Sorption and transport behavior of radionuclides in the proposed low-level radioactive waste disposal facility at the Hanford site, Washington

A series of batch sorption and column experiments was conducted to investigate sorption and transport behavior of 99Tc, 129I, 79Se, and 90Sr on and through borehole sediments collected from the proposed low-level radioactive waste disposal facility at the Hanford Site (200 East Area). Batch sorption experiments were conducted on Hanford sediment using uncontaminated Hanford groundwater and simulated glass leachates spiked with individual radionuclides. Strongest sorption occurred for 90Sr, while 79Se sorption was intermediate, and 129I and 99Tc showed the least sorption affinities on Hanford sediment among these radionuclides studied. The results of column experiments that measured transport behavior of these radionuclides through Hanford sediment were similar to the mobility that can be calculated from the batch sorption results, that is high mobility for 99Tc and 129I compared to the intermediate and strong retardation for 79Se and 90Sr, respectively. These contaminant sorption data on sediments from below the proposed disposal facility, especially the tests using simulated glass leachate, corroborate values obtained for sediments collected in the past from near by locations and for generic solutions such as regional groundwater. These new data should provide more technical defensibility for past performance assessment predictions that did not use site-specific sediments and leachates. Further, the new data will be incorporated into future performance assessment activities that will update and improve past predictions. (orig.)