Method of decreasing the radioactivity at nuclear power plants

Purpose: To decrease the radioactivity in the portions of a nuclear power plant in contact with high temperature and high pressure purified water containing radioactive materials. Constitution: In a method of decreasing the radioactivity by forming oxide layers at the surface of constituent components, oxide layers relatively porous but having a sufficient thickness are formed by the primary processing and then thin but dense layers are formed thereover the secondary processing. That is, oxidation is conducted with hot water or steam of low oxidizing property in the primary processing, while oxidation is conducted by hot water or steam of increased metal ion concentration in the secondary processing. The metal ions used herein are ions of Be, Mg, Al, Ca, V, Cr and Mn capable of having at least bivalent positive charges selected from those metals which are lower in atom number, standard electrode potential and electrical negativity than Fe. In this way, by filling the pore of the porous and thick layers with dense oxides, it is possible to provide improve corrosion suppressing effect in the nuclear reactor circumstance, that is, suppressing effect for the deposition of radioactive materials. (Kamimura, M.)