A Study on extrusion behavior of buffer material into fractures using X-ray CT method

Tanai, Kenji ; Matsumoto, Kazuhiro*

The buffer that will be used as a component of the engineered barriers system for geological disposal of high-level radioactive waste is designed to swell when it becomes saturated by groundwater. As a result of the swelling, bentonite buffer material may penetrate through open fractures into the surrounding host rock. If it is sustained for extremely long periods of time, the bentonite extrusion could lead to reduction of the buffer density, which may in turn degrade the expected performance (e.g. low permeability, diffusion control, colloid filtration, load-bearing capacity, etc). In this study, extrusion test with X-ray CT measurement was carried out to clarify the mechanical behavior of bentonite extrusion through fractures in the surrounding rock. In the extrusion test, the out flow distance into fracture is affected by bentonite content ratio and ionic strength of ground water. X-ray CT measurement is available to evaluate the density distribution of bentonite into the fractures. The X-ray CT measurement will play an important role for study of extrusion behavior of buffer material, particularly for development of extrusion models for compacted bentonite.