Naomi Hirose, president of Tokyo Electric Power Company (Tepco), admitted on 21 June that the company had concealed the reactor meltdowns at its Fukushima Daiichi nuclear plant immediately after the March 2011 earthquake and tsunami. The utility did not officially admit the meltdowns until more than 2 months after the accident.

In February this year, it was revealed the utility could have ascertained a meltdown three days after its occurrence if workers had followed an in-house manual. Tepco asked a third-party panel to investigate the matter and the panel released a report on 16 June saying the company's then-president, Masataka Shimizu, had instructed officials not to use the words "core meltdown".

The instruction was made through a public relations official during a press conference on the night of 14 March 2011, three days after the plant was damaged. The panel report said Shimizu had received instructions on the matter from the prime minister's office. But it's not known what exactly he was told or who gave the orders. Both then-Prime Minister Naoto Kan and then-Chief Cabinet Secretary Yukio Edano have denied giving such instructions.

During that press conference, Tepco vice president Sakae Muto received a memo from Shimizu passed to him by a company employee, saying, "By instruction of the prime minister's office, don't use 'core meltdown.'" Shimizu's position was conveyed within the company by phone and other means. The report concluded that "an understanding was shared within Tepco that statements acknowledging a meltdown should be avoided."

After Tepco employees switched to the term "core damage". The report pointed out, "If the memo had not been passed over, vice president Muto may have responded differently." The third-party investigative committee searched for the memo, which was said to be handwritten, but did not find it. The committee questioned Shimizu on two occasions over a period of about four hours, but the report concluded, "His memory has faded and clear facts could not be confirmed."

However, it quoted a Tepco employee who was summoned in April by then Minister of Economy, Trade and Industry Banri Kaieda as saying that Kaieda had told him: "There doesn't appear to be a clear definition of a core meltdown, so let's make it the melting of fuel pellets." After that, a fax was distributed within the company saying, "'Melting of fuel pellets' is to be used. This is because 'core meltdown' conveys the image that the whole core has melted, like the China syndrome."

This was in spite of a manual that was "discovered" at Tepco in February this year, which defined a core meltdown as having occurred when over 5% of the reactor core had been damaged. The third-party panel report stated that quite a few of some 55 Tepco employees in charge of external reports had checked the manual, and rejected the claim that "nobody had noticed" it until its "discovery".

On 16 June, Democratic Party Secretary-General Yukio Edano, who was Chief Cabinet Secretary at the time of the meltdowns, told reporters in Yokkaichi, Mie Prefecture, that he had never issued any orders to avoid use of the phrase "core meltdown". He said: "Neither I or then Prime Minister Kan made any such request to Tepco," adding, "During news conferences at the time I myself acknowledged core meltdowns. Putting the brakes on (the use of the term) would have been out of the question."

Hirose said he considers Shimizu's instruction as an attempt to hide the conditions at the plant at the time. He told a news conference that the company's concealment of the meltdowns is a grave issue. He said it is natural for the public to interpret the decision as a cover-up. "We deeply regret that our previous leadership failed to live up to the standards of transparency and thoroughness that we strive to meet today," he said. "We sincerely apologize for it."

President Hirose stressed that Tepco has in recent years worked to improve the timeliness, thoroughness, and clarity of its communication with the public, both inside Japan and internationally. It been learning this lesson and breaking from its past, as it works to build trust with the public and with government through the implantation of its Nuclear Safety Reform Plan. Improvements in communication represent an important element of that Plan, which is overseen both by the company's Nuclear Safety Oversight Office and by an independent Nuclear Reform Monitoring Committee chaired by a former head of the US Nuclear Regulatory Commission.