A thermochemical representation of the Na-Al-Si-B-O system relevant for nuclear waste glass has been developed based on the associate species approach for the glass solution phase. Thermochemical data were assessed and associate species data determined for binary and ternary subsystems in the Na_2O-Al_2O_3-B_2O_3-SiO_2 system. Computed binary and ternary phase diagrams were compared to published diagrams during this process, with adjustments in data made as necessary to obtain consistent thermodynamic values. The resulting representation for the four oxide system was used to help understand the problem of nepheline precipitation in certain waste glass formulations.
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