Advanced Characterization and Modeling of Nuclear Fuels: Microstructure, Thermo-physical Properties: Thermo-physical and Microstructure Properties of Nuclear Fuels Special Session - Early Career
Sponsored by: TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Energy Committee, TMS: Nanomechanical Materials Behavior Committee, TMS: Nuclear Materials Committee
Program Organizers: David Frazer, Idaho National Laboratory; Fabiola Cappia, Idaho National Laboratory; Tsvetoslav Pavlov, Idaho National Laboratory; Peter Hosemann

Monday 8:30 AM
February 28, 2022
Room: 202B
Location: Anaheim Convention Center

Session Chair: David Frazer, Idaho National Laboratory ; Fabiola Cappia, Idaho National Laboratory ; Tsvetoslav Pavlov, Idaho National Laboratory

8:30 AM  Invited
Investigation of Hot-cell Capable Thermal Conductivity Measurements for Ceramic Fuels: Troy Munro1; Justin Loose1; Brian Merritt1; Peter Hartvigsen1; Ryan Ruth1; 1Brigham Young University
    This presentation is focused on the current development, modeling, and implementation status of non-traditional thermal characterization techniques. These techniques are the Fluorescent Scanning Thermal Microscope (FSTM) and Raman thermometry-based techniques (RTT). The FSTM is a low cost, modular, laser-based device that uses variations in fluorescent light from a deposited dye to determine the thermal properties of a material. The FSTM has been specifically designed as a modular unit for use in hot cells. Results from the FSTM on reference materials are presented and compared to results from Idaho National Laboratory’s Thermal Conductivity microscope. Additional, FSTMv2 is presented to address the need for improved accuracy compared to the first design. A numerical comparison of potential uncertainties of multiple RTTs applied to UO2 are also presented to determine the suitability of using Raman-thermometry to measure the thermal conductivity of UO2.

8:50 AM  Invited
Thermal Stability of Uranium Compounds and Advanced Nuclear Materials under Extreme Conditions: Elizabeth Sooby1; 1University of Texas at San Antonio
    With a societal goal of moving toward a low carbon footprint, investigators across the globe are advancing clean energy solutions, and high temperature thermochemical stability is a hallmark property of many materials enabling technological advancements in the energy sector, particularly nuclear energy. Thermochemical attack of both structural and fuel materials is driven by high temperature oxidizing and/or reducing service atmospheres, resulting in some cases in bulk material failure. Presented are the experimental approaches to precision, high temperature testing of both fuel and moderator materials of relevance to the current fleet of reactors as well as proposed advanced reactor designs. The microstructure evolution of these materials following exposure to high temperature oxidizing and reducing atmospheres will be presented along with the experimentally observed thermochemistry governing the dynamic response of nuclear materials to extreme environments.

9:10 AM  
An Atomistic Study of the Anisotropic Elastic Response of Defects in Alpha Uranium: Yuhao Wang1; Benjamin Beeler2; Andrea Jokisaari3; 1University of Michigan Ann Arbor; 2North Carolina State University; 3Idaho National Laboratory
    The alpha-uranium phase can play an important role in the performance and structure evolution of metallic fuels under irradiation. However, an atomistic understanding of alpha uranium is still lacking in the areas of fundamental defect structural and transport properties, especially at non-zero temperatures. In this work, molecular dynamics is used to determine the energetic and thermodynamic properties of point defects in alpha uranium. The formation energy and crystallographically-dependent diffusion coefficients of single defects and small defect clusters were determined, along with the anisotropic thermal expansion and the heat capacity of a bulk crystal. The elastic response for different types of defects is evaluated by calculations of the volumetric strain, elastic dipole tensor, and λ-tensor. These results will serve as important inputs for mesoscale phase-field simulations and provide insight into the anisotropic growth of alpha uranium under irradiation.

9:30 AM  
Micromechanical Behavior of Thermally Loaded Monoclinic U-6Nb: Daniel Savage1; Bjorn Clausen1; Travis Carter1; Joshua White1; Sven Vogel1; Donald Brown1; 1Los Alamos National Laboratory
    Uranium alloyed with Nb enhances corrosion resistance and for 6 wt% Nb when cooled rapidly from austenite to martensite, a substantial ductility increase is observed compared to unalloyed U. The martensitic microstructure de-twins upon mechanical loading following variant selection rules and proceeds with a number of twin and slip modes which allow microstructure design by manipulating deformation paths. The martensite also exhibits massive, anisotropic thermal strains up to 2.5% and bulk expansion or contraction can be tailored through texture manipulation. During thermal loading, large intergranular stresses should exist due to large expansion or contraction of neighboring grains; however, the role of these stresses on property evolution is not understood. To reveal the coupling between microstructure and thermal behavior, insitu neutron diffraction of differently textured samples cycled from 4K to 473K will be presented. To help interpret insitu data, polycrystalline self-consistent modeling will be employed to isolate thermal and elasto-plastic contributions.

9:50 AM  Invited
Thermal Energy Transport in Defect-bearing and Uranium-doped Single Crystal Thorium Dioxide: Cody Dennett1; David Hurley1; 1Idaho National Laboratory
    Actinide fluorite oxides form an important class of nuclear fuel materials. Thorium dioxide is of particular interest as a fuel candidate due to its extremely high melting point and fixed tetravalent cation oxidation state. Potential operating environments, however, include high radiation fields which directly generate lattice defects or require uranium doping for fuel utilization. Defects and doping drastically influence thermal transport, a controlling safety and performance property. Little experimentally-validated understanding has been generated on the role of defect formation and doping chemistry on thermal transport due to the lack high-quality starting material. Here, single crystals of pure thoria are exposed to proton irradiation to generate defects, while a subset are grown with low uranium doping (maximum 16at%). The mesoscale thermal conductivity of damaged and doped crystals is measured using a spatial thermoreflectance technique. Experimental values are compared with calculated conductivity from thermal transport models, considering the relevant phonon scattering mechanisms.