Diffusivities of Cesium and Strontium in Concretes and in Mixtures of Sodium Bentonite and Crushed Rock

Abstract

Diffusivities of Cs and Sr in concretes and in mixtures of sodium bentonite and crushed rock were measured.The order of magnitude of the apparent diffusivities (Da) for Cs and Sr in concretes was 10-14-10-13 m 2 /s and in the mixtures of bentonite and crushed rock 10-13-10-11 m 2 /s. The calculated effective diffusivities (De) in the mixtures of bentonite and crushed rock seemed in some cases to exceed the corresponding values in water, which suggests that the pore diffusion/sorption model cannot explain the transport phenomena in all cases.The experiments where the sorption factors were varied in the diffusion samples suggest that the nuclides diffuse also while being sorbed. A combined pore diffusion-surface diffusion model has been used to explain the transport and the corresponding diffusivities have been evaluated. This paper will give the measured diffusion and sorption data and discuss the models used to describe diffusion in porous sorbing agents.

Effects of Mineral Compositions on Matrix Diffusion and Sorption of 75Se(IV) in Granite

“…In the past, the modeling experts used K d from batch sorption experiments to predict the diffusion of some radionuclides in the environmental media, such as granite or clay, 41 and the effective diffusion coefficient was calculated directly by the batch sorption K d : D e = D a •(ε + K d •ρ). Since we know that the batch sorption K d is obtained at equilibrium conditions, while the sorption of radionuclides in the media during the diffusion experiments usually occur at a nonequilibrium conditions (for example, we obtained diffusion coefficients from all data points by using the difference schema method).…”

Waste Volume Reduction Using Surface Characterization and Decontamination By Laser Ablation

“…Concrete is a complex material comprising many distinct chemical and physical phases on a variety of size scales [6][7][8]. Most studies of radionuclides in cements and concrete are for the most part restricted to phenomenological treatments of diffusion of ions, particularly Cs, in and out of model waste forms and engineered barriers [9][10][11][12][13][14][15][16][17][18][19][20][21]. Few studies exist on the chemical speciation of the contaminants themselves in concrete [22][23][24][25].…”

Sorption and Diffusion of 1-125 and Sr-90 in a Mixture of Bentonite and Crushed Granite Backfill of a Radioactive Waste Repository

“…Muurinen [10] and Cheung [4,11 ] have proposed a combined pore diffusion-surface diffusion model to explain the discrepancy between experimental data and the pore diffusion model. This model assumes that the ions diffuse through two different pathways, namely, the pore water and the particje surface of clay-based materials.…”

“…Muurinen et al [10] and Cheung et al [4,11] stated that the experimental data were not easily accommodated by the pore diffusion model, and they proposed a combined pore diffusionsuface diffusion model to explain such the discrepancy.…”