The present work focuses on the development of intensified small-scale extraction units for spent nuclear fuel reprocessing using advanced process engineering with combined experimental and modelling methodologies. It discusses a number of novel elements, such as the intensification of spent fuel reprocessing and the use of ionic liquids as green alternatives to organic solvents. The use of ionic liquids in two-phase liquid-liquid separation is new to the Multiphase Flow community, and has proved to be challenging, especially in small channels, because of the surface and interfacial properties involved, which are very different to those of common organic solvents. Numerical studies have been also performed to couple the hydrodynamics at small scale with the mass transfer. The numerical results, taken together with scale-up studies, are used to evaluate the applicability of the small-scale units in reprocessing large volumes of nuclear waste.