Analysis of neutron-irradiation-induced defects using nanometer-sensitive dilatometry : Recovery rate study

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Irradiation response of ceramics induced by neutron irradiation varies material to material with different crystal structure. In this research, recovery behavior of defects, which induce small volume change, by heat-treatment was precisely measured using a high-precision dilatometer at high temperature.(1) At first, performance of the dilatometer was checked. Using this dilatometer, the specimen was heated up to a designated temperature, and then it was kept for 6 h, and length change of the specimen was continuously monitored. Then, the temperature of the specimen was increased 50℃ higher temperature, and the length change was measured. These measurement was conducted sequentially up to the specimen length became the original length before irradiation.(2) Based on the analysis of the length change of the two kind of neutron-irradiated SiC specimens obtained at each temperature, it was clarified that length recovery curves at each isothermal annealing consisted from two components, for … More shorter time and for longer time, if the process composed from the first order reactions. These recovery rates were obtained. From the Arrhenius plots of the rate at each temperature, apparent activation energies were obtained.(3) Resemble measurement was conducted on neutron-irradiated single crystal silicon, that crystal structure is similar with silicon carbide. Whereas the change induced by irradiation was very small, the recovery stage could be measured successfully.(4) High-resolution electron microscope observation on irradiated and annealed SiC was performed, and it was clarified that the void was formed after annealing up to 1400℃ in the specimen neutron-irradiated up to 20 dpa at relatively higher temperature. In these specimens, lattice parameter increased less than that of the macroscopic length, and included many tiny interstitial loops.(5) Based on the results obtained in this study and previous studies, the relation between crystal structures and irradiation response and recovery behavior was discussed. Less