Long-term corrosion of Zircaloy before and after irradiation

Recently analyzed long-term Zircaloy autoclave corrosion data were used to develop new Zircaloy corrosion correlations. Twenty-two different autoclave tests were analyzed. The tests included specimens from 46 different heats, of both Zircaloy-2 and Zircaloy-4. The material conditions included different heat treatments and various prefilms. Approximately 14500 data points were generated. Maximum exposure time was 10507 days (approximately 29 yr) in a 316 °C, test and maximum weight gain was 1665 mg/dm2 (approximately 114 μm of oxide film) for a 338 °C experiment. A single linear post-transition rate constant was determined in tests where maximum corrosion film thicknesses did not exceed approximately 30 μm. At the highest temperatures, where oxide film thicknesses in excess of approximately 30 μm were generated, the post-transition corrosion data can best be described by two successive linear equations, each active over a different range. Special in-reactor tests demonstrated that accelerated in-reactor effects on corrosion dissipate after growth of an additional oxide film, on the order of the thickness of the pre-transition oxide layer.