LEACHING OF URANIUM-DIOXIDE UNDER CONTROLLED REDOX CONDITIONS

UO2 leaching tests have been performed in granitic groundwater in orde r to assess the alteration mechanisms involved and particularly the ef fectiveness of the control of uranium solubility by alteration product s. A special attention was payed to synthesize a leachant, characteris tics of which correspond as much as possible to natural deep groundwat er (pH, Eh, concentration of complexing anionic species such as CO32-) . Under oxidising conditions uranium solubility seems effectively cont rolled by the formation of hydrated and carbonated species while under reducing conditions, uranium content in the leachate remains as low a s 10(-11) mol/l giving no evidence for the formation of a solubility c ontrolling-secondary phase.