Investigation of the Reaction Path from UO2 to UF6 using Density-functional Theory

Abstract A detailed investigation of the reaction mechanism for UO2 reacting with F2 to form UF6 is performed by using density functional theory (DFT). We divide the whole reaction chain into four main steps, UO2+F2→UO2F2, UO2F2+F2→UO2F4, UO2F4→UF4+O2and UF4+F2→UF6. Contrary to what has been mostly expected that F2 molecule should directly replace two O atoms in UO2 molecule, two F2atoms actually combine with UO2 successively in the first two steps. The third step is relatively complex and one F atom in UO2F4 molecule plays a key role of carrying an O atomclose to the other O atom. In last step, F-F bond in F2 molecule fractures and two F atoms are bonding with U atom in UF4 molecule successively. Spin-flip appears in two elementary reactions owing to the existence of heavy atom U.