Migration of Cesium, Strontium and Cobalt in Water-Saturated Inada Granite.

Abstract

Diffusivities of Cs, Sr and Co were measured in a water-saturated granite in an attempt to investigate the migration of radionuclides into the matrix of the rock. The measured penetration profiles of every tracer were composed of two parts. There were a steep slope near the surface and a gradual slope in the deeper part. These profiles were successfully explained by considering two diffusion paths in the granite. One diffusion path was fissure with a width of a few microns and another was network of submicron pores. The volume of submicron pores was approximately 80% of the total pore volume in the granite. The orders of magnitude of apparent diffusivities for all nuclides were 10-11 to 10-12 m2/s through the fissure and 10-14 m2/s through the network of pores. The ratio of geometrical factors in the two paths was also calculated from each apparent diffusivity and was almost unity. This calculated ratio suggests that the pore network in the granite matrix has a similar shape to the fissure, thus the microstructure of the granite seems to be fractal.