Experimental study on effect by cementation on self-sealing capability of bentonite buffer material

In Japanese project for disposal of high-level radioactive waste, the self-sealing capability of bentonite buffer material, which results from the swelling deformation to fill the gaps between waste container and wall of disposal pit, must be retained thousands of years. However, because of the effect of high pressures, occurrence of cementation and property changes of the buffer material are a concern. Few studies had examined cementation effects because of the difficulties for simulating long-term alteration process experimentally. In this paper, swelling properties of consolidated buffer are regarded as similar as those of naturally consolidated bentonite ore. Therefore, three kinds of bentonite ores were used for experiments to elucidate influences of cementation on self-sealing capabilities. Undisturbed and reconstituted specimens were prepared to assess their swelling pressures after filling a preset gap in a swelling pressure apparatus. Results show that for Japanese ores, the swelling pressure of undisturbed specimens is about half that of reconstituted specimens. For American and Chinese ores, the difference of swelling pressure is greater when the preset gap is smaller. Results imply that effects of cementation on self-sealing capability are smaller when swelling deformation is allowed.