Geochemical information for the West Chestnut Ridge Central Waste Disposal Facility for low-level radioactive waste

Geochemical support activities for the Central Waste Disposal Facility (CWDF) project included characterization of site materials, as well as measurement of radionuclide sorption and desorption isotherms and apparent concentration limit values under site-relevant laboratory test conditions. The radionuclide sorption and solubility information is needed as input data for the pathways analysis calculations to model expected radioactivity releases from emplaced waste to the accessible environment under various release scenarios. Batch contact methodology was used to construct sorption and desorption isotherms for a number of radionuclides likely to be present in waste to be disposed of at the site. The sorption rates for uranium and europium were rapid (> 99.8% of the total radionuclide present was adsorbed in approx. 30 min). With a constant-pH isotherm technique, uranium, strontium, cesium, and curium exhibited maximum Rs values of 4800 to > 30,000 L/kg throughout the pH range 5 to 7. Sorption ratios were generally lower at higher or lower pH levels. Retardation factors for uranium, strontium, and cesium, explored by column chromatographic tests, were consistent with the high sorption ratios measured in batch tests for these radionuclides. The addition of as little as 0.01 M organic reagent capable of forming strong soluble complexes with metals [e.g., ethylenediaminetetraacetic acid (EDTA) or citric acid] was found to reduce the sorption ratio for uranium by as much as two orders of magnitude. Substitution of an actual low-level waste site trench water for groundwater in these tests was found to give a similar reduction in the sorption ratio