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-Al2O3, AlN, β-Si3N4 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 × 1026 n/m2) 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-Al2O3 and AlN showed relatively large swelling and degradation of thermal diffusivity than β-Si3N4 and β-SiC. This difference is related to the crystal structure of each material. The dependence of swelling on irradiation dose, that is, α-Al2O3 showed linear inclination but β-Si3N4 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.