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Human error is the cause of at least 110 gallons of radioactive water spilling when workers at the Fukushima Dai-ichi nuclear plant overfilled a storage tank without a gauge that could have warned them of the danger.

While the amount of liquid spilled is small compared to other issues at the crippled nuclear facility, it just goes to show how many problems they are continuing to have at the plant since a massive earthquake and tsunami sent it into meltdown in 2011. But the error is one of many the operator has committed as it struggles to manage a seemingly endless, tainted flow. Since the quake and tsunami, thousands of tons of radioactive water leaked into the Pacific Ocean.

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Plant operator Tokyo Electric Power Co. (Tepco) 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 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, radiation levels in sea water samples taken just off the plant’s coast remained below detectable levels.

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The overspill, the latest of several mishaps in less than a month, prompted the Nuclear Regulation Authority to summon the utility president and reprimand him in public. Katsuhiko Ikeda, administrative head of the agency, ordered Tepco President Naomi Hirose on Friday to ensure better on-site management and prevent human error, and submit improvement plans in a report.

“It is extremely regrettable that contaminated water leaked because of human error,” Ikeda said. “We must say on-site management is extremely poor.”

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 a news conference Thursday 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 maximize 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.

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

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