TOKYO (Kyodo) -- Tokyo Electric Power Co. said Wednesday it could have determined nuclear core meltdown occurred at the Fukushima plant sooner than it did following a massive earthquake and tsunami on March 11, 2011.
The utility known as TEPCO initially said reactors cores had been damaged, but did not admit until May 2011 that core meltdown occurred. Early in the crisis it said there was no basis to determine reactor core meltdown.
But this month TEPCO discovered its internal operation manual defines core meltdown as damage to more than 5 percent of a reactor core.
"We could have concluded as of March 14 that core meltdown occurred," a TEPCO official said at a press conference.
The No. 3 unit had damage to 30 percent of its reactor core as of 5:03 a.m. on March 14, while 55 percent of the No. 1 reactor's core was damaged as of 7:18 a.m. that day, according to TEPCO.
The company revealed its operational standard for determining reactor meltdown nearly five years after the 2011 calamity. It did so while investigating -- at the request of Niigata Prefecture where a nuclear power plant that TEPCO aims to restart is located -- how it responded to the Fukushima disaster.
Niigata Gov. Hirohiko Izumida said in a statement "it is highly regrettable" that TEPCO had not disclosed the finding for five years. The governor also asserted company officials must have known of the meltdown definition when the disaster was unfolding.
Fukushima Gov. Masao Uchibori said the true state of the reactors should have been reported to the municipal government on March 14, 2011, and urged TEPCO to ensure that it releases information in an accurate and speedy fashion.
The power company said it will launch an in-house investigation involving third party experts to examine why the reference to meltdown in the manual was overlooked.