A centrifugal contactor of unique design has been developed for solvent extraction processing of high-plutonium-content fuels. The unit has a vertically suspended rotor that has a 4-in. inside diameter and is 15 in. long (with a 12-in.-long separating zone). Aqueous and organic phases are fed into the annulus between the contactor casing and the spinning rotor and are mixed by skin friction. The mixture flows down the annulus and then up through an orifice in the bottom of the rotor. The phases are separated by centrifugal force as they flow up the inside of the rotor and are discharged at the top. Separating capacities (throughput) ranged from 4.5 gal/min at 2000 rpm to 15 gal/min at 3500 rpm. Essentially 100% stage efficiency was demonstrated in extraction and stripping of uranium between nitric acid and 30% tri-n-butyl phosphate in n-dodecane diluent. The basic annular-mixer design is suitable for contactors with larger or smaller diameters.