The disaster followed an earthquake and huge tsunami on March 11, 2011, that knocked out crucial cooling systems, allowing three of the plant’s six reactors to melt down.

In the report, Tepco said that before the accident it had been afraid to consider the risk of such a large tsunami, fearing admissions of risk could result in public pressure to shut plants down as unsafe.

“There were concerns that if new countermeasures against severe accidents were installed, concern would spread in host communities that the current plants had safety problems,” the report said.

The report also repeated Tepco’s position that it did not know such a large tsunami was possible on the coast of Fukushima, which faces the Pacific Ocean. Tepco’s executives have argued that because the tsunami was larger than what some experts had predicted to be possible, the accident should be considered an act of nature for which the company should bear no legal responsibility.

The company has also admitted, however, that even its own engineers had predicted a far larger tsunami was possible in Fukushima, a finding that the company and regulators both chose to ignore or not make public.

The report Friday was issued to coincide with the first meeting of a panel of outside experts, including a former United States Nuclear Regulatory Commission chairman, who will oversee improvements at the company’s nuclear division. The company listed several new measures to prevent severe accidents, such as creating more backup systems, better crisis management and a corporate culture more willing to acknowledge problems.

All but two of the country’s 50 undamaged nuclear reactors remain idled as the government works to convince the public that they are safe. The government has recentlygiven conflicting signals about when those reactors might be turned on, or even who could make that decision.

A newly created nuclear watchdog at first seemed to say that no more plants could be turned on until it drew up new safety guidelines, a process that might take until next year, but then seemed to back off by saying that it did not have the authority to do anything more than issue guidelines.

Last week, the trade minister, Yukio Edano, said the new agency’s guidelines would be used to determine which reactors could be turned back on, without saying how long it would take to create those new rules.

While the disaster, which spewed large amounts of radioactive material across northern Japan, helped strengthen the anti-nuclear movement in the country, many people see a resumption of nuclear power as crucial to avoiding further damage to Japan’s badly shaken economy.

With its report, Tepco appeared to be arguing that it had learned its lesson from the accident, and listed new anti-tsunami walls, backup power generators and other new safety steps it has taken at its other plants. Besides the Fukushima Daiichi plant, Tepco also operates the Fukushima Daini plant, also in Fukushima, as well as the world’s largest nuclear plant, Kashiwazaki-Kariwa in Niigata.

While saying the tsunami was unforeseeable, the report did say that Tepco could have taken steps that might have prevented the Fukushima accident, such as adding backup generators to keep cooling systems operating. It also said it failed to learn from foreign countries, such as the United States, which strengthened its nuclear plants against terrorist attacks and accidents after the Sept. 11, 2001 attacks