Fusion energy is a growing sector and Dean McGarrigle, a mechanical design engineer at the United Kingdom Atomic Energy Authority – the national research and development organisation with a mission to lead the delivery of fusion energy and maximise its economic benefits – provides an overview of the engineering involved in the industry today.

Dean McGarrigle.

Fusion is the process that takes place in the heart of stars and provides the power that drives the universe. When light nuclei fuse to form a heavier nucleus, they release bursts of energy. This is the opposite of nuclear fission – the reaction that is used in nuclear power stations today – in which energy is released when a nucleus splits apart to form smaller nuclei.

Tremendous amounts of thermal energy needed

Fusion requires tremendous amounts of thermal energy to occur, so the fuel is heated to the fourth state of matter; plasma, a super-hot gaseous state. Three main factors are considered when determining the optimum conditions for fusion to occur: temperature, plasma density, and time, which result in a 'fusion triple product'.

As the gravitational forces of stars achieve plasma density that is difficult to replicate on Earth, this means that we must increase plasma temperature significantly to compensate, achieving temperatures of about 150 million °C, 10 times hotter than the core of the sun.

Figure 1: In-vessel view of JET showing plasma on right side.

There are many different approaches to achieving fusion, with the current most prevalent approach across the world being 'magnetic confinement fusion' (MCF), where the ionised property of the plasma allows it to be influenced and contained by magnetic forces.

Another significant approach to fusion is 'inertial confinement fusion', where the US National Ignition Facility (NIF) achieved a new fusion record by firing the world’s largest and highest energy laser at a fuel pellet, resulting in more energy being produced from fusion than was absorbed by the pellet.

UKAEA’s Culham Campus in Oxfordshire, houses the MAST-U (Mega-Amp Spherical Tokamak Upgrade) device and the world’s largest operating MCF device, JET (Joint European Torus). Both devices are 'tokamaks', which generally consist of rings of magnets that form a 'doghnut' shape that confines the plasma in a continuous loop.

The UK government-funded MAST-U is a special variant of a tokamak called a 'spherical tokamak', which forms a shape closer to a cored apple than a doghnut. JET was constructed as an international collaborative project led by EU countries, but as the fusion industry expands, a UK fusion cluster is growing with private companies also building devices at Culham Campus.

Prototype fusion energy plant

UKAEA is also developing the UK’s prototype fusion energy plant, STEP (Spherical Tokamak for Energy Production), which will be built in Nottinghamshire, targeting operations for the 2040s.

Experiments conducted on JET and MAST-U are fundamental for the development of future prototype plants in addition to ITER, which will become the world’s largest tokamak fusion device.

Based in southern France, ITER involves 35 nations collaborating to prove the feasibility of fusion. This will then lead on to the power-generating DEMO device that is planned to be the EU’s first fusion device to generate power to the electric grid. ITER and DEMO is being supported by many other experiments and devices both within Europe and across the world.

Ireland is also participating in producing fusion via the National Centre for Plasma Science and Technology of Dublin City University. It is hosting the next Symposium On Fusion Technology (SOFT) in September 2024, where hundreds of expert scientists and engineers from across the globe will come to discuss their findings, potentially over a pint. Suffice to say, fusion is the up-and-coming global industry to be in.

Figure 2: UK and EU major fusion project roadmap.

I currently work in the Remote Applications in Challenging Environments (RACE) department of UKAEA, which originally branched out of the team that performed maintenance on JET.

The department uses its years of experience from maintaining JET to become specialists in remote maintenance and heavily informing the remote maintenance strategies and design for maintenance of fusion projects, including STEP, ITER, and DEMO among others.

This expertise branches out to other industries, aiding in civil nuclear decommissioning activities in Sellafield and Fukushima through the LongOps project as well as developing general robotics and AI in the RAICO project and developing strategies for maintaining satellites and space applications. I started at the company via its graduate scheme and was immediately put to work on cutting-edge technology projects.

Remote maintenance strategies

The main scope of the work I have been involved in is the development of remote maintenance strategies and design for maintenance of future tokamaks such as DEMO and STEP.

My initial package of work with UKAEA was researching high payload maintenance deployment systems (big cantilever robot arms) which highlighted the uniqueness of the constraints involved in fusion as the only similar systems are used almost exclusively within fusion devices.

Figure 3: Simulation of JET Booms performing maintenance activities within a cross-section of in-vessel JET.

The significant constraints on geometry, materials, and harsh environment resistance, introduce challenges that are not found within any other sector but should pique the interest of many, if not all engineers.

The simple fact that we are operating with some of the hottest temperatures in the universe (superhot plasmas) less than a metre away from some of the coldest (low and high temperature superconductors) is telling enough of the engineering challenges faced.

Variety of engineering disciplines

I work directly with the engineering disciplines of mechanical, electrical, electronic, mechatronic, material, chemical, structural, construction, and civil, to name but a few, as well as working with world renowned physicists. But as the physics challenges are being overcome, the engineering challenges of fusion are becoming more and more prevalent.

Material and chemical engineering is needed to develop the fuelling systems as well as materials that can withstand the harsh environments of fusion and minimise any radio-activated waste to a low or intermediate level.

The materials used must also ensure a long Mean-Time-To-Failure and carefully planned maintenance must ensure a short Mean-Time-To-Repair to increase the availability of the power plant and lower the cost of electricity produced.

Like with other heat generating power plants, the thermal energy produced will have to be extracted and converted to electricity. This could be adapted from existing technologies, but extra challenges may likely occur due to the sheer amount of thermal energy being produced, this energy also potentially being produced intermittently if the device has a pulsed operation.

Well-optimised facilities will have to be designed and built to house, transfer, and assemble the large components, with intricate piping for supporting services designed in tandem. And systems engineering is needed to bring this altogether to function like a well-oiled machine, although a goal of fusion is to reduce our reliance on oil.

Many might be asking, if it’s so difficult to achieve then why are we doing it? The answer is that fusion promises to be a safe, low carbon and sustainable part of the world’s future energy supply.

Figure 4: A concept model of the future STEP facility.

The fuel that powers tokamaks consists mainly of two forms of hydrogen: deuterium and tritium. The former can be found in abundance in seawater and the latter can be produced as a byproduct of the fusion process interacting with lithium and fed back in as fuel, becoming near self-sufficient.

The direct waste product produced from the process is helium which does not contribute to global warming and the fusion process itself produces no carbon emissions at the point of generation.

Due to the need for a continuous fuel supply as well as the fusion triple product factors, the fusion process stops as soon as any of these fall below the required levels, assuring an inherently safe operation.

The dense amount of energy produced from a small amount of fuel would take up less land than solar and wind farms but also support and complement weather-based energy production by providing a consistent base power load. These factors – as well as the technological advancements being produced alongside fusion – make it a very promising field for budding engineers. 

Author: Dean McGarrigle, mechanical design engineer, the United Kingdom Atomic Energy Authority.