Boundary conditions bentonite

Several boundary conditions must be taken into account for successful coimmobilization conservation of the DN activity upon adsorption, relationship of particle size of preimmobilized DN and resulting coimmobilizate matrix, interactions of adsorbent and DSR-S, as well as the activity ratio of both enzymes [108]. The literature-known adsorbent for DN adsorption (bentonite) could not be applied, because it completely inactivates DSR-S activity upon coimmobilization even at... 

Four research teams—AECB, CLAY, KIPH and LBNL—studied the task with different computational models. The computer codes applied to the task were ROCMAS, FRACON, THAMES and ABAQUS-CLAY. All of them were based on the finite-element method (FEM). Figure 6 presents an overview of the geometry and the boundary conditions of respective models, including the nearfield rock, bentonite buffer, concrete lid, and heater. The LBNL model is the largest and explicitly includes nearby drifts as well as three main fractures... 

Figure 6 shows the numerical model geometry for the simulation. The model includes the two heaters, bentonite, plug, tunnel and host rock. Numerical area is decided considering influence of boundary conditions. Since the site can be assumed line symmetric with the xz-plane, the model is made only in the positive part of y direction. The number of elements is 5,760. The number of nodes is 26,401. The host rock is assumed to be a homogenous media. 

The example presented here is based on the one shown in Olivella and Gens (2000) with slightly modified material properties and temperature boundary condition values. The example portrays the desaturation of bentonite due to heating in a closed system. The set-up is as illustrated in Figure 3. A bentonite block is heated to 100°C on the left side. Dimensions and initial conditions are as shown on Figure 3. The only boundary condition is the temperature boundary condition at the heater. 

This example is to test the swelling effects under capillary pressures up to 10 Pa occurring in extremely low-permeable bentonite materials. For this purpose, a simple 1-D case is set up. A one meter long bentonite column is heated on the left hand side. Element discretization length is 0.01m. The initial conditions of the system are atmospheric gas pressure, full liquid saturation and a temperature of 12°C. The heater has a constant temperature of 1(X) C. Flow boundary conditions on the left side are gas pressure of 10 Pa and 15% liquid saturation. On the right side we have atmospheric pressure, full liquid saturation and no diffusive heat flux. As a consequence, a typical desaturation process of bentonite is triggered. The complete set of initial and boundary conditions and the material properties for this example was described in detail by Kolditz De Jonge (2003). 

Based on the characterization of the bentonite and the granite a 2D model which represents a cut through heater 2 has been applied to model the saturation process of the bentonite. The evaporation of water in the vicinity of the heaters has been modelled with a boundary condition for saturation evaluated from the measured relative humidity evolution. As this approach does not represent the phase transitions this model can just give an impression of the saturation process. Figure 8 shows the calculated distributions of saturation and temperature in the bentonite 1000 d after the heaters have been turned on. 

The initial degree of saturation in the bentonite is 5 . Full saturation 5=1 is maintained at the rock boundary r = r. The moisture flux is zero at the canister boundary. The boundary conditions and the initial condition are ... 

There are many challenges facing the research teams for the study of this task, such as limitations in the different effective stress principles for the bentonite material under complex loading conditions the uncertainty of the hydraulic boundary and tbe in situ conditions and the complex and largely unknown in situ fracture properties (both geometrical and hydromechanical). 

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