Damages in ceramics for nuclear waste transmutation by irradiation with swift heavy ions

Inert matrices are proposed for advanced nuclear fuels or for the transmutation of the actinides that is an effective solution for the nuclear waste management. The behaviour of inert matrix ceramics like MgO, MgAl2O4 and cubic ZrO2 oxides under irradiation is presented in this study. The alumina Al2O3 has been also studied as a reference for the ceramic materials. These oxides have been irradiated with swift heavy ions at CIRIL/GANIL to simulate the fragment fission effects. The irradiations with the different heavy ions (from S to Pb) with energy between 91 and 820 MeV, have been realised at room temperature or 500 deg. C. The fluencies were between 5 x 101 and 5 x 1015 ions/cm2. The polished faces of sintered polycrystalline disks or single crystal slices have been characterized before and after irradiation by X-ray diffraction and optical spectroscopy. The apparent swelling evaluated from surface profile measurements after irradiation is very important for spinel and zirconia, comparatively with those of magnesia or alumina. The amorphisation seems to be at the origin of this swelling, and the electronic stopping power of the ions is the most influent parameter for the irradiation damages. The point defects characterized by optical spectroscopy show a significant amount of damage on the oxygen sub-lattice in the irradiated oxides. F+ centres are present in all irradiated oxides. However, new absorption bands are observed and cation clusters cannot be excluded in magnesia and spinel after irradiation