Abstract
Helium is generally used as a coolant in Very-High-Temperature Reactors (VHTRs), but a small amount of impurity gas will inevitably be mixed in the primary coolant during construction, operation, and maintenance. At high temperature, these impurity gases will corrode with the alloy materials of the intermediate heat exchanger, resulting in the decline of the properties of the superalloy materials. This paper mainly studied the effect of methane in helium on the tensile property of Alloy 617 and Alloy 800H. Two impure helium environments are designed, one with low methane content (10 ppm), called He1, and the other with high methane content (350 ppm), called He2. The methane content of six typical international hightemperature reactors under normal operating conditions is generally not higher than 20 ppm. The two alloys were corroded at 950°C for 50 h in two different environments and the analysis showed that in He-2, Alloy 617 underwent severe carburization and its strength and plasticity were drastically reduced. Alloy 800H had no significant change in tensile properties due to its excellent resistance to carburization.
