Electric utilities in the United States currently operate about 98 GW of nuclear generating capacity, but very little nuclear capacity has been built in the last few decades. High capital costs and lengthy licensing and approval processes have limited the expansion of nuclear power. However, several companies are developing new small modular reactor (SMR) designs aimed at reducing capital costs and increasing siting flexibility to solve challenges associated with traditional nuclear power.

The generating capacity of a large-scale nuclear design typically ranges between 550 MW and 1500 MW per unit. By comparison, SMRs have a capacity of about 300 MW per unit or less. The main components of SMRs are modular, factory-assembled parts shipped to the plant construction site for installation, which could reduce construction times. Microreactors, a subset of SMRs, generally have a capacity of 20 MW or less and can operate on the electric grid, independently of the grid, or as part of a microgrid.

Aside from providing electricity to a power grid, SMRs and microreactors could power applications where large plants are not needed or sites that lack the infrastructure to support large units. SMRs are under consideration for powering artificial intelligence (AI) data centers, or other industrial activities where developers may not want or need to connect to the grid. SMRs could also serve remote areas and communities with high transmission and distribution costs.

SMR designs may employ light water as a coolant, or other non-light-water coolants such as gas, liquid metal, or molten salt. Several designs use high-assay low-enriched uranium (HALEU) fuel, which is uranium enriched between 5% and under 20% uranium-235, the main isotope that produces energy during a chain reaction. HALEU is more highly enriched than the sub 5% low-enriched uranium (LEU) fuel currently used in most nuclear reactors. The higher enrichment has a higher burn-up rate, which could improve efficiency and performance, allow smaller reactor footprints, and reduce spent fuel waste.

The US Energy Information Administration (EIA) reviewed specifications for commercial SMR and microreactor designs under development in the United States as of February 2026 and has compiled the following tables:

Light Water-Cooled Reactors

Light water-cooled SMR designs are typically smaller versions of existing large reactor designs that use the hydrogen in water as a moderator, slowing neutrons and increasing the likelihood of a fission event. In most cases, they are pressurized water reactors that use the type of low-enriched uranium fuel used in US reactors today and are intended to provide scalable baseload electricity to a traditional power grid.

Vendor	Design Name	Capacity (MWe)	Fuel
Deep Fission	Gravity Nuclear Reactor	15	LEU
GE Vernova Hitachi	BWRX-300	300	LEU
Hadron Energy, Inc.	Hadron MMR (Micro Modular Reactor)	10	HALEU
Last Energy	PWR-20 (Pressurized Water Reactor)	20	LEU
NuScale	NuScale Power Module	77	LEU
REPLOY Power, Inc.	Submerged Power System (SPS)	300	LEU
Rolls-Royce SMR Limited	Rolls-Royce SMR	470	LEU
SMR, LLC (Holtec)	SMR-300	300	LEU
Westinghouse	AP300 (Advanced Passive)	330	LEU

Data source: US Nuclear Regulatory Commission (NRC), Department of Energy, and company websites
Note: MW=megawatts electricity; LEU=low-enriched uranium, enriched to less than 4.95%, standard in currently operating reactors in the United States; HALEU=high-assay low-enriched uranium (enrichment above 4.95% and below 20%)

High-Temperature Gas Reactors

High-temperature gas reactor (HTGR) designs use graphite as a moderator and helium gas as a coolant. HTGRs can operate at very high temperatures, which could make them suitable for powering industrial processes that require high heat input, such as thermochemical processes using electrolyzers for hydrogen production. Some HTGRs are designed to use HALEU, and others are designed to use Tristructural Isotropic (TRISO) particle fuel, a fuel structure designed to be highly durable and withstand extreme temperatures that are well beyond the threshold of current nuclear fuels.

Vendor	Design Name	Capacity (MWe)	Fuel
General Atomics – Electromagnetic Systems	Energy Multiplier Module (EM2)	265	HALEU
General Atomics – Electromagnetic Systems	Fast Modular Reactor (FMR)	44	HALEU
NANO Nuclear Energy Inc.	KRONOS MMR (Micro Modular Reactor)	3.5–15	TRISO
NANO Nuclear Energy Inc.	LOKI MMR (Micro Modular Reactor)	0.01–3	TRISO
BWX Technologies, Inc.	Project Pele Mobile Nuclear Reactor	1.5	TRISO
Radiant Industries, Inc.	Kaleidos	1	TRISO
Terra Innovatum	SOLO Micro-Modular Reactor	1	LEU/HALEU
Valar Atomics	Ward 250	5	TRISO
X-Energy LLC	Xe-100	80	TRISO
X-Energy LLC	XENITH	3–10	TRISO

