Japan has declared an emergency at two nuclear power plants as technicians struggle to restore crippled cooling systems and prevent catastrophic meltdowns following the devastating earthquake and tsunami.
Thousands of people had been evacuated from their homes on Friday after the Japanese government declared a nuclear emergency, and the trade minister admitted that a radiation leak was a distinct possibility as concerns mounted that the cooling system at the Fukushima-Daiichi nuclear power station had failed, with grave implications for the integrity of hundreds of tonnes of radioactive fuel at the site. The sight of 2,800 local residents forced to flee their homes evoked the scenes after the Chernobyl accident in theUkraine, almost exactly 25 years ago.
Japanese authorities said pressure was rising inside the plant with the risk of a radiation leak, according to the Jiji news agency. One British atomic engineer said the evacuation of 2,800 citizens suggested a radioactive leak remained a possibility.
"It looks very serious. Obviously we do not know exactly what is going on but evacuating people is normally only a matter of last resort when there is only one containment layer left to be breached," said John Large, a member of the British Nuclear Engineering Society and a fellow of the Royal Society.
A Japanese nuclear safety panel said radiation levels were 1,000 times above normal in a reactor control room after the quake. Some radiation had seeped outside the plant, with levels just outside the facility's main gate measured at eight times normal, Public Broadcaster NHK quoted nuclear safety officials as saying.
The safety officials said there was "no immediate health hazard" to nearby residents from the leakage, which they described as "minute", and people were urged to evacuate calmly.
Prime Minister Naoto Kan said as he boarded a helicopter to visit the plant that the government had expanded the evacuation radius around the plant from two miles to six.
Reports of a breakdown in the cooling systems in three of four reactors at Fukushima-Daini compounded fears of a new disaster.
For much of Friday, nuclear safety officials and the Tokyo Electric Power Company, which operates both plants, had been focused on a failed cooling system in a single reactor at Fukushima-Daiichi. But early this morning, the company reported the failure of an additional reactor at Fukushima-Daiichi and at the second plant, Fukushima-Daini.
The Japanese government ordered further evacuations and warned of a small risk of a radiation leak as technicians tried to release vapour at the Fukushima Daiichi plant to lower pressure and prevent a meltdown.
The chief cabinet secretary, Yukio Edano, said the amount of radioactive element in the vapor would be "very small" and would not endanger the environment or human health.
"With evacuation in place and the ocean-bound wind, we can ensure the safety," he told a press conference.
The authorities expanded the evacuation zone on Saturday, and ordered people within a 25km radius to stay indoors.
News reports suggested that the earthquake had shut down electricity to the cooling systems of the reactors. A back-up diesel powered generator was knocked out by the tsunami an hour later.
Without electricity, the reactor will not be able to pump water to cool its hot reactor core, possibly leading to a meltdown or some other release of radioactive material.
If radioactivity has broken through into the final dome over the top of the plant, this would put the incident on a par with the Three Mile Island accident in the US, which cost $1bn.
Another nuclear expert said that if the water cooling system had broken down, the consequences could be dire.
"One critical safety issue is the maintenance of water cooling systems to ensure that the nuclear fuel inside the reactor core does not heat up to unsafe levels," said Shaun Burnie, a consultant to the nuclear industry.
He said the reactor's operator, Tokyo Electric, had apparently been unable to pump cooling water into the 40-year-old reactors for at least three hours.
"The possibility is that the reactor fuel is already damaged. If they are unable to restore coolant pump capacity then the fuel will continue to heat up and eventually be exposed to air at which point a whole series of events can unfold, including steam explosions, fuel meltdown and in the worst case, loss of containment. The last thing the people of Japan need after the tragedy of this earthquake and tsunami is a nuclear catastrophe."
Others cautioned that it was too soon to declare that a nuclear disaster was imminent. Sue Ion, fellow of the Royal Academy of Engineering, said the evacuations could equally be a sensible precaution and noted that Japanese reactors were built to withstand the rigours of nature in an earthquake-prone part of the world. "As this is an earthquake zone, the Japanese apply very rigorous standards, with robust designs and regulations," she said.
Paul Haigh, a fellow of the Institution of Chemical Engineers, added: "All Japanese reactors are designed to withstand substantial earthquakes. Instrumentation is provided for the early detection of tremors which would lead to a controlled shutdown of the reactor. These systems appear to have successfully shut down the affected reactors. Modern western reactors, including those planned for the UK, are already designed to withstand significant seismic events."
The incident would not undermine public faith in nuclear energy, Ion predicted. "People should gain confidence from the fact that these plants have shut down as they should be."
The nuclear industry is currently in the middle of a surprise renaissance with dozens of new plants planned in Britain, America and China amid deeper public worries about energy shortages and low carbon ways of tackling climate change.
The sector had hoped fears about safety had receded in the public mind and was steeling itself for a wave of bad publicity surrounding the 25th anniversary of Chernobyl, where work is still under way to dismantle the plant and make safe spilled radioactive fuel. This plant – built and operated under the Soviet system – blew up during a safety test although the accident was blamed on a mixture of bad design and human error.
Failure of the cooling system – and the diesel back-up generator – at the Fukushima 1 plant in Onahama raises questions about what has gone wrong so far and what could happen in future. Another British nuclear engineer, who asked not to be named, said: "It is difficult to know exactly what has happened here, but any shutdown is expensive and any system failures of wider concern. The cooling systems around the reactors are driven primarily by nuclear power but if that is not working then via diesel generator."
Large said any complete power outage would quickly lead to the reactor overheating and the potential meltdown of the fuel under temperatures that could reach 1,200C. Different mechanical and chemical reactions could potentially lead to a hydrogen explosion, he added.
All of this could be "astronomically" expensive given the heavily populated and insured population of Japan, said Large, who has visited Fukushima. The engineer said he was concerned that the nuclear industry and local political system had a reputation for considerable secrecy that would not make it easy to discern what had gone wrong.
Earthquakes often close Japanese nuclear plants, some of which are built close to known fault lines. In 1999, 2004, 2005, 2007 and 2009 reactors shut down because of seismic activity.
Confidence in Japan's nuclear safety was dented by a series of scandals in the late 90s when the Tokyo Electric Power Company, owner of the Kashiwazaki-Kariwa plant, admitted falsifying safety data and concealing cracks in the core structures of its reactors. The same plant was seriously damaged by an earthquake in 2007, but the owners tried to conceal a radiation leak. Much of the plant had to be closed for 21 months at a cost of more than $3bn.
Additional reporting by John Vidal
Thousands of people were being evacuated from their homes .
