The United States is actively pursuing the development of new nuclear reactor technologies, specifically small modular reactors (SMRs) and microreactors, aiming to overcome the challenges that have historically hindered the expansion of nuclear power. Traditional large-scale nuclear power plants, with generating capacities typically ranging from 550 megawatts (MW) to 1,500 MW per unit, have faced significant hurdles including high capital costs and protracted licensing and approval processes. SMR designs, generally offering a capacity of 300 MW per unit or less, are engineered to mitigate these issues. A key feature of SMRs is their modular construction, where main components are assembled in factories and then transported to the plant site for installation, a process that could substantially reduce construction timelines and costs.
Microreactors, a subset of SMRs, are even smaller, typically with a capacity of 20 MW or less. These units are designed for greater flexibility, capable of operating connected to the electric grid, independently, or as part of a microgrid. Beyond supplying electricity to the main grid, SMRs and microreactors are being considered for a variety of specialized applications. These include powering energy-intensive operations like artificial intelligence (AI) data centers or other industrial activities where direct grid connection might be undesirable or impractical. They also present a viable solution for remote areas and communities that face high transmission and distribution costs for conventional power delivery.
SMR designs exhibit diversity in their technological approaches, with some employing light water as a coolant, a technology familiar from existing U.S. nuclear reactors. Others are exploring non-light water coolants such as gas, liquid metal, or molten salt. A significant trend across several advanced designs is the utilization of high-assay low-enriched uranium (HALEU) fuel. HALEU is uranium enriched to a higher concentration, between 5% and under 20% uranium-235, compared to the sub-5% low-enriched uranium (LEU) currently used in most operational reactors. This higher enrichment level allows for greater "burnup," potentially leading to improved efficiency, smaller reactor footprints, and a reduction in spent nuclear fuel waste.
Light water-cooled SMR designs are often scaled-down versions of established large reactor models. They typically use water as both a coolant and a moderator, a substance that slows down neutrons to facilitate fission. Most of these designs are pressurized water reactors (PWRs), utilizing the standard LEU fuel found in current U.S. nuclear facilities. Their primary aim is to provide scalable, baseload electricity to the conventional power grid, leveraging proven technology in a more compact format. These designs are crucial for utilities looking to add nuclear capacity without the immense scale and complexity of traditional plants.
High-temperature gas reactors (HTGRs) represent another significant category of SMR development. These designs utilize graphite as a moderator and helium gas as a coolant. A key advantage of HTGRs is their ability to operate at extremely high temperatures. This characteristic makes them particularly well-suited for industrial processes that require substantial heat input, such as thermochemical processes used in hydrogen production via electrolyzers. Some HTGR designs are slated to use HALEU fuel, while others will employ Tristructural Isotropic (TRISO) particle fuel. TRISO fuel is engineered for exceptional durability, capable of withstanding temperatures far exceeding the limits of conventional nuclear fuels, enhancing safety and operational potential.
Molten salt reactors (MSRs) offer a distinct approach, using molten salts either as the reactor's fuel, its coolant, or both. In designs where molten salts serve dual roles, fissile material like uranium or plutonium is dissolved directly into a molten fluoride or chloride salt. MSRs operate at high temperatures, similar to HTGRs, and can be employed for both electricity generation and providing process heat for industrial applications. This flexibility in fuel and coolant options, combined with high-temperature operation, opens up new possibilities for nuclear energy's role in industrial decarbonization and energy production.
Sodium-cooled reactors (SCRs) differentiate themselves by using liquid sodium as a coolant, in contrast to the light water used in most existing nuclear reactors. This liquid metal coolant allows SCRs to operate at higher temperatures while maintaining lower pressures, which can lead to improved thermal efficiency. Furthermore, SCR designs potentially enable a greater fraction of the nuclear fuel to be utilized within the reactor vessel before requiring refueling, enhancing fuel economy and extending operational cycles. These characteristics position SCRs as a promising option for advanced nuclear power generation.
Beyond these primary categories, several vendors are developing reactor designs that do not fit neatly into the preceding classifications. These "other designs" are undergoing pre-application reviews with the U.S. Nuclear Regulatory Commission (NRC), indicating a broad spectrum of innovation in the advanced reactor space. The diversity of these approaches underscores the industry's effort to tailor nuclear technology to a wider range of applications and operational requirements, moving beyond traditional baseload power generation.
Government support for domestic SMR and microreactor technology has seen a notable increase. In March 2025, the U.S. Department of Energy (DOE) announced a $900 million federal funding initiative aimed at promoting SMR development. Further bolstering this support, the DOE launched the Energy Reactor Pilot Program in June 2025. This program is designed to accelerate the testing and deployment of advanced reactor designs at sites outside of national laboratories. While applicants are responsible for funding their specific pilot reactor designs, the program facilitates further private investment and offers a streamlined path to licensing, aiming to bring these technologies to market more rapidly.
The U.S. military is also actively integrating commercial microreactor technology into its operations. In 2024, the Defense Innovation Unit, in collaboration with the Department of the Army and the Department of the Air Force, initiated the Advanced Nuclear Power for Installations program. By April 2025, several vendors were identified as eligible participants for this program. The Department of the Army further advanced this initiative in October 2025 by launching the Janus Program, specifically focused on the construction of microreactors. The Janus Program builds upon the foundation of Project Pele, a transportable nuclear reactor project, and will involve the DOE laboratory that contributed to Project Pele.
As part of the Janus Program's next phase, the Department of the Army has identified nine potential installation sites for microreactors. These include prominent military facilities such as Fort Benning, Fort Bragg, Fort Campbell, Fort Drum, Fort Hood, Fort Wainwright, Holston Army Ammunition Plant, Joint Base Lewis-McChord, and Redstone Arsenal. Concurrently, the Department of the Air Force is planning its inaugural nuclear microreactor at Eielson Air Force Base in Alaska. This pilot project, in partnership with Oklo, Inc., will utilize the company's Aurora design, a sodium-cooled reactor. The project, expected to deliver between 1 MW and 5 MW of electricity by 2027, will be commercially owned and operated, marking a significant step in military adoption of advanced nuclear power.
The Department of the Navy, while already utilizing advanced nuclear reactors for its aircraft carriers and submarines since the 1950s, is also actively soliciting proposals for commercial on-site SMRs and microreactors to power its shore-based installations. This indicates a broad strategic interest across all branches of the U.S. military in leveraging advanced nuclear technologies for diverse energy needs, from tactical power to base resilience and modernization.
To support the burgeoning advanced reactor sector, the DOE Fuel Line Pilot Program plays a critical role by establishing a domestic nuclear fuel supply chain specifically for testing new reactor technologies. This program leverages the DOE's authorization processes to facilitate the construction and operation of nuclear fuel production facilities. By providing a fast-tracked pathway for fuel development and licensing, it aims to remove a key bottleneck in the deployment of SMRs and microreactors, ensuring that the necessary fuel is available for testing and eventual commercialization.
In summary, the United States is experiencing a surge in the development and potential deployment of small modular and microreactors. Driven by a combination of technological innovation, government support, and military interest, these advanced nuclear technologies are poised to address limitations of traditional nuclear power and offer flexible, scalable, and potentially more cost-effective nuclear energy solutions for a variety of applications, from grid-scale power to specialized industrial and military uses.
