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 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.