Abstract Recent trends in reprocessing of spent LWR-fuel necessitate improved neptunium decontamination in uranium purification cycles. For the uranium purification cycles of the WAK plant and the EUROCHEMIC plant, respectively, the time dependent performance of the 2D-extractors has been calculated using the VISCO program for the mathematical modelling of solvent extraction processes. Results have been validated using data acquired in laboratory-scale extraction facilities and in the plant. Intercycle evaporation and thus high uranium concentration in the aqueous feed solution results in a high organic-to-aqueous flow ratio within the extraction part of the 2D-extractor. The required neptunium decontamination is achieved by allowing a considerable amount of uranium to leave the extractor with the aqueous raffinate rather than with the organic product stream. Thereby an increased amount of process control is required. As an alternative, neptunium can be sent directly to the aqueous raffinate stream by fee...