A robot has been sent to survey the condition of melted nuclear fuel at the Fukushima power plant.

Plant operator Tokyo Electric Power Co, or Tepco, has sent the robot on a quest to explore the inside of a containment vessel of a reactor at the plant, which was filled with dangerous debris following a catastrophic meltdown four years ago.

Tepco says the resilient little robot (measuring just 60 centimetres in length and 9.5 centimetres in height) will bring back data on radiation levels and temperature, as well as footage of the upper part of the vessel.

It is equipped with cameras, a thermometer and dosimeter and can run for up to 10 hours under high levels of radiation, the International Research Institute for Nuclear Decommissioning said.

Nuclear fuel inside several of the plant’s six reactors s believed to have melted through internal pressure vessels and accumulated in the outer containers.

But the extremely high levels of radiation inside the three units mean that no one has had a good look in the years after the Fukushima Daiichi Nuclear Power Station disaster.