Method for increasing the lifetime of an extraction medium used for reprocessing spent nuclear fuel and/or breeder materials

In a method for increasing the lifetime of an extraction medium containing an organophosphorus acid ester and a hydrocarbon, and being used for reprocessing spent nuclear fuel and/or breeder materials, by removing from the extraction medium impurities resulting from chemical and/or radiolytic decomposition and complex compounds of such impurities with radionuclides by washing the extraction medium with an aqueous wash solution, the improvement comprising bringing the extraction medium, after use, into intimate contact with an aqueous hydrazine hydrate wash solution having a concentration of between about 0.1 molar and 1.0 molar, at a temperature between about 20.degree. C to about 75.degree. C, and then separating the aqueous hydrazine hydrate wash solution from the extraction medium.