Dynamic update of flow and transport parameters in reactive transport simulations of radioactive waste repositories

Abstract

[Abstract:] The changes in porosity caused by mineral dissolution/precipitation and the associated changes in flow, transport and chemical parameters of porous and fractured media are relevant for the geochemical time-evolution of natural and engineered underground systems. The realistic representation of natural systems requires modeling tools accounting for the changes in porosity. Here, we investigate the significance of the dynamic upgrade of the flow, transport and chemical parameters in reactive transport models with mineral dissolution/precipitation. The water flow, heat transfer and multicomponent reactive solute transport code, CORE2DV5, was extended to take into account the changes in porosity provoked by mineral dissolution/precipitation and their effect on flow, solute transport and chemical parameters. The improvements implemented in the code were verified against analytical solutions and the numerical solutions computed with other reactive transport codes with similar capabilities for isothermal mineral dissolution/precipitation test cases. Model results computed with CORE2DV5 agree with the analytical and numerical solutions for several isothermal test cases with porosity feedback. Model results show that failing to account for the porosity feedback leads to large errors. The porosity feedback effect (PFE) is especially relevant in long-term problems with mineral dissolution/precipitation leading to strong changes in porosity. The PFE is analysed with a non-isothermal geochemically-reactive transport model of the long-term (4·104 years) interactions of compacted bentonite with corrosion products and concrete in a high-level radioactive waste repository in clay. The model predicts pore clogging in the concrete and at the concrete-clay interface. The thickness of the zone affected by pore clogging computed with the PFE is smaller than that computed without the PFE.