Thermodynamic modelling assessment of the ternary system Cs-Mo-O

Smith, A.L.; Pham Thi, T. N.; Guéneau, C.; Dumas, J.; Epifano, E.; van Burik, W.; Dupin, N.

doi:10.1016/j.calphad.2021.102350

Thermodynamic modelling assessment of the ternary system Cs-Mo-O

Title

Thermodynamic modelling assessment of the ternary system Cs-Mo-O

Author

Smith, A.L. (TU Delft RST/Reactor Physics and Nuclear Materials)
Pham Thi, T. N. (CEA Cadarache)
Guéneau, C. (Université Paris-Saclay, Paris)
Dumas, J. (TU Delft Communication Education Student Affairs; CEA Cadarache)
Epifano, E. (TU Delft RST/Reactor Physics and Nuclear Materials; Université de Toulouse)
van Burik, W. (Student TU Delft)
Dupin, N. (Calcul Thermodynamique, Orcet)

Date

2021

Abstract

This work reports the thermodynamic modelling assessment of the rather complex Cs-Mo-O system, which is key for the understanding of fission products chemistry in oxide fuelled Light Water Reactors (LWRs) and next generation Sodium-cooled and Lead-cooled Fast Reactors (SFRs and LFRs). The model accounts for the existence of the ternary molybdates Cs₂MoO₄ (α and β), Cs₂Mo₂O₇ (α and β), Cs₂Mo₃O₁₀, Cs₂Mo₄O₁₃, Cs₂Mo₅O₁₆, and Cs₂Mo₇O₂₂, for which sufficient structural and thermodynamic information are available in the literature. These phases are treated as stoichiometric in the model. The liquid phase is described with an ionic two-sublattice model, and the gas phase as an ideal mixture. The optimized Gibbs energies are assessed with respect to the known thermodynamic and phase equilibrium data in the Cs₂MoO₄-MoO₃ pseudo-binary section. A good agreement is generally obtained within experimental uncertainties. The calculated vapour pressures above Cs₂MoO₄ (solid and liquid) are also compared to the available experimental data. Finally, isotherms of the Cs-Mo-O ternary phase diagram are calculated at relevant temperatures for the assessment of the fuel pin behaviour in LWRs, SFRs and LFRs.