ML14183A157

Safety Evaluation Supporting Amend 125 to License DPR-23

ML14183A157
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Site:	Robinson
Issue date:	02/09/1990
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NUDOCS 9002220023
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UNITED STATES 0

NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 125 TO FACILITY OPERATING LICENSE NO. DPR-23

. CAROLINA POWER & LIGHT COMPANY H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 DOCKET NO. 50-261

1.0 INTRODUCTION

By letters dated August 4, 1989 and November 18, 1989, the Carolina Power & Light Company (CP&L), the licensee, requested a change to the Technical Specifications of Facility Operating License No. DRP-23 that would change Specifications 5.3.1.3, 5.4.2.1, and 5.4.2.2. for H.B. Robinson Steam Electric Plant, Unit No. 2 (Robinson 2).

The proposed changes would permit the reload of fuel assemblies with enrichments up to 4.20 +.05 (nominal 4.2) weight percent (w/o)

Uranium-235 and the storage of such fuel assemblies prior to and subsequent to loading in the Robinson 2 reactor.

2.0 EVALUATION The licensee had previously requested an enrichment increase to 3.9 w/o Uranium-235 for fuel assemblies stored in the new fuel storage racks and the unpoisoned, low density spent fuel storage racks (Reference 1).

The poisoned, high density spent fuel storage racks were already licensed to permit the storage of fuel assemblies having an enrichment of 3.9 w/o Uranium-235. The analyses contained in References 2 and 3 supported, however, the storage of fuel assemblies with an enrichment of 4.2 w/o Uranium-235 for the new fuel storage racks and the unpoisoned, low density spent fuel storage racks, respectively. The NRC approved the license request upon revision of one of the proposed changes to specifically designated acceptable fuel storage locations in the new fuel storage racks. The NRC issued a Safety Evaluation (SE) on these changes on January 20, 1987.

Thus, our review will be based on the previous submittals, analyses, and SE, as well as on the present submittal and analyses.

The analyses supporting the proposed changes to the Technical Specifications for 4.20 +.05 w/o enrichment fuel for the new fuel storage racks are presented in References 2 and 5. The reports describe the model used for the new fuel storage rack and analysis, the assumed input parameter values, the methods used for the analysis, and some of the results of the methods verification.

9002220023 900209 PDR ADOCK 05000261 P

PNU

-2 The values of fuel parameters selected for the analysis were chosen in the conservative direction.

Thus, fuel pellet density was chosen to be slightly greater than the design value, the fuel pellet dish volume was neglected, and the fuel stack length was taken as 144 inches whereas the fuel design stack length is 132 inches (enriched). There is a minimum of 12 inches of natural uranium in all fuel rods. Most importantly, no Gd 0 content was assumed in the model fuel.

Nominal values were used for rimaining fuel geometry and composition parameters. Because of the conservative assumptions indicated above, we conclude the fuel model used in the calculations is acceptable.

Conservative assumptions were made concerning the fuel storage rack, geometry and composition.

The model storage rack pitch is 20.857 inches, whereas the actual rack value is nominally 21 inches. The rack was relfected with 30 cm of concrete at the 4 walls, the floor and at 14 feet above the ceiling. All rack materials of construction were neglected in the model. Thus, the model is conservative in geometry, reflection and neutron absorption effects and is, therefore, acceptable.

The calculation methods used KENO-IV or XSDRNPM for k and k calcula tions. The calculation methods used CASMO-3 to evaluig the efct of the fuel enrichment tolerance on k Suitable cross section libraries were used. The report presents thee sults of comparison of the criticality factors for four sets of critical experiments. The results show good agreement with the measured criticalities.

We, therefore, conclude that the calculation model used is acceptable.

The calculation of the actual new fuel vault criticality with fuel bundles modeled in all 105 locations indicated that the criterion of k less than or equal to 0.98 with optimum moderation of the fuel rack woulfot be met.

This criterion and one requiring k to be less than or equal to 0.95 for the rack fully flooded (or forele worst credible accident) must be met according to the Standard Review Plan, NUREG-0800.

In view of unacceptability of the criticality of the new fuel storage racks when fully loaded, the reports present the results of four alternative loadings of fuel in the rack with empty locations interspersed between fuel-locations. These allow loading of 69-73 fuel bundles.

The alternative loading patterns all show an acceptable k for optimum moderation. Based on the previous staff SE (Reference 4)e,he licensee must physically block prohibited locations of the specific array used to ensure conformance with the uptimum moderation criticality requirements.

The most reactive option had a k of 0.961 with an uncertainty of

+/- 0.0056.

The least reactive op$

n had a k of 0 897 with the uncertainty of +/- 0.0053.

Thus, the staff cr# trion that the new fuel storage racks must have a k tless than or equal to 0.98 with all uncertainties included at ae /95 probability/confidence level for the optimum moderation condition is easily met for a fuel enrichment of 4.20 w/o Uranium-235 with a manufacturing tolerance of +.05 w/o.

-3 At flooded conditions with full density water the k of an infinite array of fuel assemblies is 0.917 with an uncertainty of +/- 0.006.

Thus the staff criterion that the new fuel storage racks must have a k less than 0.95, with all uncertainties included at a 95/95 probablifty/

confidence level for the fully flooded condition, is met for a fuel enrichment of 4.20 w/o Uranium-235 with a manufacturing tolerance of

+.05 w.o.

This result for an infinite array will be conservative for the different fuel loading options.

