The operator of the tsunami-wrecked Fukushima nuclear plant has begun removing fuel from a cooling pool at one of three reactors that melted down in the 2011 disaster, a milestone in the decades-long process to decommission the plant.
Tokyo Electric Power Co (Tepco) said on Monday that workers started removing the first of 566 used and unused fuel units stored in the pool at Unit 3.
The fuel units in the pool located high up in reactor buildings are intact despite the disaster, but the pools are not enclosed so removing the units to safer ground is crucial to avoid disaster in case of another major quake.
Tepco said the removal at Unit 3 would take two years, followed by the two other reactors.
The step comes ahead of the real challenge of removing melted fuel from inside the reactors, but details of how that might be done are still largely unknown.
Removing the fuel in the cooling pools was delayed for five years by mishaps, high radiation and radioactive debris from an explosion that occurred at the time of the reactor meltdown, underscoring the difficulties that remain.
Workers are remotely operating a crane built underneath a jelly roll-shaped roof cover to raise the fuel from a storage rack in the pool and place it into a protective cask.
The whole process occurs underwater to prevent radiation leaks.
The work is carried out remotely from a control room about 500 metres away because of still-high radiation levels inside the reactor building that houses the pool.
Robotic probes have photographed and detected traces of damaged nuclear fuel in all three reactors that had meltdowns, but the exact location and other details of the melted fuel are largely unknown.
In February, a remote-controlled robot with tongs removed pebbles of nuclear debris from the Unit 2 reactor but was unable to remove larger chunks, indicating a robot would need to be developed that can break the chunks into smaller pieces.
The plant suffered a triple meltdown after it was hit by a powerful earthquake and ensuing tsunami in March 2011. The emergency prompted hundreds of thousands of people in the region to leave their homes amid fears of radiation contamination and a nuclear explosion.