Numerical investigation of heating and cooling-induced damage and brine migration in geologic rock salt : Insights from coupled THM modeling of a controlled block scale experiment

Abstract

Controlling brine flow is important for the safe disposal of radioactive waste in salt rocks. Thermal and mechanical processes can have a significant impact on brine flow, although this has never been thoroughly investigated. In this study, we conduct fully coupled THM modeling for analyzing brine flow in rock salt, considering non-isothermal two-phase flow through deformable porous media. To rigorously represent rock salt behavior, we incorporate suitable phenomenological models for creep and shear and tensile-induced dilatancy/damage, and their effect on the flow properties. To validate such a complex model, we use it to analyze an experiment on a meter-scale salt block subjected to multistage heating and cooling under controlled laboratory conditions. The experimental data and our model predictions of temperature and brine inflow show good agreement. Our modeling shows that it is important to consider the coupling between the heating- and cooling-induced damage and the flow properties for rigorously estimating brine inflow. Based on our modeling, a cooling-induced brine inflow spike is caused by a permeability increase due to tensile dilatancy. Thus, our modeling will be useful for a proper design of a cooling phase in the salt repositories to avoid or minimize damage and the resulting brine inflow.