2018 | ANNUAL REPORT 101 Nuclear Science User Facilities (NSUF)- access-only project on microstructure characterization (TEM and APT) have been completed on neutron-irradiated Fe, Fe–Cr binary model alloy, Fe–9Cr– 0.1C and Fe–9Cr–0.5C ternary model alloys, complex F/M alloysT91, HT9 and ODS MA957.The PIE work spans over 6 years, andTEM characterization was carried out using several electron microscopes at multiple facilities: MaCS (FEITecnaiTF30-FEG STwin STEM) at the Center for Advanced Energy Studies (CAES), the Electron Microscopy Labo- ratory at Idaho National Laboratory (INL) (JEOL 2010 LaB6TEM), Irradi- ated Materials Characterization Labora- tory at INL (FEITitanThemis 200 FEG-STEM), and the Low Activation Materials Design and Analysis Labora- tory at Oak Ridge National Laboratory. The APT characterization was carried out using a LEAP 4000× HR at MaCS. Collaborating with two beamlines (1-ID and MRCAT 10-ID) at Argonne National Laboratory’s APS, in situ tensile tests with synchrotron WAXS and small-angle X-ray scattering (SAXS) have been completed on both control samples and neutron-irradiated Fe, Fe–9Cr, Fe–9Cr–0.1C, Fe–9Cr–0.5C, Fe–12Cr–0.2C, and Fe–12Cr–0.5C alloys. For the experiments at the Materials Research Collaborative AccessTeam, a customized glovebox was built for the in situ tensile tests. This set of novel experiments will provide significant new insights on the effects of neutron irradiation on the microstructure and plastic defor- mation mechanisms. An RTE project on measuring the nanohardness of neutron-irradiated Fe–Cr–C model alloys has also been completed, through collaboration with Dr. Peter Hosemann’s Nuclear Materials Laboratory at University of California, Berkeley.The data are being used to correlate the irradi- ated microstructure with changes in mechanical property. An NSUF-access-only project has also been initiated with North Carolina State University to measure the early stage of defect evolution in low- dose (e.g., 0.01 dpa and 0.1 dpa) specimens using PAS.At such low doses, a significant fraction of defects produced by neutron irradiation has not evolved into clustered form that can be resolved by conventionalTEM. The PAS technique offers the possi- bility to examine small vacancy-type clusters.The experiments are ongoing at North Carolina State University. Future Activities