The separation between actinides and fission products could be realized by a pyrometallurgical liquid/liquid extraction process. Thanks to an oxide-reductive reaction, a mass exchange occurs at the interface between a polluted molten salt layer and a containment loquid metal layer. The aims of this project is to develop the diffusion process which occurs and the thermodynamics process associated to this phenomena. This work consist in two parts: -An experimental prototype industrial type installed in the laboratory. -A bibliography on diffusivity coefficients of pollutants in molten salts.