[en] In the paper we developed a separation model for a cryogenic distillation column of hydrogen and it's isotopes, deuterium and tritium. Using the law of mass diffusion for mixtures (deduced in the frame of elementary theory of transport phenomena) we computed the components concentrations on two phases: vapor and liquid for a separation unit (theoretical plate). The multicomponent coefficients of diffusion were computed considering a Lennard-Jones potential of interaction between molecules. There were determined the concentration distribution and the mass flux vectors on vapor phase