Chubu Electric Power Company has announced that it detected fresh corrosion from seawater in the Unit 5 reactor.
The Japanese government ordered the utility to shut down all 5 reactors onsite in May 2011 due to concerns related to seismic activity in the area.
One day after the order to shutdown, workers found that over 40 pipes inside the steam condenser were damaged or fractured, while they were trying to shut the reactor down. This damage was found to have allowed over 400 tons of seawater to flow into the Unit 5 reactor building, where salt corroded pipes and other equipment, and delayed attempts to bring the reactor to a state of cold shutdown for hours.
Chubu Electric had admitted at the time that there was a possibility that 5 tons of seawater may have also entered the Unit 5 reactor, and the recent corrosion damage confirms that assumption.
In November 2012, workers used waterproof cameras to investigate the reactor containment and found multiple locations where damage was found on the steel lining of the containment.
The licensee has planned to further investigate the corrosion using ultrasonic waves.
The damage caused a delay in the Unit 5 reactor reaching a state of cold shutdown, and will likely ultimately retire the reactor permanently.