Radioactive water leaks into tunnels at Fukushima
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 yesterday 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.
Technicians, firefighters and soldiers have been battling to contain radioactive leaks since an earthquake and tsunami on March 11th. Although the plant’s reactors survived the quake intact, the tsunami that followed knocked out crucial safety systems, allowing uranium fuel to overheat and release explosive gases and radiation.
Eric Besson, French industry minister, said Tepco had requested support from French energy groups to tackle the crisis. 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 15th damaged a water tank 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 55m (180ft) from the ocean, between the reactors’ turbine buildings and the shore.
The chief of the International Atomic Energy Agency has called for a summit to strengthen nuclear safety and improve disaster management.