تجزیه و تحلیل حساسیت بر روی پارامترهای هیدروترمال حاکم بر اشباع از یک سیستم مانع رسی مهندسی شده

In this paper, we study the impact a heat source makes on the thermo-hydraulic behaviour of a system composed of an engineered clay barrier and a host rock, namely an argillite. We first perform a benchmark test case with code CAST3M and code ASTER. The results of the calculations are in good agreement, except for the gas pressure. Nevertheless, gas pressure does not seem to influence the saturation process, although the saturation kinetics is governed by the darcean water flow. The saturation process is accelerated when the heat source is taken into account. More precisely, this acceleration is due to dynamic viscosity increase with heating. In a second time, five other heating sources have been tested in code ASTER. Compared with the reference calculations, some give an identical response. However, the highest heating sources provoke a desaturation phenomenon because of the air pressure increase with temperature. The liquid saturation of the engineered barrier is then delayed.

In the framework of describing the thermo-hydraulic behaviour of a High Level Waste Repository, one objective is to evaluate the influence of high temperatures on the saturation process. As a first step of simulation, the mechanical behaviour of the clay is not modelled. A first calculation was performed with the code CAST3M at the Commissariat à l'Energie Atomique (CEA). It represents an isolated canister, surrounded by an expansive clay, and placed in a cylindrical chamber (Barnel et al., 2002). Physically, a thermo-hydraulic two-fluid model is used. It has been modelled with three nonlinear and coupled mass and energy balance equations. A special scheme to treat local complete saturation has been proposed. The results showed an acceleration of the saturation phenomenon with the temperature increase. This is due to water dynamic viscosity during a heating process. The saturation kinetic is governed by the darcean water flow. In this paper, we first check the above-described results. Three calculations were performed both with the code CAST3M and the code ASTER at the Electricité de France (EDF). The code ASTER does not take into account a local complete saturation but leaves a low air–water content in the rocks. In a second part, five different kinds of heating source are tested using the code ASTER, in order to determine whether the response of the argillaceous system submitted to heating is single or not.

The results obtained by CASTEM and ASTER on a calculation are representative of C-type waste canisters. The results of the calculations are in good agreement, except for gas pressure. Nevertheless, gas pressure does not seem to influence the saturation process. Indeed, the saturation kinetics is governed by the darcean water flow, and it is accelerated when the heat source is taken into account. More precisely, this acceleration is due to dynamic viscosity increase with heating. Five other calculations were performed with the code ASTER. They show a really strong dependence between heating source function shape and response of the system. Increasing the initial heat power has only a local effect and does not modify the saturation time. When this parameter is too strong, the end of the saturation process is delayed because of gas pressure value. Furthermore, when increasing the time of heating, the gas pressure and temperature coupling is strong enough to activate another coupling between suction and gas pressure. A desaturating phase interrupts the saturation of the EB. After a while, when temperature decreases, the second saturation process starts. It is quite different from the first one, because it depends on temperature and gas decrease. Uncertainties regarding gas pressure equation prevent further interpretations of calculations. Our next objective is to study this equation and the models used for gases more precisely. Another objective is to perform a sensitivity analysis on the thermal dependence of the thermal conductivity and the saturation retention law. The next step will be to take into account the mechanical behaviour of the clay while heating.