Effect of a trivalent dopant, Gd3+, on the oxidation of uranium dioxide

The effect of a trivalent dopant, Gd3+, on the oxidation of doped UO2 was investigated using thermogravimetry and X-ray diffraction (XRD) analysis. Gd-doped stoichiometric UO2ʹs of various dopant contents [y=0–0.29 in (U1−yGdy)O2] were prepared. Weight gains by oxygen with increasing temperature for pulverized specimens were measured to obtain the oxidation kinetic curves. The oxidation kinetic curve for undoped UO2 shows a two-step reaction: UO2→U4O9 in the first step and U4O9→U3O8 in the second step. Decrease of the gradients of the oxidation kinetic curves for the first step with increasing content of Gd suggests that Gd dopant slowed down the reaction from (U1−yGdy)O2 to (U1−yGdy)4O9. Calculated O/(U + Gd) values from the weight gains and the deflection patterns of final stage of the oxidation revealed that the degree of oxidation from (U1−yGdy)O2 to (U1−yGdy)3O8 decreased linearly with increasing content of Gd. Such behavior as the slowdown and the inhibition were interpreted by the chemical states of U atoms in the lattice structures depending on doping of Gd3+.