Crystallization study of (TiO2, ZrO2)-rich SiO2-Al2O3-CaO glasses Part I Preparation and characterization of zirconolite-based glass-ceramics

Nuclear power reactors generate long-lived radionuclides such as minor actinides (Np, Am, Cm) which are mainly responsible for the long term radiotoxicity of high level nuclear wastes obtained after reprocessing of nuclear spent fuel. Specific highly durable matrices such as glass-ceramics appear as good candidates for the immobilization of minor actinides. This work concerns the synthesis and the characterization of zirconolite (CaZrTi₂O₇) based glass-ceramics prepared by controlled devitrification of (TiO₂, ZrO₂)-rich SiO₂-Al₂O₃-CaO parent glasses for which neodymium was selected to simulate the radioactive trivalent minor actinides. The present study reports the effect of increasing TiO₂, ZrO₂ and CaO amounts in glass composition on the structure and the composition of the zirconolite crystals (formed as the only crystalline phase in the bulk of the glass), on their nucleation rate I(Z) and on the volume proportion of crystalline phase V of the glass-ceramics. It appears that I(Z) and V strongly increase when the parent glass composition changes. Neodymium electron spin resonance (ESR) shows that the total amount of Nd³⁺ ions incorporated in the zirconolite phase increases with TiO₂, ZrO₂ and CaO amounts in parent glass composition.