Creep Properties of Alloy 617 in Air and Helium Environments at 900 .deg. C

A very high temperature gas reactor (VHTR) is one of the Gen-IV reactors which aim at the safe, long-lived, proliferation-resistant and economical nuclear power plants. Its high operating temperature of over 800 .deg. C enables high energy efficiency and the production of hydrogen gas using Sulfur-Iodine process. The heat of the primary helium (He) circuit transfers to the secondary helium loop through the intermediate heat exchanger (IHX). The IHX component needs high temperature creep resistance in the He environment, and also it requires good oxidation resistance, corrosion resistance, and phase stability at high temperatures. Currently, Alloy 617 is a prime candidate material because of its excellent mechanical properties at high temperature. Its superiority originates from solid solution strengthening by various additional components such as Co and Mo. Some researchers reported that the creep rupture time varied widely at high-temperature He environments. However, it has not been well established that the test temperature and minor impure gases in the He drastically affected the rupture time. Also, the creep data for Alloy 617 in the He environment are still insufficient for design application, and it is not yet well understood enough about the creep mechanism of the He effect. In this study, to provide creep data for Alloy 617 in the air and He environments, a series of creep tests was conducted with different applied stress levels at 900 .deg. C. Their creep properties were investigated and were compared