A technique to delay hydration and maturation of borehole seals of expansive clay Roland Pusch

摘要

Sealing of deep boreholes for site selection of repositories for high-level radioactive waste can be made by inserting perforated copper tubes containing strongly compacted smectite-rich clay. The clay expands out through the perforation holes and ultimately forms a tight “skin” around the tubes at a rate that depends on the perforation geometry and the chemical composition of the water. The placement of the seals implies that they are moved through water in the borehole which can cause erosion and loss of clay if the expansion of the clay is too fast. The paper describes a method that retards the hydration and expansion of the clay sufficiently much to complete the installation before significant loss of clay has taken place. It involves addition of finepowdered talc to the smectite grains in preparing a coating of the tubes.