SMR

by Sérgio Granato de Araújo

Small in size and with a simple integration plan, small modular reactors (SMR) are advanced nuclear reactors w/ a power capacity of up to 300 MWe per unit, which is about one-third of the generating capacity of conventional nuclear power reactors, although intermediates (btw 300 to 700 MWe) can be included in this classification [WNA, 2023].

This interest in small and medium nuclear power reactors is driven both by a desire to reduce the impact of capital costs and to provide power away from large grid systems [WNA, 2023].  More than 80 commercial SMR designs being developed around the world target varied outputs and different applications, such as electricity, hybrid energy systems, heating, water desalinization, and steam for industrial applications [IAEA, 2021].

Advantages of SMR [EG, 2021]

• Fuel Security: SMRs can store 2 years of fuel on-site, and in some cases, several decades’ worth.

• Ramp Up & Ramp Down: certain SMR designs, like that of NuScale Power, LLC (“NuScale”), allow for output to be varied over days, hours, or even minutes.

• Islanding: SMR can operate connected to the grid or independently.

• Black Start: SMR can start up from a completely de-energized state without receiving energy from the grid.

• Underground Construction: SMR can be built underground, making them less vulnerable to natural phenomena, EMP, and other intentional destructive acts.

Schematic of a SMR

A key feature of the SMR is that all the main components such as i) pressurizer, ii) steam generators, and iii) reactor coolant pumps are installed inside the reactor pressure vessel, as shown in Figure 1.

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Key players

• Westinghouse Electric Company LLC (USA) – AP300 SMR

• NuScale Power, LLC (USA) – VOYGR SMR

• GE Hitachi Nuclear Energy (GEH) (USA/Japan) – BWRX-300

• X-energy, LLC (USA) – Xe-100 (HTGR)

• Terrestrial Energy Inc. (Canada) – IMSR (Molten Salt Reactor)

• Moltex Energy Canada Inc. (Canada) – SSR-W (Molten Salt Reactor)

• Rolls-Royce SMR Ltd. (United Kingdom) – PWR-based SMR

• Rosatom State Atomic Energy Corporation (Russia) – RITM-200, KLT-40S

• China National Nuclear Corporation (CNNC) (China) – ACP100 (Linglong One)

• Korea Atomic Energy Research Institute (KAERI) / Hyundai E&C (South Korea) – SMART

SMRs in commercial operation 

As of Jan/2026, only two SMR projects are in commercial operation worldwide. In Russia, the Akademik Lomonosov, the world’s first floating nuclear power plant, has been supplying electricity & heat to the remote Arctic town of Pevek since May 2020, using two KLT-40S reactor modules rated at 35 MWe each. In China, the HTR-PM high-temperature gas-cooled reactor demonstration plant at Shidao Bay entered commercial operation in late 2023, delivering approximately 200 MWe from two modular reactor units.

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Micro-reactors 

On the other hand, micro-reactors are a subset of SMRs designed to generate electrical power typically up to 10 MWe, featuring ultra-compact designs, factory fabrication, and transportability, which make them particularly suitable for deployment in remote, isolated, or infrastructure-constrained regions, as well as for providing resilient backup power and replacing diesel-based generation.  As of Jan/2026, no commercial nuclear micro-reactors are in operation; all remain in demo, licensing, or early construction.

Figure 1: Schematic of a SMR