Diffusion and sorption of radioactive cesium and cobalt in regolith materials of central Australia

Diffusion and sorption are potentially the most important factors governing the transport of radionuclides in clays and under stationary subsurface environmental conditions. Preliminary studies have been performed to measure the transport of ¹³⁷Cs and ⁶⁰Co with no advection, using reconstituted samples of three regolith materials collected from a region in South Australia. The samples were saturated with CaSO₄ solution to imitate the pore water chemistry of the in situ environment. A double diffusion cell testing apparatus made of polycarbonate resin was used to measure the transport of the selected radionuclides through the samples. A curve fitting procedure employing one-dimensional contaminant equations with a "stop-start" technique was used to estimate the diffusion (D) and sorption coefficients (K_d) from the measured concentration-time profiles. Results from these experiments are compared with those obtained from batch sorption tests.