Preliminary Neutronics Assessment of Molten Salt Blanket Concepts Mohamed Sawan Fusion Technology Institute University of Wisconsin, Madison, WI ITER TBM Meeting UCLA Feb. 23-25, 2004 1
Preliminary Neutronics Assessment ÿ Three blanket concepts analyzed 1. Self-cooled Flinabe blanket (Flinabe/Be/FS)- [SC] 2. Dual coolant blanket with Be (Flibe/He/Be/FS)- [DC-Be] 3. Dual coolant blanket with Pb (Flibe/He/Pb/FS)- [DC-Pb] ÿ The FS alloy F82H used as structural material ÿ Same reactor configuration and power loadings used for fair comparison Average reactor neutron wall loading 3.84 MW/m 2 Peak neutron wall loading: OB 5.45 MW/m 2 , IB 3.61 MW/m 2 Average neutron wall loading: OB 4.61 MW/m 2 , IB 2.80 MW/m 2 ÿ Radial build between FW and VV is 80 cm IB and 95 cm OB ÿ 25 cm thick VV ÿ Water cooled steel VV and shield ÿ TBR has a flat peak in the enrichment range 40-60%. 40% 6 Li is used ÿ 1D calculations with IB and OB blankets modeled simultaneously ÿ Several iterations were made to determine the radial build that achieves adequate tritium breeding and shielding for VV and magnet ÿ Larger margins are considered to account for uncertainties resulting from approximations in modeling ÿ Multi-dimensional calculations are to be performed later to accurately model the blanket 2
Blanket Radial Build SC Flinabe DC Flibe/He DC Flibe/He Be Be Pb Blanket 50 cm OB 65 cm OB 65 cm OB Thickness 40 cm IB 40 cm IB 40 cm IB Multiplier 7 cm 5 cm 5 cm Zone 60% Be 60% Be 87% Pb ÿ Same TBR can be achieved with a thinner SC OB blanket compared to the DC blanket with large He amount ÿ To achieve the same TBR a smaller Be zone thickness (5 cm) is required in the DC design with Flibe compared to the SC with Flinabe (7 cm) ÿ In the DC design more Pb is needed than Be although the Be is pushed farther from FW by the Flibe poloidal flow channel required to cool it 3
Tritium Breeding Potential 1.5 SC DC-Be DC-Pb Local TBR 1.0 IB 0.432 0.406 0.399 IB OB OB 0.867 0.882 0.897 0.5 Total 1.299 1.288 1.296 0.0 SC DC-Be DC-Pb Blanket ÿ If neutron coverage for the divertor is 10% the overall TBR will be ~1.17 excluding breeding in divertor region. Breeding in divertor zone could add ~0.05 ÿ The blanket design concepts have the potential for achieving tritium self- sufficiency. Some design parameters can be adjusted (e.g., multiplier thickness, blanket thickness, etc) to insure tritium self-suffiency based on calculations with detailed multi-dimensional modeling 4
Blanket Energy Multiplication 1.5 1.27 1.27 1.27 1.21 1.13 Blanket Energy Multiplication ÿ Using Be yields higher blanket energy 1.0 multiplication ß 1.27 for SC blanket with Be ß 1.21 for DC blanket with Be 0.5 ß 1.13 for DC blanket with Pb 0.0 SC DC-Be DC-Pb Blanket 5
Nuclear Heating in Components of Self-Cooled Flinabe Blanket 70 Radial Distribution of Power Density 60 in Blanket Components at OB Midplane 2 Peak Neutron Wall Loading 5.45 MW/m Power Density (W/cm 3 ) ÿ Peak nuclear heating 50 Recirculating Blanket values in OB blanket 40 Flinabe/Be/FS 55 W/cm 3 • FS • Flinabe 69 W/cm 3 30 FS Flinabe 47 W/cm 3 • Be Be 20 10 0 0 10 20 30 40 50 Depth in Blanket (cm) 6
Nuclear Heating in Components of Dual Coolant Blanket with Be 80 Radial Distribution of Power Density 70 in Blanket Components at OB Midplane 2 Peak Neutron Wall Loading 5.45 MW/m 60 Power Density (W/cm 3 ) ÿ Peak nuclear heating 50 Dual Coolant Blanket values in OB blanket Flibe/He/Be/FS 40 56 W/cm 3 • FS 70 W/cm 3 • Flibe Flibe 30 FS Be 36 W/cm 3 • Be 20 10 0 0 8 16 24 32 40 48 56 64 Depth in Blanket (cm) 7
Nuclear Heating in Components of Dual Coolant Blanket with Pb 80 Radial Distribution of Power Density 70 in Blanket Components at OB Midplane 2 Peak Neutron Wall Loading 5.45 MW/m 60 ÿ Peak nuclear heating Power Density (W/cm 3 ) 50 Dual Coolant Blanket values in OB blanket Flibe/He/Pb/FS 49 W/cm 3 • FS 40 73 W/cm 3 • Flibe FS 30 Flibe 50 W/cm 3 • Pb Pb 20 10 0 0 8 16 24 32 40 48 56 64 Depth in Blanket (cm) 8
Peak Radiation Damage Parameters in FW Structure (OB Midplane) SC DC-Be DC-Pb ÿ Based on 200 dpa damage limit dpa/FPY 76.4 74.8 84.2 blanket lifetime is ~2.4 FPY He appm/FPY 1005 983 922 Peak Radiation Damage Parameters in Shield (IB Midplane) ÿ Based on 200 dpa damage limit shield is SC DC-Be DC-Pb expected to be lifetime component with a dpa @30 FPY 18 33 41 large margin that allows for uncertainties due to modeling and possible hot spots He appm @30 FPY 100 183 213 due to streaming at module sides Total Tritium Production in Be (for 2.4 FPY blanket life) ÿ Modest amount of tritium produced in Be SC DC-Be ÿ Tritium inventory will be much smaller IB 0.78 kg 0.46 kg depending on temperatures OB 2.19 kg 1.34 kg ÿ 40% less tritium produced in Be of DC blanket Total 2.97 kg 1.80 kg 9
