Radiation damage conditions for ESS target hull and irradiation rigs

In addition to their original mission, neutron spallation sources were also considered as a possible test bed for fusion material irradiation. Accordingly an irradiation module with 0.83 l subdivided into 10 instrumented horizontal rigs was proposed in the target–reflector interface of the ESS 5 MW long-pulse target. The irradiation conditions of this irradiation module and of the front-end target hull are given on the basis of calculations with a detailed geometry model using the neutron, photon and charged particle transport code MCNPX. Neutron and primary knock-on atom spectra, displacement damage and gas production rates as well as spallation element production rates were derived and compared with those of a fusion demonstration reactor (DEMO) and the International Fusion Materials Irradiation Facility (IFMIF). In particular, it was shown that the He/dpa ratio for the ESS reflector position is between 5 and 6 in Fe-based alloys, that is about a factor of two lower than expected for the DEMO fusion reactor. While the generation of spallation products like P, S and Ca, which are known to induce structural material embrittlement, is between 40 and 90 appm per year in the ESS target hull and is comparable with their initial concentration in the alloy, their production at the reflector position is negligibly small.