Uranium dioxide leaching mechanism in a synthetic granitic groundwater in oxic conditions in function of S/V ratio at 96 C

UO, dissolution experiments under oxic conditions have been performed for one, two and five months at 96 C in function of surface to volume (S/V) ratio. The leachant is representative of a groundwater in equilibrium with a granitic medium. Two different results in function of time and S/V ratio were found. On the one hand, no sign of precipitation of secondary phases has been observed and uranium concentration is around 10-8 mol.1-1. On the other hand for the five months test, yellow perfectly crystallized phases, identified as schoepite, have been found on the surface of the UO2 pellets correlated to an uranium concentration equal to 2.77.10-4 mol.1-1. (orig.)