ML20148S058
| ML20148S058 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 07/01/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20148S054 | List: |
| References | |
| NUDOCS 9707080099 | |
| Download: ML20148S058 (3) | |
Text
- attgk UNITED STATES p
- 5 j
NUCLEAR REGULATORY COMMISSION t
WASHINGTON, D.C. 20066 4001
%...../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0225 TO FACILITY OPERATING LICENSE N0. DPR-77 AND AMENDMENT NO.216 TO FACILITY OPERATING LICENSE NO. DPR-79 TENNESSEE VALLEY AUTHORITY SE000YAH NUCLEAR PLANT. UNITS 1 AND 2 1
DOCKET NOS. 50-327 AND 50-328
1.0 INTRODUCTION
By letter dated March 13, 1997, as supplemented on June 26, 1997, the Tennessee Valley Authority (TVA) requested changes to the Sequoyah Nuclear Plant (SQN) Units 1 and 2 Technical Specifications (TS) to allow an increased limit for the U-235 enrichment of new (unirradiated) fuel stored in the new fus storage 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 +0.05 w/o, in the new fuel storage racks.
The staff has previously approved the storage of fuel assemblies with maximum enrichments of 5.0 w/o U 235 in the SQN spent fuel storage racks.
Plant operation using the higher enriched fuel will be demonstrated to be acceptable by a cycle specific reload safety evaluation performed by TVA prior to each fuel loading.
The staff's evaluation of the criticality aspects of the proposed changes follows.
2.0 EVALUATION The analysis of the reactivity effects of fuel storage in the new fuel storage racks was performed with the NITAWL, XSDRNPM, and KEN 0 IV methodology using the 227 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 reat.tivity and have been benchmarked against results from numerous critical experiments.
These experiments simulate the SQN storage racks as realistically as possible with respect to 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 SQN new fuel storage rack with a high degree of confidence.
Fresh fuel is normally stored dry in the new fuel racks.
However, to mest the criteria stated in Section 9.1.1 of the NRC Standard Review Plan (SRP), k,,,
must not exceed 0.95 with the racks fully loaded with fuel of the highest anticipated reactivity and flooded with unborated water.
Furthermore, k,,,
must be no greater than 0.98 under low density (optimum moderation) 9707080099 970701 PDR ADOCK 05000327 P
2 conditions.
The maximum calculated reactivity must include a margin for uncertainties in reactivity calculations and in manufacturing tolerances such that the true k confidence (95/N)will not exceed these limits at a 95% probability, 95%
level.
The fuel assembly parameters used in the criticality analysis are based on the Westinghouse 17x17 Standard (STD) Fuel Assembly design.
The reactivity of the STD design is equivalent to or bounding with respect to other fuel types at SQN such as the Westinghouse VANTAGE-5H and the Framatome Mark-BW assemblies.
All fuel rods were assumed to contain UO2 at a maximum enrichment of 5.05 w/o U-235 over their entire length.
No credit was taken for any natural or reduced enrichment axial blankets, fission product buildup, spacer grids or spacer sleeves, or burnable absorbers. These are conservative assumptions and are acceptable, i
For.the full density moderation analy:;is, the moderator was conservatively assumed to be pure water at a density of 1.0 gm/cc (68 F).
The calculated k*
included a method bias determined from benchmark critical comparisons, a 95/N uncertainty in the method bias, and 95/95 uncertainties arising from i
consideration of mechanical and material thickness tolerances.
The maximum calculated k,,, was 0.9416.
Since k is less than 0.95, including 1
uncertainties at a 95/95 probabilit(( confidence level, the staff's acceptance criterion for precluding criticality is met under full density water flooding conditions for storage of Westinghouse 17x17 or Framatome Mark-BW fuel assemblies with nominal enrichments up to 5.0 w/o U-235.
i For the low density, optimum moderation analysis, a limitation had to be placed on the storage configuration in order to meet the required subcriticality margin. Only 146 specific cells of the 180 available storage loc.tions were utilized as shown in TS Figure 5.6-4.
TVA has committed to installation of physical barriers in the cell locations required to be vacant i
to ensure that inadvertent loading of fuel into these locations will not occur (Enclosure 2 to letter from R. H. Shell (SQN) to NRC, dated March 13, 1997, TVA-SQN-TS-97-01).
These barriers will be verified by procedure to be in place prior to loading of fuel in the racks and an inventory will be performed after receipt is completed to verify the location of fuel assemblies and barriers.
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 the maximum k, under low density moderation conditions of 0.9660 occurs at 0.06 gm/cc,, water density.
Since k is less than 0.98, including uncertainties at a 95/95 probabiNty/confidencelevel,thestaff'sacceptancecriterionforprecluding criticality under low density, optimum moderation conditions, is met.
The following Technical Specification changes have been proposed as a result of the requested enrichment increase. The staff finds these changes as well as the proposed additional administrative changes acceptable.
3 (1) TS 5.6.1.2 has been revised to increase the new fuel (fresh fuel) rack U-235 enrichment limit to 5.0 weight percent and to include a requirement that k,,,
ired physical configuration of stored fuel assemblies, as shown in remain less than or equal to 0.95 when flooded with unborated water. The requ Figure 5.6-4, is referenced.
(2)
Figure 5.6-4 is added to show the allowable storage configuration for new fuel.
3.0 CONCLUSION
Based on the review described above, the staff finds the criticality aspects of the proposed enrichment increase to the SQN new fuel storage racks are acceptable and meet the requirements of General Design Criterion 62 for the prevention of criticality in fuel storage and handling.
In order to meet the required subtriticality margin, a limitation had to be placed on the storage configuration. Only 146 specific cells of the 180 available storage locations were utilized as shown in TS Figure 5.6-4.
TVA has committed to installation of physical barriers in the cell locations required to be vacant to ensure that inadvertent loading of fuel into these locations will not occur.
Although the SQN TS 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 i
design is evaluated to confirm that the cycle core design adheres to the limits that exist in the accident analyses and TS to ensure that reactor operation is acceptable.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Tennessee State official was notified of the proposed issuance of the amendments. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
Pursuant to 10 CFR 51.21, 51.32, and 51.35, an environmental assessment and finding of no significant impact was published in the FEDERAL REGISTER on June 16, 1997 (62 FR 32665).
In this finding, the Commission determined that issuance of these amendments would not have a significant effect on the quality of the human environment.
6.0 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 operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
Laurence Kopp, Reactor Systens Branch Dated: July 1,1997