Helium release and physical property change of neutron-irradiated α-SiC containing B4C of different 10B concentrations

Sintered α-SiC ceramics containing B4C with various 10B concentrations were neutron-irradiated, and the helium release rate during increasing annealing temperature was observed. The lattice parameter and the macroscopic length changes of the same specimens were also observed. The helium release rate from powdered specimens increased markedly above 650degC, and showed a sharp peak at ∼1,160degC independent of the 10B concentration, but the rate was higher for the specimen containing higher concentration of 10B. The macroscopic volume of the SiC specimen with higher 10B concentration was expanded larger than that of the lower one by the irradiation. The unit cell volume change was mostly independent of 10B concentration, whereas the each axis changed different manner. A-axis started to shrink around the irradiation temperature, and contracted mostly linearly with increasing annealing temperature. On the other hand, contraction of the c-axis was not parallel to that of a-axis, and was retarded between 500-1,100degC. It is supposed that helium will induce some lattice defects, which expands c-axis length of SiC. These defects retained up to 1,100degC with support of helium migration. During the annealing, the expansion of macroscopic length occurred at higher temperature than 1,300degC, where the higher 10B concentration specimen gave the larger expansion, indicating the formation of grain boundary helium bubbles. (author)