Experimental investigation and thermodynamic modelling of the ThF4-PuF3 phase diagram

•First experimental results on the phase equilibria and phase stabilities in the ThF4-PuF3 system.•New thermodynamic model for the ThF4-PuF3 system.•Re-assessment of the ThF4-PuF3 and LiF-ThF4-PuF3 phase diagrams.•Discussion on advantages and limitations of using proxy compounds to derive thermodynamic models from experimental data.•Data contribute for extension and improvement of the JRCMSD thermodynamic database on molten halide systems.