Tokyo Electric Power Co (TEPCO) had planned to begin extracting radioactive debris from one of the reactors this year -- already later than the original 2021 start date.

But the company said Thursday it needed an "additional preparation period" of up to 18 months, meaning the work could now start as late as March 2024.

TEPCO said in a statement that this was necessary "to improve the safety and ensure the success" of surveying inside the reactors and retrieving the debris.

"The timeframe has been adjusted so that the work will commence in the latter half of fiscal 2023," which ends March 2024, it said.

Engineers are fine-tuning a robotic arm specially designed for the work, including adjusting its speed and precision, TEPCO said.

A deadly tsunami on March 11, 2011 caused a meltdown at the Fukushima Daiichi nuclear plant in northeastern Japan, the world's worst nuclear accident since Chernobyl.

TEPCO, the government and a coalition of engineering firms are working to decommission the damaged reactors in a project that is estimated to take as long as 40 years.

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TEPCO - TOKYO ELECTRIC POWER