Operational Safety Post-Fukushima Impacts on Future

Event description: On 11 March 2011, the tsunami waves generated by the earthquake off the coast of Japan overwhelmed the tsunami barriers of Fukushima Daiichi NPP site. • Tsunami flooded the primary and backup power systems and equipment, as well as the ultimate heat sink systems and structures, of all six units on the site. • Compounding the off-site power loss that occurred before the tsunami due to the earthquake damage to the transmission system, the flooding caused the loss of on-site A/C power sources (and/or on-site power distribution systems). • Units 1-5 of the Fukushima Daiichi NPP experienced extended station blackout (SBO) events, which exceeded nine days in Units 1 and 2, and 14 days in Units 3 and 4. The units were unable to cope with the extended loss of electrical power and plant heat removal, and the reactors of Units 1, 2 and 3 suffered damage as the fuel overheated and melted. • The reactor pressure vessels (RPVs) that enclose the reactor cores were eventually breached in those units, and radioactive material escaped from the reactors. • The radioactive material confined in the primary containment vessels (PCVs) was further released directly to the environment either in a controlled manner, i.e. by venting of the reactors' PCVs, or in an uncontrolled manner upon damage and failure of the confinement structures. The radioactive releases resulted in radiological exposure of the workers at the site and the general public residing in the surrounding communities and caused radiological contamination of the environment in those areas. • In order to reduce radiation exposures, people within a radius of 20 km of the site, as well as other specified areas, were evacuated, and restrictions were placed on the distribution and consumption of food and drinking water. • Although no loss of life has been attributed to the radiological releases, the accident caused social and economic impacts, especially in Japan.