Robot 'race' to fix damaged Fukushima nuclear plant
Japanese company Mitsubishi has unveiled a radiation-resistant robot aimed at cleaning up the crippled Fukushima nuclear power plant.
Other firms, among them Hitachi and Toshiba, have also rolled out their own remote-controlled bots recently.
The plant was damaged during the 2011 earthquake and tsunami.
Robots are already working inside the plant, but none has been specifically designed for this kind of work.
One UK expert said that working inside a nuclear reactor was "a challenge for robotics".
Dubbed MEISTeR (Maintenance Equipment Integrated System of Telecontrol Robot), Mitsubishi's "tankbot" is about 1.3m (4ft) tall and has two arms, each able to hold loads of up to 15kg (33lb).
The robot is equipped with various tools and has electronics hardened to withstand radiation.
But Jeremy Pitt, deputy head of the Intelligent Systems and Networks Group at Imperial College London, said it was still a challenge for a remotely controlled machine to successfully replace humans in such harsh conditions.
"Operating in extreme environments requires a remarkable range of human skills that might otherwise be taken for granted," he said.
"Fundamentally, instead of programming a robot to follow a precise series of actions, in open environments the requirement is to programme it to improvise.
"This requires a fusion of conscious reasoning mechanisms, like learning, with subconscious sensing mechanisms."
Although currently there are several robots inside the plant, they have not been designed to repair a nuclear reactor.
For instance, the devices made by Qinetiq, introduced at Fukushima immediately after the disaster, were built to search for mines, said the firm's spokesman Mark Clark.
Using machines not made for such conditions was "always a compromise", he said, and better robots were needed.
"The operational environment within a large complex such as a power station poses high demands on these robots, which they were never designed to accommodate.
"If you are wishing to operate robots 24/7 inside a debris-filled power station in a radioactive area, it is much better to design the custom robot from the outset to meet specific tasks."
For instance, Toshiba says its robot has a wireless network that can be controlled in high radiation, looking for a better signal when reception is weak.
Mr Clark explained that the biggest problem associated with robots deployed into such zones was maintenance, because if repairs were needed, it would be difficult for humans to get anywhere near.
The solution would be to fix everything remotely, or while wearing heavy protective clothing.
To simplify the task, robots made to work inside a reactor would have to be "stripped of all unnecessary items", he said.
"If nuclear robots start leaking hydraulic fluid, they send an alarm before they fail so they can be quickly recovered. Others have the capability to shed or drop off parts of their manipulators so if they get caught up in debris they jettison the trapping section of robot, thus freeing them from the obstruction.
"Most nuclear robots operate on power provided by a trailing umbilical. This means there are no batteries to change and no refuelling issues to contend with."