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α-AI2O3, A1N, β-Si3N4, and β-SiC ceramic specimens were irradiated by a 30MeV electron beam up to 0.01 dpa at SO BC, and they started to recover thermal difTusivity 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-S13N4 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 α-Al2O3 and AIN 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. [ABSTRACT FROM AUTHOR]