CONTAMINATED water with dangerously high levels of radiation is leaking from a storage tank at Japan’s crippled Fukushima nuclear plant, the most serious setback to the clean-up of the worst nuclear accident since Chernobyl.
The storage tank breach of about 300 tonnes of water is separate from contaminated water leaks reported in recent weeks, plant operator Tokyo Electric Power said.
The latest leak is so contaminated that a person standing half a metre (1ft 8in) away would, within an hour, receive a radiation dose five times the average annual global limit for nuclear workers.
After ten hours, a worker in that proximity to the leak would develop radiation sickness with symptoms including nausea and a drop in white blood cells.
“That is a huge amount of radiation. The situation is getting worse,” Michiaki Furukawa, a nuclear chemist, said yesterday.
The embattled utility Tokyo Electric has struggled to keep the Fukushima site under control since an earthquake and tsunami caused three reactor meltdowns in March 2011.
Japan’s Nuclear Regulation Authority has classified the latest leak as a level one incident, the second lowest on an international scale for radiological releases, a spokesman said.
It is the first time Japan has issued a so-called INES rating for Fukushima since the meltdowns. Following the earthquake and tsunami, Fukushima was assigned the highest rating of seven.
A Tokyo Electric official said workers monitoring storage tanks appeared to have failed to detect the leak of water, which pooled up around the tank.
“We need to review not only the tanks, but also our monitoring system,” he said.
Tokyo Electric, also known as Tepco, said it did not believe water from the latest leak had reached the Pacific Ocean, about 500 metres away. Nonetheless, continued leaks have alarmed Japan’s neighbours, South Korea and China.
In recent months, the Fukushima plant has been beset with power outages and other problems that have led experts to question whether Tepco is qualified to handle the clean-up.
The government said this month it would step up its involvement in the clean-up, following Tepco’s admission, after months of denial, that leaked contaminated water had previously reached the ocean.
Fukushima governor Yuhei Sato told an emergency meeting of prefectural officials yesterday it was a “national emergency”, and that the local government would monitor the situation more strictly and seek additional steps as needed.
Massive amounts of radioactive fluids are accumulating at the plant as Tepco floods reactor cores via an improvised system to keep melted uranium fuel rods cool and stable.
The water in the cooling system then flows into basements and trenches that have been leaking since the disaster.
Highly contaminated excess water is pumped out and stored in steel tanks on elevated ground away from the reactors. About 400 tonnes of radioactive water a day has been stored at Fukushima.
In order to keep up with the pace of the flow, Tepco has mostly relied on tanks bolted together with plastic sealing around the joints.
Those tanks are less robust –but quicker to assemble – than the welded tanks it has started installing.
The latest leak came from the more fragile tank, which Tepco plans to carry on using, although it is looking at ways to improve their strength, said Tepco official Masayuki Ono.
• Japan has put its army on display in an annual exercise at the foot of Mount Fuji intended to showcase the nation’s ability to defend itself.
The exercise focused on a scenario in which Japan is attacked from the sea. As a narrator explained the attack to thousands of spectators, aircraft, artillery, tanks and helicopters fired on targets at the base of the mountain, a powerful symbol of Japan itself.
The exercises involve 2,400 troops, 30 aircraft and 80 tanks and armoured vehicles.
Defence minister Itsunori Onodera said that the exercises showed Japan’s resolve to meet “deepening uncertainties” in the region and to be able to defend its own territory.