Fluoride-conversion synthesis of homogeneous actinide oxide solid solutions

The synthesis of (U,Th)O₂ solid solutions at a relatively low temperature of 1100 °C using a new technique is described. First, separate actinide oxides were reacted with ammonium hydrogen fluoride to form ammonium actinide fluorides at room temperature. Subsequently, this fluoride was converted to an actinide oxide solid solution using a two-phase reaction process, which involved heating of the fluoride first at 610 °C in static air followed by heating at 1100 °C in flowing argon. Oxide solid solutions of UO₂ and ThO₂ were synthesized for a ThO₂ content from 10 to 90 wt %. Microscopic investigation showed that the (U,Th)O₂ solid solutions synthesized using this method had high crystallinity and homogeneity up to nanoscale.