b'2.2 LWRs FUEL DEVELOPMENTCrystal Structure Characterization of U-Si Accident Tolerant FuelsPrincipal Investigator: Sven C. VogelTeam Members/ Collaborators: Tashiema L Ulrich, Joshua T. White, A. David R. Andersson and Theodore M. BesmannFigure 1. Visualization of the refined crystal structure of U 3 Si 2+xoverlaid with the difference Fourier maps at room temperature (a), 1273 K (b) and room temperature after heating (c). U1 sites are blue, U2 are green and Si are red.Datasets needed asD ecades of research andthermal expansion anisotropy, defect operational experiencebehavior, radiation damage, and inputs for silicide-basedhave produced an extensivefuel-cladding interactions, among fuel performance codesdatabase supporting the performanceothers. The goal of the project is have been providedof oxide fuel during normal powerto provide the datasets needed for through neutronoperations and during postulated acci- fuel performance codes that model diffraction experimentsdent conditions. Achieving the goalthe aforementioned properties. The and DFT calculations. of developing advanced fuel conceptsexperimental objectives of the project that meet the Department of Energyare: 1) investigate the crystal structure (DOE) objectives of being robust,of U 3 Si 2and other compounds as a demonstrating high performance, andfunction of temperature to provide are more tolerant of accident condi- datasets for the lattice parameters, tions than current fuel systems willanisotropic atomic displacement require a thorough understandingparameters, defects (interstitial of the intrinsic properties of theatoms), and atomic positions as a constituent materials. Unlike oxidefunction of temperature, 2) provide fuel, the knowledge on non-oxideinformation regarding the solubility fuel concepts such as uranium silicidelimit as a function of temperature and contains gaps and contradicting infor- composition by testing stoichiometric mation. Specifically, there are concernsU 3 Si 2as well as hyperstoichiometric regarding the stability of the crystalU 3 Si 2+x . The objective of this research structure for the uranium sesquisilicdeis to use density functional theory (U 3 Si 2 ) phase, which is of interest as(DFT) calculations to predict the a component for non-oxide accidenturanium and silicon defects and their tolerant fuel concept. formation mechanisms and validate Project Description: against experimental data collected by Understanding the crystal structure ofneutron diffraction. The data obtained phases in the U-Si system, in partic- from the successful completion of ular the U 3 Si 2structure, is importantthis project can directly be used in as it influences fuel properties such asfuel performance modeling to assess fission product location and transport,the performance of silicide based fuel compared to the current fuel system.44 2020|AFC ACCOMPLISHMENTS'