TOKYO (AP) — The operator of the wrecked Fukushima nuclear power plant said Thursday it is further postponing the start of the removal of highly radioactive melted fuel from its damaged reactors because of delays in the development of a remote-controlled robotic arm.

Tokyo Electric Power Company Holdings had originally planned to begin removing melted fuel from the Unit 2 reactor at the Fukushima Daiichi plant last year, 10 years after the disaster triggered by a massive earthquake and tsunami on March 11, 2011.

That plan was postponed until later this year, and now will be delayed further until about autumn next year because of additional work needed to improve the performance of the robotic arm, TEPCO said.

The giant arm, jointly developed by Veolia Nuclear Solutions of Britain and Japan’s Mitsubishi Heavy Industries, has been transported to Japan and is being adjusted at a testing facility south of the Fukushima plant.

The delay won’t affect the overall decommissioning at the plant, which is expected to take 30-40 years, TEPCO said. Experts have said the completion target is too optimistic.

During the accident, an estimated 880 tons of highly radioactive nuclear fuel in the three damaged reactors melted and fell to the bottom of their primary containment vessels, where it hardened, most likely mixed with broken parts of the reactor and the concrete foundation. Its removal is by far the toughest challenge of the decommissioning process.