Ceramic Materials for Nuclear Energy Research and Applications: Advanced Sintering, Characterization, and Measurement
Sponsored by: TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Energy Committee, TMS: Nuclear Materials Committee
Program Organizers: Xian-Ming Bai, Virginia Tech; Yongfeng Zhang, Idaho National Laboratory; Maria Okuniewski, Purdue University; Donna Guillen, Idaho National Laboratory; Marat Khafizov, Ohio State University; Thierry Wiss, European Commission- JRC -Institute of Transuranium Elements – Germany

Tuesday 2:00 PM
February 28, 2017
Room: Palomar
Location: Marriott Marquis Hotel

Session Chair: Maria Okuniewski, Purdue University; Larry Aagesen, Idaho National Laboratory

2:00 PM  Invited
Thermal-Mechanical Properties of Sintered UO2: Tiankai Yao1; Jie Lian1; 1Rensselaer Polytechnic Institute
    The advanced ceramic fuel development program is exploring revolutionary ceramic fuels with enhanced high thermal conductivity, oxidation resistance, high temperature mechanical properties, and thus improved accident tolerance. The US NEAMS program is developing science-based next generation fuel performance modeling, and critical experimental data are needed to validate phase field-based MARMOT models, particularly on effective thermal transport and fracture behavior. In this talk, recent advancements of using spark plasma sintering (SPS) in fabricating advanced fuels and engineering fuel matrix with tailored properties will be highlighted. The sintering fuels by SPS include monolithic UO2 with well-controlled microstructure, grain size and porosity across multiple length scales from nano-metered to micron-sizes, and the impact of the microstructure on the fuel properties is discussed within the context of the MARMOT predictions. Composite UO2 fuels are also fabricated in which heterogeneous secondary phases are used as the additives to improve thermal conductivity and mechanical properties.

2:30 PM  
Correlation Between Particle Size and Grain Size Distributions in Single/Multiphase Ceramic Oxide Surrogate Materials: Keyur Karandikar1; Austin Travis2; Kenta Ohtaki2; Martha Mecartney2; Olivia Graeve1; 1University of California, San Diego; 2University of California, Irvine
    This study evaluates the correlation between powder particle and grain size distributions in ceramics prepared by spark plasma sintering. Sample compositions consisted of yttria-stabilized zirconia, MgAl2O4 spinel and alpha-alumina powder mixtures of various particle sizes. Powder characterization was performed using dynamic light scattering using stable colloidal suspensions. Sintered samples were characterized for density, grain size and microstructure. Sintering curves were formulated to study the complex sintering behavior of the multiphase ceramics. The composites were also tested for Vickers hardness (1500-2000HV). Results of three phase composites with average grain sizes as small as 135 nm and 215 nm for corresponding starting particle sizes of 100 nm and 132 nm, respectively, will be presented. These multiphase materials have been developed to enhance thermal conductivity, strength and high temperature plasticity of nuclear fuel for better performance, reliability, and safety.

2:50 PM  
Phase Field Modeling of Uranium Dioxide Sintering and Densification: Ian Greenquist1; Michael Tonks1; Yongfeng Zhang2; 1Penn State University; 2Idaho National Laboratory
    The phase field approach can predict UO2 properties such as microstructure, heat conductivity, and fission-gas release rate. Current fuel-performance models are often limited by assumptions of the fuel’s initial microstructure. To improve the initial microstructure, a phase field model of the fuel manufacturing process could be used. The result of the manufacturing model could be used as the initial condition of the fuel-performance model. UO2 pellets are sintered to densities of 95% or greater. The porosity has a large impact on fuel performance. Once the fuel is in a reactor, it continues to condense. The current work seeks to develop a mechanistic phase field model that describes densification of UO2 both during sintering and during reactor operation in the MARMOT mesoscale fuel performance code. In this presentation we will illustrate how the model has been implemented and demonstrate how it extends the capabilities of MARMOT to model fuel fabrication.

3:10 PM  
Study of Oxide Dispersion Strengthened 316L Austenitic Steel by Mechanical Milling: Supriya Koul1; Joysurya Basu1; Kausik Chattopadhyay1; Krishanu Biswas2; Nilay Mukhopadhyay1; 1Indian Institute of Technology (BHU) Varanasi; 2Indian Institute of Technology Kanpur
    Oxide-dispersed-strengthened (ODS) ferritic-martensitic steels are examined to a great deal as possible candidate materials for High-Temperature Gas-Cooled nuclear reactors; similar gains are possible with austenitic alloys. An ODS austenitic stainless steel alloy with varying composition of yttria and titanium was synthesized by mechanical alloying. Microstructure and phase composition of without a titanium additive, as well as alloyed with varying Ti content, has been studied. Micromechanical testing confirms their highly superior mechanical properties at elevated temperatures due to enhanced strengthening effects. Consolidation of the powder particles was done by spark plasma sintering at 1050˚ C with holding time of 12 minutes. Upon an increase of the titanium concentration in the steel the average size of the particles decreases, while their number density grows. Due to the similar type of diffraction patterns of Y2O3, Y2Ti2O7 and YTiO5 it becomes difficult to understand which one has formed for which electron microscopy was done.

