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Garnets have been considered as host phases for the safe immobilisation of high-level nuclear waste, as they have been shown to accommodate a wide range of elements across three different cation sites, such as Ca, Y, Mn on the a-site, Fe, Al, U, Zr, and Ti on the b-site, and Si, Fe, Al on the c-site. Garnets, due to their ability to have variable composition, make ideal model materials for the examination of radiation damage and recovery in nuclear materials, including as potential waste forms. Kimzeyite, Ca 3 Zr 2 FeAlSiO 12 , has been shown naturally to contain up to 30 wt% Zr, and has previously been examined to elucidate both the structure and ordering within the lattice. This study examines the effects of radiation damage and recovery using in-situ ion beam irradiation with 1 MeV Kr ions at the IVEM-TANDEM facility, Argonne National Laboratory. The complementary Hf containing system Ca 3 Hf 2 FeAlSiO 12 was also examined, and found to have a different response to irradiation damage. A sample of irradiated Ca 3 Zr 2 FeAlSiO 12 , at 1000 K, was characterised using aberration corrected (S)TEM and found to contain discreet, nano-sized, crystalline Fe rich particles, indicating a competing process during recovery is occurring. [ABSTRACT FROM AUTHOR]

The mechanical properties of zirconolite glass-ceramics designed for immobilising actinide-rich nuclear wastes, have been investigated through micro-compression tests pre and post 12 MeV gold ion irradiation at room temperature to a peak damage level of 100 displacements per atom (dpa). Whilst zirconolite crystals have become amorphized because of irradiation, transmission electron microscope analysis found no voids within the irradiated zirconolite. Nevertheless, voids of ∼25 nm in diameter were observed within the glass phase and appear to be homogeneously distributed. Surprisingly, micro-compression testing found the zirconolite glass-ceramic to exhibit a lower modulus, lower compression yield and greater toughness post irradiation. [ABSTRACT FROM AUTHOR]