The derivation of chemical-diffusion coefficients of oxygen in UO2+x over the range 180–300 °C. Spectroscopic procedure and preliminary results

Abstract

An optical spectroscopic technique has been developed to derive the chemical diffusion coefficient of oxygen in UO_2+x. Single crystals of UO_2+x have been oxidised in nitrogen containing 10% oxygen between 182 and 304 °C in a u.v.–visible absorption spectrophotometer. Spectra were recorded over the range 580–750 nm and the increase in x during oxidation was determined from the measured increase in the absorption coefficient. By solving the time-dependent diffusion equation for a square well, the chemical-diffusion coefficient of oxygen has been derived at four temperatures assuming a local surface stoichiometry after the passage of oxygen over the crystal. The results are consistent with other workers' high-temperature extrapolated data.