Abstract
The proposed use of active clays for the isolation of radioactive wastes in deep geological repositories has been followed by a deeper understanding of this type of soils. This increased knowledge has led to the need for both conceptual and numerical models capable of capturing the main trends in behaviour and the different couplings between different physical-chemical phenomena. In addition, the model must have a high degree of flexibility that enables it to accommodate future developments or new relevant phenomena. This work presents a numerical THMC code developed entirely on the COMSOL Multiphysics numerical implementation platform, which provides the required adaptability. This model includes, for the first time in this environment, a reactive transport model in unsaturated porous media for a relevant geochemical system (consistent with the MX-80 bentonite) together with a THM model based on a double porosity approach. The chemical potentials of water and solutes are used for the definition of thermodynamic equilibria between both porosity levels. Trends in the behaviour of a bentonite sample under oedometric conditions are satisfactorily simulated in response to a process of saturation and change in salinity conditions. Variations in swelling pressure, porosity distribution or dissolution/precipitation of the main accessory minerals are analysed and explained by means of the proposed conceptual model.
Highlights
Active clays, especially compacted bentonite, are considered one of the most important engineering barrier elements in many deep geological repository concepts for spent nuclear fuel due to their characteristics such as low hydraulic conductivity, high swelling potential and high retention capacity. [1,2,3,4]
Several studies [7, 8] show that the hydro-mechanical response of the bentonites depends on the level of salinity and chemical composition of the surrounding groundwaters in deep geological repositories
The composition of these waters can be very different [9, 10]. This aspect together with the complex geochemical system of the MX-80 [11] makes it necessary to develop models that consider the effect of chemical conditions [12]
Summary
Especially compacted bentonite, are considered one of the most important engineering barrier elements in many deep geological repository concepts for spent nuclear fuel due to their characteristics such as low hydraulic conductivity, high swelling potential and high retention capacity. [1,2,3,4]. Especially compacted bentonite, are considered one of the most important engineering barrier elements in many deep geological repository concepts for spent nuclear fuel due to their characteristics such as low hydraulic conductivity, high swelling potential and high retention capacity. Several studies [7, 8] show that the hydro-mechanical response (hydraulic conductivity and swelling pressure) of the bentonites depends on the level of salinity and chemical composition of the surrounding groundwaters in deep geological repositories. The composition of these waters can be very different [9, 10]. This aspect together with the complex geochemical system of the MX-80 [11] makes it necessary to develop models that consider the effect of chemical conditions [12]
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