2018 | AFC ACCOMPLISHMENTS 146 There is an ongoing need to evaluate the effects of neutron irradiation on the structure and mechanical properties of existing and candidate nuclear reactor core structural materials. However, performing neutron irradiations is expensive, time consuming, creates radioactive material, and the available neutron irradiation facilities across the world have become much more limited. Using ion irradiations to estimate neutron irradiation effects has been a known technique for more than 40 years. Ion irradiations are quicker to perform, much less expensive, and do not produce radioactive material. But until recently it was not a favored technique because there was a concern that ion irradiations do not sufficiently estimate neutron irradiation effects. In recent years, there has been a strong push to improve ion irradiation techniques with the intent of providing a better simulation of neutron irradiation effects, and studies are underway to evaluate the effectiveness of using ion irradiations to simulate neutron irradiation effects. The results of one such study are presented here. Project Description: The work described here is a comparison of the microstructure (structure at the micrometer to nanometer scale that plays a significant role in the properties of structural materials) of the oxide dispersion strengthened ferritic steel MA957 (a candidate advanced material for nuclear reactor fuel cladding) after exposure to neutron irradiation and ion irradiation. It is part of a larger effort at PNNL to investigate, optimize, and use ion irradiations to estimate neutron irradiation effects to develop improved alloys for core structural materials in nuclear reactors. Being able to use ion irradiations as a first line irradiation effects screening tool allows for much more rapid and cost efficient development of advanced alloys. It has the potential to benefit all reactor types including existing light water reactors and future advanced nuclear reactors such as sodium cooled reactors and molten salt reactors.The development of such materials is very important because it makes for a more robust nuclear reactor that will operate more cost effectively. Accomplishments: The approach to evaluating the effectiveness of ion irradiations to simulate neutron irradiation effects on reactor core structural materials has been to compare to the microstructure of materials after neutron and after ion irradiation.This is a common approach that has been used several times over the last 40 years.An important difference with the work at PNNL compared to previous research is that the ion irradiations were conducted using optimized methods to simulate neutron irradiation effects.A key part of PNNL's contribution to the AFC program over the last eight years has been the optimization of ion irradiation techniques. The use of Ion irradiations to estimate how materials behave in a nuclear reactor core environment may allow for much more rapid development of advanced materials for reactor core structural components and fuel assemblies. Evaluation of the Use of Ion Irradiation to Simulate Neutron Radiation Effects in MA957 Principal Investigator: Jing Wang, PNNL Collaborators: Mychailo B.Toloczko, PNNL