ML14183A291
| ML14183A291 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 01/05/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML14183A290 | List: |
| References | |
| NUDOCS 9501110407 | |
| Download: ML14183A291 (5) | |
Text
epREG, UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 156 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 letter dated July 28, 1994, Carolina Power & Light Company (CP&L) requested changes to the H. B. Robinson Steam Electric Plant, Unit No. 2, (HBR2)
Technical Specifications (TS) to allow an increased limit for fuel enrichment.
In support of these requested changes, CP&L also provided supporting Siemens Power Corporation report, EMF-94-113, "H. B. Robinson New and Spent Fuel Criticality Analysis," dated July 1994. The current new (fresh) and spent fuel storage rack maximum enrichment is 4.2 + 0.05 weight percent (w/o) U-235.
The proposed changes would allow for the storage of fuel with an enrichment not to exceed 4.95 + 0.05 w/o U-235 in the new and spent fuel storage racks.
The fresh fuel storage racks are used for temporary storage of unirradiated reload fuel and contain 105 storage cells located on 21-inch centers. The high density spent fuel storage racks have a nominal 10.5-inch cell center-to center spacing and contain Boraflex on each cell wall face.
The NRC 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 and spent fuel storage racks was performed with the SCALE system of computer codes with the three-dimensional multi-group Monte Carlo computer code, KENO.Va.
Neutron cross sections were generated by the NITAWL and BONAMI codes using the 16-group Hansen-Roach library. The CASMO integral transport theory code was also used for the determination of small reactivity increments due to temperature effects and manufacturing tolerances, as well as for comparison with KENO.Va calculations. These codes are widely used for the analysis of fuel rack reactivity and have been benchmarked against results from numerous critical experiments. These experiments simulate the HBR2 fuel storage racks as realistically as possible with respect to parameters important to reactivity, such as, enrichment, assembly spacing, and absorber thickness.
The intercomparison between two independent methods of analysis (KENO.Va and CASMO) also provides an acceptable technique for validating calculational methods for nuclear criticality safety. To minimize the statistical uncertainty of the KENO.Va reactivity calculations, a minimum of 30,000 neutron histories (100 generations of 300 neutrons) were accumulated in each 9501110407 950105 PDR ADOCK 05000261 P
PDR_
-2 calculation. Experience has shown that this number of histories is quite sufficient to assure convergence of KENO.Va reactivity calculations. The staff concludes that the analysis methods used are acceptable and capable of predicting the reactivity of the HBR2 storage racks with a high degree of confidence.
The fresh fuel storage racks are normally maintained in a dry condition,
- i. e., the new fuel is stored in air. However, the NRC criteria for new fuel storage requires that the effective multiplication factor, keg, of the storage rack be no greater than 0.95 if accidentally flooded y pure water and no greater than 0.98 if accidentally moderated by low density hydrogenous material (optimum moderation). The new fuel storage racks were analyzed for 5.0 w/o U-235 enriched fuel for the full density flooding scenario and for the optimum moderation scenario.
The calculated worst-case k ff for a full rack of 5.0 w/o U-235 fuel could not meet the applicable acceptance criteria stated above. Therefore, restrictions were imposed on the storage configuration to prevent fuel from being placed in certain locations, as stated in proposed TS 5.4.2.1, reducing the number of allowable storage locations to 72.
For the fully flooded accident condition, the resulting kff was 0.9447. The optimum moderation condition occurred at about 5 percent interspersed water volume and resulted in a keff of 0.9536. Appropriate biases and uncertainties due to the calculational method and material tolerances were included at the 95/95 probability/confidence level.
This meets the NRC staff's acceptance criteria of 0.95 for full density water flooding and 0.98 for optimum moderation conditions and is, therefore, acceptable.
Fuel stored in the high density spent fuel storage racks is normally flooded by water borated to at least 1500 ppm. However, the NRC criterion for spent fuel storage requires that k ff of the storage rack be no greater than 0.95 when flooded by unborated water, including all appropriate uncertainties at a 95/95 probability/confidence level.
Each storage location contains a sheet of Boraflex secured by a stainless steel wrapper on all four walls. Thus, there are two Boraflex sheets between any pair of stored fuel assemblies. Based on measurements made at similar plants, a maximum length shrinkage of 3 to 4 percent was observed in Boraflex panels due to accumulated gamma radiation.
The HBR2 analysis conservatively assumed a total shrinkage of over 6 percent in length and is, therefore, acceptable.
Reactivity calculations for the high density spent fuel racks indicated that fuel with an enrichment greater than 4.6 w/o U-235 could not meet the NRC criterion of keff no greater than 0.95.
Therefore, additional calculations were performed to establish required gadolinia limits for fuel enriched to 5.0 w/o U-235. These calculations indicated that fuel assemblies containing four U02-gadolinia bearing rods with gadolinia loadings greater than 1.8 w/o would meet the NRC keff criterion.
Only certain assembly designs containing only two 1.8 w/o gadolinia rods were found to be acceptable. Uncertainties (95/95) due to temperature, rack tolerances, and fuel tolerances, as well as the method bias and uncertainty were used with the most limiting arrangement of
-3 four gadolinia rods and resulted in a maximum keff of 0.9466. This meets the NRC acceptance criterion of 0.95 for unborated water flooding and is, therefore, acceptable.
The following Technical Specification changes have been proposed as a result of the requested enrichment increase. The staff finds these changes acceptable.
(1) TS 5.3.1.3 is being modified to allow fuel with an enrichment of no more than 4.95 + 0.05 w/o U-235.
(2) TS 5.4.2.1 is being modified to allow fuel with an enrichment of no more than 4.95 + 0.05 w/o U-235 and to specify required secured location restrictions on new fuel storage.
(3) TS 5.4.2.2 is being changed to allow fuel with an enrichment of no more than 4.95 + 0.05 w/o U-235 in the spent fuel storage pit. Fuel assemblies with maximum planar enrichments greater than 4.55 + 0.05 w/o U-235 have requirements for minimum integral burnable absorber (gadolinia) content as given in EMF-94-113, "H. B. Robinson New and Spent Fuel Criticality Analysis," which has been added as a TS reference.
3.0
SUMMARY
Based on the review described above, the staff finds the criticality aspects of the proposed enrichment increase to the HBR2 new and spent fuel pool storage racks are acceptable and meet the requirements of General Design Criterion 62 for the prevention of criticality in fuel storage and handling.
Although the HBR2 TS have been modified to specify the above-mentioned fuel as acceptable for storage in the fresh or spent 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 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 State of South Carolina official was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
Pursuant to 10 CFR 51.21, 51.32, and 51.35, and environmental assessment and finding of no significant impact have been prepared and published in the Federal Register on January 4, 1994 (60 FR 493). Accordingly, based upon the environmental assessment, the Commission has determined that the issuance of this amendment will not have a significant impact on the quality of the human environment.
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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: L. Kopp Date: January 5, 1995
AMENDMENT NO. 156 TO FACILITY OPERATING LICENSE NO. DPR H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 DISTRIBUTION:
Docket File PUBLIC PD II-1 Reading File S. Varga J. Zwolinski OGC G. Hill, IRM (2)
C. Grimes - DOPS/OTSB L. Kopp -
SRXB ACRS (4)
OPA OC/LFDCB Region IV, WCFO (4)
E. Merschoff, R-II cc:
Robinson Service List