INVESTIGATION OF UO2 LEACHING BEHAVIOR IN GROUNDWATER USING A NUCLEAR MICROPROBE - PRELIMINARY-RESULTS

Rutherford backscattering spectrometry with a 1.5 MeV He-4+ microbeam was used to quantify the variation of the surface composition of sintered UO2 pellets submitted to groundwater corrosion in oxidizing conditions. MuRBS data indicate the transformation of UO2 both into higher oxides such as U4O9, U3O7, U2O5 and U3O8 and into hydrated and/or carbonated species. Comparison of these results with millibeam RBS and NRA experiments, scanning electron microscopy observations and calculations using the thermodynamics geocode PHREEQE suggests an oxidation/dissolution phenomenon controlled by precipitation of uranium insoluble compounds such as betaUO2(OH)2, rutherfordine, betaUO3 or CaUO4.