A Japanese parliamentary panel is to release its report into the handling of the nuclear disaster at Fukushima, after months of hearings.
The report is expected to be critical of both government officials and plant operator Tokyo Electric Power (Tepco).
Meanwhile, the first nuclear reactor to be switched back on since the March 2011 disaster has started generating electricity.
The restart, ordered by PM Yoshihiko Noda last month, was met with protests.
The parliamentary panel, formed last May, said in December 2011 in its interim findings that Tepco and the country's nuclear body had failed to ''take precautionary measures in anticipation that a severe accident could be caused by a tsunami such as the one which hit''.
The government of then Prime Minister Naoto Kan was also criticised for being slow to respond to the crisis and delaying the dissemination of information to the public.
Some members of the panel said Mr Kan and his aides distracted workers at the power plant by making numerous phone calls, says the BBC's Mariko Oi in Tokyo. His visit to the plant shortly after the accident was also criticised as a distraction to workers.
When he appeared before the panel, Mr Kan said he had been unable to get a full picture of what was happening at the plant.
More than 20,000 people were killed when the earthquake and tsunami struck north-eastern Japan.
The six-reactor Fukushima Daiichi nuclear plant was badly damaged, in what was regarded as the worst nuclear disaster since Chernobyl in 1986.
Tens of thousands of people had to be evacuated after the tsunami knocked out cooling systems to reactors, leading to meltdowns and the release of radioactivity.
A 20-km (12 mile) exclusion zone remains in place around the plant.
All of Japan's nuclear plants were shut down in the wake of the disaster. But on Sunday the first reactor was restarted in the town of Ohi in Fukui prefecture.
The restart sparked large protests in Tokyo but Mr Noda urged support for the move, saying a return to nuclear power was essential for the economy.
The government is continuing to assess whether other nuclear plants are safe to be restarted.