Thermally induced gallium removal from plutonium dioxide for MOX fuel production

A dry process for separating Ga2O3 from PuO2 – 1 wt% Ga2O3 powder was developed. PuO2–Ga2O3 powder was exposed to flowing Ar–6% H2 at 600–1200°C. Under these conditions, Ga2O3 is reduced to Ga2O, a volatile species. Ga2O, which is stable in a reducing environment at temperatures greater than 800°C, evolves and is collected downstream. Different process parameters were varied in an effort to optimize thermally induced gallium removal (TIGR). Exposure temperature had the greatest effect on TIGR. Temperatures of at least 1000°C were required to obtain discernible TIGR. As little as 25 wppm Ga remained after processing PuO2 at 1200°C. It is likely that a further reduction in retained Ga can be attained by increasing the processing temperature. Ga removal was shown to increase with process time. However, the benefit in processing beyond 4 h is limited for this system. The lack of effect of sample volume and gas flow rate on TIGR suggests that Ga removal is limited by mass transport within the powder particles. The fact that Ga removal is less efficient in more coarse PuO2 powders supports this hypothesis.