Speeding up MRO for the world's largest experimental reactor

For the last 10 years, Third Dimension has been working with the UK Atomic Energy Authority’s (UKAEA) RACE (Remote Applications in Challenging Environments) department to facilitate the development of nuclear fusion by speeding up the MRO (maintenance, repair and overhaul) process of the world’s largest experimental reactor.

As the world's largest nuclear fusion power experiment, the JET (Joint European Torus) nuclear fusion tokamak1 is designed to harness energy with the intention of furthering the development of fusion power generation. Fusion is based on the same principle that powers our Sun and stars and is a key stepping stone towards a carbon free world in energy production.

ccfe reactor

Operated by the UKAEA at Culham Science Centre near Oxford for the EUROfusion consortium of European fusion scientists, the project started in 1983 and is at the absolute cutting edge of scientific development. Third Dimension supports quality control and MRO of JET with our advanced profile measurement systems.

When we originally started working with UKAEA, a third generation GapGun was installed onsite and used for inspection, in and out of the fusion rig. However, the GapGun, was upgraded last year to the recently launched Vectro system and has been specifically designed to be installed as an integrated robotic inspection tool. Already, Vectro has proven to deliver significant improvements to the speed and productivity of maintenance procedures for UKAEA. This has been achieved with the Authority’s MASCOT robot.

 During operation, the reactor runs for 30 seconds every half hour, with scientists from around the world eagerly awaiting their data and test results.

The tokamak1 has a heating capacity of around 40 megawatts. To achieve power generation through nuclear fusion, plasma temperatures of over 100 million degrees Celsius are required. This makes the reactor the hottest temperature in the solar system, hotter than the sun. Inside the reactor specially designed tiles are densely packed to cover the inner area of the tokamak core and protect it from the extreme temperatures and hostile environment generated by the process. These castellated, beryllium-coated Inconel tiles are made in the USA at a cost of over $700 per hundred grams.

Tiles are around 1 cm square and are slightly offset at an angle to encourage the hot gas – known as plasma - in the core to circulate in a controlled manner. This presents a challenge to ensure that the tiles are within a strictly controlled tolerance band.

Any excessive amount of step or gap between tiles increases the danger that plasma could cause tiles to detach or get damaged. This would then mean expensive replacements and so inspection and the correct positioning carried out on these tiles is critical to the project. However, inevitably tiles do get damaged from time to time, often by plasma escaping from JET’s powerful magnetic fields. Therefore, as part of regularly scheduled maintenance procedures, the JET facility is closed for six months every two years for an overhaul, and this is when the Vectro comes into play.

JET fusion

Due to the hostile environment of the reactor, it is left to cool for a couple of months before the MRO begins; though even then it is still unsafe for humans to enter the tokamak safely without the use of protective suits. However, Vectro thrives and is effective under these conditions and is operated remotely with a robotic device called MASCOT.

MASCOT is mounted onto an in-vessel transporter system to enable Vectro to check for damage to the surface of every single tile lining the reactor. Each tile is inspected to see if it needs to be replaced and if so, to ensure that the replacements are re-positioned in exactly the right place and orientation. The MASCOT master station is driven by experienced remote handling operators and can be positioned around the vessel by a transporter system; a 12-meter-long articulated robot.

ccfe control room 2







During a regularly scheduled shutdown, around 600 tiles are removed and replaced during the six- month period including many sample divertor tiles for chemical and physical examination. Vectro is used to check any tile that is replaced and to quality check new tiles before they are installed into the JET wall.

Our award winning GapGun technology is the only way to check that the tiles are in the right position, within 10 microns, which ensures minimal damage when the reactor is operational. It is impossible for the human eye to detect to such accuracy.

Before GapGun and Vectro, operators had to check quality by eye, using a standard gap flush test, compare against a check-list and manually input all data into a spreadsheet. This was slow and prone to error. GapGun, and now Vectro, deliver the results immediately and electronically, so operators have a record of what has been done. Saving the project time and money, they deliver repeatable results time and time again. This inspection method means not only is it possible to reduce the number of tiles that fail during experiments (allowing for a higher chance of successful tests), but that in the future it could also be possible to meet even tighter tolerances.

For more information on nuclear fusion visit  https://www.gov.uk/government/organisations/uk-atomic-energy-authority, http://www.race.ukaea.uk/.

  1. Tokamak - an experimental machine designed to harness the energy of fusion.
  2. ITER is the world's largest fusion experiment, and will be the largest fusion reactor when it becomes operational. Thirty-five nations are collaborating to build and operate the ITER Tokamak in the south of France.
  3. Skilton, R., Fusion Engineering and Design (2018), https://doi.org/10.1016/j.fusengdes.2018.03.026