Induced activity and damage of superconducting materials for a fusion reactor

The induced activity, radiation damage, and compositional change of several superconductor materials, such as Nb-based alloys, V-based alloys, and MgB2, for the toroidal field (TF) and central solenoid (CS) magnets of a tokamak-type fusion reactor have been evaluated under the first wall neutron loading of 1 MW/m2 with a numerical calculation. The damage rates of both Nb- and V-based alloys calculated are about (1–3) × 10−4 dpa/y at the TF coils adjacent to the vacuum vessel and (2–6) × 10−7 dpa/y at the surface of CS coil. The damage rate of MgB2 is about 1 order magnitude higher than those of Nb- and V-based superconducting materials. Most of the induced activity of V-based alloys and MgB2 after shutdown of the reactor is controlled by 60Co formed from Cu. Nb-based alloys are predicted to emit gamma rays for tens of thousands years due to 94Nb from Nb. In the case of the CS coils, the formation of 94Nb is minimal, and the gamma ray decay of Nb-based alloys is expected to be faster than that of V-based alloys.