Data source: US Nuclear Regulatory Commission (NRC), Department of Energy, and company websites
Note: MW=megawatts electricity; LEU=low-enriched uranium, enriched to less than 4.95%, standard in currently operating reactors in the United States; HALEU=high-assay low-enriched uranium (enrichment above 4.95% and below 20%) 

Molten Salt Reactors

Molten Salt Reactor (MSR) designs use molten salts to serve as the reactor fuel and/or coolant. MSRs can generally be categorized as either reactors with nuclear fuel dissolved in a molten salt or reactors using solid fuel with molten salt as a coolant. When molten salts act as both fuel and coolant, a fissile material, such as uranium or plutonium, is dissolved directly into a molten fluoride or chloride salt coolant. They operate at high temperatures and, like HTGRs, can be used for electricity generation and heat for industrial processes.

Vendor	Design Name	Capacity (MWe)	Fuel
Kairos Power, LLC	Kairos Power Fluoride High-temperature Reactor (KP-FHR)	75	TRISO
Natura Resources	Molten Salt Reactor (MSR-1 / MSR-100)	1 / 100	Molten Fissile Salt
TerraPower, LLC	Molten Chloride Fast Reactor (MCFR)	N/A	Molten Fissile Salt
Terrestrial Energy USA INC	Integral Molten Salt Reactor (IMSR)	195	LEU

 

Data source: US Nuclear Regulatory Commission (NRC), Department of Energy, and company websites
Note: MW=megawatts electricity; LEU=low-enriched uranium enriched to less than 4.95%, standard in currently operating reactors in the United States; TRISO=tristructural isotopic particle fuel fabricated from HALEU; Molten fissile salt=molten salted mixed with uranium 235, uranium 233, or plutonium

Sodium-Cooled Reactors

Sodium-cooled reactor (SCR) designs use liquid metal (sodium) as a coolant instead of light water, which is typically used in operating nuclear reactors. These designs allow the reactor to operate at higher temperatures and lower pressures, potentially improving efficiency. They also potentially allow for a greater portion of the fuel to be used or burned inside the reactor vessel.

Vendor	Design Name	Capacity (MWe)	Fuel
Aalo Atomics	Aalo-1	10	LEU
ARC Clean Technology	Advanced Reactor Concepts (ARC-100)	100	HALEU
Oklo Inc.	Aurora Powerhouse	75	HALEU
TerraPower & GE – Hitachi Natrium	Natrium	345	HALEU

 

Data source: US Nuclear Regulatory Commission (NRC), Department of Energy, and company websites
Note: MWe=megawatts electricity; LEU=low-enriched uranium enriched to less than 4.95%, standard in currently operating reactors in the United States; HALEU=high-assay low-enriched uranium (enrichment above 4.95%); TRISO=tristructural isotopic particle fuel fabricated from HALEU 

Other Designs

Vendors with designs not readily classified in the preceding categories are also engaged in pre-application activities with the Nuclear Regulatory Commission (NRC).

Vendor	Design Name	Capacity (MWe)	Fuel
Antares Nuclear, Inc.	R-1 Microreactor	N/A	TRISO
Deployable Energy	Unity Nuclear Battery (UNB)	1.0	LEU
Westinghouse	eVinci	0.2–5	TRISO

Data source: U.S. Nuclear Regulatory Commission (NRC), Department of Energy, and company websites
Note: MWe=megawatts electricity; LEU=low-enriched uranium enriched to less than 4.95%, standard in currently operating reactors in the United States; HALEU=high-assay low-enriched uranium (enrichment above 4.95%); TRISO=tristructural isotopic particle fuel fabricated from HALEU 

Looking Ahead

Federal government support for domestic SMR technology has increased. In March 2025, the US Department of Energy (DOE) reissued a tender for US$900 million in federal funding to promote SMR development. In June 2025, the DOE announced the Energy Reactor Pilot Program. The program aims to expedite the testing of advanced reactor designs authorized by the department at sites outside the national laboratories. Applicants are responsible for funding their individual pilot reactor designs, but the program is intended to support further private funding and provide a fast-track approach to licensing. The DOE has selected the following vendors for the program: Aalo Atomics Inc.; Antares Nuclear Inc.; Deep Fission Inc.; Last Energy Inc.; Oklo Inc.; Natura Resources LLC; Radiant Industries Inc.; Terrestrial Energy Inc.; and Valar Atomics Inc.

The US military is in the process of adopting commercial microreactors. In 2024, the Defense Innovation Unit, with the Department of the Army and the Department of the Air Force, launched the Advanced Nuclear Power for Installations program.

