Abstract: Process for treating spent nuclear fuel (SNF) to make mixed metal oxides of UO3 and PuO2 to prevent nuclear proliferation. The process comprises the steps of (1) dissolving spent nuclear fuel in an acidic solution in the presence of an agent that reduces Pu+6 to Pu+4 and an agent that oxidizes Pu+3 to Pu+4; (2) extracting U+6 and Pu+4 from acidic solution with an organic solvent comprising a ligand that binds U+6 and Pu+4 and which is soluble in the organic solvent; (3) jointly extracting U+6 and Pu+4 from the organic solvent with an acidic aqueous solution; and (4) precipitating a mixture of U+6 and Pu+4 by adding a carboxylic acid to the acidic aqueous solution. The U+6 and Pu+4 precipitate is then be calcined to form a mixed metal oxide of UO3 and PuO2. Additional steps can result in the formation of a mixed metal oxide of UO3, PuO2 and NpO2 as well as the removal and isolation of technecium from the SNF.