ML25217A192
| ML25217A192 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 08/11/2025 |
| From: | Duke Energy |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| Download: ML25217A192 (1) | |
Text
McGuire Nuclear Station New Fuel Vault / Spent Fuel Pool Criticality Safety Analysis Proposed License Amendment Request Pre-submittal meeting - August 11, 2025
Meeting Purpose 2
Help ensure an efficient, predictable NRC review of the LAR Foster a high-quality submittal Discuss key aspects of the proposed License Amendment Request (LAR)
Duke Energy Team 3
Criticality Safety Team within Nuclear Fuels Engineering Bob Hall Dave Orr Brad Lambert, Manager Licensing/Regulatory Affairs Dennis Earp Ryan Treadway, Director
Topics Purpose and Scope of the License Amendment Request (LAR)
New Fuel Vault and Spent Fuel Pool Background High-level outline of proposed changes to Technical Specifications (TS)
Criticality safety analysis (CSA) overview NEI 12-16, Guidance for Performing Criticality Analyses of Fuel Storage at Light-Water Reactor Power Plants, Revision 4, Appendix C checklist, comparison of anticipated LAR to current guidance Review individual items by request/as time permits Potential inclusion of exemption request for enrichment limit in 10 CFR 50.68 Anticipated timeline for submittal/review/implementation Note: CSA results described herein are provided to clarify description of the methodology, are preliminary and are subject to change.
4
Background - New Fuel Vault Four 8x3 modules Concrete separators Concrete floor, walls and ceiling Open rack structure Ceiling hatches No neutron absorbers 5
Background - Spent Fuel Pool 6
Two Region 1 Boral neutron absorber flux trap racks 10.4-inch cell pitch Boral with coupon testing in accordance with NEI 16-03 Six Region 2 Boraflex egg-crate racks 9.125-inch cell pitch No Boraflex credit Region 1
Background - Spent Fuel Pool 7
Region 1 Region 2
License Amendment Purpose and Scope Update criticality safety analysis for new fuel vault (NFV), Region 1 and Region 2 of the spent fuel pools (SFP) for both units at McGuire Nuclear Station (MNS)
Enable storage of fuel for future uprated core power and 24-month cycles Increase central zone enrichment limit to 7 wt.% U-235 Update codes and methods to meet current guidance/expectations CASMO5 and SCALE 6.2.4 KENO-V.a (ENDF/B-VII.1 cross-section data)
NEI 12-16 Rev 4 / NRC Regulatory Guide (RG) 1.240 Revise Technical Specifications (TS)
Require minimum integral poison as a function of enrichment in the NFV Revise storage configurations in the SFP Update SFP loading curves for discharged fuel inventory and current 18-month cycles Add new SFP loading curves for future inventory from uprated 24-month cycles No change to existing SFP boron dilution analysis or SFP minimum boron TS 8
High-Level Outline of NFV Technical Specification Changes Current NFV requirements described in TS 4.3.1.2 All-cell storage of current fuel design
Westinghouse RFA-2 with 5 wt.% U-235 enrichment Full flooding with water and low-density moderator (water)
RFA - Robust Fuel Assembly 9
Proposed NFV requirements All-cell storage of current fuel design
Westinghouse RFA-2 with 5 wt.% U-235 enrichment All-cell storage of 24-month cycle fuel design
Similar to Westinghouse RFA-2 with 24-month cycle modifications
Gadolinia or Integral Fuel Burnable Absorber (IFBA) required for enrichment between 5 and 7 wt.% U-235 Full flooding with water and low-density moderator (water)
High-Level Outline of SFP Technical Specification Changes Current Region 1 requirements described in TS 3.7.14, 3.7.15, 4.3 All-cell storage of current fuel design
Westinghouse RFA-2 with 5 wt.% U-235 enrichment
No burnup required 10 Proposed Region 1 requirements All-cell storage of current fuel design
Westinghouse RFA-2 with 5 wt.% U-235 enrichment
No burnup required All-cell storage of 24-month cycle fuel design
Evolution of Westinghouse RFA-2 fuel
Gadolinia or IFBA required for enrichment between 5 and 7 wt.% U-235
No reactivity increase with burnup based on the expected amount of IFBA credit needed (no burnup required for storage)
Example of TS Region 1 Burnable Absorber (BA) Requirement 0
5 10 15 20 25 30 35 40 5
5.2 5.4 5.6 5.8 6
6.2 6.4 6.6 6.8 7
Minimum Number of IFBA rods (X.XX mg / in.)
