Workers at Japan's crippled Fukushima nuclear plant yesterday scrambled to check 300 tanks storing highly radioactive water, after one sprang a leak that is feared to have seeped into the Pacific.
About 300 tonnes of toxic liquid was believed to have escaped from one of the tanks that hold water used to cool the broken reactors, while operator Tokyo Electric Power Co warned some of it might have flowed into the ocean.
"We are hurriedly checking if some 300 tanks of the same type holding contaminated water have the same leak problem," a Tepco spokesman said.
"We have finished pumping out water from the troubled tank, while we have continued removing the soil soaked by the water," he said.
Spokesman Tsuyoshi Numajiri said that traces of radioactivity were detected in a drainage stream.
"We cannot rule out the possibility that part of the contaminated water flowed into the sea," he said.
On Wednesday, nuclear regulators said the leak represented a level-three "serious incident" on the UN's seven-point International Nuclear Event Scale, which measures radiation accidents.
The alert was raised from level one, which indicates an anomaly.
It is the most serious single event since the plant was declared to be in a "state of cold shutdown" - effectively indicating it was under control - at the end of 2011.
The quake and tsunami-sparked meltdowns at the plant in March of that year were ultimately declared to be level seven on the INES scale. The Chernobyl disaster in 1986 is the only other incident to have been given the most serious ranking. Tepco has said puddles of water near the tank were so toxic that anyone exposed to them would receive the same amount of radiation in an hour that a nuclear plant worker in Japan is allowed to receive in five years.
The utility did not have a water-level gauge on the 1000-tonne tank, which experts say would have made it a lot more difficult to detect the problem.
Yesterday's safety checks on 300 tanks came after Nuclear Regulation Authority chairman Shunichi Tanaka voiced concern that there could be similar leaks from other containers.
"We must carefully deal with the problem on the assumption that if one tank springs a leak the same thing can happen at other tanks," he said.
The company - which faces huge clean-up and compensation costs - has struggled to cope with the disaster.
More than two years after the meltdowns, it continues to be beset by difficulties, chief among which is how it should handle the vast amounts of water used to cool the broken reactors. Problems and delays have added to the impression that the huge utility is not on top of the clean-up.
Urgent work needed
• About 300 of the 1000 steel tanks built across the plant complex containing nearly 300,000 tonnes of partly treated contaminated water are less durable ones with rubber seams.
• Tepco says the tanks that have leaked use rubber seams that were intended to last about five years. Tepco spokesman Masayuki Ono said it plans to build additional tanks with welded seams that are more watertight, but will still have to rely on ones with rubber seams.
• Figuring out what to do with the radioactive water is among the most pressing issues affecting the cleanup process, which is expected to take decades.