An in-house investigation by Tokyo Electric Power Co. has found that the crisis at the Fukushima No. 1 nuclear plant was triggered by tsunami that flooded key structures after the March 11 earthquake, causing equipment inside to fail, sources said.
In an interim report of its investigation into the world’s worst nuclear crisis in 25 years, Tepco says it plans to take thorough measures to prevent buildings and important equipment from being exposed to water, the sources said Monday.
While vowing to take steps to avoid accidents that would result in further reactor core damage, Tepco says in the report that it also plans to have measures in place to prevent hydrogen explosions and massive releases of radioactive substances into the environment.
But the report fails to answer why the utility had not acted to bolster its tsunami defenses despite being aware of the threat prior to March 11, the sources said.
The report states that major facilities at the plant did not lose their functions as a direct result of the magnitude 9.0 earthquake, while recognizing that the scale of any direct damage from the quake has “not been clearly confirmed” because the tsunami hit within an hour.
As for an in-house study conducted in 2008 that projected that tsunami as high as 10.2 meters could hit the plant, the report says the figure was “just something based on an assumption without specific evidence” and that the 14- to 15-meter-high tsunami that ravaged the plant on March 11 “largely exceeded” the utility’s expectations.
Hit by the earthquake and tsunami, the coastal nuclear plant lost nearly all of its power sources and consequently the ability to cool the reactors and spent fuel pools.
Kashiwa cesium link
High levels of radioactive cesium found in Kashiwa, Chiba Prefecture, in October were probably from fallout from the Fukushima No. 1 nuclear power plant, the Environment Ministry said in an interim report.
The cesium is highly likely to have been concentrated in the soil on city-owned land after rainwater seeped from a ditch nearby, the ministry said Monday, discounting the possibility that the contaminated soil had been brought in from elsewhere.
During monitoring at around 30 spots within a 4-sq.-meter area, radiation measured up to 4.11 microsieverts per hour 1 meter above ground, and up to 450,000 becquerels of radioactive cesium per kilogram of soil was detected in the soil between 5 to 10 cm below the surface near the ditch.
There were other spots near the area where high levels of cesium were detected below the surface.
The ministry said it will therefore expand the area monitored, planning to produce a final report, possibly by the end of the year.