Numerical models of laboratory steel corrosion tests in contact with compacted bentonite

Abstract

Carbon steel and compacted bentonite have been proposed as candidate materials for the overpack and buffer, respectively, in the multi-barrier system of deep geological repositories for high-level radioactive waste. The corrosion of the carbon steel may induce buffer alterations, which could result in changes in bentonite parameters such as porosity, permeability and sorption and swelling capacities. Here we present coupled thermo-hydro-chemical-mechanical (THCM) models of several types of heating and hydration experiments on compacted bentonite (at laboratory and in situ scale) to study the interactions of iron-bentonite under repository conditions. The model results for the corrosion tests on small cells indicate that: 1) Magnetite and Fe(OH)2(s) are the main corrosion products which compete for Fe2+ precipitation; 2) The corrosion products penetrate a few mm into the bentonite; and 3) The numerical results fit the measured iron weight data. Model results of the corrosion tests on medium cells show no magnetite penetration in the bentonite as indicated by the experimental observations.