The influence of vacuum annealing on the uranium–hydrogen reaction

•Apparent activation energies of the U–H2 reaction.•Enhanced H2 reactivity occurs with vacuum annealed uranium.•Transition from nucleation to growth mechanisms is demonstrated.•Elevated nucleation kinetics affords the enhanced H2 reactivity observed.

The constant pressure hydriding kinetics of uranium have been measured as a function of temperature for as-polished and vacuum annealed uranium between 65 °C and 385 °C. Enhanced hydrogen reactivity was observed for vacuum annealed uranium between 65 °C and 120 °C and is the result of elevated nucleation kinetics promoting steady state kinetics.