Abstract: A process for the extraction of uranium and plutonium from spent nuclear fuels or breeder reactor materials. The spent nuclear fuels or breeder reactor materials are dissolved in nitric acid to provide an aqueous acid solution containing uranium, plutonium, neptunium, other transuranium elements, fission products, corrosion products, activation products and other contamination products. This aqueous acid solution is fed, as an aqueous phase, at a controllable flow rate into a liquid-liquid extraction apparatus also having an organic solvant phase flowing at a controllable rate. The organic phase contains an extraction agent. The temperature of solutions in the extraction apparatus and/or the concentration of the aqueous acid solution before the said aqueous acid solution is fed into the extraction apparatus, is adjusted to satisfy the following inequality: ##EQU1## where T.sub.E =the temperature of the solutions in the extractor (.degree.C.);U.sub.f =the uranium concentration of the feed solution (g/l);Pu.