Unique environments require unique robotic solutions: And environments don’t get much more unique than those inside an experimental nuclear fusion reactor.
However, as Robotics Business Review discovered while investigating the robots designed to work in these harsh conditions, even the most customized robotic solutions can have broader commercial potential.
When the environment is too hot, too airless, or simply too dangerous for humans to work in, we often call on robotic solutions. When the environment is an experimental nuclear fusion facility however, we call on a set of bespoke robotic maintenance and virtual reality-based remote handling systems being developed at facilities in Finland and the U.K. respectively.
These systems are designed to meet the very specialized conditions inside fusion reactors and some fairly uncommon technologies have resulted, from water hydraulics-based actuation and hard-wired sensors through 3D virtual reality remote handling systems specially built with public-safety in mind.
Fusion reactions promise cheaper, cleaner energy than that provided by conventional nuclear fission reactor facilities. While fission involves splitting elements, fusion works by overcoming certain elements’ natural repulsion to fuse them together, releasing huge amounts of kinetic energy in the process.
To make fusion happen extremely high temperatures –in excess of 100 million degrees Kelvin (180 million degrees Fahrenheit)– need to be reached in the reactor core (known as the ‘torus’). At these temperatures, the Deuterium-Tritium gas mixture used as the fuel source becomes a scorching hot, electrically charged gas known as a plasma.
Containing the plasma within the fusion reactor core and harnessing its energy without the reactor itself being destroyed is the main challenge scientists working on fusion energy face. But researchers have had some success keeping the plasma in place using ring-shaped magnetic fields, resulting in the Tokamak design on which current fusion reactors are based.
It’s a pipe dream to some –and no one has built a full-scale fusion reactor capable of feeding power to the grid just yet– but there are some major players heavily invested in making fusion energy a reality.
The Joint European Torus (JET) facility, in Oxfordshire, U.K. has been running plasma physics experiments since 1983. Initially under the control of the European Atomic Energy Community, the facility is now run under the auspices of the European Fusion Development Agreement (EFDA) ?a collaboration between fusion research institutions and the European Union.
That’s no way to treat a robot!
But JET is just the first step towards full-scale fusion reactors. If, as expected JET proves that the scientific basis for fusion is sound, all eyes will move towards the south of France where the International Thermonuclear Experimental Reactor (ITER) plant will, it is hoped, demonstrate the feasibility of fusion on a reactor-level scale. Funded by seven member entities –the European Union (EU), India, Japan, the People’s Republic of China, Russia, South Korea and the United States– ITER is due to swing into operation in 2019.
The robotic reactor maintenance and remote handling technologies being developed by scientists at EFDA-JET and at the ROViR (Remote Operation and Virtual Reality) center in VTT, Finland are being created with the ITER plant in mind.
With temperatures in excess of 50 degrees Centigrade and high radiation levels, the lower part of the ITER fusion reactor –a place called Divertor– is not a suitable environment for a human. Unfortunately, Divertor is not all that hospitable for a robot either.
Operations in ITER will take place under extremely harsh conditions in terms of gamma radiation, explains Jim Palmer, Remote Handling Engineer, based at ITER, France.
?These radiation levels preclude the use of modern-day electronics in the reactor vessel, requiring robot actuators and sensors to be hard-wired and the selection of radiation-hard cameras whose technology has changed very little over the past decades,? says Palmer.
Oil-based hydraulics are not feasible either, since a single drop of oil leaking from a robot inside ITER could necessitate in the entire reactor being shut down for cleaning.
?Although the robots will operate at atmospheric pressure, the design of the equipment must respect the need to maintain high levels of cleanliness inside the vessel to allow it to return to the Ultra-High Vacuum (UHV) conditions necessary for plasma operations. For this reason, high load applications are achieved using water hydraulic systems to avoid the risk of contamination by organic materials, like oil,? explains Palmer.
‘Off-the-shelf ‘ meet ‘Out-of-the-box’ thinking
There were no off-the-shelf robotic solutions available to tackle these unique conditions, so scientists around Europe started designing and developing their own.
