A new leak of 100 tonnes of highly radioactive water has been discovered at Fukushima, the plant's operator said yesterday, after it revealed that only one of nine thermometers in a crippled reactor was still working.
The toxic water was no longer escaping from a storage tank on the site, a Tokyo Electric Power spokesman said, adding that it was likely contained. But the news is a further blow to the company's already-battered reputation for safety.
"As there is no drainage way near the leak, which is in any case far from the ocean, it is unlikely that the water has made its way into the sea," he said.
The tank - one of hundreds used to store water contaminated during the process of cooling broken reactors - sits about 700 metres from the shore. The water it contains is highly radioactive, with a beta radiation reading "at 230 million becquerel per litre", the spokesman said.
That contamination level compares with government limits of 100 becquerels per kilogramme of food and 10 becquerels per litre of drinking water. A becquerel is a unit of measurement for radioactivity.
Beta radiation, including from cancer-causing strontium-90, is very harmful to humans and can cause damage to DNA. But it is relatively easy to guard against and cannot penetrate a thin sheet of aluminium.
"We are now in the process of recovering the leaked water and the earth it has contaminated," the spokesman said.
The tank holds water filtered to remove caesium, but which still contains strontium, a substance that accumulates in bones and can cause cancer if consumed. About half the beta radiation from the leak was thought to be strontium-90, Tepco said, meaning its concentration level is nearly four million times the legal limit of 30 becquerel per litre. Japan's Nuclear Regulation Authority said it saw no serious risks to the environment outside the plant at this point.
The accident came a day after Tepco revealed that one of the two thermometers in the lower part of the No 2 reactor pressure vessel was out of order. There were originally nine thermometers in the vessel.