Mechanical and Microstructural Analysis of Incoloy 800H for High-Temperature Gas-Cooled Reactor (HTGR) Applications

The U.K. government's financial investment underscores its commitment to the research and development of high temperature gas-cooled reactors (HTGRs) (WNN.,2022), positioning them as the primary choice in nuclear technology. However, uncertainties persist regarding the selection of materials for specific components, as the high- temperatures associated with HTGRs make it challenging to identify materials capable of withstanding such extreme conditions. HTGRs have the capability to produce high-temperature outlet gas ranging from 950-1000 degrees C, utilizing helium as the primary coolant and a graphite moderator (Fujiwara et al., 2021). Nickel alloy 800H, known as Incoloy alloy 800H is a promising candidate that is under consideration for the use in heat exchangers, piping, and internals of the reactor. Incoloy 800H is ideally suited for temperatures up to 850 degrees C and holds codecertification for nuclear system applications, with approved reliability up to 760 degrees C. However, contradictions and a lack of research exist in understanding the microstructural effects on the mechanical properties of Incoloy 800H at elevated temperatures. (Maloy et al., 2019)