Patent ID: 8175211

Claim:
A method for mitigating a stress corrosion cracking of structural material in a nuclear power plant, comprising the step of: injecting hydrogen and a reductive nitrogen compound containing nitrogen having a negative oxidation number into a reactor water of a boiling water nuclear power plant; and stopping injection of the reductive nitrogen compound when the oxygen concentration reaches a prescribed value, wherein said reductive nitrogen compound is injected into the cooling water from at least any one of a system line selected from a group consisting of a reactor water clean up system, a primary loop re-circulation system, an emergency core cooling system and a control rod drive hydraulic system, at a time of start up operation or shut down operation of the reactor, and during a part or all of a period of injecting the hydrogen into the reactor water, wherein the injection of said reductive nitrogen compound is stopped when the oxygen concentration in the cooling water has become a prescribed value or less, and wherein the injection of said reductive nitrogen compound is controlled so that the concentration of said reductive nitrogen compound in the cooling water comes to 9.4×10 −6 mol/liter or less.