Permeability and Gamma-Ray Shielding Efficiency of Clay Modified by Barite Powder

Environmental protection around radioactive waste disposal is a very important issue for safety purposes. Consequently, permeability and radiation shielding are the two important factors for isolating radioactive disposals. Clay is relatively impermeable soil that is naturally available, cheap and environmentally friendly. In this research, the influence of modifying clay by barite powder was investigated to improve the gamma ray shielding performance while keeping the low permeability of clay soil. This research was conducted using both experimental and simulation methods. In this study, bentonite clay samples with 10%, 20%, 30%, 40%, 60% and 80% of barite powder was prepared to find the optimum percent of barite powder. A HPGe detector was used to measure the attenuation coefficients at commonly used gamma ray energies of 137Cs (661.6 keV) and 60Co (1173.2 and 1332.5 keV) for all the samples. The attenuation coefficients for samples were determined by both simulation method, using the MCNP code, and XCOM database to compare with the experimental results. Simulation results were found to be in good agreements with the experimental results. The obtained results show that with increasing the percent of barite powder, radiation shielding coefficient (µ) increase while permeability coefficient becomes grater. However, according to the obtained results, the bentonite clay with 40% of barite powder is the optimum composition with a permeability factor of 8.87 × 10−11 m/s and attenuation coefficient of 16.46 m−1, 12.2 m−1 and 11.99 m−1 at 661.6, 1173.2 and 1332.5 keV energies, respectively. In addition, the results for clayey soil samples were compared to the concrete mixture. It was found that clay mixture with 40% barite powder would overcome concrete regarding gamma-ray shielding performance. As a result, the clay composite particularly due to its imperviousness and availability, seems to be an appropriate alternative for radiation shielding in radioactive waste disposal landfills.