Neutron irradiation effects of ceramics insulator

This article reviews various studies on the effects of neutron irradiation on the properties of ceramic insulators. Neutron irradiation generally cause swelling and extension of ceramic materials. Swelling occurs over a wide temperature range. In Al₂O₃ and BeO, swelling increases nearly proportionally with increasing exposure. The mechanisms of the volume increase and extension of ceramic materials have been interpreted in terms of the expansion of crystal lattice due to radiation-induced lattice defects (low temperature, small exposure) or the formation of voids and bubbles due to clustering of lattice defects or He and H atoms (high temperature, large exposure). Few systematic studies have been reported concerning the effects of neutron irradiation on the strength of ceramic materials. The strength of SiC decreases while that of Al₂O₃, MgAl₂O₄ and MgO increases with increasing exposure. Heat conductivity and thermal diffusivity generally decreases with exposure, finally reaching 20 - 70 percent of the values before the irradiation. Neutron irradiation causes point defects (due to knocking-out damage) and electron hole pairs (due to electron excitation), which affect the electric conductivity of ceramics. (Nogami, K.)