Thermally induced gallium removal from plutonium dioxide for MOX fuel production

A dry process for separating Ga2O3 from PuO2 - 1 wt% Ga2O3 powder was devel oped. PuO2-Ga2O3 powder was exposed to flowing Ar-6% H-2 at 600-1200 degree sC. Under these conditions, Ga2O3 is reduced to Ga2O, a volatile species. G a2O, which is stable in a reducing environment at temperatures greater than 800 degreesC, evolves and is collected downstream. Different process param eters were varied in an effort to optimize thermally induced gallium remova l (TIGR). Exposure temperature had the greatest effect on TIGR. Temperature s of at least 1000 degreesC were required to obtain discernible TIGR. As li ttle as 25 wppm Ga remained after processing PuO2 at 1200 degreesC. It is l ikely 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 sys tem. 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 supp orts this hypothesis. (C) 2000 Elsevier Science B.V. All rights reserved.