NATIONAL NUCLEAR SECURITY ADMINISTRATION GLOBAL THREAT REDUCTION INITIATIVE Core Modifications to address technical challenges of conversion

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1 NATIONAL NUCLEAR SECURITY ADMINISTRATION GLOBAL THREAT REDUCTION INITIATIVE Core Modifications to address technical challenges of conversion G17 G18 G19 G20 G21 G16 F15 F16 G22 F17 F F18 G15 G F13 E13 F19 E12 E14 G G E11 E15 F12 F D G13 E10 D D11 E16 G25 F F D8 D C G12 E9 E17 G C C F10 D D13 F E8 C5 B4 C9 E18 G11 G B F9 D6 D F B E7 C C10 E19 G10 A TR B G28 F8 D D15 F B E6 C B1 C11 E20 G G F7 D4 D16 F C2 C E C E21 G D D G30 F F E4 D2 D18 E D1 G G31 F F27 E3 E E2 E24 G6 F4 E F28 G F3 F29 G F G33 F1 F G4 G34 > 17 kw/rod > kw/rod > kw/rod > kw/rod > 9-11 kw/rod 9 kw/rod Graphite Air hole Aluminum Slug Water filled G3 G2 G1 G36 G35 John G. Stevens, Ph.D. Nuclear Engineering Division, Argonne National Laboratory Technical Lead of USHPRR and EUHFR Reactor Conversion, GTRI Conversion Program the Conversion of Research Reactors to Low Enriched Fuel, 8-10 June 2011, Moscow, Russia

2 Core Modifications to address technical challenges of conversion Philosophy of Core Conversion Examples of Changes Deployed or Proposed: Change in Uranium Loading and Burnable Absorber Loading Change in Fuel Plate Thickness and Reflector Location Change to Distinct Fuel Meat Thickness in Plates of LEU Assemblies Change in Uranium Loading and Burnable Absorber Loading Change in Fueled Height of Core Summary 2

3 Philosophy of Core Conversion Simply Stated: Change as little as possible Fuel will be changed (by definition) Burnable Absorber should be tuned to fuel composition Reflector changes highly effective, if cost acceptable 3

4 Addressing the Common Barrier to Conversion Principle of Fuel Acceptability for Conversion QUALIFIED Fuel Assembly Fuel assembly that has been successfully irradiation tested and is licensable from the point of view of fuel irradiation behavior COMMERCIALLY AVAILABLE Fuel Assembly Fuel assembly that is available from a commercial manufacturer SUITABLE Fuel Assembly Safety criteria are satisfied Fuel Service Lifetime comparable to current HEU fuel (e.g., Number of FA used per year is the same as or less than with HEU fuel) Performance of experiments is not significantly lower than with HEU fuel To be ACCEPTABLE for LEU conversion of a specific reactor, a fuel assembly must be qualified, commercially available, and suitable for use in that reactor, then reactor operator & regulator must agree to ACCEPT fuel assembly for conversion 4

5 Change in Uranium Loading and Burnable Absorber Loading OSTR TRIGA Mark II reactor Oregon State University 1.1 MW License power Can be pulsed to ~2500 MW Peak thermal flux ~1.0e13 n/s-cm 2 in the B1 position TRIGA UZrH Fuel G11 G10 G9 G12 G8 G13 G7 F9 F8 G14 GRICIT F10 F7 G6 F11 F6 G15 F12 E8 E7 E6 F5 G5 E9 E5 G16 F13 E10 D6 D5 E4 F4 G4 D7 D4 G17 Source F14 E11 D8 C5 C4 AFCR D3 E3 F3 G3 C3 G18 G19 G20 HEU Fuel: 8.5 wt% U at 70% enrichment, 134 g U-235/element 1.6 wt% Erbium burnable absorber F15 E12 D9 C6 B3 C2 D2 E2 F2 B2 G2 Rabbit D10 FFCR B4 IFE F16 E13 C7 A1 C1 B1 D1 FFCR E1 F1 G1 B5 F17 E14 D11 C8 B6 C12 D18 E24 F30 G36 D12 C9 C10 FFCR C11 G21 F18 E15 D17 E23 F29 G35 D13 D16 G22 F19 E16 D14 D15 E22 F28 G34 E17 E21 G23 F20 E18 E19 E20 F27 G33 F21 G24 F26 F22 F25 G32 G25 F23 F24 G31 G26 G30 G27 G28 G29 Fuel Element Instrumented Fuel Element Fuel Followed Control Rod Air Followed Control Rod, or G-ring Experiment Graphite Aluminum Plug Water filled LEU Fuel: 30 wt% U at 19.75% enrichment, 163 g U-235/element 1.1 wt% Erbium Converted

