Uranium self-diffusion in UC doped with Y, Zr, La or Ce

Abstract

Metal diffusion in UC and (U, Pu) C is increased at intermediate temperatures (e.g. 1200 to 1600°C) by factors of between 10 and 1000 by small additions of impurities (e.g. 0.1 to 2% of Fe, Ni, Ta). This can be explained by impurityvacancy interactions. All impurities studied so far had smaller atomic sizes than the substituted U and Pu atoms. In the present work, the effect of the bigger impurity atoms La and Ce on uranium self-diffusion in UC 1 ± x is studied. Further data are reported on Zr and Y as additives. The results show that Zr, Ce, and possibly Y can decrease metal atom self-diffusion rates. This effect can, however, easily be overcompensated by other impurities such as Fe and W which increase uranium self-diffusion. There is no obvious relation between the enhancement or diminution factor of the impurities and the lattice parameter of the doped carbide or the atomic size of the impurity atom.