Design of a New Reactor to Work at Low Volume Liquid/Surface Solid Ratio and High Pressure and Temperature: Dissolution Rate Studies of UO 2 Under Both Anoxic and Reducing Conditions.

A flow-through experimental reactor has been designed in order to perform studies at both high pressure and high temperature conditions. A chromatographic pump is used to impulse the leachant throughout the reactor in order to work at very low flows but high pressures. Therefore, high surface solid to volume leachant ratios, similar to the ones predicted in the final repository, can be obtained. The reactor allows working at different atmospheres at pressures up to 50 bars. The temperature inside the reactor can be set using a jacket. Using this new reactor the evolution of uranium concentrations released from an UO 2 sample was studied at different conditions. The results show that at hydrogen pressures between 5 and 7 bars, hydrogen peroxide does not seem to significantly oxidize the uranium (IV) oxide. Uranium concentrations in those experiments remain between 10 −8 mol·l −1 and 10 −9 mol·l −1 .