In order to provide missing data for storage of actinide containing solidified radioactive waste in deep underground dry geological formations such as salt domes, the tracer diffusion of U-233 was measured in single crystals of NaCl and in actual salt of a repository site (Asse mine in FR Germany). Experiments on interdiffusion between actinide-doped waste glasses and salt were also performed. The mean actinide penetration at the expected maximum temperature of the interface waste matrix/salt in 106years is extrapolated to be ≤ 1 μm for volume diffusion and ≤ a few μm for grain boundary diffusion.