TOKYO (AP) — The operator of the tsunami-hit nuclear plant in Fukushima announced Thursday a delay of several more months before launching a test to remove melted fuel debris from inside one of the reactors, citing problems clearing the way for a robotic arm.

The debris cleanup initially was supposed to be started by 2021, but it has been plagued with delays, underscoring the difficulty of recovering from the plant’s meltdown after a magnitude 9.0 quake and tsunami in March 2011.

The disasters destroyed the Fukushima Daiichi nuclear plant’s power supply and cooling systems, causing three reactors to melt down, and massive amounts of fatally radioactive melted nuclear fuel remain inside to this day.

The government and the Tokyo Electric Power Company Holdings, or TEPCO, initially committed to start removing the melted fuel from inside one of the three damaged reactors within 10 years of the disaster.

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In 2019, the government and TEPCO decided to start removing melted fuel debris by the end of 2021 from the No. 2 reactor after a remote-controlled robot successfully clipped and lifted a granule of melted fuel during an internal probe.

But the coronavirus pandemic delayed development of the robotic arm, and the plan was pushed to 2022. Then, glitches with the arm repeatedly have delayed the project since then.

On Thursday, TEPCO officials pushed back the planned start from March to October of this year.

TEPCO officials said that the inside of a planned entryway for the robotic arm is filled with deposits believed to be melted equipment, cables and other debris from the meltdown, and their harder-than-expected removal has delayed the plan.

TEPCO now is considering using a slimmer, telescope-shaped kind of robot to start the debris removal.

About 880 tons of highly radioactive melted nuclear fuel remain inside the three damaged reactors. Critics say the 30- to 40-year cleanup target set by the government and TEPCO for Fukushima Daiichi is overly optimistic. The damage in each reactor is different and plans need to be formed to accommodate their conditions.

TEPCO has previously tried sending robots inside each of the three reactors but got hindered by debris, high radiation and inability to navigate them through the rubble, though they were able to gather some data in recent years.

Getting more details about the melted fuel debris from inside the reactors is crucial for their decommissioning. TEPCO plans to deploy four mini drones and a snake-shaped remote-controlled robot into the No. 1 reactor’s primary containment vessel in February to capture images from the areas where robots have not reached previously.

TEPCO also announced plans Thursday to release 54,000 tons of the treated radioactive wastewater in seven rounds of releases from April through March 2025 as part of the ongoing discharge plan.

Japan began releasing the plant’s treated and diluted radioactive wastewater into the sea in August, a decades-long project to remove it and make room for facilities needed for the decommissioning.

While Japan says the water is way safer than international releasable standards, the discharges have been strongly opposed by fishing groups and neighboring countries including China and South Korea.