Advanced Characterization and Modeling of Nuclear Fuels: Microstructure, Thermo-physical Properties: Poster Session
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

Tuesday 5:30 PM
March 1, 2022
Room: Exhibit Hall C
Location: Anaheim Convention Center

Session Chair: David Frazer, Idaho National Laboratory ; Tsvetoslav Pavlov, Idaho National Laboratory; Fabiola Cappia, Idaho National Labortory; Peter Hosemann, University of California, Berkeley

N-1: 3D Reconstruction and Quantification of Oxide Nano-porosity in Zirconium Alloys: Hongliang Zhang1; Adrien Couet1; Taeho Kim1; William Howland2; 1University of Wisconsin-Madison; 2Naval Nuclear Laboratory
    In the corrosion of Zirconium alloy, the oxide grows at a decreasing rate until reaching critical thickness, followed by the sudden loss of the protective property and a new cycle of oxide growth. The oxidation-induced pores in oxide may provide pathways to oxidizing species. TEM is commonly used to determine pore density and size. However, some of the small-sized pores are invisible in TEM at only one angle. Manually counting pores will also bring some artifacts. We precisely quantify the oxide porosity in corroded Zircaloy-4 as a function of exposure time and temperatures using machine-learning-based quantification. The size, spatial distribution, morphology, and interconnectivity of the pores are obtained and quantified through the 3D reconstruction. Furthermore, the chemical composition in different regions of the oxide is studied using APT and correlated to pore distribution to further our understanding of alloying elements effects on corrosion.

N-2: An Experimentally Validated Mesoscale Model for the Effective Thermal Conductivity of UZr Fuels: Monika Singh1; Timothy Coffman1; Fergany Badry1; Moiz Butt1; Mohammed Gomaa Abdoelatef1; Katie Anderson2; James Jewell2; Rory R. Kennedy2; Collin J. Knight2; Mitchell Meyer2; Sean McDeavitt1; Karim Ahmed1; 1Texas A&M University; 2Idaho National Laboratory
    The effective thermal conductivity of nuclear fuels strongly depends on the underlying microstructure. We conducted a combined experimental and computational work to investigate this relationship in UZr fuels with different microstructures and theoretical densities. A microstructure informed model was developed to simulate effective thermal conductivity of UZr fuels at different temperatures and porosity levels. The model accounts for the thermal resistance of the interfaces and able to predict the effective conductivity of the fuel for different fuel densities, microstructures, and temperatures. A companion experimental work was also conducted to correlate the effective thermal conductivity of U-10Zr pellets and the underlying microstructure using 3D x-ray tomography and the laser flash method. The model was validated against the experimental data obtained in this work.

N-4: Atomistic Modeling of Transport Properties and Interaction with Point Defects of α-U Tilt Grain Boundaries: Khadija Mahbuba1; Benjamin Beeler1; Andrea Jokisaari2; 1North Carolina State University; 2Idaho National Laboratory
    Metallic fuel has demonstrated excellent safety during off- normal reactor conditions and provides benefits over oxide fuels with respect to ease of fuel fabrication and reprocessing. Though metallic fuel has been used in reactor for over sixty years, many fundamental and thermodynamic properties are still unknown. The anisotropic α-U exists in metallic fuel to some extent. A large amount of initial porosity in metallic fuel forms due to alpha tearing, which is strongly related to grain boundary properties and evolution. In the present study, grain boundary properties of α-U are investigated. Molecular dynamics is utilized to evaluate both the interaction of defects with grain boundaries and the diffusion within grain boundaries. A temperature regime between 300 K and 600 K is considered to explore the thermal dependence of the observed behaviors. Results from the current nanoscale bi-crystalline α-U modeling will be useful in the larger scale poly-crystalline α-U modeling.

N-5: Characterization of Additively Manufactured UO2 Fuel Pellets with Pulsed Neutron Techniques and 450 keV X-ray CT: Sven Vogel1; Donald W. Brown1; Bjorn Clausen1; Alexander M. Long1; Erik B. Watkins1; D. Cort Gautier1; Cheryl Kendall1; Cheng Sun2; Chuting Tan2; 1Los Alamos National Laboratory; 2Idaho National Laboratory
    In recent years, significant development of advanced manufacturing technologies allows novel designs to overcome limitations imposed by conventional nuclear fuel fabrication methods and fabricate fuel geometries that accommodate swelling much better, hence enabling higher burnup and therefore improve the economy of nuclear power generation. To develop and ultimately license additively manufactured nuclear fuels, characterization of the 3D-printed fuel pellets is required. While optical, X-ray and electron-based techniques can characterize essentially the surface of such materials, few bulk characterization methods exist to probe entire fuel pellets (~1 ccm). Here, we report the non-destructive characterization of two annular UO2 fuel element fabricated via digital light processing using neutron diffraction, neutron CT as well as 450 keV high resolution X-ray CT.

N-6: Characterization of Nuclear Materials from the Millimeter to the Nanometer: Robert Ulfig1; Anne-Sophie Robbes1; Paula Peres1; 1Cameca Instruments Inc.
     Characterization of Nuclear Materials from the millimeter to the nanometer Nuclear materials research encompasses a wide range of structural, protective, and fuel materials including metals, insulators, and composites. Quantitative micro and nanoscale post irradiation examination (PIE) often requires highly modified sample handling and preparation to protect the microscopist. CAMECAŽ offers nuclearized versions of instruments from their electron probe microanalysis (EPMA), atom probe tomography (APT), and secondary ionization mass spectrometer (SIMS) product lines enabling quantitative analysis from the millimeter to nanometer spatial range and from the percent to parts-per-trillion detection range. These instruments include custom specimen handling, contamination control, and personal protection modifications as well as key design changes to minimize the risk of damage or the introduction of errant noise to the detection systems during PIE. The modifications of these instruments and the typical applications will be discussed.

N-7: Investigation of the Impact the 3D Fission Product Structure has on the Local Thermal Conductivity in FBR MOX Fuel: Casey McKinney1; Tsvetoslav Pavlov2; Assel Aitkaliyeva1; 1University of Florida; 2Idaho National Laboratory
    Large thermal gradients across the radius of fast breeder reactor (FBR) mixed oxide (MOX) fuel pellets generate regional microstructures with varied solid and gaseous fission product structures. These fission products have different individual thermal conductivities that can be higher or lower than the fuel matrix. Understanding how each one affects the local thermal conductivity of the fuel is vital as the potential generation of hot spots due to these products could lead to fuel failure. In this work, 3D reconstructions of the fission product structure are used to predict the local thermal conductivity of different regions on a MOX fuel pellet. The predicted local thermal conductivities will be complemented by regional measurements of thermal conductivity by a thermal conductivity microscope (TCM). Analyzing the predicted and experimentally measured thermal conductivities with respect to the local fission product structure will elucidate the impact the fission products have on the thermal conductivity.