In-situ measurement of cerium reduction during calcination of Ce-doped phosphate phases

Crystalline ceramics have been suggested as potential immobilization matrices for high-level radioactive wastes generated in the late stages of the nuclear fuel cycle. Lanthanide orthophosphate ceramics have been shown to be excellent candidates for the incorporation of trivalent dopants such as Cm3+, Am3+, and Pu3+. It is further known, that monazites can accommodate tetravalent actinides. Their incorporation requires coupled substitution reactions, which preserve charge neutrality within the phosphate ceramic structure, such as An4+ + M2+ = 2 Ln3+. This can be achieved via varius synthesis routes. For U4+ and Th4+, several records of successful substitution exist. In contrast, for Ce4+ acting as an analogue for Pu4+ it has been argued that incorporation is extremely limited due to a change in the oxidation state. In the present study we aim at understanding such redox phenomena in Ce-doped phosphate phases at elevated temperatures.