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Quantum-mechanical methods are used to assess the energy barriers to dissociation and recombination reactions of UF 6  ↔ UF 5  + F and UF 6  ↔ UF 4  + F 2 . The energy characteristics of these reactions are found to be strongly asymmetric: the dissociation reaction barriers exceed the recombination reactions barriers by more than 4 eV. The equilibrium atomic configurations of F 2 , UF 4 , UF 5  and UF 6  have been determined using precision quantum mechanical calculations. The U-F bond lengths obtained as a result of the calculations are in good agreement with experimental data. It was found that the decay reaction UF 6  → UF 5  + F is either barrier-free, or the energy barrier for such a reaction is less than the resolving power of the method (~ 0.1 eV). For the decay of UF 6  → UF 4  + F 2 , there is an energy barrier with a height of about 0.3 eV. An initial approximation was proposed for the arrangement of UF 6  atoms in order to find the saddle points of the UF 6  dissociation reactions. In this initial configuration, all 7 atoms of the UF 6  molecule are located in the same plane. The F atoms are located at the vertices of a regular hexagon, and the U atom is at the center of such a hexagon. The results of this work can be used to determine the constants of thermal reactions of dissociation and recombination UF 6  ↔ UF 5  + F и UF 6  ↔ UF 4  + F 2 . These constants are necessary for modeling the physicochemical processes occurring during the enrichment of spent nuclear fuel ( SNF ).

Determination of the energy characteristics of the reactions UF 6 ↔ UF 5 + F and UF 6 ↔ UF 4 + F 2