An optical spectroscopy method was used to measure the chemical diffusion coefficient of O in UO2+x. Single crystals were oxidized in an absorption spectrophotometer under a N2-10%O2 ambient at temperatures of between 182 and 304C. The spectra were recorded between 580 and 750nm, and the increase in x during oxidation was deduced from the measured increase in the absorption coefficient. By solving the time-dependent diffusion equation for a square well, the chemical diffusivity of O was measured at various temperatures. The diffusivity was between 10-11 and 10-14cm2/s at 304C and between 10-17 and 10-14cm2/s at 182C.

T.R.Griffiths, H.V.S.Hubbard, G.C.Allen, P.A.Tempest: Faraday Transactions 1, 1988, 84[12], 4377-86