## 3 Results  
As was introduced above, for the analysis of the THC state of the bentonite barrier of a geological repository in granite, several cases were defined. They differed in the geochemical model and the consideration of CO\({}_{2}\) gas transport. Firstly, the importance of chemical processes relevant to the bentonite and related porosity changes were analysed by investigating the impact of THC processes interactions on the transport of non-reactive Cl and other species. Then, modelling of the evolution of CO\({}_{2}\) across the bentonite barrier was presented and the THC state potential impact on long-term safety was discussed. Mineral Dissolution/Precipitation, Cation Exchange and Surface Complexation Effect on THC State of Bentonite  
The effect of chemical processes, such as mineral dissolution/precipitation, ion exchange and surface complexation, on the THC state of the bentonite barrier was assessed through the analysis of the results when chemical reactions were not considered in the model (Case A) and the comparison with the case when chemical reactions were taken into account (Case B). The temperature evolution and hydration progress over time across the barrier for Case A is presented in Figure 4. In this case, the porosity remains constant, and thus the water content is directly proportional to the saturation evolution. Figure 4: Bentonite hydration modelling results: temperature (**a**) and water content (**b**) profiles at time steps 1, 5, and 18 years. Figure 3: Boundary conditions: (**a**) TH; (**b**) for transport. As can be seen from Figure 4, the hydration took place under a constant temperature gradient. The overall saturation of the barrier increased in time as the groundwater is infiltrating in the bentonite despite the evaporation taking place near the heater. Based on the modelling results, the barrier did not reach the full water saturated state \(\mathrm{S_{w}}<0.95\) (with the prescribed water retention curve) within the simulation time (18 years of hydration). The diffusivity of the initially present Cl\({}^{-}\) within the bentonite was dependent on inflowing groundwater (increasing with increasing water saturation) and temperature (increasing with increased temperature). The advective-dispersive transport of the dissolved Cl resulted in Cl\({}^{-}\) concentration profiles presented in Figure 5a. The concentration profiles of another solute (Na\({}^{+}\)) are presented in Figure 5b. The modelling results showed that both Cl\({}^{-}\) and Na+ concentrations in the bentonite gradually decreased due to their transport from the bentonite towards the granite, where a much lower concentration was retained. The consideration of the mineral dissolution/precipitation, cation exchange, and surface complexation reactions (Case B) resulted in slight changes in porosity (Figure 6). The most significant porosity changes (increases) were observed near the bentonite-granite interface (\(\sim\)3%), while some decrease in porosity was observed near the heater. These porosity changes were driven by changes in the volume fraction (Figure 6a) of minerals, such as calcite, anhydrite, and quartz. Calcite and quartz dissolution was responsible for the porosity increase near the granite, while the porosity decrease near the heater was governed mainly by the anhydrite precipitation. According to [13], anhydrite is more stable (lower solubility) than gypsum for temperatures above a threshold temperature ranging from 43 \({}^{\circ}\)C to 56 \({}^{\circ}\)C, and thus, no gypsum mineral was observed in the analysed system. Anhydrite transformation into gypsum would be expected during cooling (not simulated in the current study). These porosity changes were considered in the governing equations describing the water mass balance in the bentonite; therefore, the water content was affected. As can be seen in the Figure 7, the porosity changes were reflected in the slightly higher water content near the outer boundary of the bentonite.