Governments around the world are racing to develop small modular reactors (SMRs) as part of their plans for a nuclear power renaissance, and significant progress has been made in recent years. Among them, the United States appears to be leading the way in nuclear microreactor development, following a major investment in the technology recently announced by the U.S. Army.

SMRs are advanced nuclear reactors with a power capacity of up to 300 MW(e) per unit, roughly one-third of the generating capacity of a conventional nuclear reactor. Because they are much smaller than traditional plants and modular in form, they can be manufactured in factories and transported to their destination sites. Their reduced size allows them to be installed in locations unsuitable for larger reactors, and they are considerably cheaper and faster to build than conventional nuclear plants. SMRs can also be developed incrementally to match a site's growing energy demand.

A microreactor is smaller still than an SMR. A range of designs is currently under development in the United States, with the aim of launching the first versions within the next decade. These compact nuclear reactors will be small enough to be transported by truck, boat, or plane and could deliver significant quantities of clean energy directly to a site — a feature particularly useful for rural locations with no connection to the main power grid.

Like SMRs, microreactors will be produced and assembled in factories before being transported to a wide range of sites, reducing capital costs and accelerating production. They are expected to feature a simple, responsive design that allows them to self-adjust without requiring many specialised operators, and they will incorporate safety systems designed to prevent overheating or a reactor meltdown.

Most microreactor designs currently target between 1 MW and 20 MW of thermal energy, which can be used directly for heating or converted into clean electricity. They will run on a higher concentration of uranium-235 than is used in conventional reactors and can be connected to microgrids alongside renewable energy sources. Potential applications include emergency response following natural disasters. In addition, microreactors are expected to operate for up to 10 years without refuelling and can be quickly removed from sites and replaced with new units.

In the United States, the Department of Energy (DoE) supports a variety of advanced reactor designs, in line with President Trump's backing of a nuclear power resurgence. Trump has voiced support for a wide range of nuclear technologies — from conventional nuclear plants to SMRs and microreactors — with the aim of quadrupling U.S. nuclear power production by 2050. The push also aligns with growing electricity demand, as the rapid expansion of AI data centres has intensified interest in firm, around-the-clock clean power sources that can complement intermittent renewables.

In July, Texas-based Aalo announced that its Critical Test Reactor (CTR) had achieved criticality — the point at which a nuclear reactor is capable of sustaining a controlled, self-supporting chain reaction. "Our CTR went from groundbreaking to a sustained chain reaction in less than eight months — one of the fastest reactor builds in 80 years — and our company has gone from founding to fission in less than three years," Aalo said in a statement. The company is focusing on producing 10 MWe reactors for deployment in 50 MWe Aalo Pods to power AI data centres.

Beyond private-sector development, the U.S. Army has taken the lead in microreactor development in recent years, following Trump's Executive Order 14299 — Deploying Advanced Nuclear Reactor Technologies for National Security — which established the the Army as the lead agency for military nuclear energy efforts. The directive required the Army to create an official programme with a deadline of September 30, 2028, for an operational reactor at a domestic military installation. The effort builds on earlier Defence Department work in this area, including the Pentagon's Project Pele microreactor programme, and reflects the military's longstanding concern that many bases depend on the civilian grid, leaving critical installations exposed to outages.

In August, the U.S. Army announced plans to award up to $2.2 billion to five companies to construct new-generation microreactors at military bases across the United States. The deployment of these reactors will be supported by the federal easing of regulations for innovative reactor designs, part of a broader overhaul of the Nuclear Regulatory Commission's licensing framework for advanced reactors intended to shorten approval timelines.

The Army will provide financing to Antares Nuclear at Fort Bragg in North Carolina; BWX Technologies at Fort Campbell in Kentucky; General Atomics at Fort Hood in Texas; Radiant Industries at Fort Benning in Georgia; and Westinghouse Government Services at Fort Drum in New York, with the goal of deploying at least one microreactor by the third quarter of 2028. The selected companies will be expected to raise billions of dollars in private investment to support their development efforts.

Jeff Waksman, the principal deputy assistant secretary of the Army for installations, energy and environment, stated: "We believe that this will be the spear tip not just for microreactors but for all advanced reactors in the United States… There have been a lot of microreactor companies that have popped up recently, but we need to get them over the hump."

While much of the public discussion has centered on SMR development, the United States is also investing heavily in microreactor construction, aiming to launch the first reactors within the next two years. Whether the five selected vendors can meet the 2028 deployment deadline — and how their performance at military bases shapes subsequent commercial licensing — will be closely watched as the programme proceeds. Funding from the DoE, combined with supportive national policies and regulations, is expected to help advance development rapidly in the coming years.

By Felicity Bradstock for Oilprice.com