small modular reactor
What is a small modular reactor?
Where are operational small modular reactors located?
What are the advantages of small modular reactors over conventional nuclear reactors?
small modular reactor (SMR), any nuclear reactor designed to have a lower energy output and a relatively small physical footprint compared with those of a conventional nuclear reactor. SMRs are intended to be less expensive while also easier and faster to build than a typical nuclear plant. They can generate a peak load of up to 300 megawatts of electricity—which can power somewhere between 150,000 and 300,000 homes—whereas conventional nuclear reactors typically generate between 1,000 and 1,700 megawatts (see also nuclear power). So far, only three SMRs are operational, one in Russia (starting in 2020), one in China (starting in 2021), and one in Japan (a test reactor was brought online in 2024). Although there are no SMRs operating in the United States at present, several companies and electrical utilities plan to build them using a variety of designs, pending approval from U.S. regulatory bodies.
SMRs and conventional nuclear reactors have a similar design, with control rods, radiation shielding, coolant, and water as a working fluid (see also nuclear reactor); however, SMRs are made up of prefabricated modular components, which allows pieces of the reactor to be constructed and at least partially assembled off-site. These components are then transported to the installation location for final assembly. In contrast, conventional nuclear reactors require custom parts and processes and must be constructed on-site, which increases overall construction time and adds to the cost.
Applications
SMRs are attracting interest from power companies, governments, and high energy-consuming industries, such as AI data centers, because they could potentially add much-needed electricity to standing electrical grids quickly and cleanly (that is, without releasing carbon emissions). In addition, SMRs can be more easily integrated into the network of voltage transformers, transmission cables, and other energy infrastructure. Connecting a new source of power generation to the electric grid is a long bureaucratic process that sometimes requires upgrades to local electrical transmission infrastructure. SMRs have an advantage over their larger counterparts because connecting a 1,000-megawatt conventional nuclear reactor to the grid presents greater regulatory and logistical challenges than bringing a 300-megawatt reactor online. Conventional nuclear reactors also need to operate in areas with strong electrical grids. SMRs, on the other hand, can operate in areas with weaker grids or in rural areas away from conventional electrical grids.
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In addition, SMRs may be useful in powering decarbonization activities in industry. Some of these activities require high temperatures to catalyze chemical processes (see also chemical reaction), which nuclear reactors are mostly able to achieve without releasing greenhouse gas emissions. Although conventional nuclear reactors also generate heat that could be used in the same way, the size of SMRs is more in line with the energy needs of industrial facilities, and the smaller footprint of an SMR makes it more logistically possible to locate close to an industrial user. SMRs may be ideal for remote operations, since many decarbonization efforts take place far from the standing electrical grid. As decarbonization (and energy generation) operations scale up, additional SMRs can be brought online or “stacked” with one another to provide levels of power commensurate with the task.
Although SMRs are touted by some experts as being safer than conventional nuclear reactors, they still generate many of the same safety concerns. SMRs are vulnerable to natural disasters and weather- and climate-related events that can cut power used to control reactor operations or prevent the transmission of electricity from the reactor. Consequently, nuclear experts recommend backup power sources (such as diesel generators) to prevent an SMR from shutting down and causing an accident (see also Fukushima accident and Chernobyl disaster). In addition, since SMRs are powered by enriched uranium or plutonium, they contribute to the problem of radioactive waste.
Adoption
There is support for SMRs in the U.S. federal government. In March 2025 the Department of Energy reissued a $900 million program begun under Pres. Joe Biden to support the development and deployment of SMRs. The World Bank has also specifically mentioned supporting the development of SMRs. A number of companies and electrical utilities are working through various stages of the regulatory and permitting processes for SMR designs at the Nuclear Regulatory Commission (NRC). These include X-energy and Dow Chemical, which are seeking permits to build four 80-megawatt modules in Calhoun county, Texas, and NuScale Power, which became the first company to have its initial SMR design approved by the NRC in 2022; a later design was approved in 2025. In addition, the Tennessee Valley Authority submitted a construction permit in 2025 to build a small modular reactor in Oak Ridge, Tennessee.