Characterization of reactor materials exposed to high-energy proton

To keep the safety of nuclear reactor, it is necessary to elucidate the behaviors of materials to be used under the conditions of proton irradiation and assess the applicability to such environments. This report describes the structural damages caused by exposing to high-energy proton at a GeV level in the materials for proton beam incident window and solid target. Generally, the assessment of such damages has been conducted on the basis of the value of dpa, but not the cascade damages due to primary knock-on atom (PKA). From the analysis of cascade damages due to high-energy proton, it was demonstrated that the elements produced by nuclear spallation were light elements such as He and Li, and heavy ones like the components of the material exposed to proton. PKA energy levels of the former and latter elements were more than dozens of NeV and several MeV, respectively. Most of the damages such as Frenkel pair were caused by those heavy elements. The materials of the incident window and target were damaged at a high speed and the damages were large. Moreover, the material's damages in the window and target materials were greater than the damages in the wall of the fission reactor. Therefore, it is thought necessary to assess the radiation damages not only using the value of dpa but also taking consideration of the material's behaviors under heavy radiation including the effects of elements produced by nuclear spallation. (M.N.)