Diffusivity Measurements and Electrical Resistivity Measurements in Rock Samples Under Mechanical Stress

摘要

If radionuclides are released from an underground repository and enter the groundwater, they would be transported with the moving groundwater in fissures in the rock. Besides fissures the rock also contains micropores filled with stagnant groundwater. If the nuclides are able to diffuse into these micropores, a significant retardation of the nuclides can be expected. At repository depths, the rock is exposed to rather high stresses caused by the large overburden of rock. When drill cores are taken up from the gound, this overburden no longer exists. As a result of this, there might be an increase in the porosity of the rock samples. The effective diffusivity measured in rock samples under atmospheric pressure in the laboratory would then be higher than the effective diffusivity in the rock “in situ.” To simulate the stress that may exist in the bedrock at large depths, diffusion experiments with iodide and electrical resistivity measurements in rock materials under mechanical stress have been performed. It was found that the diffusivity in rock samples at 300–350 bars stress was reduced to 20–70% of the value in the samples under atmospheric pressure. This reduction of the diffusivity in stressed rock is probably of minor importance because of the rather large variation in diffusivity between