Abstract: The invention relates to a process for the determination of uranium (VI) or dialkyl dithiophosphoric acid present in an organic solvent.In this process, a dialkyl dithiophosphoric acid or a uranium (VI) salt is added to the organic solvent so as to convert all the uranium or dialkyl dithiophosphoric acid present in said solvent into a mixed uranium (VI) - dialkyl dithiophosphoric acid-organophosphorus compound complex. The optical density of the solvent containing the complex in solution is measured so as to determine the concentration of this solvent in the complex, together with its uranium dialkyl dithiophosphoric acid content.Application to the determination of traces of uranium in tributylphosphate obtained from the reprocessing of irradiated fuels.

Abstract: Process for the recovery of the ruthenium present in an aqueous nitric solution, wherein the ruthenium is extracted in an organic solvent by contacting the nitric solution with an organic phase comprising an organophosphorous compound having at least one electron donor sulphur atom in the presence of a compound able to displace NO.sup.+ ions of the ruthenium complexes present in the nitric solution. Application to the recovery of ruthenium contained in a nitric solution obtained by dissolving irradiated fuel elements.