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March 28, 2011 6:38 pm
Dangerously radioactive water has leaked from Japan’s crippled Fukushima Daiichi nuclear power station, in the latest breakdown of containment systems at the plant battered by an earthquake and tsunami.
Tokyo Electric Power, the plant’s operator, said on Monday that a network of underground maintenance tunnels connected to the four most damaged reactors had been flooded close to overflowing with the highly contaminated water.
Radiation readings in the tunnel closest to reactor No 2 were strong enough to prevent crews entering the area, stalling efforts to restore the unit’s electrical and fuel-cooling systems. Doses of 1,000 millisieverts per hour were detected in the water, Tepco and nuclear safety officials said.
Exposure to 1,000 millisieverts in one dose can cause acute radiation sickness, while cumulative exposure to the same amount is believed eventually to cause a fatal cancer in 5 per cent of cases.
“The radiation seems to have come from fuel rods that temporarily melted and came in contact with water used to cool the reactor,” Yukio Edano, the government’s senior spokesman, said.
Meanwhile plutonium has also been found in soil at various points at the nuclear complex but does not present a risk to human health, Tepco said on Monday.
Several hundred technicians, firefighters and soldiers have been battling to contain radioactive leaks at the plant, 240km north of Tokyo, since an earthquake and tsunami on March 11.
Although the plant’s six reactors survived the magnitude 9 quake intact, the tsunami that followed knocked out crucial safety systems, allowing uranium fuel to overheat and release explosive gases and radiation.
The focus of emergency efforts has shifted several times during the two-week crisis – from rising heat and pressure inside several of the reactors, to airborne radiation from storage pools for spent uranium fuel, and now to leaks of contaminated water.
Eric Besson, French industry minister, said on Monday that Tepco had requested support from French energy groups to tackle the crisis at the Fukushima site. The nature of the support sought was not immediately clear.
Nuclear safety officials in Japan said they were unsure how the contaminated water escaped the reactor’s steel pressure vessel, the innermost protective shield around its uranium fuel rods.
Hidehiko Nishiyama, a senior official at the Nuclear Industry and Safety Agency, the country’s atomic power regulator, said he did not believe the pressure vessel had been breached – a prospect that would increase the danger. Instead, he said the water had most likely escaped as steam and then condensed beneath the reactor’s containment structures. An explosion on March 15 damaged a water tank, known as a suppression pool, at the bottom of the containment unit.
Mr Nishiyama said there was no evidence that contaminated water had leaked beyond the tunnels, either into the ground or the sea. The tunnels, which contain water pipes and electrical cables, are about 55 metres from the ocean, between the reactors’ turbine buildings and the shore.
●Yukiya Amano, the chief of the International Atomic Energy Agency, the UN’s nuclear watchdog, called on Monday for a summit to strengthen nuclear safety and improve disaster management after Japan’s crisis. Mr Amano said he wanted ministers from the agency’s 151 member states to attend the summit in Vienna.
Additional reporting by Jennifer Thompson in Paris
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