Neutron-irradiation effect in ceramics evaluated from macroscopic property changes in as-irradiated and annealed specimens

Macroscopic length (linear swelling) and thermal diffusivity changes were measured for heavily neutron-irradiated α-Al 2O 3, AlN, β-Si 3N 4 and β-SiC that were irradiated under the same capsule to compare the difference between these materials. And in addition, several capsules were irradiated under different temperatures (646–1039 K) and to different neutron doses (0.4–8.0 × 10 26 n/m 2) in the Japanese experimental fast reactor JOYO. The swelling and the thermal diffusivity of as-irradiated specimens showed some dependence on the neutron-irradiation dose and the irradiation temperature, and that indicates stability under neutron-irradiation environments. Alpha-Al 2O 3 and AlN showed relatively large swelling and degradation of thermal diffusivity than β-Si 3N 4 and β-SiC. This difference is related to the crystal structure of each material. The dependence of swelling on irradiation dose, that is, α-Al 2O 3 showed linear inclination but β-Si 3N 4 and β-SiC showed saturation, supports the model of defect structures. In addition, annealing behaviors of swelling and thermal diffusivity were compared to analyze the behavior of defects at higher temperature.