Thermophysical properties of sodium nitrate and sodium chloride solutions and their effects on fluid flow in unsaturated media

Xu, Tianfu ; Pruess, Karsten

Lawrence Berkeley National Laboratory

关键词: Sodium Nitrates;    Radioactive Waste Storage;    Thermal Conductivity;    Liquid Wastes;    Density;   

DOI  :  10.2172/790019
RP-ID  :  LBNL--48913
RP-ID  :  AC03-76SF00098
RP-ID  :  790019

美国|英语

来源: UNT Digital Library

【 摘 要 】

Understanding movement of saline sodium nitrate (NaNO{sub 3}) waste solutions is important for assessing the contaminant migration near leaking waste storage tanks in the unsaturated zone at the Hanford site (Washington, USA). The purpose of this study is to contribute a basic understanding of effects of the thermophysical behavior of NaNO{sub 3} solutions on fluid flow in unsaturated media. We first present mathematical expressions for the dependence of density, viscosity, solubility and vapor pressure of NaNO{sub 3} solutions on both salt concentration and temperature, which were determined by fitting from published measured data. Because the previous studies of thermophysical behavior of sodium chloride (NaCl) solutions can provide a basis for those of NaNO{sub 3} solutions, we also present a comparison of thermophysical properties of both salt solutions. We have implemented the functional thermophysical properties of NaNO{sub 3} solutions into a new TOUGH2 equation-of-state module EWASG-NaNO{sub 3}, which is modified from a previous TOUGH2 equation-of-state module EWASG for NaCl. Using the simulation tool, we have investigated effects of the thermophysical properties on fluid flow in unsaturated media. The effect of density and viscosity of saline solutions has been long recognized. Here we focus our attention on the effect of vapor pressure lowering due to salinity. We present simulations of a one-dimensional problem to study this salinity-driven fluid flow. A number of simulations were performed using different values of thermal conductivity, permeability, and temperature, to illustrate conditions and parameters controlling these processes. Results indicate that heat conduction plays a very important role in this salinity-driven vapor diffusion by maintaining a nearly constant temperature. The smaller the permeability, the more water is transferred into the saline environment. Effects of permeability on water flow are also complicated by effects of capillary pressure and tortuosity. The higher the temperature, the more significant the salinity driven fluid flow.