Japan's government considered evacuating the capital Tokyo because it feared a nuclear disaster caused by the worsening crisis at the Fukushima power station after last year's tsunami.
As thousands still work around the clock to ensure that the power complex remains stable, the full scale of the crisis and the mistakes that led to it, are becoming clear.
Last month the prime minister at the time of the March 11 tsunami, Naoto Kan, admitted he considered the possibility that the tens of millions living in and around Tokyo would have to flee if the crisis spiralled out of control.
"At one point, we faced a situation where there was a chance that people might not be able to live in the capital zone including Tokyo and would have to evacuate," he told interviewers. "If things had reached that level, not only would the public have had to face hardships but Japan's very existence would have been in peril."
In what became the worst nuclear disaster since Chernobyl in 1986, floodwaters disabled the electricity supplies and emergency generators at the Fukushima complex, knocking out power for cooling functions. As a result, fuel rods in three of the six reactors began to melt and buildings housing four reactors were damaged by fires and explosions.
The authorities feared "a devil's chain reaction" in which thousands of spent nuclear fuel rods would have melted and released vast amounts of radiation, the government's former chief spokesman, Yukio Edano, told investigators from the Rebuild Japan Initiative Foundation private think tank.
Mr Kan's insistence that the plant's operator, Tokyo Electric Power Co, retain a skeleton staff to stabilise the facility was seen as key to ensuring the disaster did not escalate. Helicopters dropped water and seawater pumps helped cool overheating reactors and stabilise spent fuel pools in a rescue effort headed by workers who were dubbed the "Fukushima 50". Tepco denies it ever considered abandoning the plant.
The former prime minister admitted the authorities were "totally unprepared" for the incident. "Not only the hardware, but our system and the organisation were not prepared. That's the biggest problem," he said.
A 20 kilometre exclusion zone around the plant was imposed and more than 150,000 people evacuated from their homes, around half from within the exclusion zone. Bans were imposed on produce grown locally.
Fukushima is the world's second-worst civilian nuclear power accident, with about 15 per cent as much radiation released as emitted during the worst, the 1986 Chernobyl accident in Ukraine. Along with Chernobyl, it is one of only two incidents classified at the highest possible level seven on the International Nuclear and Radiological Event Scale.
By September the power supply had been restored and in December the authorities announced that the facility was in "cold shutdown", meaning the reactors had been cooled to a stable temperature.
Preserving this fragile stability is costly and labour-intensive, with more than 3,000 people maintaining the complex cooling system and beginning decontamination, which is likely to take four decades.
Unlike after Chernobyl - where the plant was covered with a concrete sarcophagus and the surrounding area abandoned - the aim is to clean up contaminated areas. In Fukushima prefecture, decontamination work began in January with the spraying of buildings and the removal of contaminated soil, and it is estimated that up to 31 million cubic metres of material may have to be disposed of. The 20km exclusion zone around the plant remains in place.
"Nobody has ever tried to clean up radiation on this scale before," said James Acton, senior associate in the nuclear policy programme at the Carnegie Endowment for International Peace. "The time scale they're talking about is three to four decades for remediating the surrounding area and returning the area to a greenfield site. The cost is somewhere north of US$100 billion [Dh367bn]."
Mr Acton, who co-authored a report analysing the disaster released this week, said the main reason for the incident was that Japan did not follow guidelines to mitigate the risk of a tsunami. Tepco and the Nuclear and Industrial Safety Agency (Nisa) watchdog, he said, failed to heed historical data indicating a major tsunami approximately every 1,000 years. The last one was in the year 869.
While the plant was well protected from earthquakes, tsunami safeguards such as placing key components in waterproof bunkers were not taken. The plant was designed to withstand a 5.7-metre tsunami but 13.1-metre waves struck the facility.
Mr Kan too said last month the plant should have been better protected against tsunamis. "The plant was built by people who never imagined the risk of a major tsunami, and that's the very beginning of the problem," he said.
To improve oversight, the Japanese authorities are creating an independent nuclear watchdog to overcome the potential conflict of interest Nisa faced from being a part of the ministry of economy, trade and industry. The new regulator has power to order operators to carry out safety improvements.
"Nisa was not independent from the government agency responsible for promoting nuclear energy. That was a definite problem, but not the only problem. There was a lack of independence from industry," said Mr Acton.
Not surprisingly, there is considerable hostility to nuclear power among the Japanese public, clouding the industry's future in Japan.
Just five of Japan's 54 nuclear reactors are functioning, with local governments and residents often complaining if proposals are made to restart facilities that were shut down for checks.
Longer term, Japan has said it wants to reduce its reliance on nuclear energy, although some existing plants will have an active lifespan of as much as 60 years.
The international fallout from the disaster has been considerable, with many nations reconsidering their nuclear programmes. So far though, Germany is the only country to pledge to phase out nuclear power completely, while Italy has voted not to resume its programme.