Treatment of Liquid Waste and Regeneration of Spent Ion Exchange Resin Using Electrochemical Techniques

Abstract

Liquid waste and spent ion exchange resin are generated during the decontamination, refurbishment and decommissioning of nuclear power reactors and nuclear facilities. The liquid waste and spent resin may contain radionuclides, metals, organic chelating (complexing) agents and inorganic reagents. The liquid waste is treated at high cost, and the dewatered spent resin is transferred to containers and stored in a radioactive waste storage facility. During storage of resin waste, radiolytic and other decomposition processes can occur resulting in gas generation and release of free liquids. Therefore, storage facilities are built to allow continuous monitoring of the resin waste container for at least 50 years. It is therefore ideal to develop methods for the treatment of liquid and resin waste in order to treat the waste as soon as it is generated.

An electrochemical method is being developed at Chalk River Laboratories which has potential to be used for treating liquid waste and for regenerating spent ion exchange resin. A three compartment electrochemical cell has been designed and fabricated; the central compartment contains liquid waste or spent ion exchange resin, while the anode and cathode compartments contain electrolytes. This paper discusses the results of cyclic voltammetry tests performed in simulated spent CAN-DEREM™ reagents to determine the iron redox potential in these electrolytes. CAN-DEREM™ is a dilute regenerative chemical decontamination process developed by Atomic Energy of Canada Limited for use in the primary heat transport system of CANDU®¹ reactors, pressurized water reactors and boiling water reactors. The paper also presents the results of tests to study the current efficiency of iron deposition as a function of solution pH, cathode material and temperature. The influence of three commercial cation exchange membranes on the transport efficiency of iron is also discussed.

The ultimate goal of the project is to force (under an electric field) the migration of metal ions in spent ion exchange resin through a membrane into the cathode compartment where they can be reduced to metal and deposited on the cathode. As a result, the spent ion exchange resin can be regenerated and reused, lowering the volume of ion exchange resin required. The reduced solid metal on the cathode would have a significantly lower volume and be much easier to dispose of.