Behavior of radioactive nuclides in saturated sandy layers

The diffusion and adsorption of radioactive nuclides in the sandy layer of sea bottom were investigated. A diffusion equation for nuclides was introduced, and diffusion coefficients were derived from experiments. The adsorption distributions of Sr-85, Cs-137, Mn-54, Zn-65 and Co-60 in fine sand after two weeks of diffusion experiments were measured. The diffusion of Sr-85 was especially large. The behavior of iodine in saturated sandy layers was also observed. The nuclide used for the experiment was I-131. The breakthrough curves for iodine ion slugs were measured under various conditions of leaching. It was found that the iodine ions consisted of the component which is not adsorbed to sand layer and the component which can be adsorbed irreversibly. The relation between the relative concentration of adsorption distribution and the distance along the column was obtained, in which the introduced pore volume of tracer solution was used as a parameter. The effect of pH on the transportation distribution of I-131 along the column was measured. The amount of adsorption was larger as pH value was smaller. The distribution ratio of iodine from 5 x 10-4M CaCl2 solution to methyl isobuthyl keton in relation with pH and the initial iodine concentration in salt solution was also measured. (Kato, T.)