Excavation Damaged Zone (EDZ) is created by the excavation of deposition holes and disposal tunnels at high-level radioactive waste repository that causes macro- and micro-fracturing in the surrounding rock. Since EDZ can significantly increase the hydraulic transmissivity in the rock and act as a major pathway of leaked radionuclides, consideration of EDZ in terms of safety assessment is very important. Moreover, long-term stress changes such as stress redistribution due to excavation of nearby deposition holes and disposal tunnels, thermal stress due to temperature rise, effective stress change due to pore pressure change, and swelling pressure of bentonite buffer can increase EDZ size and change in thermal-hydraulic-mechanical properties, and consequently, it can affect the transport of radionuclides. Therefore, in order to analyze the effect of long-term evolution of EDZ on radionuclide transport, it is essential to conduct numerical analysis considering the coupled Thermal-Hydraulic- Mechanical (THM) behavior in EDZ. In order to simulate the behavior of EDZ, coupled THM model was developed using the Adaptive Process-based total system performance assessment framework for a geological disposal system (APro) proposed by the Korea Atomic Energy Research Institute (KAERI). The concept of damage was introduced to demonstrate the jointed rock as a continuous medium. Among several damage models, Mazars damage model was applied in this study. Mazars damage model is the most well-known model for concrete which has similar behavior with rock as brittle material, and the input data of the model can be easily obtained through laboratory testing. If damage occurs due to the influence of thermal-hydraulic-mechanical coupled behavior at the bedrock, the properties change according to the degree of damage, and as a result, the migration of the radionuclide is affected. Based on this conceptual model, radionuclide transport model in the near field considering the long-term evolution of EDZ was developed. To investigate the effect of EDZ in terms of process-based performance assessment, the modeling results with and without EDZ were compared. Finally, by simulating the coupled THM behavior of EDZ with damage model, the effect of long-term evolution of EDZ on radionuclide transport was investigated.

• Jaewon Lee(Korea Atomic Energy Research Institute (KAERI)) Corresponding author
• Jung-Woo Kim(Korea Atomic Energy Research Institute (KAERI))