Microscale Problem of HA for Bentonite

We present here the HA results for diffusion in bentonite and compare these with the experimental results. For a pure smectitic bentonite, Kunipai F , we apply the two-scale HA By solving the microscale equation (9.26) using a finite element method 

First we consider a pure smectitic bentonite, Kunipia F , which consists of stacks of clay minerals including interlayer water, and external water. We assume a simple stack with eight clay minerals in the micro-domain (Fig. 9.11). From MD results, we know the diffusivity and viscosity as a function of the distance from the surface of a clay mineral. 

Tritium water HTO ( H20) consists of a tritium atom, which is an isotope of hydrogen, an oxygen atom and a normal hydrogen atom. The chemical property is almost same as the normal water H2O, and in a bentonite saturated with normal 

The water in the pme smectitic bentonite is classified as interlayer water, which exists in the interlayer space between the clay stacks, and external water, which exists externally to the clay stacks. Both the physical and chemical properties of each type of water are strongly affected by the charged state of the mineral surface, and the interlayer water is also affected by the interlayer cations. In Fig. 9.12 we show the distribution of the self-diffusion coefficient of water as a function of the distance from the clay surface. 

We assume that the profile of diffusivity of tritium water HTO is the same as the normal water shown in Fig. 9.12 however, its diffusivity in the bulk water is specified by experiments as 2.44 x 10 cm /s at 25°C (Klitzsche et al. 1976), therefore the maximum value in Fig. 9.12 is replaced by this experimental value. The diffusivity in the clay mineral is, of course, nuU. 

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