Another leak of radioactive water has been found at Fukushima, the plant's Japanese operator said Thursday, the latest setback for the troubled clean-up at the broken nuclear power station.
Tokyo Electric Power said highly-polluted water, which spilled out of a storage tank as it was being filled, may have made its way out to the Pacific Ocean.
The utility, whose efforts to fix the mess at Fukushima have been derided as sloppy, said 430 litres (110 US gallons) with a radioactive load of up to 580,000 becquerels per litre, had leaked from one of the 450-tonne tanks because of recent typhoon-brought heavy rainfall.
A spokesman said it was possible "contaminated water may well have flowed into the sea."
The tank holds water filtered to remove caesium but still containing strontium, an element that accumulates in bones and can cause cancer, if consumed.
The contamination level of the water in the new leak compares with government limits of 100 becquerels per kilogramme in food and 10 becquerels per litre in drinking water.
TEPCO has found increasing difficulty in dealing with waste water at the plant, which ran out of control following a huge earthquake and tsunami in 2011.
The company poured thousands of tonnes of water onto runaway reactors to tame them and continues to douse them to keep them cool.
Thousands of tonnes of radioactive water are being stored in temporary tanks at Fukushima, and the new leak was found at a section where five 450-tonne tanks are placed on slightly sloping ground, the official said.
"Workers were storing water very close to tanks' capacity because of the volume of typhoon rainfall," he said. "As a result, the water overflowed and leaked outside the gutter."
Only one of the five inter-connected tanks had a water-level gauge, he said.
The leak is the latest to hit the plant and will further undermine TEPCO's credibility in the eyes of an increasingly sceptical public, both domestically and internationally.
In August, 300 tonnes of toxic water was discovered to have leaked from a separate tank, with part of it believed to have flowed into the Pacific Ocean.
TEPCO said it had informed the Japanese government of the latest leak and the country's Nuclear Regulatory Authority has ordered the company to stem the flow and remove any contaminated soil.