(457b) Comparison Between the OLI-MSE and eNRTL Models in Predicting Thermodynamic Properties of the NaNO3-HNO3-H2O Ternary System

Chemical engineers engaged in spent nuclear fuel and nuclear waste processing have pursued high fidelity process modeling and simulation as have their counterparts in the conventional chemical industries. Although current modeling and simulation is capable of representing the physical and chemical processes in nuclear waste treatment at a certain level of sophistication, accurate thermodynamic models for the systems involved are essential not only to predict their chemical and physical properties correctly, but also to support high fidelity process simulation. Since reprocessing usually involves extraction with concentrated nitric acid followed by neutralization with caustic soda (e.g., the PUREX process), large amounts of sodium nitrate are formed. Consequently, three compounds â?? nitric acid, sodium nitrate, and water â?? are typically the most abundant species in nuclear waste liquids. The OLI-MSE (mixed solvent electrolyte) and eNRTL (electrolyte non-random two-liquid) are two of the activity coefficient models most widely used in the nuclear industry for aqueous nitric acid solutions. In the present work, the two models are compared side-by-side for the first time by having their results checked against literature experimental data on vapor-liquid equilibrium, calorimetric properties (i.e., heat capacity and liquid molar enthalpy), and speciation for the NaNO₃-HNO₃-H₂O ternary system and its subsystems.