ML20195G014
| ML20195G014 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 06/08/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20195G010 | List: |
| References | |
| NUDOCS 9906150187 | |
| Download: ML20195G014 (4) | |
Text
5.
'4' p nst UNITED STATES S
NUCLEAR REGULATORY COMMISSION
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WASHINGTON, D.C. 20086 00M
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
' RELATED TO AMENDMENT NO.226TO FACILITY OPERATING LICENSE NO. DPR-49 IES UTILITIES INC.
CENTRAL IOWA POWER COOPERATIVE CORN BELT POWER COOPERATIVE DUANE ARNOLD ENERGY CENTER DOCKET NO. 50-331
1.0 INTRODUCTION
By letter dated January 22,1999, IES Utilities Inc. (licensee) requested changes to the Duane Amold Energy Center (DAEC) Technical Specifications (TS) to update the criticality reouirements (k-infinity and U-235 enrichment limits) for storage of fuel assemblies in the spent fuel racks. The change would allow for storage of fuel assemblies with new designs, including GE-12 with a 10x10 fuel rod array.
2.0 EVALUATION The DAEC spent fuel pool includes storage racks designed by the par Corporation and by
' Holtec intemational. The par racks are composed of 0.125-inch thick aluminum boxes with a 0.080-inch thick boral absorber panel located between boxes in a 0.2185 inch cavity. The fue!
assemblies have a lattice spacing of 6.625 inches and the boral absorbers have a minimum loading of 0.0232 g B-10/sq cm and are clad on both sides with 0.0175-inch thick aluminum.
The Holtec racks consist of 0.060-inch thick stainless steel boxes on a 6.06-inch lattice spccing with a 5.90-inch inside opening. The 0.070-inch thick boral absorber has a nominalloading of 0.0162 g B_-10/sq cm. The DAEC spent fuel storage racks are presen *v licensed for storage of boiling-water reactor (BWR) fuel assemblies having a maximum k-infinity (k-inf) of 1.31 in the normal reactor core config'Jration at cold conditions and an average U-235 enrichment of 4.6 -
weight percent (w/o).
sThe analysis of the reactivity effects of fuel storage in the DAEC racks was performe1 with both the CASMO3 two-dimensional transoort theory code and the NITAWL-KENO 5a three- -
' dimensional Monte Carlo code package using the 238-group SCALE cross-section library.
Independent check calculations were made with the MCNP Monte Carlo code. CASMO3 was
' used to determine the peak reachvity over bumup and to evaluate small reactivity increments associated with manufacturing tolerances and pool temperature changes. These codes are widely used for the analysis of fuel rack reactivity and have been benchmarked against results -
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.2 from numerous critical experiments. These experiments simulate the DAEC spent fuel racks as realistically as possible with respect to important parameters such as enrichment, assembly -
spacing, and absorber thickness. In addition, the two independent methods of analysis (MCNP
- and KENO 5a) showed very good agreement with each other. The intercomparison between i
different analytical methods is an acceptable technique for validating calculational methods for nuclear criticality safety. The staff concludes that the analysis methods used are acceptable and capable of predicting the reactivity of the DAEC storage racks with a high degree of confidence.
The criticality analyses were performed with several assumptions which tend to maximize the rack reactivity. These include:
\\
(1)-
Racks contain most reactive fuel for the case being analyzed, without any control rods or i
any bumable poison, except gadolinia, as appropriate.
J (2)
Unborated pool water at the temperature yielding the highest reactivity (4*C) over the expected range of water temperatures.
(3)
, Assumption of infinite array (no neutron leakage) of storage cells in the radial direction.
.(4)
Neutron absorption in minor structural material is neglected (i.e., spacer grids are analytically replaced by water).
~(5)
The fuel assemblies were evaluated using a uniform average (planar) enrichment and do not include the natural UO blankets at each end.
2 (6)
The flow channel was homogenized with the immediately surrounding water in the CASMO3 model.
The staff concludes that appropriately conservative assumptions were made.