Central Zone U-235 Enrichment (wt.%)
Minimum Burnable Absorber Requirement for SFP Region 1 Storage 11 This analysis is still in progress
High-Level Outline of SFP Technical Specification Changes (2)
Current Region 2 requirements described in TS 3.7.14, 3.7.15, 4.3 Separate loading curves for 7 fuel types
Initial enrichment, burnup, and decay time Four fuel assembly reactivity classifications related to storage patterns
Filler (lowest reactivity)
Unrestricted
Restricted
Checkerboard (highest reactivity, 3 out of 4 with one empty cell)
Three storage patterns
Basic pattern is a 2x2 array (Unrestricted)
Checkerboard allows 3 of 4 storage
Restricted/filler allows 4 of 4 storage
Interface effects mitigated with restrictions (empty row or other rules between different configurations)
Soluble boron credit (normal and accident conditions)
TS minimum SFP boron 2675 ppm 12
High-Level Outline of SFP Technical Specification Changes (3)
Proposed revised Region 2 requirements Separate loading curves for 6 fuel types
Initial enrichment, burnup, and decay time (three variants consolidated and bounded, 24-month cycle added)
Five fuel assembly reactivity classifications related to storage patterns
Category 1 (lowest reactivity) through Category 5 (highest reactivity)
Five storage patterns
Basic pattern is a 3x3 array with at least one empty cell (8 of 9) and no Rod Cluster Control Assembly (RCCA) credit Basic empty cell pattern is fixed in Region 2 racks
Three patterns have RCCA credit (8 of 9 1 RCCA, 8 of 9 2 RCCA. 7 of 9 1 RCCA)
Lowest density storage pattern is 6 of 9 with no RCCA credit
Interface effects mitigated with storage pattern reactivity penalty and restrictions if needed Soluble boron credit (normal and accident conditions)
TS minimum SFP boron 2675 ppm Storage rack edge row credit (neutron leakage)
Vary rack distance from SFP wall 13
High-Level Outline of SFP Technical Specification Changes (4)
Five storage configurations Five reactivity categories Empty cells (black)
RCCA credit (blue) 14 8 of 9 8 of 9, 1 RCCA 8 of 9, 2 RCCA 1
1 2
2 3
3 1
1 1
1 2
2,R 3
3 4,R 1
1 1
1 2
2 4,R 3
3 7 of 9, 1 RCCA 6 of 9 4
4 4
5 2
5 5
5 5,R 4
5 5
5
High-Level Outline of SFP Technical Specification Changes (5)
Region 2 Full rack Fixed minimum empty cell pattern Pattern extends across rack boundaries Increased pitch Seismic event evaluation performed to address rack shifting 15
Criticality Code Validation/Benchmark SCALE 6.2.4 (KENO-V.a) benchmark analysis Follows NUREG/CR-6698, Guide for Validation of Nuclear Criticality Safety Calculational Methodology (ADAMS Accession No. ML010870155)
Includes additional critical experiments with enrichments between 5 and 7 wt.% U-235 (LEU+)
Includes Mixed-Oxide (MOX) and Haut Taux de Combustion (HTC) critical experiments Covers expected area of applicability in the SFP environment
Rack cell structure materials
Installed neutron absorbers (e.g., Boral)
Soluble boron
RCCA components (Ag-In-Cd, B4C)
Neutron spectrum (EALF)
No significant trends on U-235 enrichment, Pu/Pu-239 enrichment, EALF, BA B-10 areal density Conservative approach taken to bound all trended parameters in the benchmark results EALF - energy of the average lethargy of neutrons causing fission 16
CSA Overview - Fuel Changes/Codes New fuel product will be implemented with the transition to power uprate, 24-month fuel cycles Modest CSA-related fuel changes as compared to current fuel design Axial blanket and annular blanket specifications
Length and enrichment cutback Doped fuel pellets
Pellet density will be bounded in the CSA Gadolinia and IFBA burnable absorber (BA) combinations will be used
No removable BA use is anticipated Computer codes updated CASMO5 for fuel depletion (will be used consistent with topical report)
KENO-V.a / SCALE 6.2.4 / ENDF/B-VII.1 cross section data 17
CSA Overview - Bounding Depletion Conditions Separate sets of bounding conditions selected for each unique fuel design Fuel density BA history RCCA history Cycle average soluble boron Maximum depletion average power (burnup dependent)
Maximum fuel and moderator temperature
Nodal values determined in combination with axial burnup profile Minimum decay time for legacy populations (isotopic data calculated with CASMO5)
Axial blanket credit for RFA; under review for 24-month cycle fuel
No axial blanket credit for legacy fuel 18
CSA Overview - Axial Burnup Profiles McGuire-specific 24-node profiles for RFA, RFA-2 Over 10,000 18-month cycle, 2.6 wt.% axial blanket shapes Binned in +/- 5 GWd/T bins (15, 25, 35, 45, 55 GWd/T nominal)
Sorted by lowest top 1/6 and 1/4 assembly relative burnup (essentially the same limiting profiles)
