Nuclear reactor decontamination

The CAN-DECON system was developed by Atomic Energy of Canada in collaboration with Ontario Hydro, and is under licence to London Nuclear Decontamination. A CANDU reactor is decontaminated as follows. The reactor is shut down, and the coolant at about 900C is purified with mixed-bed ion exchange resin. Next, typically 0.05 to 0.1 weight percent of a mixture of organic acid chelant and reducing agent is added to the coolant, which is continuously passed through cation exchange resins and filters to remove solids and regenerate the reagents. Decontamination is achieved by solubilizing magnetite in which cobalt ferrite and other impurities are contained. When the desired decontamination (typically by a factor of 3 to 7) has been obtained, the reagents are removed from the coolant by continuous passage through mixed bed ion-exchange resin, and finally a corrosion preventer such as LiOH is added to the coolant prior to startup. The system works well with BWRs, and has been used on Vermont Yankee. An oxidizing agent can be used for PWRs. (NDH)