Treatment of ion exchange resins used in nuclear power plants by super- and sub-critical water oxidation – A road to commercial plant from bench-scale facility

A super-critical water oxidation (SCWO) process has been developed to effectively reduce the quantities of waste ion exchange resins from the pressurized water reactors (PWR) in Korea. First of all, waste ion exchange resins were separated into cationic and anionic resins by a specific gravity difference in the fluidized bed. The separated resins were wet pulverized in a ball mill for 24 h to make uniformly dispersed slurry in high concentration. The optimal decomposition conditions for waste cationic and anionic resins from thermal power plants were obtained in a bench-scale facility of reactor of 220 mL volume. Then scale-up experiments were performed in a pilot plant with a 24 L reactor. The optimal values of such parameters as process temperature, process pressure, residence time, amount of oxidant, and amount of additives (NaOH and CH3NO2) for decomposition were determined by the pilot plant. The optimal process condition on cationic ion exchange was found under the sub-critical condition. The process temperature for anionic ion exchange resins was lowered to 515 °C. By using nitromethane as a denitrification agent, total-nitrogen (T-N) in the treated water was lowered as well as almost no NOx was emitted from the exhausted gases. Based on the production rate and the stored amount of waste resins in the nuclear power plant “A”, a commercial facility with process capacity of 150 kg/h was designed in detail. In this paper, we present the procedure to scale-up from a bench-scale facility to a commercial plant and major check points in each stage.

► A SCWO process developed to reduce the quantity of waste ion exchange resins from PWR in Korea. ► For cationic ion exchange resins the optimal process was found under sub-critical condition. ► For anionic ion exchange resins, T-N was lowered and no NOx was emitted by using nitromethane. ► The scale-up procedure to commercial plant (150 kg/h) and major check points are introduced.