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

Abstract

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 18O 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 18O distribution in the scales exposed either to 18O2 or to 18O2 + N2 atmosphere at high temperature. Results were assessed against more conventional SIMS mapping. The use of the 18O 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.