The operator of the damaged Fukushima Daiichi nuclear plant on Monday began removing spent and stored fuel from one of the three damaged reactors, marking a new step towards their decommissioning.

The operation was being carried out remotely on Unit 3 of the plant. This process marks the first nuclear fuel removal from one of the reactors badly damaged by the earthquake and tsunami on Mar. 11, 2011, according to a statement from Tokyo Electric Power Company (TEPCO), the owner of the plant.

This phase of the decommissioning work has been delayed for more than four years from the date originally scheduled by TEPCO due to various problems and failures suffered by electronic and robotic devices when exposed to extreme levels of radiation that would be deadly to human workers.

On Monday TEPCO planned to remove seven of the 566 units of spent or unused uranium and MOX (a mixture of uranium and plutonium oxides) stored in cooling pools inside reactor 3 and transfer them to other pools located in the facilities of the Fukushima Daiichi power plant.

The operator plans to complete the removal of the fuel from Unit 3 by March 2021, followed by the other two damaged reactors.

Apart from these units of fuel, they have also detected the presence of atomic fuel at the bottom of the containment vessel of reactors No. 1, 2 and 3, as shown in the images captured by multiple remote devices of TEPCO.

This highly radioactive waste is the result of the partial merger of the units during the 2011 nuclear catastrophe, and its removal presents great technical difficulties.

Reactors No. 1, 2 and 3 underwent partial mergers of their cores after running out of power due to the natural disaster that occurred almost eight years ago.

TEPCO has already completed the removal of fuel stored in reactor No. 4 of the plant, where the damages were less than in the other units.

The nuclear crisis of Fukushima is considered the worst nuclear accident since Chernobyl, Ukraine, in 1986.