Materials for Nuclear Applications: Nuclear Fuels and Cladding
Program Organizers: Philip Edmondson, Oak Ridge National Laboratory; Yutai Katoh, Oak Ridge National Laboratory; Jake Amoroso, Savannah River National Laboratory; Levi Gardner, University of Utah; Amy Gandy, University of Sheffield; Karl Whittle, University of Liverpool; Monica Ferraris, Politecnico di Torino

Monday 2:00 PM
September 30, 2019
Room: E148
Location: Oregon Convention Center

Session Chair: Karl Whittle, University of Liverpool

2:00 PM  
Compatibility of U3Si2 fuel with FeCrAl and SiC/SiC Based Cladding: Denise Lopes1; Vancho Kocevski1; Theodore Besmann1; 1University of South Carolina
    U3Si2 fuel with FeCrAl or SiC/SiC composite cladding are being considered as advanced concepts and accident tolerant fuels for light water reactors. Understanding their chemical compatibility under operational and accident conditions is fundamental to predicting fuel behavior and validation. In this work, experimental determination of interactions and first-principle calculation methods were employed to assess U3Si2 compatibility with the novel cladding candidates. Diffusion-couple experiments were performed to simulate fuel-cladding conditions and the samples were characterized by microanalysis and x-ray diffraction. First-principles calculations using density functional theory (DFT) were used to obtain incorporation and defect formation energies for silicon, carbon, iron and uranium in the U3Si2, α-Fe, and SiC phases. Together, the experimental and DFT results have allowed evaluation of the nature of potential interactions in these fuel-cladding systems. This research is being performed using funding received from the DOE Office of Nuclear Energy’s Nuclear Energy University Programs [grant number DE-NE0008570].

2:20 PM  Invited
Uranium Nitride and High Temperature Irradiation Resistant Thermocouples towards Accident Tolerant Nuclear Fuel: Ember Sikorski1; Lan Li1; 1Boise State University
    We have performed atomistic modeling to better understand nuclear fuel and materials. For the application of accident tolerant fuel, uranium nitride UN instability in air and water must be mitigated. To examine the initiation of corrosion, we studied dissociated water and oxygen on UN surfaces. Different concentrations and temperature were analyzed to probe the causes of formation of various products. The electronic structure was calculated to reveal its electronic behavior. In addition, High Temperature Irradiation Resistant Thermocouples (HTIR-TCs) are under development to monitor the temperature of research reactors in real time. The voltage produced with respect to temperature can be determined with the Seebeck coefficient of each HTIR alloy leg. However, changing structure at high temperature leads to drift in the accuracy of the TCs. To better understand the atomistic and electronic causes of drift, we calculated the Seebeck coefficient of HTIR alloys before, during, and after heating.

3:00 PM  
Characterization of the Impact of Fission Product Inclusion on Phase Development in U3Si2 Fuel: Kaitlin Johnson1; Denise Lopes2; Tashiema Wilson1; Theodore Besmann1; 1University of South Carolina; 2Westinghouse Electric Co., LLC
    Solid fission products produced during burnup accumulate in the fuel and may lead to the development of secondary phases, contributing to swelling and causing changes to the thermophysical properties. Yet, the impact of fission products on accident tolerant advanced fuels under development, such as U3Si2, is largely unexplored. Five fission product metals (Ce, Gd, Mo, Y, Zr) were chosen as surrogate fission products and a “SIMFUEL” representing high fuel burnup was fabricated by doping U3Si2 with up to 10 at% of the metals and heat treated. The SIMFUEL pellets were characterized using XRD and microanalytical methods to identify structural changes and secondary phase formation and determining the solubility limits of the various fission products in U3Si2. The results are being used to develop thermodynamic models of U3Si2 and to describe its in-reactor behavior.

3:20 PM  
Steam Oxidation and Microstructural Characterization of U3Si2 alloyed with Al, Cr, Nb, Y, and Zr: Elizabeth Sooby Wood1; Cole Moczygemba1; Geronimo Robles1; Christopher Grote2; Lu Cai3; Peng Xu3; Edward Lahoda3; 1The University Of Texas At San Antonio; 2Los Alamos National Laboratory; 3Westinghouse Electric Company
    Uranium silicides have proven of interest as advanced technology reactor fuels due to their enhanced thermal conductivity and high uranium density (U3Si and U3Si2) compared to traditional UO2. However, susceptibility to oxidation and wash out, could limit the potential for deployment of silicides as accident tolerant fuels. Mitigating the water reaction for U3Si2 could enable its use as an accident tolerant, high uranium density fuel or as a composite fuel constituent. In support of the work presented, U3Si2 was alloyed with Al, Cr, Y, Nb, and Zr, ranging from 2-12 volume percent, using the arc melting method. Reported are thermogravimetric data for these alloyed compositions exposed to high temperature (300≤T≤ 1000°C) oxygen and steam alongside screening data for unalloyed U3Si2 and UO2. The microstructural degradation will be presented, and the modified reaction kinetics for the alloyed compositions will be assessed and impact to deployment in water cooler reactor systems discussed.

