Determination of Local Corrosion Kinetics on Hyper-Stoichiometric UO[sub 2+x] by Scanning Electrochemical Microscopy

Abstract

A method has been developed to determine cathodic reaction rates and the corrosion kinetics at individual substrate grains on the micrometer scale using scanning electrochemical microscopy measurements. By fitting experimental probe approach curves to numerically simulated curves, "standard" rate constants for the cathodic reduction reaction on the grains are determined. Because the cathodic reduction is coupled to the anodic behavior of the at the corrosion potential, these constants can be used to determine the corrosion kinetics of the substrate. The results quantitatively demonstrate that corrosion rate constants vary over a broad range , and that this range is determined by the degree of nonstoichiometry of the grains and the diversity of structures on the surface. Our results suggest that corrosion will be enhanced at nonstoichiometric sites, probably located at grain boundaries in the spent nuclear fuel, leading to higher rates for the release of radionuclides from these locations.