Decommissioning work at the Fukushima Daiichi nuclear power plant has suffered a setback after a robot sent in to a damaged reactor to locate melted fuel stalled hours into its mission and had to be abandoned.

The plant’s operator, Tokyo Electric Power (Tepco), said the robot stopped moving on Friday during its first inspection of the containment vessel inside reactor No 1, one of the three reactors that suffered meltdown after the plant was struck by an earthquake and tsunami in March 2011.

Tepco, which recently conceded that the technology for robots to retrieve the nuclear fuel had yet to be developed, said on Monday it would cut the cables to the stranded robot and postpone a similar inspection using a separate device.

Developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning, the robot was supposed to be able to function for about 10 hours even when exposed to radiation at levels that would cause ordinary electronic devices to malfunction.

The “transformer” robot, which can alter its shape depending on its surroundings, was sent in to photograph the inside of the reactor containment vessel and record temperatures and radiation levels.

It had covered 14 of 18 locations when it stalled, about three hours after it began its journey around the vessel, officials said, adding that they had yet to establish the cause of the problem.

More than four years after Fukushima Daiichi suffered the worst nuclear accident since Chernobyl a quarter of a century earlier, radiation levels inside the three reactors are still far too high for humans to enter.

Tepco is pinning its hopes on a new generation of remote-controlled robots, the first of which will monitor the state and location of the melted fuel before others remove it from the reactors’ outer containers.

Last year the dangers posed by high radiation forced Tepco and the government to delay the planned start of fuel removal from reactor No 1 by five years, to 2025. Decommissioning Fukushima Daiichi is expected to take at least 40 years and cost tens of billions of dollars.

Dale Klein, a former chairman of the US nuclear regulatory commission who now advises Tepco, said dangerously high radiation inside the three damaged reactors had made extracting the melted cores particularly difficult.

“Radiation levels in these structures is higher, and working inside them is problematic,” Klein said recently. “This is a challenge that has never been faced before in the world, and there will have to be new equipment developed to make that happen.

“There’s an inherent advantage to the technology that exists here in in Japan to develop those new skills and techniques,” given its expertise in robot technology, Klein added. “Those tools and equipment do not exist today, but the fundamental knowledge of robotic, remotely controlled devices will, I think, be sufficient.”