Effect of Annealing on Thermal Diffusivity in Ceramics Irradiated by Electrons and Neutrons

α-Al2O3, AlN, β-Si3N4, and β-SiC ceramic specimens were irradiated by a 30 MeV electron beam up to 0.01 dpa at 80°C, and they started to recover thermal diffusivity with annealing from 300{500°C. In previous studies, similar ceramics were heavily neutron-irradiated in a fast reactor, JOYO, and the neutron-irradiated β-Si3N4 and β-SiC also showed recovery above 400°C, though they were irradiated at 502°C or 738°C. This result is explained by the hypothesis that a ‘primary’ irradiation occurred at the set temperature, and after that, a ‘secondary’ irradiation occurred at a lower temperature during the shutdown process of the reactor. In contrast, the neutron-irradiated β-Al2O3 and AlN did not show such unexpected recovery, but showed recovery above 800-900°C. This difference is explained on the basis of structural models of dislocation loops namely, the ‘pileup’ model and the ‘nano-partition’ model.