Structural material for nuclear power plant

Ni-58 contained in an Ni based alloy used as a structural material of a BWR type power plant is put to isotope separation, and the removed Ni is contained as Ni in the structural material. Then the amount of radioactive nuclides of a long half-time such as Co-58 formed by activation of Ni in the reactor core can be suppressed. Ni-58 is separated and removed from natural Ni and the content of Co is also reduced simultaneously by the isotope separation method. Ni having reduced content of Co-59 as an impurity is added to form a metal material by a method using the difference of mass between each of the isotopes. (T.M.)