Thermodynamics of Materials in Extreme Environments: Thermodynamic Studies of Nuclear Materials
Sponsored by: ACerS Basic Science Division, ACerS Energy Materials and Systems
Program Organizers: Xiaofeng Guo, Washington State University; Kristina Lilova, Arizona State University; Kyle Brinkman, Clemson University; Alexandra Navrotsky, Arizona State University; Jake Amoroso, Savannah River National Laboratory; Xingbo Liu, West Virginia University; Gustavo Costa, NASA Glenn Research Center
Tuesday 2:00 PM
November 3, 2020
Room: Virtual Meeting Room 22
Location: MS&T Virtual
Session Chair: Kyle Brinkman, Clemson University
2:00 PM Invited
Thermochemical Modeling of Molten Salt Systems for Reactors and Simulations with the Molten Salt Thermodynamic Database: Theodore Besmann1; Kaitlin Johnson1; Johnathan Ard1; Jacob Yingling1; Matthew Christian1; Juliano Schorne Pinto1; Jacob McMurray2; Markus Piro3; 1University of South Carolina; 2Oak Ridge National Laboratory; 3Ontario Tech
Molten salt reactors (MSRs), with salt as the fuel/coolant or solely the coolant, requires a close understanding of salt properties to be able to simulate normal and off-normal operations. Among the most important are the thermochemical properties of the salt, that is the Gibbs energy relations for the complex liquid and solid solutions as these provide thermal properties as well as critical phase equilibria such as solidus and liquidus. Models for the pseudo-binary and -ternary fluoride and chloride salt systems are being compiled, and where necessary developed, to provide a thermochemical resource. The molten salt thermochemical database (MSTDB) is being implemented with the thermochemical solver THERMOCHIMICA in prospective MSR simulation codes for use in reactor design, simulated reactor operations, and assessment of off-normal scenarios to support regulatory activities. The presentation will cover current modeling and development of MSTDB, and provide the context for its use in reactor simulation.
2:30 PM
Effect of Physically Determined Coordination-numbers for Modeling Molten Salt Fuels Using the Modified Quasi-chemical Model (MQM): Matthew Christian1; Juliano Pinto1; Theodore Besmann1; Timothy Lynch2; Wilson Chiu3; Nancy Birkner4; Kyle Brinkman4; 1University of South Carolina; 2University of Connecticut ; 3University of Connecticut; 4Clemson University
Accurately modeling the thermochemical properties of fuel-coolant in molten salt reactors (MSRs) is critical to simulating conditions under operating and accident scenarios. The modified quasi-chemical model (MQM) is frequently used to represent the molten salt’s thermochemical state as it accounts for short-range ordering that arises from strong ionic interactions via atomic coordination numbers. The values for each atomic species are typically approximated from representative crystalline phases and thus may not be reflective of the molten state. Therefore, the short-range ordering imposed by the coordination numbers may not accurately yield Gibbs energies for the liquid and result in incorrect phase relations for molten salt mixtures. In this presentation, we will show how using coordination numbers, predicted by density-functional theory (DFT) and confirmed with experiment, influences modeled phase diagrams generated using MQM for the melt.
2:50 PM
The LiF–ZrF4 System Revisited - An Updated Thermodynamic Description Using New Information Data: Juliano Schorne Pinto1; Matthew Christian1; Timothy Lynch2; Wilson Chiu2; Theodore Besmann1; 1University of South Carolina; 2University of Connecticut
The LiF-ZrF4 system has been revisited and incorporated into the Molten Salt Thermodynamic Database (MSTDB). This study reviewed the structural information and phase equilibria of the LiF-ZrF4 system by checking the consistency of previous thermodynamic models with experimental data and supplemented with calculations using density-functional theory (DFT). This improves the system model using the modified quasi-chemical model (MQM) to simulate the salt’s molten state. The model is compared to results from density-functional theory and experimental observations of the LiF-ZrF4 system.
3:10 PM
Thermodynamic Modelling of Vacancies in Zirconium Carbide: Theresa Davey1; Ying Chen1; 1Tohoku University
Zirconium carbide is of interest in nuclear and aerospace industries due to its stability and strength at extremely high temperatures. Its properties are strongly affected by significant carbon vacancies that give a wide range of stability. In conventional CALPHAD thermodynamic modelling, these vacancies are assumed to be randomly distributed and properties relating to the vacancies are not directly considered. However recent experimental and first-principles insights suggest the presence of vacancy-ordering and different regimes within the phase diagram that are dominated by either structural or thermal vacancies. Using first-principles calculations, the character of the vacancies is elucidated and mapped. Calculations of defect-related properties are used to inform development of Gibbs energy models that may be used where the thermodynamic properties are highly dependent on point defects and their ordering. Incorporating such information directly into the thermodynamic database provides a physically consistent description which should allow further predictive ability.