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

The UK government has announced a raft of tiny nuclear power projects, while Russia, China and a host of tech giants are also betting big on small nuclear reactor designs. Does the idea make sense and can they really be built any time soon?

By Matthew Sparkes, New Scientist 15th Sept 2025,

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. 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. Michael Bluck at
Imperial College London 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.

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 capacitySmaller 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. 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.” https://www.newscientist.com/article/2496252-modular-nuclear-reactors-sound-great-but-wont-be-ready-any-time-soon/