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Producing clean power - the future is fusion

06 November 2017

Tokamak Energy is aiming to realise the first-ever reactor that could produce clean power from fusion, the process that happens in the centre of the Sun, reports LTi Metaltech.

The requirement for pressure vessel integrity is no more acute than in the nuclear fusion sector, where tolerances and integrity of seals leave absolutely no room for error. In this development, LTi Metaltech (LTi) - recognised as industrial experts in high integrity welded structures - have supported Tokamak Energy with its aim to create the ST40 fusion reactor, a crucial prototype step towards a device to produce electricity for the first time in 2025.

The globe’s over reliance on fossil fuels is unsustainable and solutions for meeting our ever-growing energy demands has thus far proved limited and/or unstable to the environment and surrounding ecosystems. These limitations are conceivably non-existent with fusion reactors, as in fact, radioactive waste is minimal and meltdown is physically impossible.

Fusion is what happens in the Sun – when ions in a plasma collide, they fuse together to form larger atoms and release huge amounts of energy. Every nuclear reactor ever made so far has been a fission reactor whereby heavy atoms such as uranium decay into smaller atoms when energy is released. Fusion is a different, safer and cleaner process, but the trouble is that it has not yet been proven as a technology. 

Tokamak Energy’s solution combines two emerging technologies – spherical tokamaks (the most advanced fusion concept in the world) and high-temperature superconductors. The concept behind this is to harness heat right here on Earth within ring shaped chambers that produce cheaper and greener results, hence ‘tokamaks’, derived from the Russian word meaning ‘ring shaped chamber’. The fusion reaction happens between two light hydrogen isotopes, deuterium and tritium, within a plasma hotter than the centre of the sun. The fusion process creates energy which can then be used to power electric generators.

Culham Science Centre has led fusion research for the past 50 years in the UK. In an attempt to provide a real scientific breakthrough in the industry, Tokamak Energy, at just six years old, has been championing a need to build smaller reactors faster, and turned to high-spec vessel specialists LTi for assistance with its vessel development. The most challenging path to fusion energy has been to effectively, consistently and safely heat plasma to the required temperature to stably sustain fusion, whilst doing so within a realistic investor friendly time-frame and budget. Bigger is certainly not better in this field and Tokamak Energy has shown that smaller reactors can confidently manage the task of creating safe fusion energy. This new technology will help realise that hundreds of these smaller reactors could be manufactured like jet-engines on a production line once initial tests prove successful.

Designed and constructed by LTi, the UK-based firm and lead manufacturer of the cryogenic pressure vessels used in Siemens MRI Scanners, has used its fabrication expertise to support Tokamak Energy to create the world's first high-field spherical Tokamak ST40 reactor. Manufacturing of the tokamak reactor began late last year at the heart of Milton Park, Oxfordshire. 

Conceptualising the IVC Angled Support fabrication structure, LTi envisaged the formation of single-sided welds including the gap requirements for a backing at a minimum of 4mm, extending to 10mm from the edge of the joint to prevent burn through. This would be engineered by a raised surface around the flanges to act as location and weld backing.

Solutions were discovered that reduced welding times – eliminating the requirement to grind back on some double-sided welds. The structure was simplified whilst maintaining function by placing prep angles and creating square edges on the coned features. Furthermore, the design was enhanced so that the IVC outer wall is cylindrical and the resulting voids inputted would not affect the cone sections. 

The reactor vessel is produced using stainless steel, although the companies are considering alternatives to withstand erosion. Maintaining the plasma within the magnetic field and preventing it from hitting the walls by retaining a small gap requires accurate control of magnetic coils and the current that passes through. The fast route to this fusion programme to provide zero carbon and safe fusion power is anticipated to be grid ready by 2025.

The latest ST25 reactor, which combines high-temperature superconducting (HTS) magnets with a smaller than standard spherical tokamak, demonstrated a world record of 29 hours of continuous plasma in 2015. It is expected that the new ST40 reactor will eventually produce plasma temperatures of 100 million°C – several times hotter than the centre of the Sun, relying on magnetic coils which trap hot plasma within a field, keeping it away from the walls of the vessel. This will not only prove that fusion power is a viable alternative to environmentally damaging fossil fuels, but that the technology is achievable.

The world needs abundant, clean energy. Nuclear fusion - with no CO2 emissions, no risk of meltdown and no long-lived radioactive waste – seems like the optimum solution. It is an ambitious challenge that requires serious investment, government backing, R&D initiatives and creative scientists. But if we are successful in progressing with further development to bring tokamak technologies closer to commercialisation, are we poised to make the science fiction of fusion energy a sustainable reality? 

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