Details from a report by the International Atomic Energy Agency have criticised Japanese nuclear regulators.
It says the country underestimated the threat from tsunamis to the crippled Fukushima power plant and urges sweeping changes to its regulatory system.
The detailed assessment from the team of experts who inspected the site is the first outside review of Japan’s nuclear crisis which says there was insufficient defence provisions for a tsunami.
The experts did praise the way workers on the ground dealt with the situation after the shut-down.
The 160-page report was prepared for a nuclear safety meeting that gets under way on Monday in Vienna at which ministers from 150 nations will discuss nuclear safety.
The details were released on a day a survey in Japan shows that 82 percent of Japanese want their government to abandon nuclear power.