1. Bohm 1 Preliminary Neutronics Analysis of 3x2 Toroidal and Poloidal Legs of ELM Coils Tim Bohm and Mohamed Sawan University of Wisconsin 7/22/2010

2. Bohm ITER ELM and VS Coils 2 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

3. Bohm ELM Coils 3  ELM coil locations Upper Mid-plane Lower  Legs analyzed here: poloidal toroidal (View from outside)

4. Bohm 4 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)

5. Bohm 5 Issues for Ceramic Insulators Candidate materials include Al 2 O 3, MgO, and spinel (MgAl 2 O 4 ) 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 Al 2 O 3 swell anisotropically leading to the onset of structural microcracking even at modest fluences Swelling in solid ceramics with cubic structure (e.g. MgO and MgAl 2 O 4 ) 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 1.1x10 22 and 4x10 22 n/cm 2 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)

6. Bohm ELM Coil Analysis with Gap Streaming 6  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/m 2 (to be conservative)  Cumulative end-of-life parameters calculated for the 0.3 MWa/m 2 total average FW fluence (based on 0.56 MW/m 2 average NWL that corresponds to 0.54 FPY)

7. Bohm 7 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-Al 2 O 3 ) insulator ELM Vacuum Vessel FW Shield

8. Bohm 8 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-Al 2 O 3 ) insulator Vacuum Vessel FW Shield Manifolds

9. Bohm Nuclear Heating (W/cm 3 ) in Toroidal Leg 9 Peak heating in Cu conductor nearest the FWS module gap 1.68 W/cm 3

10. Bohm Nuclear Heating (W/cm 3 ) in Poloidal Leg 10 2.52 W/cm 3  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)

11. Bohm Nuclear Heating Profiles in Toroidal Leg 11 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

12. Bohm Average Nuclear Heating by Cell in Toroidal Leg 12 CellComponentHeating (W/cm3) 101bracket0.212 102spacer0.445 103stub1.075 111case10.902 112case20.476 113case30.273 114case41.075 115case50.555 116case60.311 121insulator10.368 122insulator20.199 123insulator30.110 124insulator40.476 125insulator50.241 126insulator60.131 131conductor11.004 132conductor20.549 133conductor30.310 134conductor41.252 135conductor50.639 136conductor60.363 141coolant10.295 142coolant20.157 143coolant30.086 144coolant40.450 145coolant50.205 146coolant60.105

13. Bohm Average Nuclear Heating by Cell in Poloidal Leg 13 CellComponentHeating (W/cm3) 101bracket0.503 102spacer0.708 103stub1.830 111case11.265 112case20.653 113case30.398 114case41.804 115case51.071 116case60.795 121insulator10.545 122insulator20.276 123insulator30.163 124insulator40.745 125insulator50.440 126insulator60.321 131conductor11.426 132conductor20.724 133conductor30.448 134conductor41.999 135conductor51.203 136conductor60.884 141coolant10.442 142coolant20.227 143coolant30.130 144coolant40.542 145coolant50.330 146coolant60.234 Volume averaged heating 20-150% greater in poloidal leg

14. Bohm Peaking near the Gap in Toroidal Leg 14 SS case: He prod. =4.68 appm Cu conductor : Heating=1.59 W/cm 3 (1.11) Cu dpa=0.259 (0.229) Spinel insulator: Fast fluence=2.77e20 n/cm 2 (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

15. Bohm Peaking near the Manifold in Poloidal Leg 15 SS case: He prod. =5.78 appm Cu conductor : Heating=2.39 W/cm 3 (1.42) Cu dpa=0.251 (0.121) Spinel insulator: Fast fluence=2.70e20 n/cm 2 (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

16. Bohm 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 n  m 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 n  m depending on purity and Cu alloy Expected only to be a second order consideration since most effects could be annealed by baking out at 200-300 o C Transmutation products are Ni, Zn, Co that build up as impurities with time resulting in changing conductor resistivity 16 SoluteTransmutation rate (appm/dpa) Solute resistivity (  m/at. Frac.) Resistivity increase for toroidal peak 0.26 dpa ( p  m) Resistivity increase for poloidal peak 0.25 dpa ( p  m) Ni1901.1255.353.2 Zn900.37.06.7 Co76.411.611.2 Total73.971.1

17. Bohm Other Relevant Parameters in Toroidal Leg 17 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)

18. Bohm Other Relevant Parameters in Poloidal Leg 18 1.0 appm 2.7 appm 3.8 appm 2.9 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 appm Case Volume Average 23.1 appm Case Volume Average 11.4 appm VV SS He production:

19. Bohm 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) 19

20. Bohm Neutronics Issues and Resolution Plan IssueResolution PlanExpected 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 searchPre-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 20