NUREG/CR-6801 18-node profiles for legacy fuel Expect McGuire 18-month profiles will bound 24-month profiles Transition and equilibrium 24-month cycle profiles currently in development 19 NUREG/CR-6801, Recommendations for Addressing Axial Burnup in PWR Burnup Credit Analyses (ADAMS Accession No. ML031110292)
CSA Overview - Reactivity Credits NFV Minimum integral absorber SFP Region 1 Boral neutron absorber SFP Region 2 Empty cells Axial blankets (RFA)
BA axial cutback (RFA)
RCCA (3 storage configurations)
Decay time Edge row neutron leakage (shaded ovals) 20
CSA Overview - Eccentric Positioning New Fuel Vault Shift assemblies toward center and away from center of 3x8 module Shift assemblies in separate modules toward each other (center of vault)
Region 1 Base case: fuel assemblies centered in storage cells in a 6x6 model Case 1:
shift the central 4x4 set of assemblies inward Case 2:
shift the central 4x4 set of assemblies outward Full flooding and low-density moderator Result in each case is applied as a bias 21
CSA Overview - Region 2 Eccentric Positioning - Method 1 Configurations for each storage pattern
Base case: fuel assemblies (FAs) centered in storage cells Next, shift the central 4x4 FAs
Toward the model center
Away from the model center
Toward empty cells
Away from empty cells
Diagonally toward storage cell corner 1
Diagonally toward storage cell corner 2
Diagonally toward storage cell corner 3
Diagonally toward storage cell corner 4 Preliminary results show a small effect Maximum: 150 pcm 22 8 of 9 (no RCCA) fission density map with central assemblies moved toward model center
CSA Overview - Region 2 Eccentric Positioning - Method 2 Random Positioning Method Centered, +/- max. shift X,
+/- max. shift Y 6x6 model 9 possible positions for each fuel assembly Single and mixed storage configurations Generate 100 sets of random placements Evaluate statistically Assume normality and non-parametric Results to date bounded by method 1 23
CSA Overview - Interface Effects (Region 1 to Region 2) 24 Determine equal reactivity in infinite lattice models Region 1 Region 2 Load into 2 rack model Actual size X direction Infinite Y direction 2 racks Change rack-to-rack spacing K-effective K-infinite 2 empty cells added
CSA Overview - Interface Effects (Internal Region 2 storage patterns) 25 Substitute alternate 3x3 pattern equal reactivity fresh fuel clusters into full rack base configuration 12 cases per substitution, 10 pattern substitutions (120 cases)
Determine interface reactivity penalty (if any) needed to achieve k(substitute) k(infinite)
Interface reactivity penalty is applied to loading curve calculation
CSA Overview - Horizontal Burnup Gradient Conservative generic model developed based on precedents (limit analysis scope)
Similar plant LARs, Oak Ridge National Lab study Result confirmed bounding by limited set of validation cases 8 to 16 adjacent assemblies in 6x6 model 26
CSA Overview - Misload Accident Approach 27 Single misloads Mis-manufacture, administrative error, spotting error Multiple misload of burned fuel Administrative error No multiple fresh assembly misloads in Region 2 No shiny fuel in the dull fuel racks (independent 2nd barrier) - reinforced through training, independent procedures (move sheet development separate from fuel movement procedure).
Error Model Type Analysis Model Number of Misload FAs Region No required BA in one fuel assembly (FA)
Infinite lattice Single FA 1
1 Fresh assembly in a Category 1 cell Infinite lattice 6x6 1
2 Fresh assembly in empty Region 2 cell at interface Finite 2 full racks 2 Racks 1
1-2 Category 5 assemblies in a Category 1 6x6 pattern Finite Region 2 rack 16x12 32 2
NEI 12-16 Revision 4 Appendix C Checklist See attached preliminary checklist/review items by request, time permitting 28
Exemption Request 29 Exemption will be requested to the U-235 enrichment limit in 10 CFR 50.68 (b)(7)
Current limit: 5.0 wt.% U-235 enrichment Seek exemption to allow what is justified by the criticality code benchmark and the criticality safety analysis for the application For the McGuire Nuclear Station application, this will be up to 7.0 wt.% nominal U-235 enrichment Exemption would be supported by draft rulemaking materials and other technical materials presented (EPRI workshop, upcoming ANS meetings, etc.)
Anticipated Timeline for Submittal/Review/Implementation 30 Analysis completion will depend on availability of final design information for 24-month cycles at uprated power with new fuel product Finalized fuel design information Transition core and equilibrium core cycle depletions Target LAR submittal 3rd quarter 2026 NRC review 18 months (or less)
SE issuance mid-2028 Fuel order September 2028 Revised TS implementation refueling outage M1R33 (Fall 2029)