Nuclear fusion has the potential to deliver nearly limitless power – but before it can even get started, the world must build a massive supply of enriched lithium fuel from scratch.

“One of the biggest missing pieces of technology is the enrichment stage, where a specific type of lithium is concentrated,” says at Woodruff Scientific LTD, a UK consultancy focused on nuclear fusion. “We don’t have a solution that can be scaled to produce the required quantities of fuel for a future fleet of fusion power plants.”

Lithium is a critical fuel for the most common fusion technology in development, which merges two different forms of hydrogen to generate energy. And the rare lithium-6 form of the metal, which makes up only 7.5 per cent of all naturally occurring lithium, is the most efficient for sustaining the fusion process. So most fusion power concepts rely on “enriched” lithium, where the lithium-6 content has been boosted to more than 50 per cent, and sometimes up to 90 per cent, of the total.

Just one demonstration – designed to go beyond experimental fusion reactors by supplying net electricity to the grid – would require between 10 and 100 tonnes of enriched lithium to start and sustain operations, Ward and his colleagues found in an analysis. Each new demonstration plant that may come online would add to that demand.

The first such plant will not be ready until about 2040, which gives the world time to enrich more lithium. But enrichment plans will need to move quickly – one says the current lithium-6 supply is “practically zero”. The US does have a stockpile from the cold war: to support nuclear weapons production, the government produced about 442 tonnes of enriched lithium between 1952 and 1963. However, that process relied on toxic mercury, which contaminated the environment so much that the damage is still being cleaned up decades later.

Today, the need has shifted from limited amounts of highly enriched lithium – the nuclear weapons requirement – to much larger amounts of enriched lithium at lower purities for nuclear fusion, says at the US Department of Energy’s Princeton Plasma Physics Laboratory.

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To support early fusion power, researchers have proposed a modernised and cleaner of the enrichment process – although it still relies on mercury. Last year, the German government awarded funding to a that aims to scale up this type of lithium enrichment and make it cost-effective. “We plan to commission the first enrichment plant in Karlsruhe in 2028,” says at Argentum Vivum Solutions, a consulting firm in Germany involved in the effort.

“The only thing that could provide sufficient enriched lithium [in the] short and mid term is a mercury-based process,” says at the Karlsruhe Institute of Technology in Germany, who is also involved in the project. However, that same type of process will not be sufficient to meet the eventual demands of hundreds or thousands of commercial fusion plants.

“It is well accepted that a mercury-based process is not sustainable to support the deployment of fusion energy at a large scale,” says at the Breakthrough Institute, a research centre in California.

Some mercury-free enrichment methods are being investigated, but they won’t be ready in the near future, says Giegerich. The UK Atomic Energy Authority has also been of cleaner lithium enrichment processes, such as using microbes to efficiently isolate lithium-6.

“While other processes have not been demonstrated at commercial scale due to a lack of current demand and the need for additional innovation, one will need to be successful,” says Stein.

Extreme in scale and ambition, this is ITER, the €20-billion energy project being built in southern France. It is set to pave the way to fusion power, akin to that which fuels the sun.

Work started on the world’s biggest fusion experiment in 2006 through an international effort, including the European Union, the US, China and Russia. The first run of the reactor, during which it will create superhot matter known as plasma – a state necessary for nuclear fusion to occur – was scheduled for 2020. This was first pushed back to 2025, and fresh delays have now postponed it to 2035.

Meanwhile, exclusive photographs taken by offer a glimpse into ITER’s construction and potential.

The main imageĚý shows the size involved, with a 30-metre-deep assembly pit for the tokamak, a device responsible for confining spiralling plasma to a doughnut-shaped torus using magnetic fields. Pictured above is a shot of one of the toroidal coils that produce these fields.

The below images show some of the nine sectors that make up the ITER vacuum vessel. This weighs 5200 tonnes and provides a highly resilient “cage” for experiments, ensuring that continuously spiralling plasma doesn’t touch its walls.

The image above shows part of the vacuum vessel being transported for repairs, while the below shots show supports lining the wall of blanket modules that shield the structure and magnets from the heat and high-energy neutrons of the reactions.

The UK government has declined an invitation to become an official member of the ITER nuclear fusion experiment, having lost access to the project following Brexit. Instead, it plans to focus on UK-based fusion efforts, both public and private.

ITER, the world’s largest fusion experiment, is under construction in France and is expected to be completed in 2025 after many delays. The project is being funded by a huge international collaboration including China, India, Japan, Russia, South Korea, the US and the European Union.

The UK did have access to ITER through the EU, but, since Brexit, has fallen outside of it. Negotiations with the EU have subsequently seen announcements that the UK would rejoin Horizon Europe, a joint scientific research effort, but not Euratom, which focuses on nuclear power.

The head of Euratom Research, , seemingly called for the UK to officially rejoin the ITER experiment this week, but the UK government has said it stands by its decision to step down and believes private sector investment in fusion research will be a more efficient and cost-effective path to commercial reactors.

Righi was speaking at an event in Oxfordshire, UK, to celebrate the achievements of the JET fusion reactor, which was permanently shut down late last year and will now be decommissioned.

“The Commission and the Council of the EU, in a joint statement, noted with regret that the United Kingdom decided not to associate to the Euratom programme and the Fusion for Energy joint undertaking,” said Righi. “For the next period starting in 2028, the EU institutions called emphatically [for] the UK to participate in all the four programmes [ITER plus the European Commission’s ±Ő.”

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“This will allow a truly European fusion community to continue its integrated efforts and to resolve the current ambiguous participation of the UKAEA [UK Atomic Energy Authority] to EUROfusion [the European fusion research group] and enable the UK’s fuller integration in the construction and operation eventually of ITER.”

żěè¶ĚĘÓƵ asked the European Commission to clarify Righi’s statement, but received no response.

At the same event, , the UK minister responsible for nuclear energy, told żěè¶ĚĘÓƵ that the UK stands by its decision not to rejoin the effort, as doing so ,Ěýwhich can be instead used to fund a mix of private and public research.

“For all the experiments, for all the research, for all great work here at JET, the ultimate aim of all of this is to get fusion onto the grid, generating power into homes and businesses,” says Bowie. “To make it a commercial reality, to bring the power of the sun into peoples’ homes, we’re going to need significant buy-in from the private sector as well.”

“The decision not to reassociate was the right one. We had, here in the UK, moved to such a place that reassociating would divert, we believe, time and resource and money away from where we wanted to take our fusion projects. It’s not that there was an ideological decision not to reassociate, it was a practical decision,” he says.

Bowie says that the UK can get more bang for its buck from private sector investment, but is “very open” to finding new ways of collaborating with ITER, such as personnel exchanges. “We’re not saying no to working with ITER,” he says. Bowie also explicitly ruled out an official re-entry to the ITER project: “We stand by that decision.”

The UK is also developing plans for the Spherical Tokamak for Energy Production (STEP), a nuclear fusion power station, which it hopes will create plasma by 2035 and reach net energy gain – where more power is created than input – five years later.

at the University of Manchester’s Dalton Nuclear Institute in the UK says that spherical reactors like STEP, if successful, offer the promise of smaller and cheaper fusion power than large designs like ITER, which is experiencing its own problems.

“It’s continually being delayed,” says Matthews. “It’s got the big project syndrome where things are just not coming in on time and costs are going up. The STEP initiative, and losing contact with ITER, could be an impetus which would result in [the UK] demonstrating power generation earlier than Europe. I’m very optimistic about the use of spherical tokamaks.”