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

Rutherford backscattering spectrometry with a 1.5 MeV He-4+ microbeam was used to quantify the variation of the surface composition of sinte red UO2 pellets submitted to groundwater corrosion in oxidizing condit ions. MuRBS data indicate the transformation of UO2 both into higher o xides such as U4O9, U3O7, U2O5 and U3O8 and into hydrated and/or carbo nated species. Comparison of these results with millibeam RBS and NRA experiments, scanning electron microscopy observations and calculation s using the thermodynamics geocode PHREEQE suggests an oxidation/disso lution phenomenon controlled by precipitation of uranium insoluble com pounds such as betaUO2(OH)2, rutherfordine, betaUO3 or CaUO4.