Kinetics of hydrogen reduction of uranium trioxide

Document Type


Publication Date



The reaction between uranium trioxide (UO3) and pure hydrogen was investigated in the temperature range 575 to 750°. It was determined that, after an induction period in which the reduction rate reached its maximum value, the reaction proceeded at a constant rate which was independent of the thickness of the reduced uranium dioxide (UO2) layer. The rate-limiting step in the reduction was the reaction at the UO3-UO2 interface. Microscopic examination and X-ray powder patterns of samples partly reduced below 750° failed to reveal the presence of oxides intermediate between UO3 and UO2 at this interface. The activation energy for the reduction was determined experimentally to be 33.3 ± 0.3 kcal./mole. Absolute reaction rate theory was used to develop an analytical expression for the rate of reduction assuming an immobile adsorbed H2O layer as part of a (H2O-UO2) complex. The rate constants calculated with this model agreed favorably with experimental values when compared on an equivalent basis.

Publication Title

Journal of Physical Chemistry