Accelerating Assessment of High Temperature Helium Embrittlement in Nickel-bearing Structural Materials

High temperature helium embrittlement (HTHE) is known as a major performance issue for nickel (Ni)-bearing nuclear structural materials upon neutron irradiation due to the severe reductions in ductility and shortening of creep life, posing threats to the safe operation of reactors. The mechanistic understanding of HTHE for reactor structural materials, however, remains limited due to the 1) time- and cost-consuming neutron irradiation to produce high concentration helium (He) in materials; and 2) the lack of an available experimental dataset from a systematic investigation of the temperature, stress, and He concentration dependence of HTHE. This project will focus on 1) developing and demonstrating a transformational approach, tritium charging, to introduce He into materials in a time and cost-efficient manner than neutron irradiation, and 2) combining small-scale mechanical testing and advanced electron microscope characterization with multiscale modeling to establish HTHE microstructure-properties relationship in austenitic stainless steel (SS) 316 and Ni-based X-750 alloy. The ultimate goal is to a) mature the tritium charging approach for inducing He in nuclear structural materials in a cost- and time efficient manner; b) gain insight into HTHE by exploring its dependence on the temperature, He concentration, and stress levels. The success of this project will greatly profit the development and qualification of nuclear structural materials for advanced nuclear reactors through accelerating assessment of He effects on materials.