The promise for developing new, advanced nuclear reactor concepts, and the extension of life of existing light water nuclear reactors relies on understanding how extended neutron irradiation can degrade materials that serve as the structural components in reactor cores. In high dose fission reactor concepts such as the sodium fast reactor (SFR), lead fast reactor (LFR), molten salt reactor (MSR) and the traveling wave reactor (TWR), structural materials must survive up to or over 200 dpa of damage at temperatures in excess of 400°C. A promising solution to achieving such high doses in a rapid and economical manner is high dose rate ion irradiation. The SNAP program is addressing the use of ion irradiation as a surrogate for neutron irradiation include accounting for rate effects, small irradiation volumes, accounting for transmutation and the lack of data to establish the equivalence., 2) characterization (both experimental and computational) of the evolution of the irradiated microstructure over a wide dose range relevant to fast and thermal reactors, and 3) establishment of the microstructure-property relationship for irradiated materials, and 4) engagement the worldwide radiation effects community through the creation of workshops and working groups to address ion irradiation techniques and the analysis of defects in the irradiated sample preparation and analysis of microstructure. Key elements of the program are A) both ion and neutron irradiation are performed on the same alloys/heats, B) both damage and transmutation effects are incorporated seamlessly into the irradiations, and C) the meshing of experiment and modeling efforts occurs across all length scales and all aspects of the program. This RTE project will focus on a set of alloys chosen because they are either candidate materials for advanced cladding (HT9) or similar to potential candidate alloys for fast reactors (NF616 and T91). Importantly, complementary neutron irradiation data exists for several of these alloy heats. Finally, they are amenable to inclusion in a fast reactor irradiation campaign designed to produce a substantive set of data set to allow for a comprehensive comparison of ion and neutron irradiation effects. This project will demonstrate the capability to evaluate the behavior of reactor materials at high (>80 dpa) irradiation doses. Key to this effort is benchmarking of the microstructures formed under ion irradiation and neutron irradiation by a combined experimental and analytical approach. This RTE will generate valuable data on the microstructure of candidate alloys exposed in reactor for comparison against that from ion irradiation using detailed post-irradiation examination at the Low Activation Materials Development and Analysis (LAMDA) laboratory at Oak Ridge National Laboratory. In total, the proposed experiments will require an estimation of about 48 hours for TEM lamella preparation and 72 hours for transmission electron microscopy. The final product will provide a path and a methodology for qualifying materials for service at very high doses.

The mission of the DOE Office of Nuclear Energy is to advance nuclear power to meet the nation's energy, environmental, and national security needs. This RTE focuses on the generation of data on high dose neutron irradiation in reactor for the purpose of benchmarking ion irradiation as a viable technique for rapidly advancing the development of materials for advanced reactor concepts and core structural components in life-extended LWRs. The focus on advanced cladding candidate alloys in this RTE addresses the goal of the Advanced Reactor Technologies (ART) program to conduct R&D on advanced reactor concepts. Since this is a primary candidate alloy for fuel cladding and duct components, the project also supports the mission of the Fuel Cycle Research and Development (FCRD) program to conduct R&D to develop sustainable fuel cycles. The key aspect of this research is the availability of high dose neutron data to compare with ion irradiation. The work in this RTE will characterize the irradiated microstructure in samples irradiated up to 86 dpa, thus potentially extending the available database for materials certification for advanced reactors. While these experiments will greatly expand the alloys and conditions being conducted under the core Simulating Neutrons with Accelerated Particles (SNAP) program, they are a means to generate the latest database on microstructural evolution on single-heat alloys. They are also highly significant in that they are the highest dose samples from a fast reactor other than FFTF to be part of the NSUF program. This database would provide the first high dose (>50 dpa) neutron irradiated results in HT9 and T91 (though NF616) since the FFTF and EBR-II irradiations that ceased more than two decades ago with the HT9 material being of the same heat as that characterized in the FFTF irradiation program. The benefit from performing this research lies in the examination of unique high dose neutron irradiated material which will add to our understanding of the behavior of these materials after high doses.