Method for controlling water quality in nuclear reactor and nuclear power plant to which the method is applied

A method for controlling water quality in a nuclear reactor comprising the steps of:

• applying an atmospheric oxidation heating treatment to nickel base alloy material which is used in a feed water heater and a fuel assembly of the nuclear reactor thereby to form an oxide layer on the surface of the nickel base alloy material, so that a nickel concentration in the reactor water is maintained so as to be less than 0.2 ppb;
• making an amount of iron, which is carried into the nuclear reactor and corrosively eluted from structural material within the nuclear reactor into reactor water, at least twice as much as any one of an amount of nickel, which is carried into the nuclear reactor, and an amount of nickel, which is generated in the nuclear reactor;
• limiting an upper limit of concentration value of iron in system water supplied into the nuclear reactor to up to 0.10 ppb, said iron being removed by an iron removing device for removing iron from system water supplied into the nuclear reactor;
• and
• reducing and limiting the amount of nickel in system water supplied into the nuclear reactor to less than {fraction (5/22)} of an original amount of nickel in system water supplied into the nuclear reactor so that a total amount of iron generated is at least twice as much as a total amount of nickel generated.