Pressures Acting on Waste Containers in Bentonite-Based Materials

Abstract

To design containers for disposal of nuclear fuel waste, it is necessary to establish the magnitude of the pressures that are likely to act on them. Laboratory tests and numerical analyses have been conducted to examine the mechanisms by which components of pressure interact to form the total pressure acting on the containers buri ed in a vault excavated in plutonic rock. The sources of pressure considered are, the groundwater pressure, pressure from the swelling of a bentonite-based buffer material separating the container from the rock, the ambient rock stresses, and pressures arising from differential thermal expansion between the container, rock mass and buffer. Data show that, once the buffer is saturated, the buffer swelling pressure will be superimposed fully on the pressure in t h e groundwater. More over, it is shown that, due to the significant differences between the stress-strain-time properties of the bentonite based buffer material, and the rock mass, the stresses within the rock mass should not he transferred as pressures to the waste container. In addition, pressures on the container a rising from differential thermal expansion of the container, buffer and rock will be insignificant. The ionic concentrations in the groundwater and the buffer temperature will influence the total pressure on the container, which should not exceed 13 MPa. During saturation to the vault, pressures should be less than 13 MPa. However, they may not act equally, all around the container.