Decontamination method for metal waste contaminated by UF6

Water is jetted to metal wastes contaminated by UF6 to remove loose corrosion layers on the surface of a matrix thereby exposing a crystal grain boundary thereunder. Then, they are immersed in heated nitric acid so that the nitric acid permeates into the crystal grain boundary to dissolve and leach uranium oxide as uranyl nitrate (UO2(NO3)2). Subsequently, the metal wastes immersed in nitric acid are washed with supersonic waves under water to discharge and remove fine contaminated particles such as uranium oxides and iron oxides remained in the crystal grain boundary from the permeated portion of the metal matrix. Further, blasting of jetting iron powder, as an abrasive, is applied to the metal wastes washed with supersonic waves to drop off the crystal particles on the exposed surface and polish the metal surface repeatedly thereby removing remained uranium. With such procedures, the contaminated metal wastes can be decontaminated with satisfactory reproducibility to a level of a back ground at a low cost, and processing of secondary wastes is also facilitated. (T.M.)