Thermal Transport in Crystalline and Non-crystalline Solids: Theory and Experiments: Multiscale Thermal Transport
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Marat Khafizov, Ohio State University; Michael Manley, Oak Ridge National Laboratory; Krzysztof Gofryk, Idaho National Laboratory; Aleksandr Chernatynskiy, Missouri Science and Technology University
Monday 2:30 PM
February 24, 2020
Room: 18
Location: San Diego Convention Ctr
Session Chair: Miaomiao Jin, Idaho National Laboratory; Michael Tonks, University of Florida
2:30 PM Invited
Determining the Impact of Material Microstructure on the Effective Thermal Conductivity Using Mesoscale Simulation and Modeling: Michael Tonks1; 1University of Florida
Modeling and simulation provide a means of predicting the impact of microstructure on the effective thermal conductivity of a material. Mesoscale heat conduction simulations provide a means of directly representing a microstructure and quantifying its impact on the effective thermal conductivity. However, due to the computational cost of this approach, it cannot be used to predict macroscale thermal performance. To overcome this issue, mesoscale simulation results can be used to inform the development of analytical thermal resistor models that efficiently estimate the effective thermal conductivity. In this presentation, we summarize the mesoscale approach, discuss the need for 3D simulations, and illustrate how the mesoscale results can be used to inform the development of thermal resistor models. We demonstrate the approach using various examples related to nuclear reactor fuel.
3:00 PM Invited
The Degradation of the Thermal Conductivity of Oxide Nuclear Fuel: Michael Cooper1; Ben Liu1; Chris Stanek1; David Andersson1; 1Los Alamos National Laboratory
The power density of nuclear fuels creates large thermal gradients across the fuel pellet. This is exacerbated by the poor thermal conductivity of oxide fuel, in particular UO2. Given the importance of temperature in almost all fuel properties, the thermal conductivity tightly couples a range of material processes in nuclear fuel performance. The production of fission products, radiation damage, and O/M change during reactor operation leads to the degradation of the thermal conductivity. For example, degradation due to production of fission gas in the lattice increases the temperature of the pellet and enhances fission gas diffusion and release. In order to support understanding of these coupled behaviors classical MD simulations have been applied to investigate separate phonon scattering processes due to a variety of point defects and clusters created during burnup. The effect of spin-phonon scattering has been accounted for in postprocessing. Phonon scattering in MOX fuel is also investigated.
3:30 PM
Mesoscale Modeling of Thermal Conductivity of a UO2 and BeO Composite Nuclear Fuel: Karim Ahmed1; Sean Mcdeavitt1; 1Texas A&M University
A hybrid phase field and finite-element model was developed to simulate the effective thermal conductivity of UO2-BeO nuclear fuel with different microstructural features. The effects of second-phase (BeO) fraction and morphology, temperature, and interface thermal resistance were investigated. The model predicts that the continuous second phase configuration has a higher effective thermal conductivity than the dispersed second phase configuration for the same volume fraction and temperature. Companion experiments were conducted to validate the model predictions. It was demonstrated that accounting for the interface (Kapitza) thermal resistance is necessary to improve the model predictions. The difference between the model calculations and the experimental results were about 5%, which is within the precision of the experimental measurements.
3:50 PM
Influence of Irradiation-induced Microstructural Defects on the Thermal Conductivity of Single Crystal Thorium Dioxide: Amey Khanolkar1; Zilong Hua1; Marat Khafizov2; Vinay Chauhan2; Yuzhou Wang2; Tiankai Yao1; Lingfeng He2; J. Matthew Mann3; Anter El-Azab4; Jian Gan1; David Hurley1; 1Idaho National Laboratory; 2The Ohio State University; 3Air Force Research Laboratory; 4Purdue University
Microstructural defects formed as a result of fission fragment damage are known to drastically alter thermal conductivity, a fuel property that governs the efficiency of a nuclear reactor. A fundamental understanding of radiation-induced effects on thermal transport is critical for the development of advanced fuels. Ion-irradiation has widely been used to simulate the effects of neutron-irradiation by seeding atomic-to-nanoscale defects of controllable size and density. In this work, we investigate the influence of microstructural defects, induced by ion-irradiation, on the thermal properties of single crystal thorium dioxide samples grown using the hydrothermal technique. The samples were irradiated using 1.7 MeV protons at room temperature. A laser-based modulated thermoreflectance technique was used to measure the thermal diffusivity and conductivity within the damaged ThO2 region. The experimentally measured thermal properties were compared with Boltzmann Transport Equation predictions, to determine the impact of various defect types on the thermal properties of ThO2.
4:10 PM Break
4:30 PM Invited
Thermal Transport in Crystalline Solids with Irradiation-Induced Defects: Computational Modeling and Experiments: Anter El-Azab1; 1Purdue University
We present a theory driven program for predicting thermal transport in irradiated crystalline solids, where computational models and experiments are combined to make progress. A Boltzmann Transport Equation (BTE) approach is used to model phonon transport and interactions at the mesoscale, with input consisting of phonon dispersion relations obtained by inelastic neutron scattering measurements and strain-based models for phonon scattering by lattice defects and microstructural features. Within a Monte Carlo solution scheme, point defects are represented as continuous fields that scatter phonons everywhere in the crystal while extended defects such as dislocation loops and voids are expressed as discrete strain sources that scatter phonons in a non-uniform fashion. Monte Carlos simulations of phonon transport in irradiated ThO2 are compared with Modulated Thermoreflectance measurements of conductivity in the same material. This work is performed as part of the EFRC Center for Thermal Energy Transport under Irradiation.
5:00 PM Invited
Multi-scale Thermal Transport Characterization of Nuclear Fuels: Zilong Hua1; Robert Schley1; Amey Khanolkar1; Austin Fleming1; Colby Jensen1; David Hurley1; 1Idaho National Laboratory
Thermal conductivity of nuclear fuel degrades during operation due to irradiation-induced microstructure damage. The evolution of microstructure is multiscale in nature and includes generation of point defects, line defects and larger three dimensional defects such as pores and small cracks. Laser-based thermal wave microscopy is well suited for this application. Focusing optics can be used to change the heating volume enabling probing thermal transport on multiple length scales. Modulated thermal reflectance and photothermal radiometry are used to investigate thermal transport of porous fuel surrogates on multiple length scales. The validity of a simple porosity correction factor is tested by comparing micron scale results to millimeter scale results.
5:30 PM
Impact of Irradiation Induced Nanoscale Defects on Optical and Thermal Properties of Cerium Dioxide: Vinay Chauhan1; Lingfeng He2; Janne Pakarinen3; David Hurley2; Marat Khafizov1; 1The Ohio State University; 2Idaho National Labratory; 3Belgian Nuclear Research Centre (SCKˇCEN)
Thermal conductivity is a critical physical property of ceramic materials such as oxides of uranium and thorium which are used as nuclear fuels. In this study, we use cerium dioxide as a surrogate material to study the impact of irradiation damage on thermal transport properties of nuclear fuels. Polycrystalline ceria samples were irradiated at 600 ēC at the same dose but different rates using 2 MeV protons. Thermal conductivity measured using modulated thermoreflectance approach showed a notable reduction in irradiated samples and was correlated to defects revealed by microstructure characterization. Lattice expansion detected using X-ray diffraction and Raman spectroscopy analysis were used to quantify point defects while the dislocation loops were characterized using transmission electron microscope. The changes in thermal conductivity were analyzed using a phonon-mediated thermal transport model to identify defect type responsible for these observed reduction.