Evolution of the THC conditions in the FEBEX in situ test after 18 years of experiment: Smectite crystallochemical modifications after interactions of the bentonite with a C-steel heater at 100 °C

The observed clay mineral transformations induced changes in some of the physico-chemical properties of the bentonite, decreasing the total cation exchange capacity and BET surface area. However, these modifications were restricted to the bentonite at close contact with the heater. The rest of bentonite from the FEBEX in situ test maintained its performance as an engineered barrier.