Ceramic Materials for Nuclear Energy Research and Applications: Characterization of Fuels and Materials
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee, TMS: Mechanical Behavior of Materials Committee, TMS: Energy Committee
Program Organizers: Walter Luscher, Pacific Northwest National Laboratory; Xian-Ming Bai, Virginia Polytechnic Institute and State University; Lingfeng He, North Carolina State University; Sudipta Biswas, Idaho National Laboratory; Simon Middleburgh, Bangor University
Wednesday 2:00 PM
March 22, 2023
Room: 28B
Location: SDCC
Session Chair: Lingfeng He, North Carolina State University
2:00 PM Invited
Scanning Transmission Electron Microscopy of Nanoprecipitates in Spent UO2 Nuclear Fuel: Edgar Buck1; Dallas Reilly1; 1Pacific Northwest National Laboratory
We used Scanning Transmission Electron Microscopy (STEM) to characterize the distribution and nature of noble metal particles (NMP) in ATM109 Spent UO2 nuclear fuel within specific regions of the fuel pellet. We had previously reported on the large 50 to 100 nm diameter NMPs. These possessed a well-defined composition. However, in the center of the fuel, we observed considerably smaller NMP, ranging from 2 to 5 nm across. These particles had variable compositions and there was a degree of lattice compatibility between UO2 matric and NMP that was revealed with atomic resolution STEM imaging. STEM-x-ray energy dispersive spectroscopy and STEM-Electron energy loss spectroscopy mapping was used to examine the composition of the NMP that indicated lower than expected Pd content. Further results on the characterization of these particles that impact the long-term behavior of UO2 fuels during reactor operation will be presented.
2:30 PM Invited
Soft X-ray Synchrotron Radiation Spectromicroscopy of Spent Nuclear Fuel Focused Ion Beam Sections: David Shuh1; 1Lawrence Berkeley National Laboratory
Focused ion beam (FIB) methods at Idaho National Laboratory were used to make several thin sections from a low burnup uranium oxide spent fuel. These FIB sections were measured at the oxygen K-edge, uranium N4,5-edges, and cerium M4,5-edges utilizing the scanning transmission x-ray microscope (STXM) at Advanced Light Source Beamline 11.0.2 at Lawrence Berkeley National Laboratory. The oxygen K-edge results were analyzed by non-negative matrix factorization methods and revealed two main components, the bulk of the sample which is made up largely of UO2, and a thin surface layer (~8 nm) of UO2+x resulting from oxidation following sectioning. The measurements show that Ce (~0.4 wt.%) is predominantly trivalent, although a small contribution of tetravalent Ce cannot be ruled out. These results form a foundation for future STXM measurements of spent nuclear fuel FIB sections that can be expanded to mixed-oxide, uranium nitride, and other advanced fuels.
3:00 PM
Advanced Characterization and Modeling of Nanoprecipitates in Spent Nuclear Fuel: Lingfeng He1; Mukesh Bachhav2; Chao Jiang2; 1North Carolina State University; 2Idaho National Laboratory
Spent nuclear fuel undergoes significant microstructural and chemical evolution during reactor operations. Some fission products are retained within the UO2 matrix in solid solution, while the inert gases, xenon, krypton, and the 4d group metals, molybdenum, technetium, ruthenium, rhodium, and palladium are trapped as bubbles and metallic precipitates, respectively in the UO2 matrix. In this work, atomic resolution microstructure and chemical composition of nanoprecipitates in spent UO2 fuel from Belgian Reactor 3 are characterized using high resolution scanning transmission electron microscopy, Super-X energy dispersive X-ray spectroscopy and atom probe tomography techniques. Density-functional theory is utilized to understand the formation mechanism of nanoprecipitates and their phase relationships with UO2 matrix. Molecular dynamics simulation is used to calculate the fission gas bubble pressure.
3:20 PM
Microstructural Characterization of Neutron Irradiated Concrete Minerals: David Arregui-Mena1; Ippei Maruyama2; Matheus Tunes3; Elena Tajuelo Rodriguez1; Christa Torrence4; Thomas Rosseel1; Yann Le Pape1; Philip Edmondson1; 1Oak Ridge National Laboratory; 2Nagoya University; 3Los Alamos National Laboratory; 4Texas A&M University
One of the most critical structural and safety components of Light Water Reactors, known as biological shield, is formed by a concrete structure. A typical biological shield is subjected to several degradation mechanisms and environmental conditions that promote the deterioration of this structure's mechanical properties and integrity. When subjected to neutron irradiation, most concrete aggregates experience a gradual volumetric expansion produced by the amorphization of the minerals that form the aggregates. Specifically, neutron irradiation-induced volumetric expansion in aggregates depends upon the content of neutron irradiation-sensitive minerals such as quartz or certain silicates. This research used a combination of advanced microscopy techniques to characterize the cracking induced by neutron irradiation. The results of this research show a correlation between the presence of quartz and cracking in different mineral compositions. This research is the first visual evidence of neutron-induced damage generated by neutron irradiation.
