Temperature effects on the erosion of bentonite

Compacted bentonite is a candidate barrier material (buffer, backfill and plug), a critical component of engineered barrier systems for geological disposal of high-level (heat generating) radioactive waste. The clay barrier can be subject to erosion due to interactions with groundwater at the interface between the clay and fractured host rock. The engineered barrier system undergoes a thermal period (~5k-10k years) at which potential mass loss and erosion assisted piping of clay buffer can happen under elevated temperature. This paper presents the results of laboratory experiments on the erosion of compacted bentonite at ambient and elevated temperatures. Compacted samples of Volclay bentonite (dry density 1.45 Mg/m3) were subject to a constant flow of deionised water fat a porous boundary for three months. Erosion and swelling pressure were simultaneously recorded using a bespoke constant rate of strain system (CRS) by which the eroding conditions were created at the bottom of clay sample. The results show that the mass loss increased by approximately three times at the elevated temperature (at steady state). The outflow fluid was collected at regular intervals and the eroded materials were characterised by Dynamic Light Scattering to develop an understanding of the sizes and concentrations of particles and their evolution. It was found that the particle sizes in colloidal solution range between 237 nm and 1060 nm whilst the average size was not considerably affected by the elevated temperature. The results presented provides new insights into the erosion phenomena at elevated isothermal temperature in smectite rich clays.