Induced activity of several candidate superconductor materials in a tokamak-type fusion reactor

The induced activity and compositional change of several superconducting materials such as Nb-based alloys, V-based alloys and MgB2 have been evaluated with a numerical calculation. We assume that the materials are irradiated for 10 MW a/m2 at the magnet of the inboard position of a tokamak-type fusion reactor with a neutron wall loading of 1 MW/m2. The materials are Nb3Sn, Nb3Al, NbTi, NbZr, V2Zr, V2(Zr,Hf), V3Ga, V3Si and MgB2. Most of the induced activity of V-based alloys and MgB2 after the shutdown of the reactor is controlled by the 60Co formed from Cu. After the irradiation, the dose rate decreases to a safe level of 10 μSv/h within 30 years. However, Nb-based alloys are predicted to emit gamma rays for tens of thousands years. The compositional changes and irradiation damage of V-based alloys and MgB2 are minimal.