The amount of waste ion exchange resin generated from nuclear power plants is increasing; therefore, the effective method to reduce the volume of the waste resins is required. The purpose of this paper is to reduce the weight and volume of the resin and to stabilize the radionuclide such as cobalt by reactive thermal plasmas with carbon dioxide injection, and to investigate the reaction mechanism of the resins doped with cobalt. The resins were treated by thermal plasmas under atmospheric pressure. The weight was reduced to 70% after 40 min of treatment without reactive gas injection. At 12 L/min of carbon dioxide injection, the weight reduction was enhanced to 96%. Thermal plasma treatment provides the effective and rapid reduction in weight and volume of the resins. Moreover, the treatment has good advantages for the stabilization of the doped metal. (c) 2005 Elsevier B.V. All rights reserved.