On the impact of reactive solutes on radiation induced oxidative dissolution of UO2

The impact of 2-propanol (100 mM), NaCl (0.1 – 2 M) and Fe(II)(aq) (10 μM) on the radiation induced oxidative dissolution of UO2 is investigated experimentally by γ-irradiating a UO2 pellet immersed in aqueous solution containing 10 mM HCO 3 − together with one of the studied solutes and measure the U(VI) concentration in solution as a function of irradiation time. The solution was saturated with one of the following gases; Air, N2O, inert gas (N2 or Ar) in order to vary the experimental conditions and/or avoid the influence of oxygen. The results show that, in the presence of oxygen, 2 M chloride decrease the rate of UO2 dissolution whereas the dissolution rate increases somewhat in the presence of 100 mM 2-propanol. Under oxygen-free conditions both 2 M chloride, 100 mM 2-propanol and 10 μM Fe(II)(aq) decrease the rate of UO2 dissolution. The trends in dissolution rates were reproduced by calculations based on previously determined rate constants for UO2 oxidation and oxidant concentrations obtained from numerical simulation of radiolysis in the corresponding homogeneous systems (taking reactions between the different solutes and the products of water radiolysis as well as changes in oxygen solubility into account). However, the results indicate that we cannot fully account for the G-values in 2 M chloride solution or all reactions involving Cl− in the aqueous phase. This calls for further studies of the chloride system.