Papers by Keyword: Compacted Clay

Abstract: Permeability coefficients of three compacted clay samples are measured by using Transient Water Release and Imbitions Method which is shortly named as TRIM. The curve between permeability coefficient and suction is obtained, the results of tests show that the permeability coefficient decreases in nonlinear trend along with the increasing of suction. Based on Brooks Corey model and Mualem model which is shortly named as BCM model, an analytical method is put forward to calculate the permeability coefficient of compacted clay. The results of using BCM model and TRIM are compared, which show that the permeability coefficient obtained with two kinds of methods match well when the suction is greater than the inlet value.

Abstract: Diffusion of Uranium in compacted clay was studied through the non-steady state diffusion method for the safety assessment of the radioactive waste in the storage and disposal practices. Since the permeability of the compacted clay is very low, the main mechanism for radionuclide transport is governed by the diffusion phenomenon. The diffusion process of uranium in compacted clay as a porous medium has been modeled by taking into account the effect of sorption. An increase in temperature, caused by the radiation from the canisters, takes place in the repository. Then, the effect of temperature on textural and structural properties of clay and coefficient diffusion has been examined. First, we examined the structure changes of the clay pellets under the influence of the heat in the temperature range 25–100°C. These changes are studied in the region of mesopores and macropores using the method of the mercury porosimetry. Second, the effect of temperature on the diffusion behavior of uranium was simulated. In these simulations, the experimental values of apparent diffusion coefficients of uranium were used to determine the concentration profiles versus time, depth and temperature. As conclusion, it was shown that the temperature plays an important role in the uranium transport through the compacted clay.

Abstract: The effect of compaction of bentonite on the diffusion behavior of uranium was studied for the safety assessment of radioactive waste (storage and disposal practices). Since the permeability of the compacted clay is very low, the main mechanism for radionuclide transport is governed by the diffusion phenomenon. The diffusion process of uranium in compacted clay as a porous medium has been modeled by Fick's second law taking into account the effect of sorption and considering the non-steady state. The diffusion coefficients and profiles concentration values were calculated by a computational method using a numerical program based on the Newton-Raphson algorithm. In this simulation, the experimental values were used to determine the uranium concentration profiles versus depth of the clay pellet. It was concluded that the dry density of the compacted clay and the aqueous solution properties (pH and ionic strength of background electrolyte) played an important role in the uranium transport through compacted clays.