Exploring detailed microcosmic mechanisms of sodium chloride deposition in supercritical water reactors from the aspect of solvation structure: A combination of MD and QM simulations

Abstract

The dissolution characteristics and microscopic dissolution process of salt in supercritical water (SCW) are the fundamental influence of scale formation. In this paper, molecular dynamics (MD) and quantum mechanics (QM) were used to study the solubility and solvation structure of sodium chloride in supercritical water. The potential mean force (PMF), radial distribution function (RDF) and coordination number (CN) indicate that the solubility of sodium chloride in SCW decreases with the increase of temperature and the decrease of density. As the system density decreases from 0.3 g/cm3 to 0.1 g/cm3 and the temperature increases from 600 K to 900 K, the CN of water molecules in the solvation shell decreases from 2.89 to 1.01, which is consistent with the trend of the experimental results. The electrostatic potential distribution and intermolecular interaction of the solvation shell around Na+ were obtained by QM method. The solution free energy of Na+–3H2O in implicit solvent was obtained. In the condition range of this study, when the temperature is the lowest and the dielectric constant is the largest, the free energy of dissolution is the smallest, which is −0.0991 a.u. This study will lay a foundation for the study of salt deposition in SCW.