Metal and oxygen mobilities during Zircaloy-4 oxidation at high temperature

Oxidation experiments have been carried out on Zircaloy-4 samples in water at 633 K and 200 bars and in dry oxygen at 633 K and 1 atm, in order to study the mobility of species in the growing oxide films. The transport of metal and oxygen was studied by using the inert gas implantation and the Rutherford backscattering spectrometry (RBS) techniques. For oxide thickness lower than the transition ones, both in water and in dry oxygen environment, the oxide thickening occurs only by oxygen migration. Nevertheless a substantial amount of Xe marker was lost during reoxidation in case of corrosion experiments made under high temperature water. This behaviour may be explained by the presence at the surface of the sample of a hydrated layer in which Xe diffusion is accelerated, specially in pressurised water. (orig.)