The release of uranium from three samples of UO2(S) with different particle sizes (100–300 μm, 900–1100 μm, pellet) has been studied as a function of time. In all cases, the same pH, ionic medium, temperature, and oxygen partial pressure were used.
Two distinctive trends were observed in the three cases, with a relatively fast initial uranium release followed, after 10–15 days, by a slower dissolution rate. The experiments were continued during 200 days; no change in the second dissolution rate was noticed.
The uranium released as a function of time has been successfully fitted with a mathematical expression which combines an oxidation-dissolution mechanism.