Tokyo Electric Power Company says it will postpone by up to 18 months the start of nuclear fuel debris removal from the crippled Fukushima Daiichi power plant that suffered triple meltdowns in the 2011 nuclear disaster.

The company, also known as TEPCO, explained on Thursday that the work to remove fuel debris from the three reactors is unlikely to start until the fall of 2023 at the earliest. The company had previously said the work would start this year.

TEPCO said the postponement is due to the need to fix problems with a British-developed remote-controlled robotic arm to be used in the removal operation.

Removing the highly radioactive fuel debris from the reactors is one of the biggest challenges in decommissioning the plant.

Molten fuel mixes with metal and concrete from the surrounding structures to form debris.

TEPCO officials initially planned to start the removal last year at No.2 reactor, as a survey had yielded more detailed data than the other two. That original plan has now been postponed for a second time.

Still, TEPCO and the Japanese government maintain their plan to complete dismantling of the plant by 2051.