In April 2025, the following eligible vendors were named for the program: Antares Nuclear Inc.; BWXT Advanced Technologies LLC; General Atomics Electromagnetic Systems; Kairos Power LLC; Oklo Inc.; Radiant Industries Inc.; Westinghouse Government Services; and X-Energy, LLC.

In October 2025, the Department of the Army announced the launch of the Janus Program, aimed at building microreactors. The Janus Program will build upon Project Pele, a transportable nuclear reactor intended for electricity production. The DOE laboratory that worked on Project Pele will also work on the Janus Program.

As part of the next steps for the Janus Program, the Department of the Army has selected nine bases for possible microreactor siting. These installations include Fort Benning, Fort Bragg, Fort Campbell, Fort Drum, Fort Hood, Fort Wainwright, Holston Army Ammunition Plant, Joint Base Lewis-McChord, and Redstone Arsenal.

The Department of the Air Force is planning its first nuclear microreactor at Eielson Air Force Base in Alaska, as part of a pilot program with Oklo Inc., selected as the vendor for its sodium-cooled Aurora design reactor. The project will be commercially owned and operated and aims to deliver 1 MW to 5 MW of electricity by 2027.

The Department of the Navy has used advanced nuclear reactors to power aircraft carriers and submarines since the 1950s, but is also soliciting offers for commercial on-site SMRs and microreactors to power its installations.

The EIA has also compiled a list of advanced nuclear reactor designs currently under construction as pilots or demonstration projects, as well as planned projects for future development.

Small Modular Reactor Future Development Projects

Project	Design Name	Number Of Units	Total Capacity (MWEe)	State	Status
Aalo-X	Aalo-1	1	10	Idaho	Under Construction
ACU Molten Salt Research Reactor	Molten Salt Reactor (MSR-1)	1	0.3	Texas	Under Construction
Molten Chloride Fast Reactor Experiment	Molten Chloride Fast Reactor (MCFR)	1	N/A	Idaho	Under Construction
Oklo Aurora Reactor Pilot Program	Aurora Powerhouse	1	75	Idaho	Under Construction
Project Pele U.S. Army	Project Pele Mobile Nuclear Reactor	1	1.5	Idaho	Under Construction
Utah San Rafael Energy Lab Valar Demonstration	Ward 250	1	5	Utah	Under Construction
Hermes Low Power Demonstration Reactor	KP-FHR	1	N/A	Tennessee	Under Construction
Hermes 2	KP-FHR	2	20	Tennessee	Planned
Antares Demonstration Project	Mark-0	1	N/A	Utah	Planned
eVinci Demonstration Microreactor	eVinci	1	0.2–5	Idaho	Planned
Illinois Microreactor Demonstration Project	KRONOS MMR	1	15	Illinois	Planned
Penn State FRONTIER Program	eVinci	1	0.2–5	Pennsylvania	Planned
Project TETRA	IMSR	1	N/A	Utah	Planned
Radiant Kaleidos Demonstration Unit (KDU)	Kaleidos	1	1	Idaho	Planned
Last Energy Texas A&M Rellis Pilot Project	PWR-20	1	5	Texas	Planned
Kemmerer Power Station Unit 1	Natrium	1	345	Wyoming	Planned
Clinch River Nuclear Site	BWRX-300	1-4	300–1200	Tennessee	Planned
Deep Fission – Kansas	Gravity Nuclear Reactor	1	15	Kansas	Planned
Duke Energy Belews Creek	Unspecified small reactor	1	300	North Carolina	Planned
Cascade Advanced Energy Facility Energy Northwest	Xe-100	12	960	Washington State	Planned
Joshua Falls SMR Project	Unspecified small reactor	1	N/A	Virginia	Planned
Pioneer Units 1 and 2	SMR-300	2	600	Michigan	Planned
Last Energy Haskell Project	PWR-20	1	20	Texas	Planned
Long Mott Generating Station	Xe-100	4	320	Texas	Planned
ENTRA1 TVA Facility	NuScale Power Module	12	600	Tennessee	Planned
Joint Base Anacostia-Bolling U.S. Air Force	KRONOS MMR	1	15	Washington D.C.	Planned
Radiant U.S. Air Force	Kaleidos	N/A	1	N/A	Planned
Janus Projects (Fort Benning, Bragg, Campbell, Drum, Hood, Wainwright, Holston, Lewis-McChord, Redstone)	Design not specified	N/A	N/A	Various (GA, NC, KY/TN, NY, TX, AK, TN, WA, AL)	Planned

 

Data source: US Nuclear Regulatory Commission, Department of Energy, Department of War, and company websites

About The Authors

Slade Johnson and William Walsh are research analysts with the US Energy Information Administration