Radioactive aerosols from nuclear power plant decommissioning have not been actively studied compared to those from severe accidents. However, it will be more critical issues in the future. The radioactive aerosols will deposit on the surfaces of matter and disperse in the working space. Hence, the workers in nuclear power plant decommissioning may inhale some of the aerosols during the normal operation or accident. The health effects of aerosols depend not only on the particle size but also on the aerodynamic and thermodynamic characteristics. Therefore, it is crucial to understand the distribution of radioactive aerosols regarding their aerodynamic diameters, radioactive isotopes, and chemical forms to ascertain the respirable fraction. We analyze the effect of the cutting method, cutting material, and cutting conditions on the mass and radioactivity distributions of radioactive aerosols and identify the dominant factor for the safety of workers in the nuclear power plant decommissioning process. We confirm that the chemical composition and radioactive contamination in cutting material affect the aerodynamic diameter distribution and the amount of aerosol. Finally, we suggest the underwater plasma arc cutting process that could minimize the internal dose of workers at the nuclear power plant decommissioning sites.