3:30 PM Break

4:00 PM  Invited
In Situ Synchrotron Characterization of the Field Assisted Sintering of UO2: David Sprouster1; E. Dooryhee1; L. Ecker1; R. Pokharel2; A Raftery2; D Byler2; K.J. McClellan2; 1Brookhaven National Laboratory; 2Los Alamos National Laboratory
    Field Assisted Sintering (FAS) is a rapidly developing area that employs electrical fields in combination with time, temperature, and pressure, to reduce sintering times and temperatures. Theories on the active mechanisms have been proposed and considerable work has been performed to understand this phenomenon. FAS techniques have been shown to be effective for UO2. Unprecedented rates of densification at temperatures much lower than in conventional sintering are readily achievable. This densification is, however, uncontrolled and the rate controlling mechanisms are not yet understood. In this presentation, recent in situ, time-resolved structural characterization results for UO2, under various FAS conditions will be presented. The high-Z matrix, containment, and rapid FAS events necessitate the use of a high-energy, high-flux beamline to probe the structural dynamics. The evolution of the UO2 samples was quantified in real-time via high-energy X-ray diffraction, performed at the X-ray Powder Diffraction beamline at The National Synchrotron Light Source-II.

4:30 PM  
Thermoelectric Properties of Doped and Pure UO2 at High Temperatures: Ali Massih1; Lars Jernkvist1; 1Quantum Technologies
    The thermoelectric properties of pure and doped UO2, namely the thermal and electrical conductivities and the thermopower, are assessed. We adopt the small polaron theory of the Mott-Hubbard type insulators, wherein the charge carriers, the electron and hole on the U3+ and U5+ ions, are treated as small polarons. For the thermal conductivity, the small polaron theory is applicable at temperatures above 1500 K. A review of the experimental data on the temperature dependence of the aforementioned transport properties is made. The data include UO2 with dopants such as Cr2O3, Gd2O3, Y2O3 and Nb2O5. We compare the applications of the theory with the data. Two limiting regimes, adiabatic and nonadiabatic, with the ensuing expressions for the conductivities and the thermoelectric power are considered. We discuss both the merits and shortcomings of the putative small polaron model and the simplification thereof as applied to pure and doped uranium dioxide.

4:50 PM  
Evaluation of Creep Behavior of UO2 at Sub-grain Length Scales: Benjamin Shaffer1; Bowen Gong1; Harn Chyi-Lim1; Robert McDonald1; Pedro Peralta1; 1Arizona State University
    Thermo-mechanical behavior of oxide nuclear fuels is critical to understand Pellet-Cladding Mechanical Interactions (PCMI) that can lead to fuel fracture, affecting fuel performance significantly. High temperature mechanical behavior, e.g. anisotropy of elastic properties as well as dislocation driven plasticity and creep, can also play a significant role on the mechanical behavior of fuels. This work investigates high temperature creep behavior using ex-situ mechanical testing of depleted Uranium Oxide (d-UO2) samples, heat-treated to obtain large grain sizes and different oxygen stoichiometries. Uniaxial compression testing will be performed at high temperatures under controlled atmospheres to ensure stoichiometry control, and will allow the measurement of creep strain rates and provide data to assist in the correlation of stoichiometry, crystallography, and mechanical behavior of oxide fuels. Samples will be characterized using Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD), and the measured creep behavior will be correlated to microstructurally explicit finite element simulations.

5:10 PM  
Irradiation Dependent Deformation and Thermal Properties of SiC and SiO2 Measured by Using Nanomechanical Raman Spectroscopy: Debapriya Mohanty1; Vignesh Vivekanandan1; Vikas Tomar1; 1Purdue University
    Ceramic material like SiC is a promising material for nuclear cladding due to its high temperature strength and stability under irradiation. It is subjected to irradiation and corrosion during the operation. Importance and the effect of grain orientation and grain size on the mechanical properties is studied by using a combination of nano-indentation and nanomechanical Raman spectroscopy (NMRS). The effect of ion-irradiation and corrosion on the material properties is investigated. Composition and structure of ion irradiated and corroded samples are analyzed by SEM and EDS. The stress distribution as a function of microstructure is analyzed using NMRS. The stress distribution obtained from NMRS is used to validate FEM model. The microstructural based material properties for FEM simulations are obtained from the nanoindentation. Once validated, FEM is used to predict and approximate the stress distribution at various loading conditions. The effect of corrosion and irradiation on material failure is predicted.