The operator of the wrecked Fukushima nuclear plant for the first time is 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. said Monday workers started removing the first of 566 fuel units stored in the pool at Unit 3. The fuel units in the pool are not enclosed and their removal to safer ground is crucial to avoid disaster in case of another major quake.

TEPCO says 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 are largely unknown.