Nuclear regulators declare Fukushima leak a level-three 'serious incident'

Nuclear watchdog inspectors who toured Japan's crippled Fukushima plant following the discovery of a huge radioactive leak declared Friday that water storage at the site was "sloppy".

Earlier this week around 300 tonnes of radioactive liquid is believed to have escaped from one of the hundreds of tanks holding liquid used to cool the broken reactors, in an episode dubbed the most serious in nearly two years.

"I can't help but say it was sloppy," said Nuclear Regulation Authority committee member Toyoshi Fuketa of Tokyo Electric Power Company's (TEPCO's) management of contaminated water, according to Jiji Press.

Fuketa was part of a 15-member team, including experts on radiation and water flow, who visited the wrecked power station to see for themselves how the polluted water had escaped.

The one-day inspection finished late Friday, an agency official told AFP. "We will analyse results of the inspection and discuss them at a working group next week," the official said. "We may carry out further on-site inspections if necessary."

On Thursday workers looking for other holed tanks found two areas near other containers where radiation was unexpectedly high, although they could see no leaks.

Nuclear regulators Wednesday said the leak represented a level-three "serious incident" on the UN's seven-point International Nuclear Event Scale (INES), raising the alert from level one, an "anomaly".

The quake and tsunami-sparked meltdowns at the plant in March 2011 were ultimately categorised as level seven on the INES scale. The Chernobyl disaster in 1986 is the only other incident to have been given the most serious ranking.

Plant owner TEPCO has said puddles near the holed tank were so toxic that anyone exposed to them would receive the same amount of radiation in an hour that a nuclear plant worker in Japan is allowed to receive in five years.

The company said the leak may have carried radioactive materials out to sea. Groundwater that has mixed with polluted water has already seeped into the ocean, with TEPCO launching an operation to pump it out of 28 wells, the company said Friday.

More than two years after the disaster at Fukushima, TEPCO continues to struggle with the clean-up, a project expected to take around four decades.

A catalogue of mishaps, often accompanied by a perceived unwillingness to publicly reveal the extent of problems, is leading to a growing chorus warning of the need for outside experts to step in and take control of the operation.

Critics say the utility -- which has been effectively nationalised -- is not up to the task.