The release of T from irradiated samples in a pure Ar atmosphere was investigated at temperatures of between 500 and 900C. Sintered samples with densities of between 75 and 95% of the theoretical value were irradiated with reactor neutrons to doses of up to 5 x 1020/cm2. Effective diffusion coefficients were deduced from the release data by using a model for diffusion out of a sphere. It was found that the effective diffusion coefficient decreased by about 3 orders of magnitude with increasing total neutron dose, levelled off at about 1018/cm2, and increased at doses of more than 1020/cm2. The decrease in T mobility was attributed to the effect of radiation defects which had been formed in the carbide. The activation energy of 210kJ/mol, for T diffusion in the irradiated carbide, was much higher than the value found for non-irradiated material. The effective diffusion coefficient also depended very strongly upon the density of the sintered material.

K.Schnarr, H.Münzel: Journal of Nuclear Materials, 1990, 170, 253-60