Coherent diffuse neutron scattering was used to monitor disorder in monocrystals of UO2.13 and UO2.14. At temperatures above 850K, the crystals were monophase. The presence of excess anions produced diffuse scattering. At 858K, there was an elastic diffuse scattering pattern which was explained in terms of the presence of uncorrelated simple clusters of defective anions. At 1573K, a quasi-elastic energy broadening of the diffuse scattering was attributed to the dynamic nature of the disorder. On the basis of these data, it was estimated that the O self-diffusivity in UO2.14 at 1573K was equal to 3.8 x 10-7cm2/s. This value was consistent with extrapolated published data for UO2.12 at up to 1573K. By assuming that thermally generated interstitials propagated in a similar manner in all of the compounds, it was deduced that the O diffusivity in the pure compound was equal to 2.5 x 10-6cm2/s at 2573K.

J.P.Goff, B.Fak, W.Hayes, M.T.Hutchings: Journal of Nuclear Materials, 1992, 188, 210-5