3:40 PM Break
4:00 PM Invited
Comprehensive Characterization of Damage in Ion Irradiated Ceramics for Validation of Atomistic Models: Marat Khafizov1; Joshua Ferrigno1; Erika Nosal1; Saqeeb Adnan1; Kaustubh Bawane2; Amey Khanolkar2; Miaomiao Jin3; Linu Malakkal2; Chao Jiang2; Lingfeng He4; David Hurley2; 1Ohio State University; 2Idaho National Laboratory; 3Pennsylvania State University; 4North Carolina State University
Validation of first principles models for microstructure evolution under irradiation has been hindered by availability of table-top experimental methods suitable for defect characterization at the atomic level. We discuss extensive characterization of defects in ion irradiated fluorite oxides including urania, thoria and ceria. Irradiations over a range of temperatures to a few dpa dose provide optimal conditions for producing both point and extended defects. Electron microscopy is used to characterize extended defects, while optical and Raman spectroscopies are used to characterize point defects. Quantitative analysis of dislocation loops evolution using rate theory model provides means for measuring mobility of defects. Raman and optical spectroscopies probe vibrational and electronic properties of defects all tightly coupled to atomic structure of the defect. Finally, thermal conductivity measurements are used as ultimate test. Presented methods offer an attractive solution for validation of atomistic models critical for development of material performance codes with predictive capability.
4:30 PM
Impact of Resonance Scattering on the Thermal Conductivity of ThO2: Saqeeb Adnan1; Zilong Hua2; Amey Khanolkar2; Cody Dennett3; David Hurley2; Marat Khafizov1; 1The Ohio State University; 2Idaho National Laboratory; 3Massachusetts Institute of Technology
Understanding different phonon scattering mechanisms contributing to reduction of lattice thermal conductivity in fluorite oxides is critical to developing accurate fuel performance codes. In this study, we investigate low-temperature thermal conductivity in Uranium-doped and proton irradiated single-crystal ThO2(up to 0.1 dpa at 600C). Thermal conductivity of the hydrothermally grown samples was measured using spatial domain modulated thermoreflectance and was analyzed within the framework of Klemens-Callaway method. We observed that Umklapp scattering and Rayleigh scattering are insufficient to capture observed trends of thermal conductivity. Low-temperatures trends are reproduced by including an additional term associated with resonant scattering, which is characteristic of defects with peculiar electronic structures that enable coupling of certain phonon modes to either electronic degrees of freedom or localized phonon modes. While there are reports of phonon resonance in UO2, we notice that the analysis of proton-irradiated samples also requires the inclusion of resonant scattering associated with irradiation-induced defects.
4:50 PM
Irradiation- and Dopant-induced Structural Changes in Ceramic Nuclear Fuels Probed via Elastic and Optical Properties: Amey Khanolkar1; Linu Malakkal1; Zilong Hua1; Cody Dennett2; J. Matthew Mann3; Marat Khafizov4; David Hurley1; 1Idaho National Laboratory; 2Massachusetts Institute of Technology; 3Air Force Research Laboratory; 4The Ohio State University
Radiation-induced defects and dopants are known to introduce lattice distortions that influence the thermophysical properties of nuclear fuels. A fundamental understanding of their impact on fuel performance is therefore critical for the development of advanced ceramic fuels. In this talk, the impact of small-scale lattice defects and doped uranium atoms on the optical and elastic properties of thorium dioxide (ThO2) single crystals is explored. Changes in optical properties of the irradiated ThO2 (created by color centers) and doped UxTh1-xO2 single crystals (created by band gap changes) are measured using spectroscopic ellipsometry and single wavelength reflectometry, respectively. Elastic property changes arising from defect- and dopant-induced lattice distortions are probed from changes in the frequency of laser-generated surface acoustic waves and longitudinal coherent acoustic phonons, respectively. When combined with ab initio calculations, our findings provide new insight on the impact of atomic-scale lattice distortions on the properties of advanced ceramic fuels.
5:10 PM
Defect Chemistry and Radiation Stability of (Gd & Zr) Co-doped UO2: Ritesh Mohun1; Daniel Bailey2; Martin Stennett2; Claire Corkhill2; Simon Middleburgh1; 1Bangor University; 2University of Sheffield
The irradiation behaviour of pure UO2 has been studied experimentally, but little is known about the irradiation of UO2 doped with fission products such as rare-earth elements (REEs). This study is devoted to investigating the effect of heavy-ion irradiation of UO2 when doped with both trivalent Gd and tetravalent Zr at varied concentrations.The surface characterisation of the prepared pellets revealed a significant modification of the initial UO2 microstructure due to dopant incorporation. The intrinsic defect structures induced by the multivalence dopants, as well as their behaviour as a result of ionic implantation, were investigated using experimental XRD, XANES, and Raman spectroscopy coupled with theoretical DFT+U calculations. This talk aims to discuss the key mechanisms that occur near defect-boundary interfaces in order to highlight the precise role of dopant and grain boundary areas in changing the lattice defects mechanisms and subsequent evolution in fluorite structure relevant to nuclear fuels.