6 Change in Uranium Loading and Burnable Absorber Loading OSTR Conversion Goals Lifetime Core Full Grid Plate for experiment flexibility Shutdown Margin an active constraint at BOL TRIGA 30/20 Met goals with 1.1% Erbium Excess Reactivity (%dk/k) (biased 0.48%dk/k per HEU Measurement) Depletion at 1 MW, Hot Conditions, All Rods Out (Fuel 327C, Coolant 50C) HEU FLIP Fuel (82+3) LEU 1.1% Er Fuel (86+3) LEU 0.9% Er Fuel (74+3) Did not meet goals with 30/20 standard 0.9% Er Years at 50 MWd/yr 6

7 Change in Fuel Plate Thickness and Reflector Location RPI reactor ITN, Lisbon 1 MW License power Peak thermal flux ~3.1e13 n/s-cm 2 MTR-type Dispersion Fuel HEU Fuel: U-Al x at 0.83 gu/cm 3, 93% enrichment, 265 g U-235/assembly Fuel meat 0.5 mm thick LEU Fuel: U 3 Si 2 at 4.8 gu/cm 3, 19.75% enrichment, 376 g U-235/assembly Fuel meat 0.6 mm thick 7 Converted 2007

8 Change in Fuel Plate Thickness and Reflector Location 5.5 Excess Reactivity % k/k Excess Reactivity % k/k Days at 1 MW HEU 0.5 mm Fuel Meat LEU 0.5 mm Fuel Meat RPI Conversion Goals 10 years of operation with same number of assemblies, or fewer Acceptable flux levels Silicide met goals Same meat thickness required same number of assemblies: 17 assemblies over 10 years Increased meat thickness led to savings: 13 assemblies over 10 years (i.e., 4 assemblies saved) Days at 1 MW HEU 0.5 mm Fuel Meat LEU 0.6 mm Fuel Meat

9 Change in Fuel Plate Thickness and Reflector Location RPI Fluxes improved in key locations due to change in reflector block locations Ratio of MCNP4c Tallied Fluxes: LEU/HEU at each BOC. 9 Core Maximum Single Grid Position Position(s) Ratio of Predicted Flux Be Experiment Block Ratio of Predicted Flux Be 1 Grid Rows 1 & 2 Be 1 Grid Rows 3 & 4 Beam Tube E4 Entry Ratio of Predicted Flux Thermal Flux, neutron energy < ev, in maximum 5cm segment of tube P1/2a LEU vs. P1/2 HEU LEU 13, HEU % 84% 91% 83% P1/3a LEU vs. P1/3 HEU 54 85% 99% 92% 102% P1/4a LEU vs. P1/4 HEU LEU 54, HEU % 93% 88% 102% P1/5b LEU vs. P1/5 HEU 35 95% 95% na 1 100% Epithermal Flux, ev < neutron energy < MeV, in maximum 5cm segment of tube P1/2a LEU vs. P1/2 HEU LEU 13, HEU % 86% 97% 84% P1/3a LEU vs. P1/3 HEU 54 90% 103% 100% 108% P1/4a LEU vs. P1/4 HEU LEU 54, HEU % 99% 92% 106% P1/5b LEU vs. P1/5 HEU % 101% na 106% Fast Flux, 0.821MeV < neutron energy, in maximum 5cm segment of tube P1/2a LEU vs. P1/2 HEU LEU 13, HEU % 91% 97% 92% P1/3a LEU vs. P1/3 HEU 54 91% 101% 100% 105% P1/4a LEU vs. P1/4 HEU LEU 54, HEU % 100% 95% 106% P1/5b LEU vs. P1/5 HEU % 99% na 105% 1 na indicates a position filled by a fuel assembly or Be block, thus unavailable as an experimental location.

10 Change to Distinct Fuel Meat Thickness in Plates of LEU Assemblies MURR Very Compact Core Design Core Volume 33 liters Fuel Meat 4.3 liters Peak thermal flux ~6.0e14 n/s-cm2 MURR fuel assembly 24 curved plates 45 degree arc No grid flexibility Weekly refueling for > 90% capacity factor for > 20 years (key to efficient isotope production) Power Peaking control vital to conversion to UMo Harder neutron spectrum would naturally increase power in inner-most and outer-most plates due to inner flux trap and outer Be reflector 10 Distinct UMo foil thickness in plates could solve problem

