The Tokyo Electric Power Company carried out geological and sonic surveys around the Fukushima Daiichi plant to assess the power station's resistance to earthquakes and earthquake related phenomenon, including tsunamis.
The extensive survey was carried out as part of a widespread review of nuclear power plant safety following a magnitude 6.6 earthquake struck the Niigata region in northwest Japan in July 2007, causing a leak of radioactive water from the Kashiwazaki-Kariwa Nuclear Power Plant. A fire also broke out at the facility at the time.
Nuclear safety specialists said that despite the surveys it appeared officials at Fukushima Daiichi had not considered the scenario that a tsunami might hit the power plant at a time when they would need to use diesel back up generators intended to provide emergency power to the reactor cooling systems.
Fuel tanks for the generators, positioned at ground level just yards from the sea front, were among the first parts of the facility to be destroyed by the huge tsunami wave that swept inland following last week's magnitude 9.0 earthquake.
Officials from TEPCO said the plant was designed to be resistant to an 18 foot wave but was struck by a wall of water more than 22 feet in height. (read more)