TY - JOUR
T1 - New insights and coupled modelling of the structural and thermodynamic properties of the LiF-UF4 system
AU - Ocádiz-Flores, J. A.
AU - Gheribi, A. E.
AU - Vlieland, J.
AU - Dardenne, K.
AU - Rothe, J.
AU - Konings, R. J.M.
AU - Smith, A. L.
PY - 2021
Y1 - 2021
N2 - © 2021 The Authors LiF-UF4 is a key binary system for molten fluoride reactor technology, which has not been scrutinized as thoroughly as the closely related LiF-ThF4 system. The phase diagram equilibria in the system LiF-UF4 are explored in this work with X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The short-range ordering in the molten salt solution is moreover surveyed with Extended X-ray Absorption Fine Structure spectroscopy (EXAFS) and interpreted using a combination of standard fitting of the EXAFS data and Molecular Dynamics (MD) simulations with a Polarizable Ion Model (PIM) potential. The density, excess molar volume, thermal expansion, heat capacity, and enthalpy of mixing are extracted from the MD simulations across a range of temperatures and compositions; the behavior is non-ideal, with reasonably good agreement with the experimental data. Also calculated is the distribution of heteropolyanions in the liquid solution, and modelled using the quasi-chemical formalism in the quadruplet approximation taking into account the existence of the single-shell complexes [UF7]3−, [UF8]4−, and the dimeric species [U2F14]6−. Subjecting the optimization of the excess Gibbs energy parameters of the liquid solution to the constraints of the phase diagram data and local structure of the melt as derived from the EXAFS and coupled MD simulations, a CALPHAD-type assessment is proposed, linking structural and thermodynamic properties, with a rigorous physical description of the melt.
AB - © 2021 The Authors LiF-UF4 is a key binary system for molten fluoride reactor technology, which has not been scrutinized as thoroughly as the closely related LiF-ThF4 system. The phase diagram equilibria in the system LiF-UF4 are explored in this work with X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The short-range ordering in the molten salt solution is moreover surveyed with Extended X-ray Absorption Fine Structure spectroscopy (EXAFS) and interpreted using a combination of standard fitting of the EXAFS data and Molecular Dynamics (MD) simulations with a Polarizable Ion Model (PIM) potential. The density, excess molar volume, thermal expansion, heat capacity, and enthalpy of mixing are extracted from the MD simulations across a range of temperatures and compositions; the behavior is non-ideal, with reasonably good agreement with the experimental data. Also calculated is the distribution of heteropolyanions in the liquid solution, and modelled using the quasi-chemical formalism in the quadruplet approximation taking into account the existence of the single-shell complexes [UF7]3−, [UF8]4−, and the dimeric species [U2F14]6−. Subjecting the optimization of the excess Gibbs energy parameters of the liquid solution to the constraints of the phase diagram data and local structure of the melt as derived from the EXAFS and coupled MD simulations, a CALPHAD-type assessment is proposed, linking structural and thermodynamic properties, with a rigorous physical description of the melt.
KW - CALPHAD
KW - Differential scanning calorimetry
KW - EXAFS
KW - Molten salt reactor
KW - Polarizable ion model (PIM)
KW - X-ray diffraction
UR - http://www.scopus.com/inward/record.url?scp=85102106473&partnerID=8YFLogxK
U2 - 10.1016/j.molliq.2021.115820
DO - 10.1016/j.molliq.2021.115820
M3 - Article
AN - SCOPUS:85102106473
SN - 0167-7322
VL - 331
JO - Journal of Molecular Liquids
JF - Journal of Molecular Liquids
M1 - 115820
ER -