Experimental and Computational Exploration of the NaF-ThF4Fuel System: Structure and Thermochemistry

Maarten B.J.W. Schreuder, Jaén A. Ocádiz Flores, Aimen E. Gheribi, Ondrej Beneš, Jean Christophe Griveau, Eric Colineau, Rudy J.M. Konings, Anna Louise Smith*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

The structural, thermochemical, and thermophysical properties of the NaF-ThF4 fuel system were studied with experimental methods and molecular dynamics (MD) simulations. Equilibrium MD (EMD) simulations using the polarizable ion model were performed to calculate the density, molar volume, thermal expansion, mixing enthalpy, heat capacity, and distribution of [ThFn]m- complexes in the (Na,Th)Fx melt over the full concentration range at various temperatures. The phase equilibria in the 10-50 mol % ThF4 and 85-95 mol % ThF4 regions of the NaF-ThF4 phase diagram were measured using differential scanning calorimetry, as were the mixing enthalpies at 1266 K of (NaF/ThF4) = (0.8:0.2), (0.7:0.3) mixtures. Furthermore, the β-Na2ThF6 and NaTh2F9 compounds were synthesized and subsequently analyzed with the use of X-ray diffraction. The heat capacities of both compounds were measured in the temperature ranges (2-271 K) and (2-294 K), respectively, by thermal relaxation calorimetry. Finally, a CALPHAD model coupling the structural and thermodynamic data was developed using both EMD and experimental data as input and a quasichemical formalism in the quadruplet approximation. Here, 7- and 8-coordinated Th4+ cations were introduced on the cationic sublattice alongside a 13-coordinated dimeric species to reproduce the chemical speciation, as calculated by EMD simulations and to provide a physical description of the melt.

Original languageEnglish
Pages (from-to)8558-8571
Number of pages14
JournalJournal of Physical Chemistry B
Volume125
Issue number30
DOIs
Publication statusPublished - 2021

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