Environmental protection around radioactive waste disposal is a significantly important issue for safety purposes. Consequently, permeability and radiation shielding are the two important factors for isolating radioactive disposals. Clay is a relatively impermeable soil that is naturally available, cheap and environmentally friendly. In this research, the influence of modifying clay by barite powder, barite aggregate, steel slag, basalt fiber and nano clay were 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 different percentages of additives were 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 137 Cs (661.6 keV) and 60 Co (1173.2 and 1332.5 keV) for all the samples. The attenuation coefficients for samples were determined by both simulation methods, using the MCNP code, and XCOM database to compare with the experimental results. Simulation results were found to be in a good agreement with the experimental results. The obtained results show that with increasing the percent of barite powder, barite aggregate, steel slag and basalt fiber, radiation shielding coefficient (µ) increase while permeability coefficient becomes greater. While, adding nano clay decreases the linear attenuation coefficient (µ) and permeability factor (K). Finally, considering the two objective functions of radiation shielding protection and water permeability, according to the results, mixture of bentonite clay with 40% barite powder, bentonite with 40% barite and bentonite aggregate with 30% steel slag depending on the available materials, are the suitable alternatives for the coating layer usage of low-level radioactive waste disposal.
