Large amounts of concrete, metal, soil, and other radioactive waste are generated not only from nuclear power plants operating in Korea but also from nuclear power plant decommissioning. If it is confirmed through measurement of residual radioactivity that the concentration is below the allowable clearance level, they can be managed as general or industrial waste in accordance with the Nuclear Safety Act. The Korea Radioactive Waste Agency predicts that very low-level radioactive waste will be generated the most, at about 67.1%. If waste below clearance level among very low-level radioactive waste can be evaluated and reduced, a lot of costs can be saved. Among radioactive wastes, metal wastes in particular have various sizes, shapes, and densities. If radioactivity is measured without properly considering this, a large error occurs in the measured value even if the radioactivity value is the same. This requires a conservative measurement method using density correction taking into account the self-absorption effect. For conservative measurements, it is essential to compare measured values with calculated values using MCNP6 (Monte Carlo N-Particle). You must enter the geometry of the measurement environment and derive calculated values using F8 Tally. Clearance level of radioactive waste is determined through the above method. In addition, sufficient MDA (Minimum Detectable Activity) must be secured to determine clearance level by using NaI(Tl), plastic scintillator configuration, and lead shielding. Nuclide analysis is performed using a NaI(Tl) scintillator and the total gamma radioactivity is evaluated using a highly efficient plastic scintillator.