Geological disposal of high-level radioactive waste (HLW) is a critical shared issue for countries that use nuclear energy. Ensuring long-term safety requires an understanding of coupled thermal–hydrological–mechanical–chemical (THMC) processes, as they directly affect the performance of both engineered and natural barriers. This study reviews the literature on THMC phenomena demonstrated in Japanese underground facilities, their reproduction in laboratory-scale experiments, and approaches for predicting the long-term evolution of host rock properties. Synthesizing these findings, we clarify the progress to date and identify research required for future repository development. The review highlights key directions for further work: improving the understanding of coupled THMC behavior in host rock after waste emplacement; establishing repository design methodologies considering the THMC interactions between EBS and host rock mass; and enhancing computational efficiency through the use of surrogate modeling and advanced artificial intelligence technologies. Such innovations are expected to refine repository design and improve the reliability of long-term safety assessments, thereby contributing to the implementation of HLW geological disposal.
Aoyagi et al. (Tue,) studied this question.