Some effects of temperature increase due to the emplacement of radioactive waste on the mechanical and hydraulic behavior of saturated clays are studied numerically. A mass-transfer model is adopted which simulates a possible degeneration of adsorbed water into bulk water at temperatures up to 150 °C. In contrast with a previous paper by the authors the heat output decreases with time to realistically simulate the effect of nuclear waste. Numerical results show that in the vicinity of the line heat source, a much lower value of excess pore pressure and faster propagation of the excess pore-pressure front are obtained because of the substantial increase in permeability arising from the adsorbed water degeneration at elevated temperatures. Moreover, the adsorbed water degeneration accelerates the water flow around the heat source. It is also concluded that over a long term the thermally induced degeneration of absorbed water into bulk water mitigates the possibility of thermal failure of clays surrounding the heat source. Key words : heating, adsorbed water, bulk water, adsorbed water degeneration (mass transfer), permeability, specific discharge, pore pressure.
SUMMARYNumerical results of the simulations of the saturated clay response to a line heat source with a constant power output are presented and compared to the analytical solutions. Mixture theory of two interacting thermoelastic constituents is employed for the modelling. In this theory, mass transfer between the adsorbed water and bulk water is included to simulate the degeneration of adsorbed water into bulk water occurring at elevated temperatures. A finite difference method with non-uniform mesh is adopted to determine both the near-and far-field behaviour. The degeneration of adsorbed water into bulk water is more pronounced close to the heat source. This may produce a lower excess pore water pressure, a higher permeability increase, and accelerate the water flow in the vicinity of the heat source.
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