2018 | AFC ACCOMPLISHMENTS 96 Multi-modal microscopy of irradiated materials for advanced reactor development Principle Investigator: Dr. Kevin G. Field (ORNL) Collaborators: Dr. Benjamin P. Eftink (LANL), Dr.Tarik Saleh (LANL), Dr. Stewart A. Maloy (LANL) The deployment of advanced reactors will require materials which can withstand excess irradiation dose (>50 displacements per atom – dpa) at elevated tempera- tures for prolonged periods of time. Several candidate materials are under investigation for such applications including advanced ceramic-matrix composites and high chromium (>8 wt.% Cr) body centered cubic (BCC) ferritic/martensitic (FM) steels. FM steels are of significant interest due to their high resistance to radiation- induced swelling in typical advanced reactor conditions and generally low cost.To accelerate the development of the FM steel class, an alloy – HT9 – has been subjected to a series of advanced multi-modal microscopy experiments after high dose neutron irradiations to determine the root microstructural features which promote their high dose swelling resistance. Project Description: Neutron irradiation to FM steels generates a population of point defects (interstitials and/or vacancies) and small vacancy and interstitial clusters. Under elevated temperature irradiations these point defects and defect clusters can diffuse, annihilate, or agglomerate resulting in the formation of extended defects and promote additional phenomena such as radiation-induced precipitation. These defects and secondary features lead to degradation in the FM steels properties and could ultimately limit the lifetime of a component manufactured from FM steel in advanced reactor applications.The nucleation and growth of these radiation-induced or radiation- enhanced features is ultimately a complex process.To fully understand this process, and hence mitigate it, correlated microstructural examinations at length scales smaller than the width of a human hair are needed. Figure 1. Image montage at varying specimen tilts taken at 1° increments from 40° to -40° in a left-to-right, top-down fashion. Individual image scale: 336×336 nm.