A Coupled Continuum-Discontinuum Framework for Thermal-Hydro-Mechanical Modeling of Deep Geological Repository for Nuclear Waste Disposal

ABSTRACT: Ensuring the long-term safety of nuclear repository centers around assessing the evolution of damage to the repository due to repository-induced and geological perturbations and evaluating the stability of the placement rooms for the duration of the regulatory period. The problem is challenging because it involves multiple physical processes. These processes are coupled and occur across temporal and spatial scales, including stress redistribution due to excavation, temperature-induced stresses after emplacement of the waste, groundwater pore pressure changes due to mechanical and temperature changes, and stress changes due to environmental loading. In this paper, we present a coupled continuum-discontinuum framework to merge near- and far-field models into one, keeping the needed spatial and temporal discretization levels, with the near-field model seamlessly incorporated into the far-field model for thermal-hydro-mechanical (THM) modeling analysis. The near-field model uses the distinct element methods (DEM) approach to evaluate damage and explicitly capture fracture formation and rock fragmentation, while providing full THM coupling. The far-field model uses a continuum approach to represent the behavior of the repository as a whole interacting with the in-situ geological environment mechanically, as well as capturing the hydro-thermal responses.