11 Change to Distinct Fuel Meat Thickness in Plates of LEU Series1 Assemblies HEU 13" Power & Heat Flux Peaking Factors Series1 LEU 13" Power Peaking Factors Series2 Peaking Factor MURR HEU: All Meat Same Thickness Series Height in Fuel Plates (inches) Power Peaking controlled with LEU UMo Monolithic Lower peaking than HEU case was achieved Plate 1 (Inner): 0.23 mm foil Plate 2: 0.31 mm foil Plates 3-23: 0.46 mm foil Plate 24 (Outer): 0.43 mm foil Series3 Series4 Series5 Series6 Series7 Series8 Series9 Series10 Series11 Series12 Series13 Series14 Series15 Series16 Series17 Series18 Series19 Series20 Series21 Series22 Series23 Series24 P o w e r P e a k in g F a c t o r H e a t F lu x P e a k in g F a c t o r Series Series22 Series23 Height in Fuel Plates (inches) Series24 Series1 LEU 13" Heat Flux Peaking Factors Series2 MURR LEU : Four Distinct Meat Thicknesses Series3 5.0 Series MURR LEU : All Meat Same Thickness Height in Fuel Plates (inches) Series3 Series4 Series5 Series6 Series7 Series8 Series9 Series10 Series11 Series12 Series13 Series14 Series15 Series16 Series17 Series18 Series19 Series20 Series5 Series6 Series7 Series8 Series9 Series10 Series11 Series12 Series13 Series14 Series15 Series16 Series17 Series18 Series19 Series20 Series21 Series22 Series23 Series24

12 Change in Uranium Loading and Burnable Absorber Loading BR2 reactor SCK-CEN, Mol, Belgium Typical power: MW Maximum possible power: 125 MW Unique hyperboloid of revolution defines remarkably flexible set of straight channels Peak thermal flux e15 n/s-cm 2 MTR-type fuel assembly 6 concentric tubes formed by 18 bent plates HEU: U-Al x in Al matrix, with AG3-NET Cladding gu /cm³, 93% enriched, 400 g U-235/assembly Burnable poisons: 3.8 g B nat (B 4 C) 1.4 g Sm nat (Sm 2 O 3 ) 12 LEU: UMo in Al matrix, with AG3-NET Cladding 8.0 gu/cm³, 19.75% enriched, 491 g U-235/assembly Burnable poisons: Cd wires outside fuel plates

13 Change in Uranium Loading and Burnable Absorber Loading HEU LEU High volume fraction of UMo in LEU dispersion makes integral burnable absorber unattractive SCK-CEN has pursued use of Cd wires in swage joints of assembly stiffeners 13

14 Change in Fueled Height of Core RHF reactor ILL, Grenoble, France Typical power: 53 MW Maximum possible power: 58 MW Prolific beam reactor, including ultra-cold neutrons Peak thermal flux 1.5e15 n/s-cm 2 in reflector Involute plate type fuel assembly 280 plates in one-time use assembly HEU: U-Al x in Al matrix, with AlFeNi Cladding 1.18 gu/cm³, 93% enriched, 8.6 kg U-235/assembly Burnable poisons: Borated zone in top and bottom of plate 5.77 g B-10/assembly 14 LEU: UMo in Al matrix, with AlFeNi Cladding 8.0 g U/cm³, 19.75% enriched, 13.1 kg U-235/assembly Burnable poisons: 2.07 g B-10 in belt outside fuel plates

15 Change in Fueled Height of Core RHF HEU case Boron zone Extended Meat LEU case Fuel zone Fuel zone 15 Boron zone

16 Change in Fueled Height of Core HEU 57MW (nominal power) RHF Choice to maintain the 50 days cycles Relative weighted brightness LEU 57MW HEU 52MW (current power) LEU 55MW HEU 57MW to LEU 55MW Cycle length: +9 ± 1% Brightness : -16 ± 3% Factor of Merit (FOM) ~ -7 ± 4% HEU 52MW to LEU 55MW Cycle length: 0 ± 1% Brightness : -7 ± 3% FOM ~ -7 ± 4% Cycle length (days) Proposed LEU at 55MW: between 5 and 10% of losses with respect to the current HEU configuration

17 Summary: Core Modifications to address technical challenges of conversion Simply Stated: Change as little as possible Fuel will be changed (by definition) OSTR, BR2: Change in Uranium Loading & Burnable Absorber Loading RPI: Change in Fuel Plate Thickness and Reflector Location MURR: Change to Distinct Fuel Meat Thickness in Plates of LEU RHF: Change in Fueled Height of Core Reflector changes highly effective, if cost acceptable Compact Core designs highly effective, when grid & cooling flexibility allows 17 Change enough to find an ACCEPTABLE fuel and core design for LEU conversion of a specific reactor, a fuel assembly must be qualified, commercially available, and suitable for use in that reactor, so that reactor operator & regulator can agree to ACCEPT fuel assembly for conversion

18 Thank you for your attention! 18