Electrochemical treatment of alkaline nuclear wastes

Production of nuclear materials within the DOE complex has produced large volumes of high-level waste (HLW) containing hazardous species such as nitrate, nitrite, chromium, and mercury. Some of the waste also contains large amounts of organic complexants and degradation products, which presents safety concerns due to the formation of flammable gases. It has been estimated that 250 million kilograms of sodium nitrate are stored in HLW throughout the DOE complex, primarily as alkaline wastes solutions and slurries. Processes being developed for the permanent disposal of these wastes are focused on separating the bulk of the radioactivity, primarily cesium-137 and strontium-90, into a smaller volume for incorporation into a vitrified wasteform, with the remainder being incorporated into a low-level, high-volume cement wasteform. Electrochemical treatment of the HLW is one of the candidate technologies being evaluated for the destruction of nitrate, nitrite and organic compounds as well as for the removal of radionuclides and hazardous metals from the different wastes. Previous testing has investigated the destruction of nitrate and nitrite in laboratory-scale flow reactors with non-radioactive simulated salt solutions. Results of testing with actual waste from the Savannah River Site in flow reactors are presented