Radiation Effects in Metals and Ceramics: Irradiation of Ceramics and Uranium Fuels
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Djamel Kaoumi, North Carolina State University; Thak Sang Byun, Oak Ridge National Laboratory; Dane Morgan, University of Wisconsin-Madison; Maria Okuniewski, Purdue University; Mahmood Mamivand; Geoffrey Beausoleil, Idaho National Laboratory; Philip Edmondson, The University Of Manchester; Khalid Hattar, University of Tennessee Knoxville; Aurelie Gentils, Université Paris-Saclay; Joel Ribis, Cea

Thursday 8:30 AM
February 27, 2020
Room: Theater A-7
Location: San Diego Convention Ctr

Session Chair: Geoffrey Beausoleil, Idaho National Laboratory; Assel Aitkaliyeva, University of Florida


8:30 AM  
Microstructural Changes in Graphite and the Corresponding Bulk Property Evolution: Anne Campbell1; José Arregui-Mena1; 1Oak Ridge National Laboratory
    Graphite and carbon-based materials are key structural materials for current and future nuclear reactors. The microstructure of these materials is complex, even though they are a single element material, and difficult to quantify because the microstructure features range in sizes over multiple length scales. The evolution of the bulk property changes is currently being studied through multiple irradiation programs at multiple research facilities, but these programs primary driver is engineering data without the fundamental understanding of the microstructural changes that cause the bulk property evolution. Work at Oak Ridge National Laboratory (ORNL) is leveraging samples from several of these irradiation campaigns to begin understanding how the microstructure changes. This presentation will discuss the general bulk property evolution that occurs in graphite and present the current work being performed at ORNL to study the link between the microstructure evolution and the bulk properties.

8:50 AM  
Microstructural Characterization of Nuclear Graphite Irradiated at Temperatures below 230˚C: David Arregui-Mena1; Wenjing Li2; Lori Walters2; Philip Edmondson1; Cristian Contescu1; 1Oak Ridge National Laboratory; 2Canadian Nuclear Laboratories
    Graphite is a moderator material and structural materials of multiple Generation IV reactors concepts and British Advanced Gas-cooled Reactors (AGR). Failure of multiple graphite components can limit the lifetime of an AGR and some Generation IV designs. As part of the endeavor to understand the neutron irradiation effects in graphite Transmission Electron Microscopy (TEM), the Brunauer-Emmett-Teller (BET) and other characterization techniques will be combined in this research to determine the effects of irradiation under low temperature conditions (<300˚C). It is expected that temperatures below 300˚C and neutron irradiation will lead to significant changes of the crystal structure of graphite. In this case the Brunauer-Emmett-Teller (BET) method will be use to understand the pore evolution in graphite. TEM characterization will elucidate the possible lattice effects induced by low temperature and irradiation. Neutron irradiation defects using these techniques at these low temperatures have never been documented before making this research unique.

9:10 AM  
Near-surface Disorder in 4H-SiC Induced by MeV light Ion Irradiation: John Demaree1; Noel Guardala2; Zois Tsinas3; Eaman Karim3; Mohamad Al-Sheikhly3; 1CCDC Army Research Laboratory; 2The George Washington University; 3University of Maryland
    Single-crystal silicon carbide (4H-SiC) was irradiated with H and He ions at energies near significant elastic scattering resonances in order to determine whether the enhanced production of high energy recoils at those resonances can significantly affect the radiation damage induced in the material. The extent and nature of this disorder was investigated with ion beam channeling and Raman spectroscopy. The amount of chemical disorder in the crystal - i.e., the number of antisite defects and homonuclear bonds as measured by Raman spectroscopy - suggests that the Monte Carlo program SRIM correctly predicts the number of target atom displacements, and no evidence of enhanced damage from resonant scattering is observed. Furthermore, ion beam channeling measurements indicate that the overall amount of amorphization (loss of crystallinity) is significantly lower than expected, likely due to ionization-induced recrystallization or recombination in the defect cascade, as has previously been noted in heavy ion irradiation studies.

9:30 AM  
Defects Generation during Irradiation-induced Alpha/Gamma Phase Transformation in Uranium Alloys: Yipeng Gao1; Benjamin Beeler1; Yongfeng Zhang1; 1Idaho National Laboratory
    The phase transformation between alpha and gamma in uranium alloys has been widely observed, driven by either temperature or irradiation. Because of the unique crystal symmetry of the alpha phase, diversified types of defects are generated during the phase transformation, which plays a critical role on the mechanical integrity of nuclear metal fuels. By utilizing advanced crystallographic and simulation tools, we analyze the symmetry breaking during the phase transformation and its relation with transformation-induced defects. A new defect generation mechanism is demonstrated and the characteristic types of transformation-induced defects are systematically predicted, through a combined theoretical and experimental study. Our approach can be directly generalized to analyze crystalline systems and phase transformations with similar symmetry, e.g., in titanium alloys and zirconium alloys, which provides a new insight to understand the intrinsic coupling between crystalline defects and irradiation-induced phase transformations.

