The Advanced Materials and Manufacturing Technologies (AMMT) program within the Department of Energy (DOE) Office of Nuclear Energy has developed its current recommendation for promoting the use of combined ion irradiation and neutron irradiation for the accelerated qualification of materials to be deployed in nuclear reactors. This plan is intended to provide a collaborative path forward that can be adopted by academia, national laboratories, and industry, and has been developed with input from the regulatory research arm of the U.S. Nuclear Regulatory Commission (NRC). In the context of nuclear energy, the U.S. Department of Energy is responsible for nuclear energy-related research and development and promotion of nuclear technologies, while the U.S. Nuclear Regulatory Commission is an independent regulatory agency responsible for the safety of the civilian use of nuclear technologies. These two agencies thus have distinct but interconnected roles regarding the development and deployment of nuclear technologies. As the needs for the nuclear energy industry continue to evolve in the $21^{st}$ century, the pace that new technological solutions can be accepted by regulatory agencies is critical for timely industry adoption. New ways of collecting and utilizing data for regulatory purposes have become a necessity to accelerate the deployment of advanced nuclear technologies. To deploy new materials or materials manufactured with new technologies, such as additive manufacturing, materials must be evaluated for reactor-induced degradation from the combination of harsh temperatures, corrosive environments, and radiation fields. However, rapid deployment of materials necessitates accelerated testing methods rather than relying on years of neutron irradiation in a material test reactor. Ion irradiation has demonstrated success in reproducing material microstructure and select property evolution resulting from neutron irradiation with three to four orders of magnitude reduction in time and cost, making it an ideal candidate for accelerated irradiation testing. Because microstructure has a large impact on bulk material properties, in principle, accelerated testing results can be combined with modeling and simulation as well as limited neutron irradiation data at lower damage levels to form an accurate prediction of microstructure evolution and select properties under different neutron irradiation conditions and at higher damage levels. This document is divided into seven chapters designed to provide context governing both the scientific and regulatory aspects of the proposed goal. The discussion is aimed at a broad audience including researchers from industry, national laboratories, and academia. Thus, it is not intended to be a deep dive into any one topic, but to be a technical generalist level overview on the complex interplay of topics. The regulatory context can be summarized as follows: the NRC governs materials for nuclear reactors. While it relies on consensus standards from the American Society of Mechanical Engineers and other organizations for as-built material properties, radiation effects are encompassed within reactor-specific safety cases assessed by the NRC. In addition, several chapters discuss the fundamental basis for comparison of ion- and neutron-induced microstructures, testing methodologies, and the theory, modeling, and associated software to interpret radiation damage across length and time scales. The current state of the art for correlating ion irradiation and neutron irradiation results is discussed as well as needs anticipated for regulatory acceptance, such as software quality assurance programs. A forward-looking discussion is presented regarding additional challenges to deploying additively manufactured materials for advanced reactors, and why the regulatory acceptance of combined ion irradiation and neutron irradiation testing is even more important for additively manufactured materials than conventionally manufactured materials. The recommended path forward is presented as a conceptual framework of specific steps. In brief, the strategy entails developing an integrated ion and neutron irradiation test plan for the material property of interest based on the fundamental tenet of the linkage of microstructure and properties in materials. Physics-based modeling interprets ion irradiation data and predicts neutron irradiation microstructure and properties with uncertainty bounds. The first round of testing is sufficient for an initial licensing application using a risk-informed approach, while a minimum required neutron irradiation test plan reduces cost and time requirements. A surveillance program with witness specimens in-reactor provides additional data over time to improve model predictions to higher damage levels and further reduce uncertainty bounds, which can be used for license extensions or longer lifetimes in new license applications.
