Modeling was carried out on vapor-liquid equilibria of nitric acid containing highly concentrated fission product nitrates to simulate the evaporation characteristics of a reprocessing plant high-level liquid waste (HLLW) concentrator. Results obtained with the model verified its reliability for prediction of vaporliquid equilibria of nitric acid containing highly concentrated nitrates. The results compared well with experimental data obtained with a pilot plant for HLLW concentration (capacity of 40 dm3).