Sorption behavior of selected radionuclides on Columbia River basalts

The sorption behavior of selected radionuclides on the Columbia River basalts has been investigated. Radionuclide distribution coefficients, using a batch-equilibrium technique, have been determined for iodine, selenium, technetium, strontium, cesium, uranium, radium, plutonium, americium, and neptunium. Since the distribution coefficient value is an empirical value, the effects of temperature, pressure, groundwater composition, and Eh conditions on the distribution coefficient value for these isotopes have been investigated. In addition, sorption isotherms, describing the dependence of radionuclide sorption on radionuclide concentration for cesium, strontium, radium, plutonium, and uranium (under both oxidizing and reducing conditions) have been determined. Based on these sorption data, it appears that, under the expected ambient repository conditions (e.g., reducing, alkaline conditions), the Columbia River basalts are capable of strongly retarding cesium, strontium, radium, and neptunium migration and moderately retarding uranium, technetium, and plutonium migration. The basalts are not capable of significantly retarding the migration of iodine and selenium