The disposal of heat-generating nuclear waste in salt host rock generates a thermal gradient around the waste package that may cause brine inclusions in the salt grains to migrate toward the waste package. In this study, a dual-continuum model is developed to analyze such a phenomenon. In this model, fluid flow in terms of advective and diffusive fluxes in the interconnected pore space and diffusive and thermal-diffusive fluxes in the salt grains is considered. Due to the very distinct behavior of fluid flow in the interconnected pore space versus in the salt grains, this process is simulated based on a dual-continuum model. In the dual-continuum model, the mass balance of salt and water in the two continua is separately considered, and the coupling between the two continua is represented by flux associated with brine migration in one medium and out of another. The energy balance is simulated assuming thermal equilibrium among different components and phases in the whole system. For mechanical analysis, a new formulation (extended finite volume method, XFVM) is proposed and is applied with a Voronoi tessellated mesh. The coupling between the hydraulic and mechanical fields in terms of pore-volume effects is consistent with Biot’s theory, while thermal and mechanical fields are linked in terms of thermal expansion. The resulting fully coupled THM model is capable of modeling strongly nonlinear features, involving salt concentration effects on fluid mass associated with advection, and thermal effects on brine migration. A Newton-Raphson iteration formula is used to generate the linearized equations for this nonlinear problem. The model was verified step by step for each component of the coupling terms, including thermal-hydraulic (TH) and hydro-mechanical (HM) couplings, and was applied to analyze diffusion in single continuum and dual continua, small-scale brine migration, and large-scale brine migration induced by thermal gradient. The results show that the model is able to quantify brine under different conditions and thermal gradients, making it a valuable tool for performance assessment for nuclear waste disposal in salt.

盐核岩中发热核废料的处置会在废料包周围产生一个热梯度，这可能导致盐粒中的盐水夹杂物向废料包迁移。在这项研究中，建立了一个双连续谱模型来分析这种现象。在该模型中，考虑了相互连通的孔隙空间中的对流和扩散通量以及盐粒中的扩散和热扩散通量的流体流动。由于相互连接的孔空间中流体流与盐颗粒中流体流的行为截然不同，因此该过程基于双连续模型进行了模拟。在双连续体模型中，分别考虑了两个连续体中盐和水的质量平衡，两个连续体之间的耦合由与盐水在一种介质中迁移出另一种介质相关的通量表示。假设整个系统中不同组件和各相之间达到热平衡，则模拟能量平衡。对于机械分析，提出了一种新的公式（扩展有限体积方法，XFVM），并与Voronoi棋盘格化网格一起应用。就孔隙体积效应而言，水力场与机械场之间的耦合与Biot的理论是一致的，而热场与机械场在热膨胀方面是相关的。生成的完全耦合的THM模型能够对强烈的非线性特征进行建模，其中包括与平流有关的盐浓度对流体质量的影响以及对盐水迁移的热影响。Newton-Raphson迭代公式用于生成此非线性问题的线性方程。针对耦合项的每个组成部分逐步验证了该模型，包括热力（TH）和液压-机械（HM）耦合，并用于分析单连续体和双连续体中的扩散，小规模盐水迁移，和热梯度引起的大规模盐水运移。结果表明，该模型能够量化不同条件和热梯度下的盐水，使其成为评估盐中核废料性能的有价值的工具。并用于分析单连续体和双连续体中的扩散，小规模盐水迁移和热梯度引起的大规模盐水迁移。结果表明，该模型能够量化不同条件和热梯度下的盐水，使其成为评估盐中核废料性能的有价值的工具。并用于分析单连续体和双连续体的扩散，小规模盐水迁移和热梯度引起的大规模盐水迁移。结果表明，该模型能够对不同条件和热梯度下的盐水进行定量，使其成为评估盐中核废料处理性能的有价值的工具。