As the world’s leading fusion energy project, and the nation’s biggest scientific experiment, approaches its 40th birthday, the UK’s fusion community has received a boost with the announcement this week by the Government of the site of ground-breaking new kind of fusion power plant, STEP.
Fusion energy not only enables our local star to shine but is crucial in addressing climate change through a safe, sustainable, efficient and low-carbon energy supply.
STEP, the UK’s first prototype fusion power plant, which will be built in West Burton, North Nottinghamshire, is being planned by the UKAEA team that works on the Joint European Torus (JET) in Culham.
Opened by Her Majesty The Queen in 1984, JET remains the world’s largest and most powerful operational machine used to study fusion power, based on a special ‘magnetic bottle’ to confine its hot heart, and has spawned a thriving fusion community around it in Oxfordshire.
During the process of fusion, the process that powers the Sun, atoms of light elements like hydrogen are fused together at high temperatures to form helium and release tremendous energy as heat.
Within JET, temperatures are 10 times hotter than the centre of our Sun and the soup of charged particles it contains, called a plasma, are held away from its walls by powerful magnets enfolding the tokamak, a vacuum chamber which is six metres across and has a D-shaped cross section that is 2.5 metres wide and 4.2 metres high.
The engineers and scientists who designed the machine showed great foresight, according to Ian Chapman, CEO of the UK Atomic Energy Authority, UKAEA. JET attracted a ‘significant amount of taxpayers money from this big European consortium to build a large machine where the tokamak that preceded it would have fit on your desk.’
At the time, it was known that the interior of the tokamak would become radioactive and would rely on yet-to-be designed robots to carry out maintenance. ‘They put a big port on the side and said that the robot needs to fit through this,’ he said, ‘and it is a huge testament to that team that the design is still at the forefront 40 years later.’
Earlier this year, landmark results were reported by JET, providing the clearest demonstration worldwide of the potential for fusion energy to deliver safe and sustainable low-carbon energy.
The project notched up a record-breaking 59 megajoules, or 59 million joules of sustained fusion energy over a five second period (the duration of the fusion experiment). This translates to an average output of 11 megawatts which, if used to power a steam turbine, would be about 4MW of energy, showing an important proof of concept.
The previous energy record from a fusion experiment, achieved by JET in 1997, was 22 megajoules of heat energy. But it has taken time to exceed the peak power of 16MW achieved briefly in the nineties because of issues that emerged when they started to use deuterium and tritium, the kind that would be used to fuel a commercial fusion plant. ‘You don’t get anywhere near breakeven unless you use tritium and JET is the only machine in the world that can run with tritium,’ said Chapman.
The deuterium-tritium fusion reaction produces subatomic particles called neutrons that make the interior of the fusion plant radioactive, making it harder to service, and they discovered in the 2000s that tritium was being absorbed into the wall of the tokamak, a carbon fibre composite that was cheap, easy to clean and would simply burn off if touched by the ultra-hot plasma in the fusion machine.
‘We had to come up with a new skin for the inside of the machine,’ said Chapman. ‘We completely stripped out the inside of the vessel – that’s 16,000 components and four tons of metal. It was all taken out robotically and then a replacement reinstalled robotically, so the interior now consists of a mixture of tungsten, which melts at more than 3,000 °C where most of the heat goes, and beryllium, which melts at 1,300°C, is lighter than aluminium and stiffer than steel.’
However, when JET started to operate again in 2012, it was ‘very low performance,’ he said. One issue they had to overcome was tungsten contamination of the fusion fuel, which causes performance to plummet: ‘a tiny little droplet of tungsten is all you need to ruin that performance,’ he explained.
It has taken JET a decade to ramp up its performance and, reassuringly, they have observed that, as planned, the tritium fuel absorbed by the tungsten-beryllium wall ‘was more than ten times lower than with the carbon wall,’ he said. ‘This year we actually broke the world record for fusion energy and did better than we did in 1997.’
This was a milestone for the researchers from the EUROfusion consortium – 4,800 experts, students and staff from across Europe, co-funded by the European Commission – and more than doubled previous records achieved in 1997 at JET using the same commercial deuterium tritium fuel mixture.
A sustained pulse of deuterium-tritium fusion at this power level – nearly industrial scale – also represent a major boost for ITER, the larger and more advanced version of JET under construction in the south of France. ‘ITER is essentially a bigger version of JET,’ he said. ‘It is twice as big in terms of linear dimensions and pretty much the same design and uses the same deuterium-tritium fuel.’
In a few days’ time, at FUSION22 in the Science Museum, a first of its kind global conference will showcase the goals and vision of the international fusion community and one of the topics will be the UKAEA’s MAST (Mega Amp Spherical Tokamak) machine, a refinement of the tokamak concept. ‘In parallel to working on JET to support ITER, we’ve also been thinking about a different, spherical, design of the magnets that confine the fuel to produce a more compact plant, which is therefore much cheaper,’ said Chapman. ‘MAST is our little test device for that, which makes more efficient use of magnetic fields than the tokamak.’
One version ran from 2000 to 2013, part of which will be on display in the Science Museum’s forthcoming Energy Revolution gallery, ‘Nuclear fusion experiments around the world are hoping to bring us closer to achieving clean and plentiful low-carbon electricity generation. MAST was one of the largest fusion experiments and we’re delighted to be giving our visitors a look at its central solenoid, the “beating heart” of the machine, which generated pulses of energy to ignite the fusion reactions,’ commented curator Oliver Carpenter.
A £55M upgrade of MAST went into operation last year to deal with a central issue with the spherical design: the plasma, at 100 million degrees, has to be confined into an even smaller space in this design, so heat extraction becomes hugely important. ‘Using a conventional design would definitely melt the walls, so we needed a better way of exhausting the heat,’ said Prof Chapman. ‘So, essentially, we’ve tried to design a new exhaust pipe called the Super-X divertor.’
Super X is designed to channel the hot contents of the fusion experiment – plasma – out of the machine at temperatures low enough for its materials to withstand to achieve a tenfold reduction in heat arriving at the internal surfaces of the machine. This has the potential to be a game-changer, said Chapman.
‘We turned that on in 2021, to reduce the heat that got to the wall by about ten times, a huge jump. Now we’re now about twenty times better, and that is opening a pathway to power plants, which are smaller and much cheaper.’
Based on MAST, the UK government is investing in a new design, the prototype fusion power plant, Spherical Tokamak for Energy Production (STEP), which is due for completion by 2040 and will generate electricity.
‘We are well underway with that concept design,’ said Chapman. ‘We’ve now pulled together a big consortium of industry partners and university partners to work on that.’
The price tag has yet to be determined but will be somewhere between the £2 billion invested in JET and the £20 plus billion in ITER. That sounds a lot but, he says, fusion could be a game changer when it comes to curbing harmful climate change.
The UK, points out Chapman, spent more than £20 billion on a test and trace program in a single year of the pandemic. ‘I came to fusion because I want to change the world and make a big difference. And I think that’s what most people working in this sector desperately want too.’
Although Brexit has meant that the UK is in a ‘no man’s land’ when it comes to collaborating with European partners in European projects, such as the European Atomic Energy Community, or Euratom, he added, ‘our collaborative links with our European partners are as strong as they’ve ever been and scientist-to-scientist, collaborative, relationships haven’t changed at all.’