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

摘要

In high-level radioactive waste disposal, one ofthe key issues is predicting the behavior of bentonite, which is animportant component of the engineering barrier system (EBS).However any existing macro-phenomenological models arebasically insufficient for assessing the true behavior of bentonite clay.Clay is a typical micro-inhomogeneous material. It consists ofclay minerals, macro-grains (quartz etc.), water, air etc. as itsmicroscopic level components. There are two essential issues tobe considered in analyzing the behavior of such micro-inhomogeneous materials: one is how to determine thecharacteristics of constituent components, which are directlyaffected by molecular movement; and the other is how to relatethe microscopic characteristics to the macroscopic behavior. Forsolving the first problem, we apply the molecular dynamicsmethod (MD) to determine the material properties of eachconstituent component, then homogenization analysis (HA)(Sanchez-Palencia, 1980, Non-homogeneous Media andVibration Theory. Springer-Verlag, Berlin; Bakhvalov andPanasenko, 1984, Homogenization: Averaging Processes inPeriodic Media, Nauka, Moscow) is used for estimating themicro to macro behaviors. This unique combination procedure ofthe MD and the HA is called the unified MD/HA method, and weapplied this method to the time-dependent visco-elastic problem(Kawamura et al., 1997, A new approach for predicting the longterm behavior of bentonite: the unified method of moleculardynamics and homogenization alaysis. Proc. Scientific Basis forNuclear Waste Management XXI, Davos, Switzerland, materialResearch Society, p.359-366) and the seepage problem (Ichikawaet al., 1998, Unified molecular dynamics/homogenizationanalysis for water flow in bentonite, Proc. 1998 Int. High-levelRadioactive Waste Management Conf., Las Vegas, AmericanNuclear Society, pp. 422-428).We present here a summary of the previous works, and discussthe further possibilities of the unified MD/HA procedure.