Patent Number: 
Section: claims

1. 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,wherein said reductive nitrogen compound is injected into the cooling water at the time of normal operation of the reactor, from at least one system line selected from the group consisting of a feed water system, a reactor water clean up system, a primary loop re-circulation system, an emergency core cooling system and a control rod drive hydraulic system,wherein the injection of said reductive nitrogen compound is controlled to set the concentration of said reductive nitrogen compound in the cooling water at 9.4×10−6 mol/liter or less,wherein said reductive nitrogen compound is injected into the cooling water at the time of normal operation of the reactor, from a system line of a reactor water clean up system,wherein said reductive nitrogen compound is hydrazine, andwherein a site of the injection of the reductive nitrogen compound from said reactor water clean up system line is an injection connection provided on the line connecting the down stream of filter demineralizer and the reactor pressure vessel.