Code Qualification of Alloy 709 for High Temperature Reactor Applications

Through a material down-selection and intermediate testing program, Alloy 709 (UNS S31025), an advanced austenitic stainless steel, was selected by the U.S. Department of Energy (DOE), Office of Nuclear Energy (NE), Advanced Reactor Technologies (ART) Program for qualification as a new Class A construction material in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section III, Division 5 for high temperature reactor components with high safety significance. A staged code qualification program was established by the DOE-NE ART Fast Reactor Program with the objective to develop Alloy 709 code cases with progressively longer component design lifetimes of 100,000, 300,000 and 500,000 hours, as sufficient test data has become available. Additional code development efforts are ongoing to support the design and construction of Alloy 709 components with lesser safety significance and the conceptual assessment of very long design lifetimes, e.g., 60 years. The data package for code qualification must contain a minimum of three commercial heats which represent the anticipated compositional ranges. In collaboration with two U.S. steel fabricators, the DOE-NE ART Program has successfully scaled up the production of Alloy 709 in rolled plate product form from a laboratory heat of 500 lb to three Alloy 709 commercial heats, totaling about 130,000 lb. A collaborative advanced materials development effort involving Oak Ridge National Laboratory, Idaho National Laboratory, and Argonne National Laboratory is ongoing to investigate the material properties for Alloy 709 and provide the technical basis needed to support its codification process. A significant portion of this effort focuses on creating a data package that is essential for establishing material-specific design parameters for Alloy 709, intended for use in sodium fast reactors, molten salt reactors, and gas-cooled reactors. Design data generation for the first 100,000-hour code case has been completed in 2024. A key component of this data package involves conducting tensile, creep, fatigue and creep-fatigue testing at elevated temperatures to develop the design parameters necessary for high temperate reactor design. This talk provides an overview of the development effort for the Alloy709 plate product, including its code qualification plan, the status of design data generation, and the development of high-temperature design parameters. A comprehensive review of the code case testing data package will be presented. The draft design parameters, including time-dependent and time-independent allowable properties, as well as fatigue and creep-fatigue performance, will be discussed. These properties will be compared with existing high temperature advanced materials to provide a complete understanding of Alloy709’s high-temperature mechanical performance.