Highly radioactive water overflowed barriers into Japan's Fukushima Daiichi nuclear power plant, its operating utility said on Monday, after it underestimated how much rain would fall at the plant and failed to pump it out quickly enough.
The utility, Tokyo Electric Power Co, also known as Tepco, has been battling to contain radioactive water at the nuclear complex, which suffered meltdowns and hydrogen explosions following a devastating earthquake and tsunami in March 2011.
Dealing with hundreds of tonnes of groundwater flowing through the wrecked nuclear plant daily is a constant headache for the utility and for the government, casting doubt on Prime Minister Shinzo Abe's promises that the Fukushima water "situation is under control."
After heavy rain on Sunday, water with high levels of radioactive strontium overflowed containment areas built around some 1,000 tanks storing tonnes of radioactive water at the plant, Tepco said. The radioactive water is a by-product of an improvised cooling system designed to keep the wrecked reactors under control in case of further disaster.
Tepco said it had planned to pump out the accumulating rainwater into empty tanks, check it for radioactivity, and if it was uncontaminated, release into the sea. But the company was overwhelmed by the amount of rainwater.
"Our pumps could not keep up with the rainwater. As a result, it flowed over some containment areas," said Tepco spokesman Yoshikazu Nagai. The company had planned for 30 to 40 millimetres of rainfall on Sunday, but by late afternoon the rainfall already stood at around 100 millimetres, he said.