A single-step process for producing solid uranium oxide and gaseous HF from UF.sub.6 which comprises bringing together two gaseous reactant streams, one of said streams comprising UF.sub.6 optionally admixed with oxygen as O.sub.2, and the second reactant stream comprising a mixture of hydrogen as H.sub.2 or as a hydrogen-containing compound and oxygen as an oxygen-containing compound, said gaseous reactant streams being brought together at a temperature and composition such that the UF.sub.6 is converted rapidly by flame reaction into readily separable solid uranium oxide and a gaseous HF product.