Radiation effects in materials for accelerator-driven neutron technologies

Accelerator-driven neutron technologies include facilities for neutron scattering research, accelerator transmutation of waste (ATW), and accelerator production of tritium. These systems use spallation neutron sources (SNS's) in which high-energy protons (E = 1000-2000 MeV) strike a heavy-metal target, producing spallation neutrons with energies extending up to the incident proton energy. The nature of the spallation process and the codes used to calculate spallation radiation damage are reviewed. Calculations of displacement and helium production in a major target material, tungsten, are described. Displacement cross sections reach about 9000 b for 1600 MeV neutrons or protons. In a simulated high-current-density ATW SNS, displacement production rates are about 0.1 and 1 dpa/d due to the spallation neutrons and incident 1600 MeV protons, respectively, and the He production rates are about 1 and 250 appm He/d, respectively. These damage rates probably represent an upper limit to what can be tolerated. More realistic solid-target SNS's will operate at lower current densities, and the damage rates are likely to be reduced by a factor of 3 or 4 from the values cited above. In any case, however, radiation damage to target and container materials is a major consideration in the design of SNS's.