The operator of the Fukushima No. 1 nuclear power plant started removing nuclear fuel on Monday from the Unit 3 storage pool, located at one of the reactor buildings damaged by hydrogen explosions in the 2011 disaster at the site.

It is the first fuel removal operation by Tokyo Electric Power Company Holdings Inc. (Tepco) from the storage pools for the Nos. 1 to 3 units, which suffered meltdowns after losing power following a powerful earthquake and tsunami.

The start of the work was delayed by more than four years due to a series of malfunctions of the devices necessary for the operation, and high-level radiation observed in the area also posed a significant challenge, the operator said.

Tepco said it plans to remove seven unspent fuel rods from the reactor’s pool, where a total of 566 spent and unspent fuel rods are stored, and transfer them to another storage pool on the premises later this month. The work is planned to be completed by the end of March 2021.

There are a total of 1,573 fuel rods, including unspent ones, inside the storage pools at the Nos. 1 to 3 units, and the large amount of spent fuel is a huge obstacle to scrapping the crippled reactors as they will continue to generate heat and high levels of radiation for an extended period.

After removing the seven unspent fuel rods that pose a relatively low risk, removal work will be intensified — possibly in June, when the storage pool to which the fuel will be transferred undergoes a regular check as is required by law.

The fuel removal was originally scheduled to start in late 2014 but it has been pushed back multiple times.

In 2014, Tepco completed fuel removal work from the pool linked to the No. 4 unit, which was offline for regular checks at the time of the accident and had all of its fuel stored in the pool. Unlike the Nos. 1 to 3 units, it did not suffer a meltdown.

The utility said it aims to start fuel removal work from pools at the Nos. 1-2 units in fiscal 2023, and has been assessing their surroundings.

Among the Nos. 1 to 6 units at the plant, the reactor buildings of the Nos. 1, 3 and 4 units suffered hydrogen explosions after the disaster.

On Sunday, Prime Minister Shinzo Abe toured the Fukushima plant complex and nearby areas to check on reconstruction progress since the 2011 crisis.

His visit came after Olympics minister Yoshitaka Sakurada stepped down last week when remarks made by Sakurada were deemed offensive to people affected by the March 2011 disasters.

“The government will do its utmost to rebuild (this area), engraving in our heart once again that each minister is in charge of reconstruction,” Abe said following his visit to the nuclear complex — his first since September 2013.

Abe said he confirmed “steady progress” in the decommissioning work at the plant but noted that “many challenges” remain.

“The state will continue to stand at the forefront of the decommissioning work and the containment of radioactive water (that is accumulating at the plant),” he said.