3:40 PM Break

4:00 PM  
Design of Alloy Chemistry to Mitigate Fuel-Cladding Chemical Interactions in Uranium-based Metallic Fuels: Rabi Khanal1; Nathan Jerred1; Indrajit Charit1; Michael Benson2; Robert Mariani2; Samrat Choudhury1; 1University of Idaho; 2Idaho National Laboratory
    In metallic fuels, lanthanide fission products react with the cladding materials leading to fuel-cladding-chemical interactions (FCCI). The FCCI results in reduced cladding integrity and eventual rupture of the cladding. Addition of dopant(s) to arrest lanthanides within the fuel-matrix by forming intermetallic compounds have generated considerable attention due to its effectiveness. However, there is lack of generic principle to choose appropriate solute that can be effective in arresting lanthanides. Here, we present ab-initio based thermodynamic alloy design principles which can be effective in identifying dopant(s) that can bind a lanthanide inside the fuel-matrix. Our approach correctly identifies both known dopants like Pd and new dopants such as As and Se which can be effective in binding all lanthanides within U-matrix. Finally, we verify the theoretically predicted new dopants by characterizing cast alloys of Nd and As/Se in U-matrix. This research is being funded by DOE-NEUP, grant # DE-NE0008557.

4:20 PM  
Anisotropic Thermal Transport in Uranium Dioxide Induced by Dislocation: Suvash Ghimire1; Bowen Deng1; 1Montana Technological Unviersity
    Thermal conductivity of uranium dioxide (UO2) is an important factor in nuclear reactor systems, as it impacts the thermal behavior of fuel during burn-up. During burn-up, the UO2 fuel pellets generate fairly high amounts of microstructures including dislocations that adversely affect the thermal behavior of the fuel. In this work, we used molecular dynamics to investigate the effect of dislocations on thermal conductivity of UO2. Most of the thermal transport research uses heat flux in the direction perpendicular to the dislocation, but in this research, we calculated the thermal conductivity of UO2 applying heat flux both in parallel and perpendicular to the direction of dislocation and compared their results. Furthermore, to understand the effect of temperature and size on thermal transport, we carried out the investigation at different temperatures and different sizes of UO2 structure.

4:40 PM  
Spectral Thermal Conductivity Predictions in UO2 with Xe Inclusions: Jackson Harter1; Aria Hosseini2; Todd Palmer1; Alex Greaney2; 1Oregon State University; 2University of California - Riverside
     Current and next generation nuclear fuels suffer a common problem: production and evolution of gaseous fission products creates phonon scattering centers that lower thermal conductivity (κ) in the fuel. Uranium dioxide (UO2) is the fuel used in most nuclear power reactors; during fuel burn up, insoluble xenon precipitates into a dispersion of Xe bubbles which evolve and significantly degrade thermal conductivity.To enable prediction of the thermal conductivity of UO2 fuel pins in operation we have developed a temperature coupled deterministic phonon transport simulator which solves the Boltzmann transport equation on geometric domains spanning nano- to micro-scales and predicts spectral κ using material properties obtained from ab initio simulations. We will demonstrate our approach on micro-scale geometric domains of UO2 with Xe inclusions and compare to existing data.

5:00 PM  
Materials for Capture of Uranium for Nuclear Fuel from Fertilizer: Allen Apblett1; Cory Perkins2; 1Oklahoma State University; 2Oregon State University
    The increasing problem of global climate change has renewed the worldwide interest in energy sources that do not produce greenhouse gases. This is expected to lead to a renaissance in the use of nuclear power but current terrestrial uranium reserves are only sufficient for several more decades Thus, shepherding our resources requires finding alternative sources for uranium. One widespread potential source is the uranium found in fertilizer – a wasted resource that may also have negative health effects. The Apblett research group has developed mineral-based nanometric ion exchangers that have proven useful for harvesting uranium from ocean water that have also proven useful for capture of uranium from fertilizer. The process for sorption of uranium and its eventual isolation as ammonium uranate will be discussed.

5:20 PM  
PVD Coating of Surrogate Fuels for Deep Space Nuclear Thermal Propulsion: Maanas Togaru1; Thomas Koenig1; Gregory Thompson1; 1The University of Alabama
    Nuclear thermal propulsion (NTP) is being considered for deep space exploration. However, the use of hydrogen gas as a propellant poses a challenge to the nuclear fuel (used for heating) where upon a deleterious reaction with the fuel can occur. One mitigating strategy to protect the fuel is to provide a conformal coating to serve as a diffusion barrier. Physical vapor deposition (PVD), using magnetron sputtering, has been employed. A rotating drum shifted the ZrO2 powder under a tungsten cathode, with conformal coating thicknesses ranging tens to hundreds of nanometers depending on coating times. As the coating thickened, the film revealed a ‘powdery’ morphology, which is contributed to the impact from powder-on-powder contact during coating. Precession electron diffraction revealed nanocrystalline grains in the coating with no preferred texture. Stoney curvature measurements of W on ZrO2 indicates compressive growth stress states, which will be explained by a kinetic model.