A novel coupled thermal-hydraulic-mechanical-chemical (THMC) simulator for fractured porous rock was developed in the present study based on explicit fracture models. This work is an attempt to describe the spatial coupled phenomena sensitive to fracture generation within rock masses by using explicit fracture representation. The simulator was then applied to numerically predict the long-term evolution in the permeability of a rock mass working as a natural barrier within a geological disposal facility of high-level radioactive waste (HLW). The predicted results showed that the fractures generated due to the excavation of the disposal cavity drastically increased the rock permeability around the cavity and that the gradual decrease in permeability with time was caused only within specific fractures where the pressure solution had been activated after the disposal of the waste package into the cavity. The maximum decrease in permeability within the fractures was more than two orders of magnitude. Overall, it was confirmed that the developed simulator can capture the heterogeneous and local permeability evolutions among multiple fractures due to geochemical creep over the long term.
When examining the performance of geological disposal facilities of high-level radioactive waste (HLW), it is essential to numerically predict the long-term evolution of the fracture permeability on the rock mass that works as a natural barrier. The fracturing within a natural barrier occurs due to the excavation of the cavity for disposing the HLW. Afterwards, the permeability of the generated fractures may be altered by the coupled phenomena among the fluid flow, earth pressure, solute transport, heat transfer, and geochemical reactions of the minerals and pore water. Therefore, both the fracture generation and the subsequent coupled thermal-hydraulic-mechanical-chemical (THMC) phenomena that may act on the rock fractures should be described reasonably. In particular, among the coupled phenomena, the geochemical reactions, such as the pressure dissolution at the contacting asperities within the rock fractures, may have a non-negligible influence on the change in fracture permeability with time over the long term [1]. Although many coupled simulators have been developed up to now [e.g., 2-4], most of them represent rock fractures based on continuum damage models and cannot explicitly capture the details of the formation of the fractures and the coupled phenomena acting on the fractures. Meanwhile, several coupled simulators based on explicit models of rock fractures have also recently been proposed [e.g., 5-7]. Despite the fact that they are able to grasp the detailed phenomena related to rock fractures, including fracture initiation/propagation and various fluid-driven transport processes through the fracture network, the occurrence of geochemical reactions within the fractures have not been considered.
