[en] The problem of heat-mass transfer in cold traps is solved to determine the efficiency of cold traps for the purification of circulated sodium in industrial and experimental reactors. The Navier-Stokes set of equations of motion, temperature distribution and impurity diffusion along the volume of the trap is solved numerically. Several physical peculiarities of the liquid flow in the trap are considered. It is shown that the hydrodynamics of the non-cooled trap differs radically from the cooled trap hydrodynamics. The calculation results obtained during the work is in a a good agreement with the experimental data of other authors