BY

The Very High Temperature Reactor (VHTR) is one of the Gen-IV reactor design concepts which embody a common goal of providing safe, longer lasting, proliferation-resistant, and economically viable nuclear energy. One of the biggest challenges in the research and development of Gen-IV reactor systems is the performance and reliability issues involving structural materials for both in-core and out-of-core applications. Currently, Ni-based superalloy alloy 617 (Inconel 617) and alloy 230 (Haynes 230) are considered as the leading metallic candidate materials for applications in the VHTR because of their favorable mechanical properties at elevated temperatures. The major damage mechanism for materials used in the VHTR is predicted to be creep-fatigue damage, which arises due to startup and shutdown or power transients during normal operation. The mechanism of synergic interaction between creep and fatigue is not well understood and there are no effective modeling methods for predicting the creep-fatigue life of both alloys at present. To better understand and address these issues, Low Cycle Fatigue (LCF) and creep-fatigue tests of alloy 617 and alloy 230 were conducted in this study. Creep-Fatigue lif