersey State official was notified of i

the proposed issuance of the amendments. The State official had no comments.

4.0 ENVIRONMENTAL CONSIDERATION

Pursuant ) 0 CFR 51.21,51.32, and 51.35, an environmental assessment and finding of no significant impact was published in the Federal Reaister on July 21,1999 (64 FR 39178).

Accordingly, based upon the environmental assessment, the Commission has determined that the issuance of these amendments will not have a significant effect on the quality of the human environment.

5.0 CONCLUSION

The Commission 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 l

operation in the proposed manner, (2) such activities will be conducted in compliance with the j

Commission's regulations, and (3) the issuance of the amandments will not be inimical to the j

common defense and security or to the health and safety of the public.

O Principal Contributor: L. Kopp Date:

July 21, 1999 i

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