New Rapid Evaluation for Long-Term Behavior in Deep Geological Repository by Geotechnical Centrifuge—Part 2: Numerical Simulation of Model Tests in Isothermal Condition

Abstract

In high-level radioactive waste disposal repositories, there are long-term complex thermal, hydraulic, and mechanical (T–H–M) phenomena that involve the generation of heat from the waste, the infiltration of ground water, and swelling of the bentonite buffer. The ability to model such coupled phenomena is of particular importance to the repository design and assessments of its safety. We have developed a T–H–M-coupled analysis program that evaluates the long-term behavior around the repository (called “near-field”). We have also conducted centrifugal model tests that model the long-term T–H–M-coupled behavior in the near-field. In this study, we conduct H–M-coupled numerical simulations of the centrifugal near-field model tests. We compare numerical results with each other and with results obtained from the centrifugal model tests. From the comparison, we deduce that: (1) in the numerical simulation, water infiltration in the rock mass was in agreement with the experimental observation. (2) The constant-stress boundary condition in the centrifugal model tests may cause a larger expansion of the rock mass than in the in situ condition, but the mechanical boundary condition did not affect the buffer behavior in the deposition hole. (3) The numerical simulation broadly reproduced the measured bentonite pressure and the overpack displacement, but did not reproduce the decreasing trend of the bentonite pressure after 100 equivalent years. This indicates the effect of the time-dependent characteristics of the surrounding rock mass. Further investigations are needed to determine the effect of initial heterogeneity in the deposition hole and the time-dependent behavior of the surrounding rock mass.