The following General Electric Company fuel assembly types were used for the criticality analyses:
(1) GE-10,8x8 assembly _with a single large water hole replacing 4 fuel rods (2) GE-13, 9xg assembly with 2 water holes replacing 7 fuel rods
' (3) GE-12,10x10 assembly with 2 large water holes replaci.ng 8 fuel rods The design basis reactivity calculations for the Holtee racks arr.ounted for uncertainties and allowances previously reviewed and evaluated by the NRC for tne Holtec racks during the spent i
fuel pool storage capacity expansion in 1994 which remain applicable. These values included manufacturing tolerances, flow channel bulging, and fuel enrichment and density. In addition, a calculational bias and uncertainty were determined from benchmark calculations as well se an allowance for uncertainty in depletion calculations.
y g
.3-The design basis reactivity calculations for the par racks accounted for uncertainties due to manufacturing tolerances in boron loading, boral width, clad thickness, lattice spacing, fuel enrichment and density, water hole thickness, and eccentric assembly position, as well.as a calculational bias and uncertainty which were determined from benchmark calculations. At the very low bumups required for the higher enrichment fuel, depletion calculational uncertainties as well as bulging of the flow channel were found to be insignificant.
1 The current fuel assemblies at DAEC have initial maximum lattice enrichments less than 3.7 w/o U-235. In BWR fuel, there is a need for distributed enrichments to avoid power peaking problems, and, since 5.0 w/o is the maximum enrichment allowed for any single fuel rod, it is not likely that a BWR assembly will exceed an average enrichment of about 4.6 w/o U-235.
Therefore, calculations were made for the fuel designs at DAEC assuming an average enrichment of 4.6 w/o U-235 in both the spent fuel storage rack configurations and. the DAEC core geometry (6.0-inch assembly pitch,20*C). The results indicate that any of the fuel types with an average initial enrichment of 4.6 w/o or less and a k-inf in the standard core geometry less than or equal to 1.40 would result in a rack effective multiplication factor (k-eff) of less than 0.95, including all appropriate uncertainties at a 95% probatality, 95% confidence (95/95) level.
This meets the staff's criterion for spent fuel pool storage and is, therefore, acceptable.
Therefore, the current TS requirement for a maximum k-inf of 1.31 and an average U-235 enrichment of 4.6 w/o remain valid.
Similar calculations for fuel initially enriched to 4.95 w/o U-235 in the par racks, which include the GE-12,10x10 array and the GE-13, 9x9 array, show that any assembly with a DAEC core k-inf of 1.39 or less would meet the 0.95 k-eff acceptance criterion for storage in the par racks, regardless of burnup.
Calculations for fuel initially enriched to 4.95 w/o U-235 in the Holtec racks, which also include the GE-12,10x10 array and the GE-13,9x9 array, show that any DAEC assembly with a core k-inf of 1.29 or less would be acceptable for storage regardless of bumup.
Most abnormal storage conditions will not result in an increase in the k-eff of the racia.
1 However, it is possible to postulate events due to temperature and water density effects, abnormal or eccentric fuel assembly positioning, and the drop of a fuel assembly on top of the storage rack which could lead to an increase in reactivity. However, such events were found to have a negligible effect and the resulting reactivity would remain below the 0.95 design basis for both the par and the Holtec storage racks.
The following changes to TS 4.3.1 have been proposed as a result of the requested criticality requirement update and are acceptable.
- Fuel assemblies having the following limits for maximum k-inf in the normal reactor core con guration at cold conditions and maximum lattice-average U-235 enrichment would be a
acceptable for storage in the DAEC spent fuel storage racks:
5 f
L
-4 K-inf weiaht oercent U-235
- 1) 7x7 and 8x8 fuel rod arrays s1.31 s4.6 (Holtec and par racks)
- 2) 9x9 and 10x10 fuel rod arrays s1.29 s4.95 (Holtec racks)
- 3) 9x9 and 10x10 fuel rod arrays s1.39 s4.95 4
(par racks) l Based on the review described above, the staff finds that the criticality aspects of the proposed update to the DAEC spent fuel storage racks are acceptable and meet the requirements of
. General Design Criterion 62 for the prevention of criticality in fuel storage and handling.
3.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Iowa State official was notified of the proposed issuance of the amendmerrt. The State official had no comments.
]
4.0 ENVIRONMENTAL CONSIDERATION
S I
, This amendment changes a requirement with respect to installation or use of a facility
)
. component located within the restricted area as defined in 10 CFR Part 20 or changes a surveillance requirement. The stsff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluent that may be released offsite, and that there is no significant incresse in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration and there has been no public comment on such finding (64 FR 9192). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b),
no environmentalimpact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLU.31QN The staff has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the h6alth and safety of the public will not be endangered by operation in the proposed manner, (2) su,h 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.
Principai Contributor: L. Kopp, SRXB Date: June 8, 1999
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