Characterization of AA6061 Alloy Oxides Obtained in High Purity Water and in Diluted NaCl Solution

Spent aluminum-clad fuel elements from Argentine experimental nuclear reactors, manufactured with AA6061 aluminum alloy, are submitted to interim storage in demineralized water basins. In order to characterize the oxides grown during the storage, immersion tests of AA6061 samples were performed for periods from 3 days to 4 months at open circuit potential (OCP) and at room temperature in high purity water and in diluted NaCl solution. Electrochemical Impedance Spectroscopy (EIS) measurements were then performed on the oxide samples. The film thicknesses of oxides grown in high purity water, measured by eddy-currents technique, can be fitted to a sigmoidal curve reaching a limit value of ∼11 μm after 60 days of immersion, while the oxides obtained in diluted NaCl solution grow according to a linear law and reach a thickness of ∼26 μm after 120 days. From data obtained of fitting the EIS spectra with equivalent circuits, the thicknesses of the barrier layer present in the oxide were estimated for samples obtained in both media.