Oxidation products of plutonium dioxide-uranium dioxide solid solutions in air at 750°C

Abstract

The oxidation in air at 750°C of solid solutions of plutonium dioxide and uranium dioxide, (Pu, U)O 2, containing up to 80 mole % PuO 2, has been studied. The reactions have been followed analytically by measuring weight changes accompanying the oxidations and crystallographically, by X-ray powder methods. Variable solid solution oxidation products are formed, either single-phase (cubic or orthorhombic) or two-phase (cubic + orthorhombic), according to the composition and physical state of the initial (Pu, U)O 2 solid solution. The cubic solid solutions are of the MO 2+χ type of a wide composition range, 40–100 mole % PuO 2, while the orthorhombic solid solutions are of an M 3O 8−χ type with a narrow composition range, 0–10 mole % PuO 2. No evidence is found for the formation of either pure PuO 2 or pure U 3O 8. Considerable cation mobility must occur during formation of two-phase oxidation products. An analytical and structural interpretation is given for the formation of variable oxidation products.