Oxidation behaviour of plutonium and uranium mixed oxide powder. Oxidation process and oxidation rate

JNC have been manufacturing MOX fuels from Plutonium and Uranium mixed powder (1:1MOX) that were prepared by microwave direct denitration method. It is well known that MOX raw material oxidize in storage and manufacturing process due to heat generation by self-radiation. The oxidation process and rate of MOX powder were examined for three kinds of powders having different surface area. The oxidized samples were analyzed by X-ray diffraction measurement. The oxidation of MOX powders proceeded in two steps and the oxidation process changed depending on the surface area of the powder as follows. Process 1 (Surface Area: 2.24 m2/g). First Step: MO2→MO2+x→MO2.25 Second Step: MO2.25→MO2.25+M3O8-y. Process 2 (Surface Area: 5.59, 3.86 m2/g). First Step: MO2→MO2+x+MO3-z→MO2.25+MO3-z. Second Step: MO2.25+MO3-z→MO2.25+M3O8-y+MO3-z. The kinetic analysis of the oxidation was evaluated by Avrami-Erofeev equation. The equation of 0/M change on the MOX powder was obtained as function of temperature, keeping time and the surface area of the powder. (author)