Barrier effect of porous medium for migration of fine soil particles labelled by cesium-137

In order to study the barrier effect of porous medium for the migration of fine soil particles which affect the migration of ¹³⁷Cs through a soil layer, the suspension of fine soil particles which adsorbed ¹³⁷Cs was poured into the water-saturated column filled with coastal sand, Toyoura standard sand or glass beads, and the concentration of ¹³⁷Cs in the effluent through the columns was measured. The experimental results showed that the concentration of ¹³⁷Cs in the effluent was independent of the water flow velocity and the shape of packed particles, and dependent of the size of packed particles. Also, the reaction constant of fine soil particles with porous medium was drived from the ratio between the concentration of ¹³⁷Cs in the effluent and that in the inflowed suspension. It was revealed that the reaction constant was proportional to the water flow velocity and inversely proportional to the square root of the particle size. Therefore, the amounts of ¹³⁷Cs which migrate through the layer of fine sand, silt or clay to a long distance will be small, because of the large reaction constant. (author)