Thermal diffusivity of ceramics at the neutron irradiation temperature estimated from post-irradiation measurements at 123–413 K

In ceramic materials, heat is mainly carried by phonon. During and after irradiation, phonon is scattered by neutron-induced defects, and the neutron-irradiated specimen showed severe degradation in thermal diffusivity. On the other hand, phonons are also scattered among each other independent of any defects, and the scattering increases with the increase in the measurement temperature. In this study, the thermal diffusivity of heavily neutron-irradiated ceramics was measured at the temperatures of 123–413 K. The dependence of thermal diffusivity on measurement temperature was approximated with a function, and with several fitting parameters, the thermal diffusivity at irradiation temperature was estimated without measurement at elevated temperature that causes annealing effect. With several assumptions, the thermal diffusivity at the irradiation temperature has been considered to represent the thermal diffusivity during irradiation. Furthermore, the estimated thermal diffusivity during irradiation was almost independent of the irradiation temperature.