Evolution of the Geochemical Conditions in the Bentonite Barrier and its Influence on the Corrosion of the Carbon Steel Canister

Abstract

This work has been focused on characterization of geochemical processes occurring in the bentonite barrier and their influence on corrosion of the carbon steel container. In the cells used for these tests, a block of compacted bentonite was subjected simultaneously to constant hydration and heating, in opposite directions, in order to simulate the conditions of the clay barrier in the repository and better understand the coupled THMC (Thermo-Hydro-Mechanical- Chemical) processes that can affect the performance of the bentonite barrier or the metallic container. In these tests, carbon steel was substituted by Fe powder in order to enhance corrosion phenomena. At present, only two out of the six cells assembled have been dismantled after 6 and 15 months. In both cases, an advective movement of salts towards the heater has been observed. CEC values increased in saturated areas. In the exchange complex, Mg was replaced by Na in saturated areas, whereas in unsaturated zones close to the heater, Mg is the prevalent exchangeable cation. Goethite and hematite were the main corrosion products found in the 6- month and 15-month tests, respectively.