The latest contaminated water leak in Fukushima has been caused by human error

Fukushima's latest leaks prompt UN nuclear mission

Another 430 litres of highly contaminated water have been reported to seep from a storage tanks in Japan’s Fukushima power plant prompting the IAEA to send experts to assess the situation.

Tokyo Electric Power (Tepco) has revealed the newest in a series of critical leaks has been discovered by patrolling personnel. The leak was said to be caused by human error as workers overfilled the tank, which reportedly doesn’t have any device warning them about the storage capacity left.

According to Tepco, the spilled water contains 200,000 becquerels per litre of beta-emitting radioactive isotopes including strontium 90. The legal limit for strontium 90 is 30 becquerels per litre.

The highly radioactive liquid was said to get through a concrete barrier surrounding the tank, probably reaching the sea via a ditch next to a river.

However, Tepco has reassured radiation levels in sea water were sampled immediately after the leak had been discovered and remained below detectable levels.

"It is extremely regrettable that contaminated water leaked because of human error," said Katsuhiko Ikeda, administrative head of the Japanese Nuclear regulation Authority, "We must say on-site management is extremely poor."

The team will evaluate the clean-up efforts and help Tepco to get the situation under control.

Tepco’s spokesman Masayuki Ono said yesterday that the recent overflow occurred at a 450-ton tank without a water gauge and standing on an uneven ground, slightly tilting toward the sea.

The tank was already nearly full, but workers pumped 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.

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

Tetsuro Tsutsui, an engineer and expert of industrial tanks, said the latest problem clearly shows how Tepco runs the wrecked plant. He said it was "unthinkable" to fill tanks up to the top, or build them on a 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 Dai-ichi. I must say these are not accidents. There must be a systematic problem in the way things are run over there."

Experts have criticised Tepco’s sloppy approach to the management of contaminated water, 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.

Yesterday’s spill prompted the Nuclear Regulation Authority to call for Tepco’s president Naomi Hirose to ensure better on-site management and prevent human error, and submit improvement plans in a report.

In August this year, Tepco admitted 300 tonnes of highly contaminated water spilling from one of the storage tanks in what has been described as the most serious mishap in Fukushima since the 2011 earthquake that triggered the plant’s meltdown.

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