Fukushima nuclear leak 'can get a lot worse'

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The radioactive leak at Japan's Fukushima nuclear plant is far from under control and could get a lot worse, a nuclear energy expert, who compiles the annual "World Nuclear Industry Status Report" warned.

"The Japanese should put aside their arrogance and call for international assistance," Mycle Schneider an independent energy expert told CNBC, adding the world needs to set up an "International Taskforce Fukushima" to deal with radioactive water leaking from the plant.

Last week, Tokyo Electric Power Co. (TEPCO), which manages the Fukushima plant damaged in 2011's earthquake and tsunami, said that 300 tons of highly radioactive water had leaked from a storage tank at the facility. It said it was not sure how long the water had been leaking or whether it had reached the Pacific Ocean.

The leak prompted nuclear regulators in Japan to reclassify the severity rating of the incident on Wednesday, raising it to Level 3 or "serious incident" on an international scale for radiological releases.

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But the chairman of Japan's nuclear regulatory authority, Shunichi Tanaka, tried to dampen news of the contamination, saying on Wednesday that TEPCO could have overstated the leak. "We have no idea whether it's actually 300 tons that leaked," Tanaka remarked. "We need to look into this issue more."

The Japanese authorities were showing that it was "definitely not a situation where they have it under control" Schneider told CNBC.

"For two and a half years the government has not been controlling or supervising the work by Tepco on the site," he said, warning that the impact of the leak could get a lot worse.

"You have 100,000 cubic meters in basements that have never been designed to deal with this water. The big danger - and it was identified by Japan's atomic energy commission - is if you lose water in one of the spent fuel pools and you get a spent fuel fire. This would lead to respiratory contamination."

This would be a worse-case scenario and could lead to the mass evacuation of 10 million people in the Tokyo region, which is 150 miles to the south of the Fukushima plant, Schneider warned.

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The world's nuclear watchdog is not impressed by Japan's response to the disaster. On Thursday it urged it to be clearer on what was happening in Fukushima and said it should avoid sending "confusing messages" about the disaster.

Specifically, the International Atomic Energy Agency (IAEA) questioned why the authorities had rated the leak "serious" when recent similar leaks had not been labelled as such.

- By CNBC's Holly Ellyatt, follow her on Twitter @HollyEllyatt