Lattice and grain-boundary diffusion of uranium ions in polycrystalline UO2 was measured at 1900 to 2150C using 237U tracer and the sectioning method. The penetration curve consisted of two regions. In the region near to the surface, lattice diffusion and grain-boundary diffusion made a contribution to the concentration of diffusants. In the second region, whose penetration depth was greater than the first, grain-boundary diffusion was dominant, and lattice diffusion was negligible. The lattice diffusion coefficient was given by:

D(cm2/s) = 5.82 x 10-5 exp[-72700/RT]

The grain-boundary diffusion obeyed:

dD(cm3/s) = 5.19 x 10-9 exp[-47200/RT]

S.Yajima, H.Furuya, T.Hirai: Journal of Nuclear Materials, 1966, 20[2], 162-70