High-Temperature Oxidation of Zircaloy-4 in Air Studied with Labeled Oxygen and Raman Imaging

High-temperature oxidation of zirconium-based cladding materials is expected to be the primary cause of the fuel assemblies' degradation in spent fuel storage pool loss-of-cooling accidents. Here, high-temperature Zircaloy-4 oxidation has been studied through two-stage oxidation experiments using O-18 isotope. Particular attention is paid to the effect of a low-temperature pre-oxidation scale which aims to simulate the corrosion scale existing on spent fuel cladding. Raman imaging was used to investigate the O-18 distribution in the scales exposed either to O-18(2) or to O-18(2) + N-2 atmosphere at high temperature. Results were assessed against more conventional SIMS mapping. The use of the O-18 isotope tracer technique associated with micro-Raman mapping of the scales is demonstrated to be a powerful method to investigate the transport properties in the scales and will help to gain understanding of the kinetic differences between different pre-oxides.