Rock-mass thermal properties

As shown in Table 2, the properties of the Lamprophyre properties and the surrounding rock are the same except for permeability and thermal conductivity. The mechanical rock-mass properties are obtained from the geological description of the Grimsel Test Site (Kneussen et al., 1989). Significantly, the Young s modulus of the rock mass was reduced to 70% of its value for intact rock. 

Abstract Geological disposal of nuclear fuel wastes relies on the concept of multiple barrier systems. In order to predict the performance of these barriers, mathematical models have been developed, verified and validated against analytical solutions, laboratory tests and field experiments within the international DECOVALEX project. These models in general consider the full coupling of thermal (T), hydrological (H) and mechanical (M) processes that would prevail in the geological media around the repository. This paper shows the process of building confidence in the mathematical models by calibration with a reference T-H-M experiment with realistic rock mass conditions and bentonite properties and measured outputs of thermal, hydraulic and mechanical variables. 

Japan (Figure 1). The in-situ state of stress and the natural thermal gradient are also based on Japanese geological data however as we will illustrate in the next section, the rock mass properties in term of strength and permeability are based on typical Canadian Shield s data. 

Table 2 shows the properties used for the coupled analysis. Thermal properties are the same for rock mass and bentonite. It is assumed that the repository consists of bentonite having very low permeability. To examine the uncertainty of up-scaling process on the performance assessment, the cases shown in Table 3 are examined. 

The complete results from the various can be found in Fredriksson (2003). The results presented in this article focus on the influence of mechanical and thermal properties of the rock mass for the horizontal section located 1.5 m below the tunnel floor, and assuming the mean value for the major principal stress, ai=30MPa. 

In this study, the thermal properties of the rock mass were modified to take the effect of groundwater and latent heat of freezing into account. The result of the analysis with these modified thermal properties shows good agreement with the measured temperature distribution. 

In this study, briefly explained is the site investigation made in earlier design stage to determine the dimension of cavern. The predicted temperature distribution around cavern was compared with measured values during the 5 years of operation. Also a practical method to evaluate the thermal properties of Jointed rock mass was suggested and verified. 

During the numerical calculation, thermal properties were changed into modified values considering the latent heat of freezing when temperature of rock mass is reached 0°C. The modification was made by using the numerical formula (1) and (2). And latent heat term is considered to evaluate the energy need to freezing the water in unit volume of rock mass. 

After the rock mass temperature reached -1 °C, thermal properties were changed into that of thermal properties calculated from 80% of rock mass and 20% of ice. Initial thermal properties and modified thermal properties are shown in table 4. 

Properties of the medium, initial condition and a boundary condition for thermal process, hydrological process, mass transport and geochemistry are shown in the Table 2. Temperature is fixed at 80°C in the inner boundary of buffer material and the outer boundary of hard rock is assumed adiabatic condition. And the buffer material is unsaturated in initial condition on the other hand hard rock is saturated in initial condition. 

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