Investigating the performance of magnetite powder-bentonite mixtures for radiation shielding and gas permeability in wet-dry cycles

• Magnetite (15–45%) was added to bentonite to improve barrier performance. • Higher magnetite content increased linear attenuation due to greater mixture density. • B70-M30 showed best resistance to permeability rise in wet–dry cycles. • Crack area in B70-M30 decreased 15–53% vs B85-M15 and B55-M45. Radioactive waste management presents significant environmental and health challenges, requiring barrier materials with strong radiation shielding and low gas permeability. Wet–dry cycles can compromise barrier integrity by inducing microstructural damage, making control of gas migration essential for durable waste isolation. This study investigates the enhancement of bentonite clay by incorporating magnetite powder at concentrations of 15%, 30%, and 45%, focusing on improvements in radiation shielding and gas permeability. Radiation shielding performance was assessed through experimental measurements using a NaI (Tl) Sodium Iodide Scintillation Detectors, complemented by simulations with the MCNP code and data from the XCOM database. The addition of 30% magnetite significantly improved shielding performance, increasing the linear attenuation coefficient by 38%, 62%, and 59% at photon energies of 662, 1173, and 1332 keV, respectively, while reducing the half-value layer (HVL) and tenth-value layer (TVL). Gas permeability tests under wet–dry cycles showed that magnetite addition initially reduced permeability due to improved compaction. In the wet state, the 30% magnetite sample (B70-M30) achieved a 73.4% reduction in gas permeability. Although permeability increased in later cycles due to micro-cracking, B70-M30 consistently exhibited the best performance compared to the 15% and 45% magnetite samples. These results highlight the potential of magnetite-enhanced bentonite as a multifunctional barrier material for radioactive waste containment.