In the Kori-1 radioactive waste storage, the concentrated waste and spent resin drums generated in the past are repacked and stored in large concrete drums. In order to dispose of radioactive waste generated before the establishment of the waste acceptance criteria, it is necessary to develop a large concrete drum treatment and waste treatment process to evaluate disposal suitability and secure technology that meets the latest technical standards. In addition, for worker safety and waste reduction, it is important to develop secondary waste treatment technology generated during waste treatment. In this study, the types and characteristics of secondary wastes that can be generated when large concrete drums are decommissioned were investigated. In addition, considering the characteristics of possible secondary wastes, suitable treatment methods and characteristic evaluations were analyzed. We plan to develop an optimal process for secondary waste treatment in consideration of on-site work space, economic feasibility, and safety.