Modular nuclear reactors sound great, but won’t be ready any time soon

The UK government has announced plans to build more than a dozen small nuclear reactors across the country, ushering in what it calls a new “golden age” for nuclear power. One of the ultimate goals is to help the country to finally divest from Russian energy within three years – but do tiny nuclear reactors make engineering and commercial sense, and can they even be built?

Ahead of a 16 September London visit by US President Trump, the US and UK announced a partnership between British firm Centrica and US start-up X-Energy to build 12 small modular nuclear reactors to power data centres, plus a “micro modular nuclear power plant” at DP World’s London Gateway port built by US start-up Last Energy.

However, no dates were given for the beginning of any of the projects, and the Department for Energy Security and Net Zero did not respond to New Scientist’s request for more detail.

The announcement fits a trend of smaller nuclear reactors. Bruno Merk at the University of Liverpool in the UK says Rosatom, Russia’s state nuclear energy organisation, recently finished building a batch of small reactors for a highly specific use in nuclear-powered icebreaker ships. Crucially, they then continued building more, showing either that there is demand from somewhere, or that Rosatom is taking a risk and building them as a commercial demonstration in the hope of selling more despite a raft of energy sanctions imposed after its invasion of Ukraine.

China, too, has built a Linglong One small nuclear reactor, but it is not clear whether it will yet be a commercially viable product. And giant technology firms like Amazon, Google and Microsoft are investing in these sorts of nuclear technologies, too.

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David Dye at Imperial College London says tiny reactors make sense for remote military installations or Arctic sites, but is sceptical about using tiny nuclear reactors to power these tech giants’ needs. He says it is far easier to build data centres near a ready supply of energy instead.

“If you’re a tech visionary multibillionaire and you want to believe… and you’ve made your billion, what is it to chuck $50 million at this cool technology?” says Dye.
”This is very rich men, or clubs of very rich men, giving a few crumbs off the table to this technology they’ve always loved the idea of, without really looking too carefully.”

One motivation could be oversight, says Michael Bluck at Imperial College London. “If you’re a data centre, you need to be on 99.995 per cent of the time,” says Bluck. “That means you really want to be in control of that electricity. You get first dibs on that electricity.”

Bluck says there is no engineering or scientific reason we can’t build tiny nuclear reactors, and build them fast. He points out the first experimental reactors were small, and many devices of a similar size operate in universities and military submarines around the world still.

“Size is not the issue. It’s the modularity, it’s the building it on a production line, it’s the standardisation of components. It’s really practical. It’s standard engineering,” says Bluck.

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But there are certainly plenty of drawbacks to miniaturising nuclear reactors. Merk says for nuclear power, scale brings useful efficiencies in both cost and energy. Small and large reactors both require the same thickness of concrete shielding to safely contain their reactions and, because the volume of a reactor grows faster than its surface area when you make it larger, bigger reactors are cheaper per megawatt of capacity. Smaller reactors also make less energy from the same amount of fuel because of inefficiencies in the chain reaction of neutron fission – smaller amounts of fuel lose more neutrons at the surface, rather than harnessing them to continue the reaction.

“You can’t avoid it. It’s physics,” says Merk. “If not, you are a magician. And I don’t believe in magic.”

Having said that, Merk points out nuclear power plants take years to plan, massive political will to fund and vast resources to build and maintain, which can make less efficient options seem more palatable. “These beasts have got so expensive,” says Merk. “Maybe it’s easier to build smaller.”

Designing new nuclear

Bluck says there are two different approaches involved in the new government announcements: X-Energy has designed a gas-cooled reactor called the Xe-100 which uses a somewhat unusual design and a type of fuel that could take 10 years to achieve regulatory approval, while Last Energy’s PWR-20 reactor is a relatively familiar pressurised water reactor, the same type as Sizewell B nuclear power station in England, using the same fuel. The former could be the way forward, but the latter may be able to come to market sooner.

But even with standard fuel and familiar technology, Bluck says Last Energy is likely five years from having even a prototype reactor built in the UK. “Everyone would like it tomorrow,” he says. “But I think they’re aware that energy isn’t like that.”

What will be vital to any plan to mass-produce and export these tiny reactors is regulatory approval, and that is something that currently has to happen from scratch in each country that will host them.

Bluck says that is where the US and UK announcement could be key, because it promises to speed up approval – at least between the two jurisdictions – by allowing a transference of sign-off. For instance, Rolls Royce has designed a small modular reactor, one far larger than those designed by many US startups, and more akin to a small traditional power plant. If it were approved by the UK, then it could immediately be sold in the US.

Still, Bluck warns the idea is not without political risk. “If you’re anti-nuclear you’ll certainly use this – you’ll say ‘What, we just accept what they give us? We can’t trust them’.” This partnership may alleviate some of that concern. “It recognises a problem, but this is the first time I’ve really seen it done between two significant manufacturing countries,” he says.