The purpose of this study was to develop a soil washing system, and to define the most suitable experimental conditions for operation of its individual components, for decontaminating the radioactive soil around a TRIGA (Training, Research, Isotope, General Atomic) reactor in Korea. Analysis results indicated that the main radionuclides were Cs137 and Co60, the soil particle size ranged from 0.063 to 1.0 mm, and the radioactive concentration was the strongest in soil particles smaller than 0.063 mm, as predicted. Meanwhile, oxalic acid was found to be the most efficient chemical agent for washing, especially for the removal of cobalt. A scrubbing time of 4 h was optimal for obtaining a removal efficiency of more than 75 % for 137Cs and 60Co. A mixing ratio of the soil weight to the volume of the oxalic acid solution of 1:10 was observed to be best for washing, and it was estimated to be reasonable for two scrubbing cycles with 1.0 M oxalic acid to avoid the generation of excessive amounts of waste solution. The removal efficiency with hydro-cyclone was 30 % higher than that without hydro-cyclone. Vertical plates and alum acted as important factors to reduce the sedimentation time. The waste-solution could be reused after passing it through a column of strong acid resin up to five times.