Overflowing tank cause of new leak at Fukushima

At least 430 litres spilled when workers overfilled a storage tank without a gauge

Another day, another radioactive-water spill. The operator of the meltdown-plagued Fukushima Dai-ichi nuclear plant says at least 430 litres (110 gallons) spilled when workers overfilled a storage tank without a gauge that could have warned them of the danger.

The amount is tiny compared to the untold thousands of tons of radioactive water that have leaked, much of it into the Pacific Ocean, since a massive earthquake and tsunami wrecked the plant in 2011.

But the error is one of many the operator has committed as it struggles to manage a seemingly endless, tainted flow.

Plant operator Tokyo Electric Power Co. Said today workers detected the water spilling from the top of one large tank when they were patrolling the site the night before.

The tank is one of about 1,000 erected on the grounds around the plant to hold water used to cool the melted nuclear fuel in the broken reactors.

TEPCO said the water then spilled out of a concrete barrier surrounding the tank and believed that most of it reached the sea via a ditch next to the river.

The company later said, however, sea water samples taken just off the plant's coast remained below detectable levels.

The new leak is sure to add to public concern and criticism of TEPCO and the government for their handling of the nuclear crisis.

In August, the utility reported a 300-ton leak from another storage tank, one of a string of leaks in recent months.

That came after the utility and the government acknowledged that contaminated groundwater was seeping into ocean at a rate of 300 tons a day for some time.

TEPCO spokesman Masayuki Ono told an urgent news conference Thursday that the overflow occurred at a 450-ton tank without a water gauge and standing on an unlevel ground, slightly tilting toward the sea.

The tank was already nearly full, but workers pumped in more contaminated water into it to maximise capacity as the plant was facing a serious storage crunch.

Recent rainstorms that flooded tank yards and the subsequent need to pump up and store contaminated rainwater also added to the shortage, he said.

"We could have, and should have, prevented the overflow," he said.

Chief Cabinet Secretary Yoshihide Suga said efforts to stop leaks were still insufficient, but defended TEPCO for detecting the problem more quickly than the last time.

TEPCO said the tank and four others in the same area were already filled up to 98 per cent of its designed capacity, as in many other tanks elsewhere on the plant.