System decontamination method

Purpose: To dissolve to remove oxide layers without roughening the surface of metal matrix material and restrict the radioactivity level to less than a limit value in a method of removing oxide layers deposited in pipeways, etc. formed upon reactor dismantling. Method: Radioactive oxide layers are adhered or deposited to metal matrix materials such as for pipeways, equipments, etc. exposed to coolants of a nuclear reactor or dissolving solutions. An acidic solution comprising a decontaminating solution containing tetravalent cerium ions or like other oxidizing material in an aqueous acidic solution incorporated with sodium fluoride is brought into contact with the oxide layers. This enable to dissolve and remove the oxide layers without roughening the surface of the metal matrix material. An anode and a cathode are immersed in a decontaminating solution containing metal ions rendered to a less oxidized state and metal ions rendered to the highly oxidized state by the decontamination, electric current is supplied between both of the electrodes, in which the metal ions of less oxidized state are oxidized at the anode and regenerated metal ions at highly oxidized state. (Takahashi, M.)