Method of suppressing the release of radioactive nuclide elements from metal material into high temperature water

Purpose: To suppress the release of radioactive nuclide elements from metal materials such as Ni, Cr, Fe alloys, etc. used for primary coolant pipeways, etc. of a nuclear power plant into high temperature water. Method: Metal material containing radioactive nuclide elements such as Co, Ni, Fe, etc. are applied with heat treatment at a high temperature above 100 deg C in atmospheric air. Even if the heat treatment is applied for a long period of time in the atmosphere lower than 100 deg C, there is obtainable no effect forsuppressing the release of radioactive nuclide elements such as Co, Ni and Fe from metal material (for example SUS 304L) into high temperature water. The effect becomes particularly remarkable by maintaining the material in the atmosphere at a temperature higher than 100 deg C. The oxide layers formed by the heat treatment form dense a single diffused layer of favorable protecting property. This can remarkably suppress the release of corrosion products containing radioactive nuclide elements such as 60Co, 58Co and 58Fe from the metal material into high temperature water. (Kawakami, Y.)