Effect of a pre-oxide on the high temperature steam oxidation of Zircaloy-4 and M5_Framatome alloys

Highlights: • Steam oxidation and hydrogen pickup at high temperature are influenced by a pre-oxide. • The effect of the pre-oxide depends on its thickness and pre-oxidation conditions. • Pre-oxide is partly reduced before a fresh oxide grows at high temperature. • Quantity of oxygen diffusing through the metal at high temperature is nearly the same either there is a pre-oxide or not. - Abstract: The effect of a pre-existing oxide layer formed at low temperature on the subsequent oxidation in steam at high temperature was studied for Zircaloy-4 and M5_Framatome alloys. Various pre-oxidation conditions (air at 550 °C, steam at 415 °C, static and flowing water at ∼350 °C), pre-oxide thicknesses (3–60 μm) and high temperature oxidation conditions (850–1200 °C, 55–9500s) were investigated. Pre-oxide has an effect on the oxidation kinetics and the hydrogen uptake at high temperature, depending on the pre-oxide thickness, the pre-oxidation conditions, the alloy and the high temperature oxidation conditions.