Shielding Requirement 150 150 OB IB Radial Build (cm) Radial Build (cm) 100 100 Blanket Shield V V 50 50 0 0 SC DC-Be DC-Pb SC DC-Be DC-Pb Blanket Blanket ÿ Radial build determined to insure that radiation limits are satisfied with adequate margins • Shield is lifetime component (<200 dpa) • VV is reweldable (<1 He appm) • Magnet adequately shielded (<10 10 Rads) 10
Peak VV Damage Parameters SC DC-Be DC-Pb IB OB IB OB IB OB Peak end-of-life dpa 0.035 0.007 0.065 0.029 0.07 0.03 Peak end-of-life He appm 0.21 0.04 0.38 0.16 0.45 0.17 Peak Magnet Damage Parameters (IB) SC DC-Be DC-Pb Design Limit Peak Nuclear Heating (mW/cm 3 ) 0.14 0.35 0.29 1 Peak end-of-life Fast Neutron Fluence (n/cm 2 ) 1.3x10 18 2.8x10 18 2.8x10 18 10 19 3.1x10 9 7.6x10 9 6.6x10 9 10 10 Peak end-of-life Dose to Insulator (Rads) 9.0x10 -4 2.1x10 -3 2.0x10 -3 6x10 -3 Peak end-of-life dpa to Cu Stabilizer ÿ Shielding effectiveness of DC blanket is lower than SC blanket due to large amount of He ÿ With same IB radial build damage parameters in shield, VV, and magnet are a factor of ~2 lower with the SC blanket ÿ DC designs with Be and Pb result in comparable radiation damage parameters 11
Summary ÿ The three design concepts have the potential for achieving tritium self- sufficiency. Several design parameters can be adjusted (e.g., multiplier thickness, blanket thickness, etc) to insure tritium self-suffiency ÿ Using He gas in the dual coolant blanket results in • Lower blanket shielding effectiveness • 15 cm thicker OB blanket ÿ Higher blanket energy multiplication with Be 1.27 for self-cooled blanket with Be 1.21 for dual coolant blanket with Be 1.13 for dual coolant blanket with Pb ÿ Smaller amount of Be required in dual coolant design with Flibe compared to self-cooled blanket with Flinabe resulting in ~40% less tritium production in the Be multiplier ÿ With total B/S/VV radial build of 105 cm IB and 120 cm OB it is possible to achieve: • shield lifetime component • VV reweldable • magnets adequately shielded 12
Issues related to multiplier choice (Pb vs. Be) Unique issues for MS blankets: • Neutron multiplier needed: Be better neutron multiplier. Smaller amount needed. • Need for REDOX and chemistry control: Be in direct contact with MS helps Issues with Be: • Be toxicity • Be resources • Tritium production in Be. How much tritium inventory retained in Be (dependence on temp.) • Need to accommodate swelling in Be Issues with Pb: • Safety issues related to Po production in Pb. Could Bi/Po be removed efficiently? Compatibility Issues: • Interaction of Be with FS. Formation of discontinuous brittle superficial layer with generation of holes in Be. Rate of layer formation depends on temp • Pb compatibility with FS. Corrosion (main mechanism is dissolution of FS) dependence on temperature and velocity. Can we accurately control oxygen content in Pb to help forming stable adherent oxide film (not much O to avoid intergranular attack) that alleviates dissolution? What is max allowable interface temp? 13
Detailed Blanket Radial Build 14
Radial Build of SC Blanket ÿ Radial build for OB blanket zone Thickness Flibe NCF Be 1 First wall 3 mm 1 2 FW Flibe channel, poloidal flow 10 mm 0.92 0.08 3 Multiplier front wall 3 mm 1 4 Multiplier region 70 mm 0.322 0.08 0.598 5 Multiplier back wall 3 mm 1 6 Flibe channel+side wall 10 mm 0.92 0.08 7 Flibe channel back wall 6 mm 1 8 Flibe + Side walls, a mixed zone 366 mm 0.932 0.068 9 Back wall, a mixed zone 29 mm 0.6069 0.3931 Total 500 mm ÿ Radial build for IB blanket zone Thickness Flibe NCF Be 1 First wall 3 mm 1 2 FW Flibe channel, poloidal flow 10 mm 0.92 0.08 3 Multiplier front wall 3 mm 1 4 Multiplier region 70 mm 0.322 0.08 0.598 5 Multiplier back wall 3 mm 1 6 Flibe channel+side wall 10 mm 0.92 0.08 7 Flibe channel back wall 6 mm 1 8 Flibe + Side walls, a mixed zone 266 mm 0.932 0.068 9 Back wall, a mixed zone 29 mm 0.6069 0.3931 Total 400 mm 15
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