Explainer: How does a small nuclear reactor work?

The global threat of climate change is making the need for clean energy more urgent than ever. In the race to reach net-zero emissions and reduce reliance on fossil fuels, nuclear power is gaining increasing support.

And Russia’s invasion of Ukraine has had a seismic effect on global energy prices, driving up costs for consumers and businesses alike. In Europe, UK annual energy bills are at their highest levels for 50 years and rising, while Germany is also seeing power prices reach record levels.

The high price of energy risks hamper efforts to reach current climate change targets, according to Fatih Birol, Executive Director, the International Energy Association (IEA). And the world is already behind on meeting its commitments. Much more investment in clean energy technologies is needed if the worst effects of unchecked global heating are to be tackled in time, he says.

Nuclear energy is not renewable, but it can be recycled. While its use does raise issues around cost, waste management and safety, in terms of greenhouse gas emissions per unit of power produced, it is as clean as offshore wind, according to the UK’s Nuclear Advanced Manufacturing Research Centre. This makes it one of the lowest carbon energy sources.

All of these factors are fuelling investment in domestic, smaller-scale power plant technology design. The International Atomic Energy Agency (IAEA) defines ‘small’ as under 300MWe while up to 700MWe as ‘medium’, according to the World Nuclear Association.

While small and medium-sized reactors are sometimes collectively described as SMRs, the industry body says this acronym is more commonly understood to mean ‘small modular reactor’.

Like conventional reactors, SMRs use nuclear fission technology, harnessing the thermal energy this produces to generate electricity. Essentially they are advanced, smaller reactors with around one-third of the processing power of traditional reactors.

At the end of July, the US Nuclear Regulatory Commission (NRC) announced it would issue a certification for a new nuclear reactor design. The NuScale Power module, which encompasses the reactor, steam generators and pressurizer, uses the principles of buoyancy-driven natural circulation.

Innovations in this field have been approved before, but not with such potential operational and cost advantages, reports technology news site, Ars Technica.

The modular nature of SMRs means that their off-the-shelf components can be assembled in factory conditions, unlike large nuclear plants which are expensive and complex to build and can be high-risk in terms of construction. This potentially makes them cheaper and quicker to produce, as well as easier to monitor, says the U.S. Office of Nuclear Energy.

At Rolls-Royce, which makes its own SMRs, around 90% of the work takes place in factories which reduces on-site disruption, the company says. Having a smaller construction footprint also means more flexibility when it comes to choosing plant locations.

In addition to a more streamlined build process, SMRs are also gaining in popularity thanks to passive safety features. Put simply, this means that if problems arise, no active intervention - by workers or external forces - is required to shut down systems. Some argue that this makes them safer than traditional nuclear power stations.

Not surprisingly perhaps, given their smaller size, SMRs also require less fuel than conventional plants.

There are currently 438 commercial nuclear reactors around the world, according to figures released by the IAEA, with a further 56 under construction. SMRs may only be at the development stage, but the Agency says that of the 50 or so concepts globally, four are in advanced stages of construction.

The World Nuclear Association says nuclear power is a safe means of generating electricity, and that the risk of accidents at plants is low and declining.

But anti-nuclear campaigners say the high cost of nuclear means the money would be better spent on renewables and energy efficiency.

The global market for SMRs is expected to be worth up to $300 billion by 2040, partly because they are regarded as making nuclear energy accessible to more countries. But can SMRs be built quickly enough to meet our future energy needs, and will the technology deliver?