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Thursday, 15 August 2013

Mission Impossible? Fukushima scientists brace for riskiest nuclear fuel clean-up yet


An aerial view shows Tokyo Electric Power Co.'s (TEPCO) tsunami-crippled Fukushima Daiichi nuclear power plant in Fukushima Prefecture (Reuters / Kyodo)


Scientists at Japan’s Fukushima nuclear power plant are preparing for their toughest clean-up operation yet – two and a half years after three of the plant’s reactors suffered a meltdown in Japan’s worst-ever nuclear power disaster.



The operation, to remove 400 tons of highly irradiated spent fuel beneath the plant’s damaged Reactor No. 4, could set off a catastrophe greater than any we have ever seen, independent experts warn. An operation of this scale, says plant operator Tokyo Electric Power Company, has never been attempted before, and is wrought with danger.

An uncontrolled leak of nuclear fuel could cause more radiation than the March 2011 disaster or the 1986 Chernobyl catastrophe, say consultants Mycle Schneider and Antony Froggatt. "Full release from the Unit-4 spent fuel pool, without any containment or control, could cause by far the most serious radiological disaster to date," the scientists say in their World Nuclear Industry Status Report 2013.

The operation has been tried before – but only with the aid of computers. This time it will be a painstaking manual process.

Here’s what needs to be done: more than 1,300 used fuel rod assemblies, packing radiation 14,000 times the equivalent of the Hiroshima nuclear bomb, need to carefully be removed from their cooling pool.

Arnie Gunderson, a veteran US nuclear engineer and director of Fairewinds Energy Education, told Reuters that "they are going to have difficulty in removing a significant number of the rods," especially given their close proximity to each other, which risks breakage and the release of radiation.

Gundersen told Reuters of an incredibly dangerous “criticality” that would result if a chain reaction takes place at any point, if the rods break or even so much as collide with each other in the wrong way. The resulting radiation is too great for the cooling pool to absorb – it simply has not been designed to do so.

"The problem with a fuel pool criticality is that you can't stop it. There are no control rods to control it,” Gundsersen said. “The spent fuel pool cooling system is designed only to remove decay heat, not heat from an ongoing nuclear reaction."

The base of the pool where the fuel assemblies are situated is 18 meters above the ground. The pool itself is 10 by 12 meters, and the rods are seven meters under the surface of the water. One problem with that pool is it has been exposed to air in the 2011 catastrophe, when its roof was blown off by the explosion.

The operation is urgent – because even a minor earthquake could trigger an uncontrolled fuel leak. read more

Fukushima leak emergency: LIVE UPDATES

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Obama Approves Raising Permissible Levels of Nuclear Radiation in Drinking Water