XPS studies of UO2 oxidation by alpha radiolysis of water at 100deg C

The effect of alpha radiolysis of water on the oxidation and dissolution of UO2 was studied at 100deg C as a function of alpha-field strength and water chemistry using X-ray photoelctron spectroscopy. In N2-purged solutions the oxidation of UO2 increases with the strength of the alpha flux; an alpha flux greater than or equal to that from a 250-μCi americium-241 source leads to oxidation of UO2 beyond the UO2.33 (U3O7) stage, and an alpha flux equal to that from a 5-μCi source does not result in UO2 oxidation beyond the UO2.33 stage. The presence of dissolved H2 in water, at a concentration ≥ 1.6x10-4 mol dm-3, reduces the oxidation and dissolution of UO2 due to alpha radiolysis at temperatures ≥ 100deg C. It is concluded that the radiolysis of groundwater at ≅ 100deg C, due to the alpha flux associated with used CANDU fuel, is unlikely to make a significant contribution to its oxidative dissolution in the geological disposal vault planned in the Canadian Nuclear Fuel Waste Management Program. (orig.)