Our 2010 IOP schools lecturer Melanie Windridge on her tour and fusion physics:
On my “fusion tour” last week I travelled between York and Chapel-en-le-Frith, finishing in the heart of the Peak District. The weather has been mostly fine and, though I’ve been in schools during the day, I’ve had some lovely evening drives through beautiful countryside. Thursday was a particularly busy day. A film crew from Physics World came to interview me and film some of the talk for a piece on their website as part of their special on nuclear power. I had a break on Friday and went for a long walk from Edale onto Kinder Scout.
I have walked there before and the views are spectacular, but Friday was so misty that we couldn’t see further than a few metres. Large, eerie rocks loomed out of the fog and the wind was so strong on the plateau that my face burned and my hands were pulled back firmly into my sleeves. On Saturday I rushed into London for the Science Is Vital rally and by Sunday I was off again to Kent for another week of lectures… but that’s next week’s story.
So, in the last couple of blogs I have written about the biggest tokamaks in the world – JET in Oxfordshire and ITER, which is now being built in France. And this time I’m going to tell you about robots. Because JET has been pioneering robots for remote maintenance of tokamaks for several years now.
The reason we are going to need robots in fusion power stations is radioactivity. Now I said in Part 1 that fusion doesn’t produce any long-lived radioactive waste, and that’s true. Fusion produces helium, which is safe. But the reaction also produces neutrons – very high-energy neutrons – that have no electric charge and so can escape the magnetic trap and fly out through the walls of the machine. And these neutrons have so much energy that that they can actually bash atoms out of place in the walls or induce nuclear reactions, changing the material properties of the walls. This makes the structure of the machine slightly radioactive.
Now this is not long-lived radioactive waste like that which comes out of a fission reactor. After 50-100 years the radioactivity will have decayed away to a safe level and the materials could be recycled. But it does mean that humans will not be able to go inside the machine to make any repairs. So we will need robots.
The robots being tested on JET look a little bit like toy, plastic snakes that you might have seen or played with when you were younger. These snakes are made of many small joints, which give the robot great flexibility and enable it to enter through a small porthole and curve around the whole doughnut-shaped vessel to make repairs.
The snakey-robot itself is 10m long and includes a manipulator section at the end that carries out all the work inside the vessel. See Picture 2 of the robot arm with a section of the tokamak. The robot is remotely controlled from a control room a safe distance away, so using the robot to maintain the machine is called “remote handling”.
The remote handling system is a sophisticated set-up that includes robotic devices, advanced computers, virtual reality and closed circuit television, as well as specialist tools required for repairs. Simulations are run before any maintenance work is started then the procedures are practised in a full-size mock-up of the tokamak. The operator is given an experience like that of actually being in the torus. CCTV gives a sense of sight and through the manipulator unit the operator has a sense of touch. Virtual reality gives accurate position perception. Here is a virtual reality animation of the JET robot.
Robots have been operating on JET since 1998 and are currently installing the new ITER-like wall for the new set of experiments beginning in 2011. Remote handling is an important technology to develop for the repair, maintenance and upgrade of future fusion power plants. There are additional benefits too. Using the robots gives increased precision and introduces fewer unwanted impurities into the vacuum vessel.
Using the robots is like having special equipment to extend the operator’s own arms. They undertake a wide range of tasks like welding, cutting and bolting as well as inspection of the vessel. Often specific tools are specially developed at JET. The operators need to get a lot of practice in controlling the robots because the tasks being performed are very precise. They practice using a full-scale mock-up of JET and dummy components or, if they want to have a bit more fun, they can play giant Jenga. Have a look at this video on the JET website.
Next week we’ll be back on to something a bit some serious – I’ll be writing about why fusion releases energy – and I’ll be travelling around the South East.