2017 | AFC ACCOMPLISHMENTS 28 Nuclear Fuel Characterization with Pulsed Neutrons Neutrons are a unique probe to interrogate entire fuel pellets, providing rich information on parameters ranging from crystallographic parameters (e.g. atomic positions, thermal motion parameters, strains), to meso-scale parameters (e.g. dislocation densities), to micro-structural features (e.g. weight or volume fractions of phases, grain orientation distribution or texture), to macroscopic features (e.g. dimensions, voids, cracks, isotope densities). Furthermore, the ability to penetrate shielding containers offers the opportunity to conduct this characterization on highly radioactive materials, ultimately providing detailed characterization of the same specimen pre- and post-irradiation. Pulsed Figure 1. Neutron computed tomography (CT) of UN/U3Si5 and U3Si5 fuel pellets with different enrichment levels. While the thermal neutron tomography, as available at a reactor, does not distinguish the differences in enrichment levels of the middle and lower pellet (8.84% and 0.2% enrichment, respectively), the reconstruction of 235 U and 238 U densities clearly provides this information. neutrons, such as provided by the LANSCE spallation neutron source, provide distinct benefits over the polychromatic neutron flux provided by a reactor source.The Advanced Post- Irradiation Examination (APIE) efforts at LANL have developed novel techniques, such as energy-resolved neutron imaging, and applied both novel and established techniques, such as neutron diffraction, to nuclear fuel forms ranging from ceramic fuels (oxides, nitrides, carbides, silicides) to metallic fuels (transmutation fuels, CONVERT fuels). In the future, availability of intense pulsed neutron sources may allow to apply the developed techniques pool-side at a research reactor. Here we summarize these efforts.