Chemical characterization, leach and adsorption studies of solidified low-level wastes

Laboratory and field leaching experiments were conducted on solidified low-level waste from a commercial boiling water reactor. Batch leaching, soil column adsorption, and soil/waste form column experiments were conducted in the laboratory, using small scale cement waste forms and Hanford ground water. The purpose of these experiments was to evaluate the ability of laboratory leaching tests to predict leaching under actual field conditions and to determine which mechanisms (i.e., diffusion, solubility, or adsorption) actually control the concentration of radionuclides in the soil surrounding the waste form.

Chemical and radionuclide analyses performed on samples collected from the field and laboratory experiments indicate strong adsorption of 134,137 Cs and ⁸⁵ Sr onto the Hanford soil. Approximately 0.5% of the available ⁶⁰Co leached from the waste forms and migrated through the soil with a retardation factor of 1. Chemical constituents present in the reactor waste streams and found at elevated levels in the field and laboratory leachates include: sodium (1383 mg/L), sulfate (2230 mg/L), and nitrate (435 mg/L field only). Plausible solid phases that could be controlling the chemical and radionuclide concentrations in the leachate were identified using the MINTEQ geochemical computer code.