TOKYO — Another day, another radioactive-water spill. The operator of the crippled Fukushima Daiichi nuclear plant says at least 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 and sent it into meltdown in 2011.
Plant operator Tokyo Electric Power Co., TEPCO, said Thursday that 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 that radiation levels in seawater samples taken just off the plant’s coast remained below detectable levels.
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The spill, 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 the ocean at a rate of 300 tons a day for some time.
TEPCO spokesman Masayuki Ono said at a 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 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.
“We could have, and should have, prevented the overflow,” he said.
TEPCO said the tank and four others in the same area were already filled up to 98 percent of designed capacity, as in many other tanks elsewhere at the plant site.
Tetsuro Tsutsui, an engineer and expert of industrial tanks, said the latest problem was emblematic of how TEPCO runs the precarious plant. He said it was “unthinkable” to fill tanks up to the top, or build them on tilted ground without building a level foundation.
“That’s only common sense,” Tsutsui, also a member of a citizens group of experts proposing safety measures for the plant. “But that seems to be the routine at the Fukushima Daiichi. I must say these are not accidents. There must be a systematic problem in the way things are run over there.”
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-high protective barriers around the tanks as being too low.