[en] Hydrogen water chemistry (HWC) was applied to the Fugen Nuclear Power Station. This is the first application of HWC in Japan as a countermeasure against stress corrosion cracking (SCC) of Type 304 stainless steel. After one year of experimental HWC, critical oxygen concentration range was determined as 10∼15 ppb to protect sensitized Type 304 stainless steel from SCC. Corrosion potential corresponding to this oxygen concentration ranged -210∼-250 mV (vs. SHE). No significant dose increase or local hydrogen accumulation was observed with HWC. Hydrogen has been injected continuously since 1985 with a water electrolysis hydrogen/oxygen generating system. Integrity of the materials constituting reactor cooling system other than Type 304 stainless steel was also confirmed in in-plant and laboratory autoclave tests. (author)