Comparative study on the application of ethanol–bentonite slurry and salt–bentonite slurry as effective injection materials for barrier sealing

• Bent showed finer particle sizes in salty condition than in ethanol condition.
• Salt-Bent slurry exhibited lower viscosity and more fluidic than Eth-Bent slurry.
• Fracture penetrability is better for Salt-Bent slurry than Eth-Bent slurry.
• Salt-Bent slurry is a better grout than Eth-Bent slurry for effective sealing.

A deep geological repository for high level radioactive waste disposal is a multi-barrier system whose overall performance depends on the effective sealing of the barriers. Effective barrier sealing can be achieved by the use of good grouting materials. A good grouting or injection material is one that is capable of penetrating very narrow voids of injection medium and effectively sealing them. The effects of both organic and inorganic solvents (ethanol and aqueous salt) on the rheological and injection characteristics of bentonite (Bent) slurry were investigated experimentally, with the aim of choosing between the two, a better injection material for effective sealing. Wyoming Bent, used as the injection material, was mixed with various concentrations of ethanol and 4% salt solution to form two separate slurries: Ethanol–bentonite (Eth–Bent) slurry and Salt–bentonite (Salt–Bent) slurry respectively. Prepared slurries were injected into a synthetic fracture of apertures 100, 80 and 60 μm under dynamic injection to determine the penetrability of the slurries into the apertures. The viscosities of the slurries were also determined. The results revealed that, both salt and ethanol are capable of suppressing the swelling property of Bent to form better injectable slurry than the slurry formed when fresh water is mixed with Bent. This was inferred from the successful injection behavior of the slurries through micro-fractures of aperture sizes 60–100 μm. Though ethanol and salt have the capability of suppressing the swelling behavior of Bent, the effect was more pronounced with salt as the viscosities were lower for salt than ethanol. Salt–Bent slurry can conclusively be considered as a more effective grouting material than Eth–Bent slurry for effective sealing.