In the EFDA-JET facility, for example, most of the robotic work is performed by a water-hydraulic based manipulator called ‘The Mascot,’ which consists of two force reflecting, master-slave, servo-manipulators with a load capacity of 44 lbs and a force sensitivity of .22 lbs per arm.
The units are linked by computer, not mechanically ?a setup that enables the slave unit to be operated at any distance from the master. The Mascot is positioned inside the reactor’s torus using a 32.8 feet-long articulated boom and performs a wide range of functions from welding and bolting, through cutting and inspection.
Those abilities were thoroughly tested during a recent scheduled refurbishment of the JET torus, when the interior of the vessel was stripped out and a new 4,000 tile wall installed, says Peter Allan, remote handling groups systems leader at JET. Fusion reactors have to have their walls replaced periodically to prevent unsafe levels of radioactive build up.
?The Mascot is quite versatile, so there are various ways the tile or carrier can be fitted. Mascot can either grasp the carrier or we can mount a tool to enable Mascot to grasp and carry the tile into the vessel. Re-tiling is like a complicated jigsaw puzzle, but Mascot is very, very effective,? says Allan.
Using The Mascot, single-bolted tiles could be fitted at a rate of about three tiles per hour. More complicated tiles took longer to fit ?and the entire process took about fifteen months to complete.
Meanwhile in Tampere, Finland, the experts at ROViR, don’t have a working reactor to test their systems on. Instead of waiting until 2019 when the ITER reactor is complete however, they do all their testing on a 1:1 scale model of the Divertor.
Modeling the future
The Divertor Test Platform (DTP2), which is housed in VTT Tampere, is being jointly developed by scientists from VTT and Tampere University of Technology, and is used to test ITER’s robotic maintenance devices. It’s all handled remotely via a dedicated control room.
In order to minimize the number of components that need to be handled during maintenance, the reactor’s Divertor is divided into cassettes ?each weighing around 9 tonnes. The robot responsible for moving these cassettes is the Cassette Multifunctional Mover (CMM). Despite the huge weights involved, there’s no room for error.
?CMM has a three meter [9.84 feet]-long arm and the cassette is about three and a half meters long. So there is six meters [19.68 feet] from the lifting point to the tip of the cassette. We’re able to control the tip point of the component to within three millimeters [.118 inches] positional accuracy. That is in a situation where we have about 80 millimeters [3.14 inches] mechanical flexibility. So, composition and control have been achieved quite well,? says Mikko Siuko, senior research scientist at VTT.
Meanwhile, the Water Hydraulic Manipulator (WHMAN) robot –with seven degrees of freedom– is installed on top of the CMM and can handle procedures like locking and unlocking the Cassette and other maintenance work.
All of this work is managed from a remote control room equipped with computers running specially-built 3D virtual reality modeling software that enables operators to models their robots’ moves in advance and then send commands directly to the robot for execution.
In typical remote handling configurations using forced-feedback manipulators the operator works with a camera of the robot’s environment. With DTP2 however, the operator will mostly work via a virtual view that has been calibrated with the camera image. The operator can then command the robot to follow a pre-programmed path or use a joystick to control the robot. It’s a system that successfully combines video, virtual reality modeling, automated operations and forced-feedback manipulation.
If DTP2 is to meet ITER’s rigorous public safety requirements, eliminating human error is key. The control room software, for example, shows operators only information relevant to the current operation at any time ?minimizing the chances of them selecting the wrong option.
Despite the very specific requirements of the project, one of the most unique things about the DTP2 system is its adaptability, says Siuko.
Precise manipulation and remote handling
The team at ROViR is also in talks with customers in industries that require precise manipulation and remote handling of heavy machinery, such as mining, forestry, and quarrying.
?Some of these projects are already running, but it is only the past year that we had sufficient resources to really expand beyond the ITER development. Now we’re starting to move our work beyond research projects and we are interested in cooperation. So, if there is any interest in any kind of cooperation we are open to that,? says Siuko.
Everyone with an hostile environment to tackle –but lacking the robotic equipment to operate there– take heed.Read More