The solubility, microstructure, and chemical durability of Ce‐doped YIG ceramics designed as actinide waste forms

Abstract

Yttrium iron garnet (YIG) is a potential matrix for immobilizing high-level radioactive waste (HLW) due to its high actinide solubility and chemical flexibility. In this study, Ce was employed as a surrogate of Pu. A series of Y3-xCexFe5O12 (0 ≤ x ≤ 1) samples were prepared by solid-state sintering at 1400°C to investigate the solubility, microstructure, and chemical durability of Ce-doped YIG. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the solubility of the Ce in a single garnet was 32 mol% at synthesis temperature of 1400°C. The SEM analysis indicated the YIG ceramic grain growth and compactness as Ce concentrations increased. The XPS analysis indicated that the amount of Ce4+ out of the total Ce increased as the CeO2 doping increased, and the maximum value was more than 75.9% in the sample synthesis at 1400°C. Static leaching experiments were also conducted on the single Ce-doped garnet synthesized at 1400°C. The normalized LRCe and LRY release rates were approximately 10−4 and 10−5 g m−2 d−1 after 42 days, respectively. The chemical durability was comparable to other ceramic matrices (such as pyrochlore and zircon, among others). These results demonstrated that YIG ceramics are suitable for immobilizing HLW, such as Pu or U. Highlights The solubility of Ce in single-phase YIG was 32 mol% at 1400°C. Grain size and compactness increased Ce content. The concentration of Ce4+ in total Ce of sample could be over 75.9%. The obtained YIG ceramics exhibit excellent chemical stability. Novelty Statement Y3-xCexFe5O12 ceramics were prepared by solid-state sintering and the solubility, microstructure, and chemical durability were investigated. The solubility of Ce was 32 mol% at 1400°C. The obtained YIG ceramics exhibit excellent chemical stability.