[en] The diffusion of liquid uranium into solid foils, 0.3 mm thick, was investigated in the temperature range 1160-1350⁰C, for reaction times up to 20 h. The tantalum foils were immersed in liquid uranium contained in zirconia crucibles. Uranium was found to cover the tantalum foils and climb upwards in amounts rising with reaction time and temperature. A scanning electron microscope study with microanalysis by EDAX revealed a multilayer structure. On the tantalum-foil surfaces, exposed to liquid uranium, layers form progressively inwards, under the outer uranium layers, in the following sequence: a uranium-tantalum layer (with a U:Ta ratio between 40:60 and 60:40) forms at 1160 ⁰C and 1185 ⁰C, and disappears completely at 1255 ⁰C; a columnar tantalum layer (containing <1W/O U); an inner uranium layer (at 1210 ⁰C and above); an inner tantalum-grain layer with uranium along grain boundaries (above 1210 ⁰C). The growth of the recrystallized columnar tantalum layer is related to the penetration of uranium as liquid into the solid tantalum foil. Cracks in this layer at 1300 ⁰C and above cause tears and failures in the tantalum. (author)