2017 | AFC ACCOMPLISHMENTS 29 Figure 2. Measured cross- sections of an energy-resolved neutron imaging measurement for pixels corresponding to volumes with different 235 U enrichment levels. The measured data is fit with known cross-sections against areal densities of each isotope. The peak in the difference curve at 18.6 eV originates from a ~400 ppm contamination with W atoms, underlining the sensitivity of the method. Project Description: TheAPIE effort consists of three pillars: (1) Method development for fuel characterization with pulsed neutrons, (2) application of these techniques to actual fuels (in part witness samples for subsequent irradiation tests), and (3) development of pulsed neutron sources which could be deployed pool-side at a test reactor. Several milestone reports were submitted describing these efforts in detail.The application of the characterization tools to fuels guides development of synthesis routes, e.g. by detecting and quantifying the presence of contamination phases (e.g. UN in U-Si fuel forms) or by microstructural changes due to melting of a phase during sintering in a composite fuel (e.g. U3Si5 in a UN/ U3Si5 composite fuel). Characterization by the multitude of parameters mentioned above provides a detailed parameters set for the pre-irradiation state of specimen to be inserted into a test reactor for irradiation.While X-rays can in principle provide similar parameters, for nuclear fuels they only interrogate a few micrometers on the surface, which is in many cases not representative of the bulk. Furthermore, these bulk properties are of value for modeling efforts, e.g. describing the effects of temperature and irradiation on microstructure evolution. When applied to an irradiated fuel, the bulk characterization of all pellets in an irradiated rodlet will guide destructive examination by identifying the most interesting regions of the entire volume based on a multitude of parameters. A science-based development of e.g. accident tolerant fuels or transmutation fuels will accelerate fuel development while at the same time providing a rigorous basis for licensing, the ultimate goal of fuel developments, and thus contributes to a reliable, and economic operation of the nation’s current reactor fleet and next generation reactors.