Separation of uranium isotopes by accelerated isotope exchange reactions

In a process for separating uranium isotopes in multiple stages, each stage comprising the step of isotope exchange reaction wherein uranium(VI) and uranium(IV) compounds are contacted in a system containing a mixed solution of said compounds and the step of separating uranium(VI) compound enriched with uranium- 235 from uranium(IV) compound after said isotope exchange reaction, uranium(VI) and uranium(IV) compounds to be contacted in each stage after the first stage being formed by reducing a portion of respective uranium(VI) compound enriched with uranium-235 isotope separated in the preceding stage, the improvement which comprises effecting said isotope exchange reaction in each stage in the presence of at least one catalyst dissolved in said mixed solution under acidic conditions wherein the absolute value of the differential redox potential .DELTA.E is not more than one volt and the concentration of the catalyst expressed in moles per liter is in the range between 0.5 times .vertline..DELTA.E.vertline. and three.