Hamaoka Nuclear Power Station Unit 5 is an advanced boiling water reactor with a generating capacity of 1.38 GW. It was shut down on May 14, 2011 at the request of the Minister of Economy, Trade and Industry. Seawater contaminated the equipment in a wide range of locations. We promptly cleaned up the reactor water and conducted an impact assessment and integrity evaluation of the equipment. The contamination areas were mainly categorized into the reactor pressure vessel and reactor internals, which are difficult to inspect and replace, and other peripheral facilities, which are relatively easy to inspect and replace.

The inspection results showed that discoloration, thinning, and adhesions due to corrosion were found in a wide range of other peripheral facilities. Basically, the minor corroded components could be removed by maintenance, so they were not considered to have an impact on the functionality of the reactor. Whereas many of the pressure vessels and reactor internals are difficult to replace, and we are currently collecting knowledge on the effects of high-temperature operation during the restart of the reactors. A large amount of seawater contamination in a nuclear reactor facility is a rare event, and this paper mainly describes the effects of seawater on the components.