PURPOSE: To prevent the generation of secondary waste having high chemical toxicity by decomposing the radioactive org. iodine compd. contained in a waste org. solvent by UV projection and removing the generated molecular iodine by washing.

CONSTITUTION: For example, 300ml n-dodecane contg. 1,000ppm methyl iodide is put into a four-port flask type vessel and a slender cylindrical 30W low pressure mercury lamp is inserted therein to project UV rays thereto. The soln. is gradually increased in temp. at this time until the temp. rises to 40W50°C when the soln. is turned pale pink by the molecular iodine. The projection is stopped after 1hr. The peak area of the methyl iodide decreases to about 1/10 as compared to the original liquid when an analysis is made by gas chromatography. The iodine is removed and the pale pink color disappears on shaking for 2min after 30ml aq. 1/100N sodium thiosulfate soln. is added to the soln. after this projection. The radioactive org. iodine having high chemical toxicity is removed by constituting the device in such a manner.