Nuclear Science User Facilities 26 Mukesh Bachhav Dr. Mukesh Bachhav has done research on three continents, but Idaho National Labora- tory is where he has found the tools essential to his efforts at high-reso- lution characterization of irradiated nuclear materials. Bachhav is an Atom ProbeTomog- raphy (APT) lead in INL’s Irradiated Materials Characterization Labora- tory (IMCL) at the Materials & Fuels Complex (MFC), an integral part of the NSUF network. A native of Nashik, India, he earned his doctorate in materials science from France’s University of Rouen and his master’s in physics from India’s University of Pune.While doing postdoctoral work at University of Michigan (another NSUF partner), Bachhav made use of the resources available at MFC and also in the Microscopy and Characterization Suite (MaCS) at the Center for Advanced Energy Studies (CAES), where NSUF leadership has its home. INL turned out to be “a perfect fit,” Bachhav said. NSUF’s Nuclear Fuels and Materials Library (NFML) and INL’s interest in elucidating irradiated nuclear materials at a nanoscale level to understand irradiation performance provided a rare opportunity to work in the Characterization and Advanced Post-Irradiation Examination Division at MFC. Much of his work is done with the APT instrument at CAES, a unique facility that allows analysis of “hot,” meaning radioactive, materials with ease.This enables research on nuclear fuels and materials to be performed on a routine basis. Bachhav was the lead author of an article, “Challenges and Opportuni- ties on Elucidating Irradiated Fuels with Atom ProbeTomography,” published Aug. 1, 2018, in the journal Proceedings of Microscopy & Micro- analysis. Co-authors included his IMCL colleagues Dr. Jian Gan, Dr. Lingfeng He and Dr. Brandon Miller, as well as Dr. Dennis Keiser of INL. The paper lays out the advantages that APT can bring to understanding microstructural evolution in nuclear fuel materials that have been subjected to extreme conditions. One of the main mechanisms guiding the micro- structural changes in fuels is damage associated with the formation and migration of fission products. This can lead to void formation and grain boundary segregation, which can cause fuel to lose integrity, they wrote. During irradiation in aggres- sive reactor conditions, interaction can occur between the fuel particle and the matrix in a dispersion fuel that results in the development of an interaction layer that is unstable under irradiation, which can contribute to fuel plate failure. To understand migration of fission products and their effect on fuel performance,APT is a unique