Development and demonstration of solvent extraction processes for the separation of radionuclides from acidic radioactive waste

The presence of long-lived radionuclides presents a challenge to the management of radioactive wastes. Immobilization of these radionuclides must be accomplished prior to long-term, permanent disposal. Separation of the radionuclides from the waste solutions has the potential of significantly decreasing the costs associated with the immobilization and disposal of the radioactive waste by minimizing waste volumes. Several solvent extraction processes have been developed and demonstrated at the Idaho National Engineering and Environmental Laboratory for the separation of transuranic elements (TRUs), Sr-90, and/or Cs-137 from acidic radioactive waste solutions. The Transuranic Extraction (TRUEX) and phosphine oxide (POR) processes for the separation of TRUs, the Strontium Extraction (SREX) process for the separation of Sr-90, the chlorinated cobalt dicarbollide (ChCoDiC) process for the separation of Cs-137 and Sr-90, and a universal solvent extraction process for the simultaneous separation of TRUs, Sr-90, and Cs-137 have all been demonstrated in centrifugal contactors using actual radioactive waste solutions. This article summarizes the most recent results of each of the flowsheet demonstrations and allows for comparison of the technologies. The successful demonstration of these solvent extraction processes indicates that they are all viable for the treatment of acidic radioactive waste solutions. (C) 1999 Elsevier Science Ltd. All rights reserved.