On March 2011 at Fukushima Daiichi NPS, seawater was injected into spent fuel pools just after the accident for emergency cooling. The temperature of the water in a pool raised up to 93 ℃, and the chloride ion concentration raised up to 1,944 ppm (maximum) after seawater injection. In this high temperature and high chloride ion concentration environment, localized corrosion including crevice corrosion may have occurred on components made of passive metals such as stainless steels. The environment is assumed to be susceptible to crevice corrosion for 304 SS based on laboratory experiments and the concept of ER, CREV. There is a low possibility of initiating localized corrosion after the water was purified and deoxygenated. However, it is not certain whether localized corrosion, once initiated and propagated under the severe condition, will repassivate after the bulk water is purified. It is necessary to examine the continuity of crevice corrosion propagation when the bulk water is purified and deaerated, which means the cathodic reactions outside the crevice will no longer contribute to the propagation of the corrosion.