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Report No.
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Oxidation behaviour of plutonium and uranium mixed oxide powder; Oxidation process and oxidation rate

Kato, Masato  ; Uno, Hiroki*; Tamura, Tetsuya*; Endo, Hideo

JNC have been manufacturing MOX fuels from Plutonium and Uranium mixed oxide powder (1:1 MOX) 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 examination of isothermal and non-isothermal oxidation was carried out by TG-DTA. 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 : 2.24m$$^{2}$$/g) First Step : MO$$_{2}$$$$rightarrow$$MO$$_{2-x}$$$$rightarrow$$MO$$_{2.25}$$ Second Step : MO$$_{2.25}$$$$rightarrow$$MO$$_{2.25}$$+M$$_{3}$$O$$_{8-y}$$ Process 2 (Surface Area : 5.59, 3.86m$$^{2}$$/g) First Step : MO$$_{2}$$$$rightarrow$$MO$$_{2+x}$$+MO$$_{3-z}$$$$rightarrow$$MO$$_{2.25}$$+MO$$_{3-z}$$ Second Step : MO$$_{2.25}$$+MO$$_{3-z}$$$$rightarrow$$MO$$_{2.25}$$+M$$_{3}$$O$$_{8-y}$$+MO$$_{3-z}$$ The kinetic analysis of the oxidation was evaluated by Avrami-Erofeev equation. The equation of O/M change on the MOX powder was obtained as function of temperature, keeping time and the surface area of the powder.

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