Modelización directa e inversa del transporte reactivo multicomponente en medios de doble porosidad

A numerical methodology for solving the inverse problem of coupled water flow and multicomponent reactive solute transport in porous media implemented in INVERSE-CORE 2D is applied here to the interpretation of a long-term permeation test performed on a sample of FEBEX compacted bentonite. FEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project dealing with the bentonite engineered barrier designed for sealing and containment of waste in a high level radioactive waste repository. Hydrogeochemical modelling of porewaters indicate that the main geochemical processes controlling the chemistry of the bentonite are: acid-base reactions, aqueous complexation, cation exchange, dissolution/ex-solution of CO2 and dissolution/precipitation of highly soluble minerals such as calcite, dolomite, chalcedony and gypsum/anhydrite. All these processes are assumed to take place under equilibrium conditions. The initial saline porewater of the bentonite is flushed with a fresh water with a chemical composition typical of granite formation. Water flux and chemical data of efluent waters were measured during the experiment. Direct and inverse modelling of this experiment has been carried out. Models of chloride breakhrough curves indicate that bentonite exhibits a double porosity behavior. The model reproduces the trends of measured data except for bicarbonate and pH which are affected by uncertainties in the evolution of CO2(g) pressures. 1. Introduccion