a large scale of earthquake of magnitude 9.0 and a tsunami caused severe core damage of the nuclear reactor in Fukushima, Japan.
Since all onsite and offsite power was lost,
the decay heat generated after reactor shutdown was not adequately removed.
Although emergency electricity was provided from storage batteries at that time,
the batteries were all failed because of flood following the tsunami.
This event showed the vulnerability of the cooling ability of current nuclear power plant during station
blackout (SBO) accidents and associated conditions