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Preliminary Neutronics Analysis of 3x2 Toroidal and Poloidal Legs of ELM

Coils

Tim Bohm and Mohamed Sawan

University of Wisconsin

7/22/2010

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ITER ELM and VS Coils

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In-vessel coils (IVCs) are used in ITER to provide control of Edge Localized Modes (ELMs) in addition to providing control of moderately unstable resistive wall modes (RWMs) and vertical stability (VS) of the plasma

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ELM Coils

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ELM coil locations• Upper• Mid-plane• Lower

Legs analyzed here:• poloidal• toroidal

(View from outside)

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Limits on Nuclear Parameters in ELM Coils

A good review of radiation limits for normal-conducting magnets in fusion environments:

• L.J. Perkins, “Materials Considerations for Highly Irradiated Normal-Conducting Magnets in Fusion Reactor Applications,” J. of Nuclear Materials, vol. 122&123, pp. 1371-1375 (1984).

• M. Sawan, H. Khater, and S. Zinkle, “Nuclear Features of the Fusion Ignition Research Experiment (FIRE),” Fusion Engineering & Design, vol. 63-64, pp 547 - 557 (2002).

Main concerns:•Mechanical and structural degradation in ceramic insulation under long-term neutron fluence

•Resistivity degradation in ceramic under instantaneous absorbed dose rates (n+)

•Resistivity increase in Cu conductor due to neutron induced transmutations

•Mechanical and structural degradation in Cu (similar to considerations for ITER FW heat sink)

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Issues for Ceramic Insulators

• Candidate materials include Al2O3, MgO, and spinel (MgAl2O4)• Degradation of mechanical properties is a concern:

• Mechanical and structural degradation in polycrystalline solid insulators depends on the crystal structure

• Non-cubic materials such as Al2O3 swell anisotropically leading to the onset of structural microcracking even at modest fluences

• Swelling in solid ceramics with cubic structure (e.g. MgO and MgAl2O4) is isotropic under neutron irradiation

• Fracture toughness increases at elevated fluences for cubic ceramics. Fluence limit is determined only by maximum swelling to be tolerated

• A maximum swelling of 3% corresponds to fast neutron fluences of 1.1x1022 and 4x1022 n/cm2 for polycrystalline solid MgO and spinel, respectively

• Neutron damage has no effect on strength of compacted powder ceramics since each grain is affected individually

• Degradation of electrical properties is a concern:• Under large instantaneous neutron and gamma dose rates, ceramic insulators exhibit

a significant and instantaneous decrease in their resistivity• Compacted powder ceramics show a greater effect than those in solid form (ref. L.J.

Perkins)

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ELM Coil Analysis with Gap Streaming

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Initial 1-D and simplified homogenized 3-D analysis was performed to determine radiation parameters expected in both poloidal and toroidal legs of the ELM coils (Bohm and Sawan memo dated 7/7/2008)

This work examines a more detailed 3x2 ELM coil along the toroidal and poloidal leg

Results were normalized for the peak outboard neutron wall loading of 0.75 MW/m2 (to be conservative)

Cumulative end-of-life parameters calculated for the 0.3 MWa/m2 total average FW fluence (based on 0.56 MW/m2 average NWL that corresponds to 0.54 FPY)

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MCNP Model for Toroidal Legs of 3x2 ELM Coils

• 5 degree sector with 45 cm height

• Reflecting boundaries• 2 cm gaps between

modules• Cu conductor, Spinel

(MgO-Al2O3) insulator

ELM

Vacuum Vessel

FWShield

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MCNP Model for Poloidal Legs of 3x2 ELM Coils

• 10 degree sector with 100 cm height

• Reflecting boundaries• 2.5 cm gaps between

modules• Cu conductor, Spinel

(MgO-Al2O3) insulator

Vacuum Vessel

FW

Shield

Manifolds

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Nuclear Heating (W/cm3) in Toroidal Leg

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• Peak heating in Cu conductor nearest the FWS module gap

1.68 W/cm3

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Nuclear Heating (W/cm3) in Poloidal Leg

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2.52 W/cm3

50% higher peak heating in poloidal leg•Larger first wall gap•More shield material removed•Presence of water in manifold (softens neutron spectrum producing more photons)

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Nuclear Heating Profiles in Toroidal Leg

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Lower profile

Upper profile

• Profiles clearly show the low nuclear heating in water cooling pipe• Lower coils have higher heating due to location in the gap

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Average Nuclear Heating by Cell in Toroidal Leg

