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Fabricating future fusion: in a battle to create a world that doesn't rely on fossil fuels, 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. Edgar Rayner, technical director of LTi Metaltech, explains the fabrication challenges.

The world needs abundant, clean energy. Nuclear fusion--with no C[O.sub.2] 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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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 (or LTi) of Oxfordshire is expert in high integrity welded structures and has supported neighbouring high-tech company 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 have 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 inside 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 is to harness heat 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 electricity generators.

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Culham Science Centre in Oxfordshire has led fusion research in the UK for the past 50 years. 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, while 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 hi-spec technology and fabrication specialist LTi, the 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 revolutionary 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 while 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 alternatives are being considered 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 [degrees]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. *

BREXATOM: COMPLICATED AND COSTLY?

The peaceful use of nuclear energy within the EU is governed by the 1957 Euratom Treaty. The Euratom (European Atomic Energy Community) community is a separate legal entity from the EU but it is governed by the bloc's institutions. According to explanatory notes to the Brexit bill, the UK intends to leave the Euratom at the same time.

The Euratom framework also includes nuclear co-operation agreements with third party countries, including Canada, Japan and the USA. It facilitates UK participation in long-term research and development (R&D) projects, and it also provides a framework for international nuclear safeguard compliance.

One tricky question is who will now inspect the British sites that generate power, fabricate fuel and manage waste, as the UN's International Atomic Energy Agency (IAEA) currently leaves much of the inspection work to Euratom. Britain (which has 15 nuclear reactors accounting for 21 per cent of its electricity) takes up about a quarter of the time Euratom spends on safeguard checks in the EU.

A further issue is that Euratom may also be forced to transfer its ownership of nuclear material to the UK, which could be complicated as it enriches, fabricates and reprocesses spent nuclear fuel on behalf of many other member states.

Membership of Euratom is also a condition for Britain hosting what is currently the largest nuclear fusion experiment in the world. Based at Culham Centre for Fusion Energy in Oxfordshire, the Joint European Torus (JET) project involves some 350 scientists exploring the potential of fusion power, backed by funding from almost 40 countries in the EUROfusion consortium.

Jonathan Leech, senior commercial and nuclear energy lawyer at Prospect Law, said: "The Euratom treaty has a separate exit process that need not be triggered at the same time as triggering exit from the EU. It may not be possible to put in place bilateral nuclear cooperation agreements with all countries with which the UK currently cooperates and trades in the nuclear industry. The alternative is to delay triggering a Euratom exit until the UK has fully explored and progressed negotiation of replacement arrangements, to the point where government and industry can be confident that those arrangements will be ready to go live within the two-year exit timetable, so avoiding potentially serious harm to the industry."

By Andy Pye, Editor

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Title Annotation:Sustainable Energy Generation
Publication:Environmental Engineering
Geographic Code:4EUUK
Date:Jun 1, 2017
Words:1234
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