Geologic Disposal Facilities (GDFs) are the preferred long-term solution for the safe disposal of radioactive waste. The construction and subsequent performance of deep geologic repositories may create damage and fractures in the rocks surrounding the waste-bearing boreholes, compromising the integrity of the geological barrier that is intended to prevent radionuclides from escaping into the biosphere.

In this work, the processes that may lead to the fracturing and damage of the host rock are numerically modelled in three dimensions with a finite element-based, monolithically-coupled thermo-mechanical simulator. Previous fracture growth methodology is extended, by incorporating continuum damage mechanics to simulate the nucleation of fractures. A novel lofting algorithm improves the meshing efficiency of fracture mechanics models, and enhances the generation of detailed three-dimensional geometries. The simulations explicitly capture the initiation and growth of new fractures, due to the changing thermo-mechanical loadings. Validations of the simulation approach are conducted at borehole and tunnel scales, based on comparisons against analytical models, and experimental measurements made at several sites.

The impact of borehole drilling, and subsequent heating and cooling, is investigated specifically for the Swedish Forsmark GDF site, using realistic properties and timelines. Single and multiple borehole geometries of varying characteristics are considered, including varying borehole shapes and spacings, tunnel effects, and in situ stress variations. Borehole spacing has a significant effect on the fracture pattern formed across interacting boreholes, whereas heating has a secondary effect on fracture growth. Material property variations are found to induce less uniform nucleation and fracture growth extension. The effect of long-term evolution of glacial cycle stresses is also evaluated for initially intact rocks. These glaciation-induced stresses are shown to also induce spalling patterns with variations in orientation and extension, depending on the loading scenario.