|There has been growing public anger over the mishandling of the tsunami-triggered nuclear crisis
A UN atomic watchdog team on a visit to Japan said the country underestimated the hazard posed by tsunamis to nuclear plants.
"The tsunami hazard for several sites was underestimated," the International Atomic Energy Agency [IAEA]said in a preliminary report on Wednesday.
"Nuclear designers and operators should appropriately evaluate and protect against the risks of all natural hazards, and should periodically update those assessments and assessment methodologies," it said.
However, the IAEA also praised Tokyo's response to the March 11 twin disaster as "exemplary".
Al Jazeera correspondent Marga Ortigas, reporting from Tokyo, said the report also emphasised that Japan needed an independent regulatory board for nuclear facility.
"At the moment the nuclear board is attached to the government or to the nuclear power corporation. So, they are not really independent regulatory board, and the IAEA implied that this could be one reason that safety measures were not updated or reassessed," she said.
The report highlighted some of the well-documented weaknesses that contributed to the crisis at Fukushima when the plant, 240km north of Tokyo, was hit by a massive earthquake and then a tsunami in quick succession.
The IAEA team said Japan's crisis offered several lessons for the nuclear industry globally, including that plant operators should regularly review the risks of natural disasters and that "hardened" emergency response centres should be established to deal with accidents.
"We had a playbook, but it didn't work," Tatsujiro Suzuki, a nuclear expert and vice chairman of Japan's Atomic Energy Commission, said.
Monitoring public health
The 14-metre wave that slammed into the plant knocked out reactor cooling systems and backup power generators, causing partial reactor meltdowns and forcing emergency crews to douse reactors with water since then.
"Now it seems the safety measure that was put in place around that particular facility could have handled a 5.4m high wave but not the kind of waves that it saw on March 11. Some of them reached as high as 14m," Ortigas said.
The embattled operator Tokyo Electric Power Company (TEPCO) has said it hopes to bring the plant to a stable state of "cold shutdown", with low pressure and temperatures, some time between October and January.
The Fukushima accident has forced more than 80,000 residents from their homes and due to radiated water leaks from the site, concerns have been raised about the safety of nearby children and food supply.
The report said that Japan needed to closely monitor public and workers' health after the crisis at the Fukushima Daiichi nuclear plant.
The IAEA also stressed the importance of "regulatory independence and clarity of roles", touching on the fact that Japan's nuclear watchdog is part of the ministry of trade and industry, which promotes atomic power.
The magnitude 9.0 seabed quake and tsunami caused the world's worst nuclear disaster since Chernobyl 25 years ago at the Fukushima plant, which has since leaked radiation into the air, ground and sea.
The IAEA sent an 18-member team of its own experts and specialists on a fact-finding mission to Japan. It will present its full report at a ministerial meeting on nuclear safety at IAEA headquarters in Vienna from June 20 to 24.
Challenge for Kan
Meanwhile, Naoto Kan, the prime minister, refused to resign on Wednesday as opposition lawmakers criticising his disaster management prepared to file a no-confidence motion in parliament.
"What is most sought by the people is for us to work together to achieve reconstruction and resolve the nuclear crisis,'' Kan told a parliamentary session.
"I must respond to their needs and that is my responsibility."
The Al Jazeera correspondent said that Kan's detractors feel he has been less than trustworthy in the way he has dealt with the twin disaster and the nuclear crisis.
"Kan says he's confident of retaining his post but according to a local survey, 80 per cent of respondents said Kan can’t be trusted with regards to announcement he has made, she said.
"In regards to Fukushima plant, changing him right now wouldn’t be in the best interest of the country, it would be like changing the captain of the ship in the middle of the storm."
Opposition says they will do better but they haven't put anybody forward for a possible replacement for Kan just yet, Ortigas said.
"At the moment Kan's party holds majority alliance in the lower house of parliament but there are fears that some of the members of his ruling DPJ might switch sides and join Liberal Democratic Party and possibly side with them, should the no-confidence vote is pushed through on Wednesday."