A study on stack configuration of continuous electrodeionization for removal of heavy metal ions from the primary coolant of a nuclear power plant

This study investigated the production of high-purity water in the primary coolant of a nuclear power plant via the continuous electrodeionization (CEDI) process, using ion exchange resins as ion-conducting media between ion exchange membranes. The effectiveness of this method was examined with respect to the removal of heavy metals. The study was carried out on a laboratory scale with an effective area of 20 cm2. The CEDI system was operated with a layered bed of cation exchange resins, anion exchange resins, and mixed-bed ion exchange resins. The stack configuration was designed to prevent a reaction between metal ions and hydroxide ions. The CEDI operation with the layered bed removed more than 99% of the ions at 30% of the current efficiency. The results showed that, with an inlet conductivity of 40 μS cm−1, a linear velocity of 4.17 cm s−1, and an applied current density of 17 mA cm−2, the CEDI process yielded an outlet conductivity of 0.5 μS cm−1, thereby preventing the precipitation of metal ions. This study therefore successfully demonstrated the feasibility of the CEDI operation for the removal of heavy metals at a very low concentration.