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Cell Component Heating (W/cm3)101 bracket 0.212102 spacer 0.445103 stub 1.075111 case1 0.902112 case2 0.476113 case3 0.273114 case4 1.075115 case5 0.555116 case6 0.311121 insulator1 0.368122 insulator2 0.199123 insulator3 0.110124 insulator4 0.476125 insulator5 0.241126 insulator6 0.131131 conductor1 1.004132 conductor2 0.549133 conductor3 0.310134 conductor4 1.252135 conductor5 0.639136 conductor6 0.363141 coolant1 0.295142 coolant2 0.157143 coolant3 0.086144 coolant4 0.450145 coolant5 0.205146 coolant6 0.105

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Average Nuclear Heating by Cell in Poloidal Leg

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Cell Component Heating (W/cm3)101 bracket 0.503102 spacer 0.708103 stub 1.830111 case1 1.265112 case2 0.653113 case3 0.398114 case4 1.804115 case5 1.071116 case6 0.795121 insulator1 0.545122 insulator2 0.276123 insulator3 0.163124 insulator4 0.745125 insulator5 0.440126 insulator6 0.321131 conductor1 1.426132 conductor2 0.724133 conductor3 0.448134 conductor4 1.999135 conductor5 1.203136 conductor6 0.884141 coolant1 0.442142 coolant2 0.227143 coolant3 0.130144 coolant4 0.542145 coolant5 0.330146 coolant6 0.234

• Volume averaged heating 20-150% greater in poloidal leg

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Peaking near the Gap in Toroidal Leg

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SS case: He prod. =4.68 appm

Cu conductor :Heating=1.59 W/cm3 (1.11)

Cu dpa=0.259 (0.229)

Spinel insulator:Fast fluence=2.77e20 n/cm2 (2.22e20)

Dose rate=203 Gy/sec (160 Gy/sec)

• Tally values volume averaged in indicated region• Peak results from 2008 homogenized 3D analysis in parenthesis

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Peaking near the Manifold in Poloidal Leg

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SS case: He prod. =5.78 appm

Cu conductor :Heating=2.39 W/cm3 (1.42)

Cu dpa=0.251 (0.121)

Spinel insulator:Fast fluence=2.70e20 n/cm2 (1.05e20)

Dose rate=279 Gy/sec (177 Gy/sec)

• Conductor heating, insulator dose, and He production higher than values in the toroidal leg

• Peak results from 2008 homogenized 3-D analysis in parenthesis

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Resistivity Increase in Toroidal and Poloidal Legs of ELM Coil Cu Conductor

• Increase in electrical resistivity of copper results from displacement damage (production of defects and dislocations) and solute transmutation products • 10200 OFHC Cu ~16 nm at 293K

• At high doses, the displacement damage component approaches rapidly a constant saturation value due to displacement cascade overlap effects with a saturation value of 1-4 nm depending on purity and Cu alloy• Expected only to be a second order consideration since most effects could be annealed by

baking out at 200-300o C

• Transmutation products are Ni, Zn, Co that build up as impurities with time resulting in changing conductor resistivity

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Solute Transmutation rate

(appm/dpa)

Solute resistivity(m/at.

Frac.)

Resistivity increase for toroidal peak 0.26 dpa

(pm)

Resistivity increase for poloidal peak 0.25 dpa

(pm)

Ni 190 1.12 55.3 53.2

Zn 90 0.3 7.0 6.7

Co 7 6.4 11.6 11.2

Total 73.9 71.1

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Other Relevant Parameters in Toroidal Leg

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VV SS He production 0.68 appm

Stub SS He production 2.12 appm

Reweldability limit He:1 appm (thick plate welds)3 appm (thin plate or tube)

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Other Relevant Parameters in Poloidal Leg

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1.0 appm2.7 appm 3.8 appm2.9 appm

Stub SS He production: 4.17 appm

Reweldability limit He :1 appm (thick plate welds)3 appm (thin plate or tube)

Manifold SS He production:Case Volume Average 11.8 appmCase Volume Average 23.1 appmCase Volume Average 11.4 appm

VV SS He production:

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Future Work

Perform full 40 degree 3-D CAD analysis (will need clean CAD drawings)– Focus on where toroidal and poloidal ELM legs meet (large

amounts of FWS removed here) – Examine VS coils– Examine Feeder regions

Detailed mid-plane port geometry may be needed to accurately characterize mid-plane ELM coils (may not be able to just model port plugs)

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Neutronics Issues and Resolution Plan

Issue Resolution Plan Expected Completion

Excess He production, Non-reweldability of Manifold and VV behind poloidal leg of ELM coil

Seek design solutions to reduce He production (add shielding material in void space)

Pre-October

Quantify decrease in powdered ceramic insulator properties due to large instantaneous dose rates

More detailed literature search Pre-October

Update nuclear analysis to cover all feeder, ELM and VS locations

Perform full 40 degree CAD based MCNP analysis of ELM and VS model (will require clean CAD model)

Pre-October

Update nuclear analysis at mid-plane ELM locations

Obtain CAD models of mid-plane port geometry

Post-October

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