Based on the consideration discussed above, we conclude that the storage of fuel with an enrichment of 4.20 + 0.05 w/o Uranium-235 in the new fuel storage racks is acceptable provided that the unused locations of the acceptable storage array that is used are physically blocked.

Because the licensee's analyses show that k can increase as the water to fuel volume ratio increases, removal of ubl rods from any fuel assembly stored in the new fuel storage racks is not permitted.

References 3 and 6 provide the results of criticality analyses of the low density (unpoisoned) and high density (poisoned) spent fuel storage racks, respectively. The criticality analyses are for a maximum fuel enrichment of 4.20 + 0.05 w/o Uranium-235.

The conservative assumptions concerning fuel and storage and rack geometry described above for the new fuel storage rack calculations were also used for the spent fuel storage rack calculations, except that the more conservative assumption of an infinite array of infinite length assemblies was used for the spent fuel storage rack calculations. In addition, the analysis of the high density (poisoned) spent fuel storage racks includes a conservative assumption on the dimensional changes of the Boraflex neutron absorber sheets.

The same computer codes were also used.

The results indicate that the maximum kg for the high density (poisoned) spent fuel storage racks, including cohervative allowances for uncertainties, is 0.919.

For the low density (unpoisoned) spent fuel storage racks, the results indicate that the maximum kgf, including conservative allowances for uncertainties, is 0.93. Ths, the staff criterion that both types of spent fuel storage racks must have ak less than or equal to 0.95, with all uncertainties at a 95/95 probability/confidence level, is met for the spent fuel pool containing pure water at full density.

A spectrum of accidents was evaluated in Reference 4 which shows that the above result for the low density (unpoisoned) storage rack is limiting, except for closer edge-to-edge fuel assembly placement during a fuel handling accident.

The analysis shows that a minimum boron concentration of 500 ppm during fuel handling will prevent exceeding the criterion of k

equal to or less than 0.95.

For these accident analyses, credit for the solution boron in the spent fuel pool water is allowed. The Robinson 2 Technical Specification 5.4.3 (Boron Concentration-Spent Fuel Storage Pit), which requires a boron concentration of 1500 ppm during refueling operations or new fuel movement in the spent fuel storage pool, is more conservative than the value used in the analysis and, therefore, is acceptable.

-4 Based on considerations discussed above, we conclude that the storage of fuel with an enrichment of 4.20 + 0.05 w/o Uranium-235 is acceptable for both the high density (poisoned) and low-density (unpoisoned) spent fuel storage racks provided that the boron concentration of the spent fuel pool is maintained at least equal to or greater than 500 ppm.

The changes to Technical Specifications 5.4.2.1 and 5.4.2.2 to an enrichment of 4.20 + 0.05 w/o Uranium-235 are acceptable for the new and spent fuel storage racks, respectively, based on the evaluation discussed above.

The change to Specification 5.3.1.3 is acceptable because it merely indicates that fuel enrichments up to 4.20 + 0.05 w/o Uranium-235 can be used in the core design. Determination of the acceptability of an actual core design must be verified in the calculation of physics parameters and transients and accidents in the reload design evaluation.

3.0

SUMMARY

Based on the review described above, we conclude that the proposed Technical Specification modifications are acceptable from a criticality aspect and that fuel assemblies having initial enrichments up to 4.20 +

0.05 weight percent uranium-235 may be safely stored in the new and spent (poisoned and unpoisoned) fuel storage racks. This conclusion is based on: (1) physical blockage of the unused locations of the new fuel storage option used and (2) the maintenance of a least 500 ppm of boron in the spent fuel pool water (Specification 5.4.3 requires a concentration of 1500 ppm).

4.0 ENVIRONMENTAL CONSIDERATION

Pursuant to 10 CFR 51.21, 51.32, and 51.35, an environmental assessment and finding of no significant impact have been prepared and published in the Federal Register on December 13, 1989 (54 FR 51253). 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 made a proposed determination that this amendment involves no significant hazards consideration, which was published in the FEDERAL REGISTER (54 FR 51253) on December 13, 1989, and consulted with the State of South Carolina. No public comments or requests for hearing were received, and the State of South Carolina did not have any comments.

-5 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, 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.

6.0 REFERENCES

1. Letter from A.B. Cutter (CP&L) to L.S. Rubenstein (NRC), dated October 13, 1986.

2. "Final Report, Criticality Safety Analysis, H.B. Robinson New Fuel Storage Vault with 4.2 Percent Enriched 15 x 15 Fuel Assemblies,"

Exxon Report No. XN-NF-86-100, September 1986.

3. "Final Report, Criticality Safety Analysis, H.B. Robinson Spent Fuel Storage Rack (Unpoisoned, Low Density) with 4.2 Percent Enriched 15 x 15 Fuel Assemblies," Exxon Report No. XN-NF-86-107, September 1986.

4. Letter from Glode Requa (NRC) to E.E. Utley (CP&L), dated January 20, 1987.

5. "H.B. Robinson New Fuel Storage Vault With 4.2% Nominal Enriched Fuel Assemblies," XN-NF-86-100, Addendum 1, January 1, 1989.

6. "Criticality Safety Analysis of the H.B. Robinson Spent Fuel Pool With 4.2% Nominal Enrichment Fuel Assemblies," Advanced Nuclear Fuels Corporation Report No. ANF-89-017, January 25, 1989.

Principal Contributors: D. Fieno R. Lo Dated:

February 9, 1990