Republic of Korea is preparing to decommission Kori Unit 1 and Wolsong Unit 1. Decommissioning of a nuclear power plant proceeds in the following stages: shutdown, transition period, decontamination, cutting, waste treatment, and site restoration. When nuclear power plant is decommissioned, It is expected that approximately 80,000 drums of radioactive waste will be generated per nuclear power plant. Therefore, various technologies are being researched and developed to reduce this to approximately 14,500 drums. Technologies for waste volume reduction are largely mechanical and electrical/thermal methods. Representative examples of mechanical volume reduction technologies include super compactors and electrical/thermal volume reduction technologies include induction and plasma torch furnaces. Both technologies are effective reduction technologies, but the reduction ratio varies depending on the type or condition of waste before treatment. For example, as a result of testing waste reduction using a super compactor at NUKEM in Germany, the reduction ratio was found to be between 1.3 and 7 depending on the type or condition of waste such as chips, ash, scrap metal, sand, etc. And according to IAEA-TECDOC-1527, when reducing the volume of metals, aluminum, lead, copper, brass, etc. using induction melting, the waste volume reduction ratio is 5 to 20. In this paper, referring to these results, a melting test was conducted using a previously developed plasma torch with an output of more than 100 kW. And volume reduction characteristics of this plasma torch was considered depending on waste type or condition.