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 Thursday 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 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 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 acknowledged that contaminated groundwater was seeping into ocean at a rate of 300 tons a day.
TEPCO spokesman Masayuki Ono told an urgent news conference Thursday that the overflow occurred at a 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 maximize capacity as the plant was facing storage crunch.
Experts have faulted TEPCO for sloppiness in its handling of the water management, including insufficient tank inspection records, lack of water gauges, as well as connecting hoses lying directly on the grass-covered ground. Until recently, only one worker was assigned to 500 tanks in a two-hour patrol.
In recent meetings, regulators criticized TEPCO for even lacking basic skills to properly measure radioactivity in contaminated areas, and taking too long to find causes in case of problems. They also have criticized the one-foot (30-centimetre) high protective barriers around the tanks as being too low.
The government has said it will spend $470 billion to build an underground "ice wall" around the reactor and turbine buildings to block groundwater inflows and prevent potential leaks from spreading. It is also funding more advanced water treatment equipment to make the contaminated water clean enough to be eventually released into the sea.
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