Abstract
High-temperature gas-cooled reactors (HTGRs) with helium gas as the primary coolant have been considered as Generation IV nuclear power reactor systems. Several iron- and nickel-based superalloys, including Incoloy 800H, Hastelloy X, and Inconel 617, are potential structural materials in pressure boundary components, such as the intermediate heat exchanger (IHX) in an HTGR. Impurities in a helium coolant, such as H <sub>2</sub> O and O <sub>2</sub> , can interact with structural materials at working temperatures of >900 °C, causing serious degradation. This study investigates the oxidation behavior of three selected alloys (Hastelloy X, Incoloy 800H, and Inconel 617) in high-temperature, gaseous environments with various levels of O <sub>2</sub> and H <sub>2</sub> O. A series of corrosion tests were conducted at test temperatures of 650 °C, 750 °C, 850 °C and 950 °C under various coolant compositions of dry air, 1% O <sub>2</sub> , 10% humidity, and 50% humidity. © The Electrochemical Society.