Abstract
The high-temperature gas-cooled reactor (HTGR) is deemed as the best candidate for next generation nuclear reactors. Helium is used as the coolant in the core of an HTGR that operates at temperatures of greater than 950 °C. Several iron- and nickel-based superalloys, including Alloy 800H, Hastelloy X, Alloy 617, and Alloy 625, with high corrosion resistance and superior mechanical strength are potential structural materials for the intermediate heat exchanger component in an HTGR. Impurities in the helium coolant, such as oxygen and water vapor, may lead to serious degradation in these alloys and increase their oxidation rates at high temperatures. In this work, the oxidation behavior of the selected alloys was investigated in high-temperature helium environments with various concentrations of O 2 and H 2 O. Preliminary results showed that relatively thick and continuous chromium oxide layers were observed on the surfaces of the tested alloys. Based on the results of mass gain and SEM analyses, Hastelloy X alloy and Alloy 625 exhibited the best corrosion resistance after all designated corrosion tests.