Advanced Characterization of Materials for Nuclear, Radiation, and Extreme Environments: Nuclear Fuels, Ceramics, and Corrosion
Sponsored by: TMS Nuclear Materials Committee
Program Organizers: Cody Dennett, Commonwealth Fusion Systems; Samuel Briggs, Oregon State University; Christopher Barr, Department Of Energy; Michael Short, Massachusetts Institute of Technology; Janelle Wharry, Purdue University; Cheng Sun, Clemson University; Caitlin Kohnert, Los Alamos National Laboratory; Emily Aradi, University of Manchester; Khalid Hattar, University of Tennessee Knoxville

Monday 2:00 PM
October 18, 2021
Room: A215
Location: Greater Columbus Convention Center

Session Chair: Marat Khafizov, Ohio State University; Christopher Barr, US Naval Nuclear Laboratory

2:00 PM  Invited
Characterization of Defects, Thermal Transport, and Elastic Properties in As-fabricated and Irradiated Single Crystal of ThO2: Marat Khafizov¹; Saqeeb Adnan¹; Joshua Ferrigno¹; Vinay Chauhan¹; Amey Khanolkar²; Cody Dennett²; Yuzhou Wang; Kaustubh Bawane²; Linu Malakkal²; Miaomiao Jin³; Zilong Hua²; Chao Jiang²; Lingfeng He²; Chris Marianetti⁴; Anter El-Azab⁵; David Hurley²; ¹Ohio State University; ²Idaho National Laboratory; ³Pennsylvania State University; ⁴Columbia University; ⁵Purdue University
    We investigate physical properties and microstructure evolution under irradiation in thorium dioxide (ThO2). Use of ThO2 single crystals fabricated using hydrothermal method helps characterizing intrinsic behavior of oxide nuclear fuels and eliminates complications associated with electron correlation effects and chemical complexity present in uranium dioxide. Transmission electron microscopy is used to characterize dislocation loop nature and evolution in proton irradiated ThO2 under different irradiation conditions. The nature of point defect is analyzed using optical spectroscopy sensitive to defects acting as color centers and probes their electronic structure, while Raman spectroscopy measures vibrational properties of defects. Use of small scale crystals and ion beam irradiation for tailored microstructure required utilization of laser based approaches for measuring thermal conductivity and elastic constants. Conductivity was measured using modulated thermoreflectance and elastic properties using picosecond ultrasonics. The results of these measurements allow as to validate atomic level modeling of microstructure evolution and material’s properties.

2:20 PM  Invited
In Situ Ion Irradiation of Gadolinium Titanate: A Perspective on Microstructure and Memory: Jessica Krogstad¹; Nathan Madden¹; Matthew Janish²; James Valdez²; Blas Uberuaga²; ¹University of Illinois at Urbana-Champaign; ²Los Alamos National Laboratory
    Defect sinks are key to reducing radiation induced damage accumulation, but not all sinks are created equal. In order to directly compare the relative efficiency of grain boundaries and pore surfaces, unique 3-zone gadolinium titanate (Gd₂Ti₂O₇) specimens capture nanocrystalline, nanoporous and single crystal microstructures within the same TEM lamella. As a result, all three microstructures could be irradiated and observed simultaneously via in situ ion irradiation experiments. Nanobeam electron diffraction was used after specific fluence intervals to assess the crystallinity of each region. The results at room temperature and 600慢 show that a free surface defect sink is more effective than grain boundaries at capturing radiation-induced defects. Additionally, once amorphized the specimens could be recrystallized via in situ heating and then subjected to ion irradiation repeatedly. Repeated cycling between the amorphous and crystalline states revealed that both the recrystallization temperature and amorphization threshold are dependent on the sample history.

2:40 PM
Insight into the Impact of Irradiation on Vibrational Properties of AlN Using Raman Spectroscopy: Saqeeb Adnan¹; Yuzhou Wang²; Aleksandr Chernatynskiy³; Marat Khafizov¹; ¹The Ohio State University; ²Idaho National Laboratory; ³Missouri University of Science and Technology
    We analyze utility of Raman spectroscopy to characterize displacement damage in ceramics. Wide optical bandgap and piezoelectric properties of aluminum nitride (AlN) make it an attractive candidate for sensor applications in radiation environments. Owing to its radiation resistance it has been chosen as a model system. Epitaxial AlN grown on sapphire substrate were placed against a boron nitride plate and irradiated to a fluence of 7.3x10¹⁷ n/cm² in OSU nuclear research reactor. Transmutation products resulting from ¹⁰B(n,α)⁷Li reactions are expected to produce the most damage. Raman spectroscopy was used to determine the effect of irradiation damage on vibrational properties of AlN across alpha-particle impacted region. A peak shift and broadening in the primary Raman E₂^high and A₁ (LO) mode peaks were observed and are attributed to disorder induced by generated point defects. Additionally, the influence of various point defects on vibrational and elastic properties are analyzed using atomistic level simulations.

3:00 PM
Optical Characterization of Defects in Proton Irradiated Fluorite Oxides: Joshua Ferrigno¹; Vinay Chauhan¹; Amey Khanolkar²; Lingfeng He²; David Hurley²; Marat Khafizov¹; ¹Ohio State University; ²Idaho National Laboratory
    Experimental methods to characterize point defects in nuclear energy materials are needed for improved understanding of their irradiation behavior. Inspired by successful implementation of optical spectroscopy to characterize oxygen vacancies (VO) in insulators such as Al2O3 and MgO, we performed optical ellipsometry to characterize irradiation induced defects in CeO2 and ThO2 used as a model fluorite oxide. Polycrystalline CeO2 and single crystal ThO2 were irradiated with protons accelerated up to 2 MeV at various temperatures and dose levels. In ThO2, distinct optical absorption peaks were observed at 1.8 eV and 2.0 eV, while in CeO2, a much broader defect peak at 1.9 eV was identified. The difference in optical spectra are attributed to difference in electronic structure of VO, where electrons are localized in vacancy sites in ThO2 and in cerium atoms in CeO2. This approach demonstrates the potential of optical spectroscopy to characterize point defects in irradiated actinide oxides.

3:20 PM
Microstructural Characterization of Oxidized Tristructural Isotropic Particles (TRISO) in Various Gas Atmospheres: Katherine Montoya¹; Brian Brigham¹; Tyler Gerczak²; Elizabeth Sooby¹; ¹University of Texas at San Antonio; ²Oak Ridge National Laboratory
    TRISO particles are composed of four refractory layers surrounding a fuel kernel and encapsulated in graphite matrix material, forming a fuel compact for a high temperature gas-cooled reactors. Off-normal conditions can result in oxidizing atmospheres leading to graphite matrix degradation that produces volatile oxidation byproducts. The evolved graphite matrix material exposes the SiC layer, which acts as the main structure support for TRISO particles, to a mixed gas atmosphere. Damage to the SiC layer can cause particle failure and fission product release. Testing of surrogate SiC exposed TRISO particles was conducted in a mixed atmosphere of steam (<0.2 atm H2O) and carbon monoxide (<1000 ppm CO), as well as at high temperatures (1300慢<T<1600慢) representative of off-normal conditions utilizing a thermogravimetric analyzer. Post exposure characterization of samples provides microstructure mapping of the oxidized SiO2-SiC interface. Advanced characterization techniques include focused x-ray photoelectron spectroscopy, ion milling beam microscopy and transmission electron microscopy.