Nuclear Analysis for Near Term Fusion Devices Page: 3 of 9
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IL2 Vacuum Vessel Radiation Damage
Since the vacuum vessel (VV) is protected from the fusion neutrons by the thin FW/tiles, the issue of
reweldability was addressed. The end-of-life helium production in the VV structure should be limited to 1
appm to allow for rewelding. For the FIRE goal of cumulative 5 TJ DT and 0.5 TJ DD fusion energy, the
peak VV He production values in the IB, OB, and divertor regions are 0.091, 0.125, and 0.013 appm,
respectively. The contribution from DD shots is very small (< 0.15%). The results imply that reweldability
of the VV should not be a concern.
IL3 Copper Radiation Damage
Table 2 gives the end-of-life peak dpa values in the Cu tiles, VV cladding, Cu heat sink in outer divertor, and
Cu TF coils for the FIRE baseline design. Although the damage levels are very low, significant effects on
physical and mechanical properties might occur. These effects are strongly dependent on irradiation
temperature and have been the subject of numerous studies as part of the ITER R&D program.
Table 2. Peak End-of-Life Cu dpa in FIRE.
Total dpa in Cu at
end-of-life
IB Tiles 0.0271
OB Tiles 0.0298
Divertor 0.0125
IB VV Cladding 0.0178
OB VV Cladding 0.0204
Magnet at IB 0.0055
Magnet at OB 6.26x10-6
Magnet at Divertor 3.78x10-4
Based on the irradiation levels and operation conditions in FIRE and the available data on Cu alloys, we can
identify the R&D needs as follows:
" Data on loss of ductility of BeCu (or OFHC) at temperatures between 80 and 373 K with doses <
0.01 dpa.
" Data on fatigue, fracture toughness and fatigue crack growth rate behavior in high-strength, high-
conductivity copper alloys.
" Thermal creep data for CuCrZr at temperatures up to 500 C. There is no need to perform irradiation
creep measurements on Cu alloys for the low doses proposed in FIRE.
IL4 Radiation Induced Resistivity in the Copper Conductors of the TF Coils
The 17510 BeCu alloy is used in the inner legs of the TF coils with 10200 OFHC copper being utilized in the
rest of the TF coils. A concern with Cu magnet conductors is the increased electrical resistivity that impacts
the performance of the TF coils through increasing the I2R heating and the redistribution of the current across
the coil. The temperature at the end of the pulse will increase with possible impact on the achievable pulse
length. The increase in electrical resistivity results from solute transmutation products and displacement
damage. In a low-fluence machine such as FIRE, resistivity increase is dominated by point defects and
defect clusters produced by displacement damage.
Figure 1 shows the resistivity increases at end-of-life from solute transmutation products and displacement
damage in the BeCu alloy as a function of depth in the inner leg of the TF magnet at midplane. It is clear
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Sawan, M.E.; Kulcinski, G.L. & Henderson, D.L. Nuclear Analysis for Near Term Fusion Devices, report, April 2, 2007; Madison, Wisconsin. (https://digital.library.unt.edu/ark:/67531/metadc888039/m1/3/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.