Small modular reactors (SMRs): what they are, how they work, and what they are good for

How do SMRs work?

SMRs are based on the same principle as any nuclear power plant: nuclear fission.

Fission is a process in which the nuclei of heavy atoms—such as uranium—are split, releasing a large amount of energy in the form of heat.

This heat is used to warm a fluid, which then drives a turbine connected to a generator. That's how electricity is generated.

So, what makes SMRs special? Their size, design, and safety.

Unlike traditional reactors, SMRs are more compact and can be mass-produced, which helps lower costs, shorten installation times, and improve quality.

In terms of safety, they represent a major step forward. Many SMRs include passive cooling systems. Therefore, in the event of a failure, the reactor can cool itself down without human intervention or external electricity.

Additionally, they are designed to be scalable. Multiple modules can be installed at the same site depending on the electricity demand. Need more energy? Just add another module.

Advantages of SMRs

• Improved safety: SMRs are equipped with passive safety systems that allow them to self-regulate without human intervention in emergencies. This would minimise the risk of accidents and simplify daily operation.
• Modular flexibility: their modular design allows for the installation of one or several reactors depending on energy needs. This scalability makes them ideal for supplying both small ommunities and large industrial hubs.
• Lower cost: since they are mass-produced in specialised facilities, construction and maintenance costs are reduced.
• Lower environmental impact: they do not emit greenhouse gases when operating, making them a clean and sustainable alternative. They can also be integrated into an energy system that combines various low-carbon technologies.
• Improved quality: overall quality is increased because operations at the site are minimised. A factory offers better quality than a construction site.
• Access to remote areas: thanks to their size and versatility, SMRs can deliver power to isolated regions or areas with limited infrastructure.
• Compatibility with renewable sources: the goal is not to replace solar or wind energy, but to complement them. Their ability to produce continuous power allows them to work in tandem with renewable sources. Moreover, some designs incorporate molten salt energy storage, which enables flexible operation.

Current status of SMRs around the world

Several countries are already investing in this technology. The United States, Canada, Argentina, Russia, the United Kingdom, and Romania are developing pilot SMR projects, some of which are already under construction.

One real-world example is the floating plant Akademik Lomonosov, which began generating electricity in December 2019 for an isolated grid in Chukotka, a remote region in eastern Russia.

A few months earlier, in June, the operating company Rosenergoatom received a ten-year license from the Russian nuclear safety authority, Rostekhnadzor.

Another notable example is the HTR-PM in China, the world’s first high-temperature gas-cooled modular reactor which entered commercial operation in December 2023.

Located in the Shidao Bay plant in Shandong Province, this project features two 250 MWt reactors powering a 210 MWe turbine that uses helium as a coolant and graphite as a moderator.

Institutional support is vital for  these processes: the International Atomic Energy Agency (OIEA) has created a dedicated platform to foster the safe and sustainable development of these reactors.

The European Union and organisations such as the OECD have also expressed interest in SMRs as a solution to meet climate targets and strengthen energy security.

Although their deployment is still in its early stages, there is a clear consensus: SMRs represent a strategic tool for moving toward a cleaner, safer, and more affordable energy system for all.