Synthesis and Dissolution of Pyrochlore Glass‒Ceramic Waste Forms for Radionuclide Immobilization

ABSTRACT The safety immobilization of high‐level nuclear waste into environmental stable matrix for further geological repository is of great significance to the nuclear waste treatment. A novel type of glass‒ceramic composite waste form, which can simultaneously accommodate actinides and environmentally mobile radionuclides, was successfully fabricated via a two‐step hot pressing method at low sintering temperature (1100°C). The as‐fabricated composite waste form with high density above 95% exhibits dual phases with the coexistence of phosphate glass and pyrochlore structure. The composite waste form demonstrates comparable chemical durability (around 50 mg/m 2 day for ceramic phase and 5 g/m 2 day for glass phase in pH = 1.0 solution) with state‐of‐the‐art glass or ceramic waste forms subjected to acidic and alkaline solutions. A thin amorphous passivation film enriched in glass components was gradually covered on the surface, leading to the dynamic switch between incongruent and congruent leaching mechanisms.