Cerium effect on decontamination of stainless steel 304 metal oxide

The primary system of the Pressurized Water Reactors (PWR) are operating in a closed cycle at a pressure of about 15 MPa and a temperature of 270 ⁓ 310°C. The main components of the system are consisted of zirconium alloy as fuel cladding material and inconel alloy and other major components are made of stainless steel with excellent corrosion resistance. As the operation of a nuclear power plants were increased, radioactive corrosion products (CRUD) generated by system corrosion attach to the surface of the primary system. It has known the two types of oxides that was impregnated on the system surface another oxides grown inside the metal. It is reported that the ratio of the radioactivity from these two oxides is almost the same. Radioactive corrosion products (CRUD) generated from the reactor coolant system are known to be composed of the magnetite and nickel ferrite (NiFe₂O₄) including various chromium oxides(FeCr₂O₄, Fe₂CrO₄, NiCr₂O₄). The composition of these oxide films are similar to that of nickel ferrite and is expressed as a non-stoichiometric mixed oxide of spinel structure (Fe)3_-xy(Ni)_x(Cr)_yO₄. The major chemical decontamination method that has been developed so far is the reduction and dissolution of Fe oxide film by a reducing agent. The chromium oxide in the corrosion oxide is oxidized to Cr (III) → Cr (IV) and the iron oxides dissolve when reduced to Fe (III) → Fe(II). In this study, the cerium effect on chemical decontamination characteristics of the metal oxide film formed on the surface of the SUS 304 material was investigated to determine the optimal conditions as function of cerium concentration and operating temperature