Unified molecular dynamics and homogenization analysis for bentonite behavior: Current results and future possibilities

In high-level radioactive waste disposal, one of the key issues is predicting the behavior of bentonite, which is an important component of the engineering barrier system (EBS). However any existing macro-phenomenological models are basically insufficient for assessing the true behavior of bentonite clay. Clay is a typical micro-inhomogeneous material. It consists of clay minerals, macro-grains (quartz etc.), water, air etc. as its microscopic level components. There are two essential issues to be considered in analyzing the behavior of such micro-inhomogeneous materials: one is how to determine the characteristics of constituent components, which are directly affected by molecular movement; and the other is how to relate the microscopic characteristics to the macroscopic behavior. For solving the first problem, we apply the molecular dynamics method (MD) to determine the material properties of each constituent component, then homogenization analysis (HA) (Sanchez-Palencia, 1980, Non-homogeneous Media and Vibration Theory. Springer-Verlag, Berlin; Bakhvalov and Panasenko, 1984, Homogenization: Averaging Processes in Periodic Media, Nauka, Moscow) is used for estimating the micro to macro behaviors. This unique combination procedure of the MD and the HA is called the unified MD/HA method, and we applied this method to the time-dependent visco-elastic problem (Kawamura et al., 1997, A new approach for predicting the long term behavior of bentonite: the unified method of molecular dynamics and homogenization analysis. Proc. Scientific Basis for Nuclear Waste Management XXI, Davos, Switzerland, Material Research Society, pp. 359-366) and the seepage problem (Ichikawa et al., 1998, Unified molecular dynamics/homogenization analysis for water flow in bentonite, Proc. 1998 Int. High-Level Radioactive Waste Management Conf., Las Vegas, American Nuclear Society, pp. 422-428). We present here a summary of the previous works, and discuss the further possibilities of the unified MD/HA procedure.