Secondary radiation damage and gas production in plasma facing materials under fusion neutron irradiation

Primary radiation damage (atomic displacements) and Helium and Hydrogen production rates in plasma facing components (PFCs) of a fusion system are usually determined by the high energy part of neutron spectra formed in its plasma chamber from the initial fusion neutron source. The energetic alphas and protons, appearing in PFC materials in the (n,α) and (n,p) threshold reactions, per se may cause an additional, secondary material damage. In most cases this additional damage is non-essentially small. Ex altera parte an extra Helium production may become apparent in water cooled systems especially. Material inventory considerations show that Os, Ni and Zn as transmutation products generated in W, Cu-alloys and steels under long term neutron irradiation account for the secondary sources of intensive Helium production in (n,α) reactions with these transmutants. These even if preliminary evaluated responses should be taken into account in new material developments for long term fusion concepts.