The diffusivity of 133Xe in the pure oxide, and in samples which contained 0.5wt%Nb2O5 or 0.2wt%TiO2, was measured at temperatures ranging from 1000 to 1600C by using a post-irradiation annealing technique. The irradiation dose was 1.2 x 1017 fissions/cm3. The effect of the O potential upon the diffusivity in UO2 was also studied at 1400C. It was found that the effect of adding Nb2O5 and TiO2 was to increase the diffusivity by factors of 50 and 7, respectively. The results could be described by:

UO2:     D (cm2/s) = 4.0 x 10-8 exp[-264(kJ/mol)/RT]

UO2-0.5wt%Nb2O5:     D (cm2/s) = 4.6 x 10-5 exp[-306(kJ/mol)/RT]

UO2-0.2wt%TiO2:     D (cm2/s) = 5.0 x 10-7 exp[-272(kJ/mol)/RT]

The diffusion coefficient for un-doped material was increased by a factor of about 3 upon increasing the O potential from -556 to -391kJ/mol at 1400C. Over the same range of O potential, the corresponding O/U ratio changed from 2.000 to 2.001.

K.Une, I.Tanabe, M.Oguma: Journal of Nuclear Materials, 1987, 150, 93-9