Nuclear Science User Facilities 48 CANada Deuterium Uranium (CANDU) Inconel X-750 spacers incur higher doses and He/dpa ratios than light water reactor (LWR) materials.They separate hot pressure tubes from cold calandria tubes, preventing low-pressure moderator from contacting hot pressure tubes. Segments at 330°C exhibit lower strength and ductility than 200°C segments. Lower temperature parts support fuel channels, preventing contact between hot and cold tubes. Weakening and embrittlement occur after 2/3 of the tubes’ expected lifetime. Inspected springs exhibited intergranular failure upon handling. Quantification of changes in failure stresses as compared to virgin materials is needed. Embrittlement occurs in Ni alloys with irradiation temperatures > 500°C, but there are few instances of low temperature effects. Failure mechanisms and degradation rates are essential for long term prediction of mechanical failure through appropriate models. Micro- scale testing will provide insight into the temperature dependence of embrittlement at operating temperatures that can then be applied to components subject to He embrittlement in all reactors. Project Description The objective of this research was to obtain quantitative mechanical properties of Inconel X-750 CANDU core components at two different irradiation temperatures and doses. A new in-situ scanning electron microscope (SEM) small-scale mechanical test, namely lift-out three-point bending, was developed and executed on active CANDU core components. Given the difficulties in manufacturing and testing multiple specimens to obtain good statistics from active bulk spring coils, the Characterization of CANDU Core Internals via Small Scale Mechanical Testing Peter Hosemann – University of California, Berkeley – The application of the Focused Ion Beam (FIB) to extract micro-scale samples of in-service components with pre-selected microstructures (i.e., individual grain boundaries) is a powerful technique that allows for insight into real-time mechanical testing observation of failure mechanisms, and the FIB research conducted at the MFC and the University of California, Berkeley moves this method to the forefront of the nuclear scientific community.