Effects of Preformed Oxide on Enhancing High-Temperature Oxidation Resistance of a Zirconium Alloy Cladding Tube

In this temperature range, the oxidation rate of a cladding becomes so high that brittle phases such as zirconium dioxide (ZrO2) and oxygen stabilized alpha zirconium (α-Zr(O)) are formed rapidly. In addition, a phenomenon called as breakaway oxidation can take place in a relatively short time. The breakaway oxidation causes rapid absorption of hydrogen to the metal substrate, and the absorbed hydrogen increases the concentration of oxygen in the metal substrate, causing the cladding to rapidly become brittle. In previous studies, it was reported that a zirconium alloy cladding tube with the high-temperature preformed oxide shows enhanced oxidation resistance during subsequent oxidation at 1000–1100 .deg. C. However, it has not been clearly accepted that how this kind of oxidation resistance enhancement can take place. Studying and understanding why these phenomena occur can give us a new solution to enhance the oxidation resistance of zirconium alloys at high-temperature. Three different types of tests were performed to confirm whether the cooling of the pre-oxidized specimens is essential for the oxidation resistance enhancement. Based on the weight gain results, it can be concluded that the cooling of the preformed oxide is essential for the preformed oxide to enhance hightemperature oxidation resistance.