Experiment and Simulation Study on Migration of 90Sr in Weakly Weathered Granite

Abstract

In this experiment, the migration of 90Sr in the weakly weathered granite was studied by using the penetration curve of 3H and 90Sr with the method of dynamic column experiment. The migration parameters of 90Sr in the weakly weathered granite were obtained. The flow rate was set at 1 mL/h during the test. With 104 Bq 3H, the migration test has been carried out for 120 h. The peak activity concentration appeares at 8.0 hour, with the peak activity concentration of 213.4 kBq/L, and the penetration curve of 3H has no obvious tailing phenomenon. With 5×104 Bq 90Sr, the migration test has been carried out for 132 d. The peak activity concentration appeares on 27.4 day, with the peak activity concentration of 46.26 kBq/L, and the concentration of 90Sr shows an obvious tailing phenomenon in the decreasing stage. By means of numerical simulation, the vertical dispersion of weakly weathered granite is 3.03 cm. By comparing the fitting results of 90Sr in weakly weathered granite under the following four models: equilibrium model, two-site sorption model, dual-porosity model, and dual-porosity model with two-site sorption, it is found that the fitting results of the four models are quite different. Dual-porosity model with two-site sorption can better explain the non-equilibrium adsorption phenomenon during the migration of nuclides in the weakly weathered granite by introducing the water content in the non-moving region, the first-order rate coefficient of solute exchange and the first order rate coefficient of non-equilibrium adsorption. The results show that distribution coefficient of 90Sr in weakly weathered granite is 1.23 mL/g, the first order rate coefficient of solute exchange is 0.227 /d, and the first order rate coefficient of non-equilibrium adsorption is 0.118 /d.

Keywords

• nuclide migration
• granite
• non-equilibrium adsorption
• dual-porosity model with two-site sorption
• first order rate coefficient
• 90sr