9:50 AM Break

10:10 AM  Invited
Investigation of High Burnup Ceramic Fuel Microstructure at Idaho National Laboratory: Fabiola Cappia1; Geoffrey Beausoleil1; Alex Winston1; Daniel Murray1; Brandon Miller1; LingFeng He1; Fei Teng1; 1Idaho National Laboratory
    Nuclear fuels are subjected to extreme conditions both in terms of temperature and radiation fields, which induce significant microstructural changes. For ceramics used in Light Water Reactors (LWRs) the most notable microstructure modification is the formation of the High Burnup Structure (HBS). The HBS is characterized by grain subdivision and a notable increase in the porosity. As the presence of the HBS could relate to the enhanced fragmentation of the fuel at high burnup during design-basis accidents, investigation of the fuel radial microstructure and its relationship to the irradiation history is of paramount importance to understand HBS formation and implications for fuel safety. Recently, experimental campaigns have been undertaken at Idaho National Laboratory (INL) to study the fuel restructuring with state-of-the-art techniques. This work presents new results related to ceramic fuels microstructure, with focus on restructuring and fission gas bubbles, both in LWR and Sodium Fast Reactor (SFR) fuels.

10:40 AM  
Neutron Irradiation Induced Intergranular Fission Product Precipitation in SiC Layer of TRISO Fuel: Isabella Van Rooyen1; Subhashish Meher1; Thomas Lillo1; 1Idaho National Laboratory
    Understanding of fission product behavior within tristructural isotropic (TRISO) layers, especially Ag-110m, due to its high mobility in intact TRISO layers, in the SiC layer during neutron irradiation is explored as part of the post irradiation examination of the Advanced Gas Reactor (AGR) irradiation campaign. This presentation provides selected results of SiC intergranular fission product precipitation in selected TRISO coated particles from the AGR-1 and AGR-2 experiments, and microstructural trends considering differences in fuel types, fabrication histories and irradiation histories. The complexity of fission product distribution and composition within the SiC layer, irradiation effects on the SiC structure as well as the variable nature of metallic fission product release, is examined by advanced characterization techniques such precession electron diffraction, scanning transmission electron microscopy, and atom probe tomography. Preliminary results suggest that CSL-related grain boundaries may have a direct influence on Ag retention.

11:00 AM  
Three Dimensional Radiation Effects in Neutron Irradiated Uranium-Molybdenum Fuel: Maria Okuniewski1; Alejandro Figueroa1; Jonova Thomas1; Sri Tapaswi Nori1; Peter Kenesei2; Jonathan Almer2; 1Purdue University; 2Argonne National Laboratory
    Uranium-molybdenum (UMo) fuels are candidate fuels for research and test reactors, as well as for advanced reactors. During neutron irradiation these fuels experience swelling, phase transformations, interactions with the cladding, and recrystallization. Synchrotron micro-computed tomography and high-energy diffraction microscopy were used to three-dimensionally characterize a monolithic UMo fuel plate irradiated to ~ 5x1021 fissions/cc. Two specimens were extracted from the plate, one of which incorporated a zirconium diffusion barrier and fuel, whereas the other specimen possessed only fuel. These techniques indicated a variety of pore morphologies within the fuel resulting from fuel swelling, from newly nucleated pores to interconnected porosity. The interaction region also demonstrated the presence of porosity. Additionally, multiple specimens were extracted from an edge-on irradiated fuel plate that was irradiated to ~6-10x1021 fissions/cc and characterized via scanning electron microscopy to reveal porosity, phases, and grain morphology. The microstructures for the range of burn-ups will be compared.

11:20 AM  Invited
Radiation Effects on Phonon Transport in UO2 and ThO2: Tiankai Yao1; Vinay Chauhan2; Maniesha Singh3; Amey Khanolkar1; Zilong Hua1; Marat Khafizov2; Matthew Mann4; Thierry Wiss5; Anter El-Azab3; Jian Gan1; David Hurley1; Lingfeng He1; 1Idaho National Laboratory; 2The Ohio State University; 3Purdue University; 4Air Force Research Laboratory; 5European Commission, Joint Research Centre
     The degradation of thermal conductivity of nuclear fuels under high radiation environment affects the energy conversion efficiency as well as reactor safety margins. For oxide nuclear fuels, phonon scattering by point defects, extended defects such as dislocation loops and bubbles, and grain boundaries plays a significant role in limiting the thermal transport properties. The 5f elections in UO2 may affect the defect evolution in a different manner than that in ThO2, which does not contain 5f electrons. In this work, the effects of point defects and extended defects on the phonon transport in UO2 and ThO2 have been investigated on ion irradiated samples by using multimodal microscopy and spectroscopy and thermal property measurement. This work is supported as part of the Center for Thermal Energy Transport under Irradiation, an Energy Frontier Research Center, funded by the U.S. Department of Energy Office of Sciences.