Government could do worse than by following the advice of Stephen Hawking, contended Ian Chapman, UKAEA CEO at the Energy Institute Fellows event. ‘When asked for a world-changing idea, Hawking said, “I’d like to see the development of fusion”.’ It is low-carbon; inherently safe – you can’t have a chain reaction; half of its fuel is readily available; it has little land use requirements and requires few natural resources; nor does it produce long-lasting radioactive waste.

But, he continued, ‘fusion is hard’. To create it on Earth, temperatures have to reach 100mn °C, generating the most intense source of neutrons that fly out everywhere and damage whatever is used to make the reactor. The reactor encounters incredible heat gradients, from the plasma, which can’t touch the wall-to-wall temperatures of 2,000°C, to nearby magnets cryogenically cooled to 4°C above absolute zero. This unforgiving environment is not safe for people, so robots must be used for maintenance and ongoing repairs. And the reactor needs enough fuel to keep going.

This process was explored at the European fusion research facility JET in Culham, Oxfordshire, which broke records in terms of the energy it produced last year, and then shut down after 21 years of operation. Chapman called it the largest operating fusion facility in the world; a big industrial plant, with a high quantity of tritium, the same mix of metals as a power plant and the largest-scale robotic maintenance.

Now, plans are taking shape for a prototype powerplant called STEP (but this time funded not by the EU but only the UK) to be located at the site of the former West Burton coal-fired power plant in Nottinghamshire. The reactor will be designed, built and operated by a public-private partnership under UKAEA called UK Industrial Fusion Solutions. A shortlist of industry partners for the one engineering and one construction partners is expected to be published before the end of the year. As the decades-long process of construction begins, vital enabling work is taking place in Oxfordshire, with a focus on its fuel.

Like its nuclear colleague fission, fusion deals in subatomic particles. But rather than splitting a huge atom of uranium, fusion aims to combine some of the smallest. Hydrogen has one proton and one electron, and different isotopes have one neutron (protium), two neutrons (deuterium) or three neutrons (tritium). In the right conditions, a deuterium atom and a tritium atom fuse to create helium, and energetic neutrons.

Unfortunately, while deuterium can be synthesised from seawater, tritium is much harder to come by (see Box 1). For that reason, once they start up, most fusion reactor designs ‘breed’ tritium by exposing a suitable material, such as lithium-6, to neutrons emitted from the fusion reaction. Their interaction with the material at a molecular level forms tritium atoms, which in theory can be harvested, processed and injected back into the reactor as fuel. This is the province of UKAEA’s new H3AT tritium fuel cycle R&D facility in Culham.

How does it work?  
At a 1/20th scale, the H3AT facility will study the steps involved in processing tritium generated in a fusion reactor. There are two inputs: gas pumped out of the reactor, consisting of unused fuel and impurities, plus tritium, deuterium and impurities released from the lithium bed (that process is being studied at a sister project, LIBRTI). Second, the resulting gas is purified to remove everything but the hydrogen. Next is to separate each of the hydrogen isotopes. Then they are processed to make new fuel and stored. Those last steps are supported by secondary processes that further remove tritium from intermediate process steps. Waste material is sent out via the exhaust stack.

It sounds straightforward. The only problem is that it hasn’t been done before. ‘Many of the proposed processes have been demonstrated at the lab scale or experimental scale, and for JET we ran many of these, but we did them in batch configuration. Now we need to do them continuously. And understand how the processes behave when coupled in a closed loop. This hasn’t been done at prototype scale,’ said Steve Wheeler, Executive Director for Fusion Tech, Fuel Cycle and ITER components, after the event.

He said: ‘We will have a default loop with the most robust candidates, but will configure the loop to bring in other candidate systems at a meaningful scale.’

Wheeler did not downplay the difficulty of the task ahead. ‘This is a challenging project,’ he said, but credits the expertise developed at Culham with the ideal mix of skills to tackle it. He commented: ‘If you just focus on physics or engineering, it’s easy to throw the problem to another team... Being able to work across boundaries is really important. That’s one of the areas where UKAEA has a real advantage through running JET; with decades of activity in fusion, the majority of the disciplines are here in one organisation.’

In terms of physical plant, the building has already been constructed, a four-floor, 2,300 m² engineering hall and office space. And there will be a supply of real tritium; the site will be licenced to work with a total of 100 grammes – the same quantity as the JET facility, that will be transferred to the H3AT site.

Wheeler explained: ‘The 100 grammes inventory for the loop was chosen very carefully, to be representative of a power plant-scale process. Hardware, software, chemistry, process control – the whole loop as an integrated system is represented. And it is large enough in scale for the data produced to be valuable for power plant scale. But the inventory is kept as low as possible to ensure it is as efficient as possible.’

How to build a supply chain from nothing?  
‘An important part of the fusion mission for UKAEA is not STEP and H3AT alone, but developing and building a supply chain based on the legacy of its expertise with JET,’ Wheeler remarked.

So far, one big H3AT contract let is to Canadian engineering contractor Atkins Realis, for detailed design of the isotope separation plant.

Wheeler emphasised that this is not just another civil nuclear project. Unlike fission, fusion is likely to be regulated with a lighter touch than the Office of Nuclear Regulation by the HSE and the Environment Agency.

‘Fusion is very keen to develop best practice with other industries, in terms of qualifying engineering systems, manufacturing technology, fabrication technologies. We are eager to learn best practices from aerospace, offshore engineering, space, or other industries where the verification and validation of engineering systems is very important, but which aren’t following fission codes or regulatory practices.’

• Further reading: ‘Why be optimistic about nuclear fusion?’ Fusion has the potential to provide low-carbon, sustainable, continuous power, and while technical challenges must be overcome on the quest to deliver fusion, it will be worth the effort, contends UK Atomic Energy Authority (UKAEA) Chief Executive Sir Ian Chapman. Beyond electricity, fusion can also be a source of high-grade heat which will be especially important in the decarbonisation of hard-to-abate sectors.
• Find out more about the race to perfect a decades-old science experiment for zero-carbon commercial energy that is being pursued by a new group of pioneers funded by the private sector.