Diffusion paths of cesium in water-saturated mortar

Diffusivities of cesium in a water-saturated mortar were measured in an attempt to investigate the migration of radionuclides into the matrix of the mortar. The measured penetration profiles of the tracer were composed of two parts. There was a steep slope near the surface and a gradual slope in the mortar interior. This kind of profile has been reported by many researchers. This prof He was successfully explained by considering two diffusion paths in the mortar. One diffusion path was through fissures with a width of a few microns, and the other was through the intact mortar network of submicron pores. This model was supported by autoradiography of some cross sections of a mortar specimen. The volume of submicron pores was ∼95% of the total pore volume in the mortar. The order-of-magnitude values for the apparent diffusivities for cesium were 10^-12 m²/s through the fissure and 10^-4 m²/s through the network of pores. The effective diffusion coefficient for cesium was estimated at ∼10^-13 m²/s by using the apparent diffusivities through the fissures, the aperture of the fissures, and the fissure interval. Geometric factors in the two paths were also estimated by using the apparent diffusivity and diffusion coefficients for free ions; they were estimated at ∼0.13 for fissures and ∼0.01 for the mortar matrix. This model was applied to other researchers' data to estimate the effective diffusion coefficient. This model and estimation method show the consistency of the data from through-diffusion and penetration experiments.