Kinetics of long-term illitization of montmorillonite—a natural analogue of thermal alteration of bentonite in the radioactive waste disposal system

Investigations of Near-Field Thermal-Hydrologic-Mechanical-Chemical Models for Radioactive Waste Disposal in Clay/Shale Rock

“…(4-3)) in the swelling model. (Xu et al, 2006b) 0 As mentioned above, illitization, the transformation from smectites to illite, is usually part of the diagenesis process of clay formation (Kamei et al, 2005;Cuadros, 2006) Mineral dissolution/precipitation affects the concentration of aqueous cations, which subsequently induce a change in the composition of exchangeable cations. The concentration of calcium increases because of the dissolution of calcite; the concentration of potassium decreases because of the precipitation of illite; the concentration of magnesium decreases because of the precipitation of chlorite.…”

“…Although the possible change in clay-rock swelling properties which has been demonstrated with short term and small-scale lab tests (Thury, 2002;Wakim et al, 2009) and by indirect measurement (such as the occurrence of illitization- Kamei et al, 2005;Cuadros, 2006) point out the need to evaluate the geochemically induced swelling/shrinkage of host clay rock, no such evaluation has been reported, as far as our literature survey has found. In this report, coupled THC models that include EBS and host clay rock are linked with a swelling model based on the Gouy-Chapman diffuse double layer (DDL) theory, in which the changes in swelling properties within the nearfield area of host clay rock are evaluated.…”

“…Wakim et al (2009) experimentally evaluated the effect of aqueous solution chemistry on the swelling and shrinkage of shales under saturated conditions, and reported that the more concentrated solution led to less swelling of shale. Kamei et al (2005) and Cuadros (2006) indicated that illitization, the transformation from smectites to illite, is usually part of the diagenesis process of clay formation. Illitization apparently changes the swelling properties of clay formation.…”

Radioactive Wastes

“…In order to develop biosphere assessment models for radioactive waste disposal, the Reference Biosphere Methodology developed in BIOMASS was applied to five locations in different European countries (Olyslaegers et al, 2005) A tertiary argillaceous rock formation in the Nishikubiki region in central Japan was investigated as a natural analog of bentonite alteration in a repository for HLW (Kamei et al, 2005). The apparent activation energy was evaluated to be ~107 kJ/mol based on the assumption that montmorilloniteillite conversion followed a first-order reaction, suggesting little possibility of illitization of bentonite in the geological disposal system in the term of 105 years as long as the temperature was not higher than water.…”

Thermal Evolution near Heat-Generating Nuclear Waste Canisters Disposed in Horizontal Drillholes

“…The heat then dissipates into the nearby engineered structures and the host formation. Predicting the temperature evolution within the disposal section of the drillhole and the surrounding host rock is necessary as it may alter the properties of the multi-barrier system by accelerating the corrosion of the waste form [2,3] and of metal components comprising the containment systems [4][5][6], by degrading bentonite [7][8][9] or cement [10] used as backfill materials, and by affecting argillaceous host rocks [11,12]. Heat-driven degradation mechanisms may also make the retrievability of the waste canisters more difficult.…”