The utility that ran the Fukushima nuclear plant has acknowledged its delayed disclosure of the meltdowns at three reactors was tantamount to a cover-up and apologized for it.

Tokyo Electric Power Co. President Naomi Hirose's apology Tuesday followed the revelation that an investigation had found Hirose's predecessor instructed officials during the March 2011 disaster to avoid using the word "meltdown."

TEPCO instead described the reactors' condition as less serious "core damage" for two months after the earthquake and tsunami wrecked the plant, even though utility officials knew meltdowns had occurred.

An investigative report released last week said TEPCO's former president instructed officials to use the milder description under alleged pressure from the Prime Minister's Office, though it found no proof. Former officials at the Prime Minister's Office denied the allegation.