Effect of preoxidation on the zircaloy-4 oxidation behavior in steam-water mixture between 700℃ and 850℃

Abstract

Experiments and numerical analysis have been performed to investigate the preoxidation effect when zircaloy-4 specimen were oxidized at a higher temperature after a period of exposure at a lower temperature. The oxidation experiments were done between $700^\circ C$ and $850^\circ C$ after preoxidation at $650^\circ C$ in steam-water mixture for 600 seconds and 1800 seconds. As the preoxidized layer thickness increases, the oxidation rate at higher temperature becomes lower than that of as-received claddings. And oxidation rate transition region exists in the preoxidized specimens, the region disappears rapidly as oxidation temperature increases. This effect appears clearly at lower temperature. In the numerical analysis, the governing equations are one-dimensional coupled diffusion equations and stresses in the oxide generated during oxidation are neglected. In this analysis, the growth rate of oxide layer thickness and weight gains was affected by the preoxidized layer thicknesses. The preoxidation effect was explained by the oxide defect structures existing at the temperature ranges considered.