Small modular reactor

Small modular reactors (SMRs) are a class of small nuclear fission reactors, designed to be built in a factory, shipped to operational sites for installation and then used to power buildings or other commercial operations. The first commercial SMR was invented by a team of nuclear scientists at Oregon State University (OSU) in 2007.^[1] Working with OSU's prototype, NuScale Power developed the first working model, available to the US market, in 2022.^[2] The term SMR refers to the size, capacity and modular construction. Reactor type and the nuclear processes may vary. Of the many SMR designs, the pressurized water reactor (PWR) is the most common. However, recently proposed SMR designs include: generation IV, thermal-neutron reactors, fast-neutron reactors, molten salt, and gas-cooled reactor models.^[3]

Military specified small reactors were first designed in the 1950s to power ballistic missile submarines and ships (aircraft carriers and ice breakers) with nuclear propulsion.^[4] The electrical output for modern naval reactors are generally limited to less than 165 MW_e and dedicated to powering turboshaft props rather than delivering commercial electricity. In addition, there are many more safety controls absent from naval reactors due to the space limitations these reactors were designed for.

Commercial SMRs can be designed to deliver an electrical power output as low as 5 MW_e (electric) or a maximum of 300 MW_e per module. SMRs may also be designed purely for desalinization or facility heating rather than electricity. These SMRs are measured in megawatts thermal MW_t. Many SMR designs rely on a modular system, allowing customers to simply add modules to achieve a desired megawatt output (MW_e). Some SMR designs^[which?], typically those using Generation IV reactors technologies, aim to secure additional economic advantage through improvements in electrical generating efficiency from much higher temperature steam generation. Ideally, modular reactors are expected to reduce on-site construction, increase containment efficiency, and claim to enhance safety. However, other SMR manufacturers claim greater safety should come through the application of passive safety features that operate without human intervention. Passive safety is a concept already implemented in some conventional nuclear reactor types. SMRs should also help reduce power plant staffing costs, as their operation is fairly simple.^[5][6] and are claimed to have the ability to bypass financial and safety barriers that inhibit the construction of conventional reactors.^[6][7]

As of 2023, only China and Russia have successfully built operational SMRs. The US Department of Energy had estimated the first SMR in the United States would be completed by NuScale Power around 2030,^[8] but this deal has since fallen through after the customers backed out due to rising costs.^[9] There are more than 80 modular reactor designs under development in 19 countries.^[10] Russia has been operating a floating nuclear power plant Akademik Lomonosov, in Russia's Far East (Pevek), since October 2022. The floating plant is the first of its kind in the world. China's pebble-bed modular high-temperature gas-cooled reactor HTR-PM was connected to the grid in 2021.^[10]

SMRs differ in terms of staffing, safety and deployment time.^[11] US government studies to evaluate SMR-associated risks are claimed to have slowed the licensing process.^[12][13][14] One main concern with SMRs and their large number, needed to reach an economic profitability, is preventing nuclear proliferation.^[15][16]