What is an SMR?

We hear about them everywhere, without ever really knowing how to define them. While the term SMR, Small Modular Reactor, has recently entered common language, the concept of small nuclear reactors is, in fact, quite old. Today, the interest lies in their potential to replace coal-fired power plants and diesel/gas generators producing electricity globally. Moreover, these small units are well-equipped to decarbonize industries and hydrogen production.

SMR stands for “Small Modular Reactor.” They are considerably less powerful than currently operational reactors. The term “modular” refers to a construction method where modules are designed for mass production in factories, then transported and assembled on-site. The goal is to improve construction timelines, mitigate associated risks, and enhance competitiveness. Beyond technical features, SMRs introduce a new economic model.

Features of an SMR

While reactors in France have a power range of 900 to 1,450 MW, reaching 1,650 MW for the Flamanville EPR, SMRs range from 20 to 300 MWe. An SMR plant can adapt to needs by multiplying the number of reactors, also called modules.

When speaking of SMRs, we often refer to light-water reactors. In other words, these are miniaturized and optimized versions of current reactors, incorporating innovative systems not feasible in high-power reactors. They operate at a thermal spectrum – slowing down neutrons – without changing nuclear materials management like fast-neutron reactors.

From a safety standpoint, they adhere to third-generation standards, ensuring that the risk of external release is minimal or excluded in the event of an incident. Additionally, these reactors can be kept in a safe state without external intervention, utilizing natural physical phenomena such as convection or gravity. These concepts are borrowed from other reactors that also employ these natural phenomena. For instance, thermosiphon operation, akin to natural convection, is a safety procedure used in pressurized water reactors during incidental or accidental situations.


Small modular reactors are not intended to replace existing power plants but to complement the nuclear offering to contribute to decarbonizing the economy. Unlike large nuclear reactors, which are generally dedicated to electricity generation for the grid, SMRs aim to meet specific local needs for heat and/or electricity. This is referred to as multi-use. Due to their lower power, they can more easily integrate into smaller electrical grids near industries and isolated sites (islands, the Canadian Arctic, etc.), currently relying on fossil fuels, from small coal plants to diesel/gas generators.

It’s called cogeneration, when reactors are designed to produce heat and electricity simultaneously. This production mode is studied for supplying electrolyzers to produce low-carbon hydrogen, generating synthetic fuels, or providing industrial and urban heat.

Key Players in France and Worldwide

The flagship SMR project in France is Nuward, which has been led since 2023 by EDF’s eponymous subsidiary. Nuward originated from an initiative launched in 2019 by EDF, TechnicAtome, Naval Group, and CEA, with the addition of Tractebel and Framatome in 2022. All these entities contribute to the design of this 340 MWe SMR with two 170 MWe modules. While several units could be built in France, Nuward is primarily intended for export to replace highly greenhouse gas-emitting coal plants. The plant is designed for a lifespan of at least 60 years, with the first unit potentially starting construction in France in 2030, according to the industrial schedule.

Digital mock-up of Nuward, Source: EDF, NUWARD

In the rest of the world, the International Atomic Energy Agency (IAEA) lists over 90 SMR/AMR projects. Notable examples include Nuscale and GE-Hitachi in the United States, Rolls-Royce’s UKSMR in the UK, RITM-200 in Russia, ACP 100 in China, and KHNP’s i-SMR model in Korea.

SMRs vs. AMRs

It’s important to distinguish SMRs from AMRs (Advanced Modular Reactors). AMRs are also small modular reactors, but their technology differs from light-water reactors (pressurized or boiling). Instead, they employ fourth-generation technologies cooled by molten salts, helium, sodium, lead, etc. This umbrella term encompasses diverse technologies with various objectives, including providing heat beyond 500°C for industry and, for some, using nuclear materials from fuel reprocessing without relying on natural uranium resources. ■

By François Terminet (Sfen)

Photo: artist’s view of Nuward – @Nuward