Critical database development of high dose microstructure evolution in irradiated advanced steels

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.