Breakthrough in Microreactors in the USA: Four Plants Reach Criticality

As MIT Technology Review reports (https://www.technologyreview.com/2026/07/09/1140235/nuclear-reactor-milestone-criticality/), four microreactors in the USA reached the so-called critical state on July 4, 2026 – a decisive step confirming that a nuclear reaction is running independently and stably. This event marks a significant advance for the American nuclear industry and underscores the role of small modular reactors (SMRs) as a promising technology for the energy supply of the future.

What does criticality mean?

Criticality is a technical term in nuclear engineering that describes the condition in which the chain reaction in a reactor proceeds in such a way that it sustains itself. This means the number of neutrons causing further fissions remains constant. This is a fundamental prerequisite for the safe and efficient operation of a nuclear reactor. Achieving this state in microreactors shows that these small plants can reliably fulfill their function.

Microreactors as a key technology

Microreactors are compact nuclear reactors with an electrical output of a few megawatts. They differ from traditional large reactors by their smaller size, mobility, and faster construction time. These characteristics make them particularly attractive for remote regions, military bases, or industrial facilities that require a stable and independent energy source.

The US government had already set the goal last year to bring at least three microreactors to criticality by mid-2026. That four plants have now reached this milestone shows that development is progressing faster than expected. This is also a signal to investors and energy providers that microreactors are becoming increasingly market-ready.

Importance for the energy transition

Nuclear energy plays a central role in decarbonizing the energy sector. Microreactors could help increase supply security, especially in combination with renewable energies such as wind and solar, which are weather-dependent. Due to their flexibility and scalability, they can balance fluctuations in the power grid and thus contribute to stability.

Furthermore, microreactors potentially offer lower construction costs and shorter approval times than traditional large power plants. This could improve public acceptance of nuclear energy and increase willingness to invest.

Challenges and outlook

Despite the progress, challenges remain. Safety issues, disposal of radioactive waste, and regulatory frameworks must continue to be carefully addressed. The US Nuclear Regulatory Commission (NRC) is simultaneously working on adapting its regulations to meet the specific requirements of microreactors.

Overall, the achievement of criticality in four microreactors shows that the USA is on the path to ushering in a new era of nuclear energy. The combination of technological progress and political will could lead to microreactors playing an important role in the energy mix in the coming years.

Context on regulation

Since June 30, 2024, binding rules for stable digital assets (stablecoins) have applied in the EU under the MiCA regulation, while since December 30, 2024, more comprehensive regulations for crypto-asset service providers have been in force. These regulatory developments demonstrate how technological innovations are increasingly accompanied by clear frameworks – an aspect that also applies to nuclear energy when new technologies such as microreactors are introduced.

Why it matters: Reaching criticality in four microreactors is a milestone that underscores the technological maturity and potential of these plants. Microreactors could represent a flexible, safe, and low-CO2 addition to the energy mix and thus contribute to the energy transition. At the same time, the event shows how innovation and regulation must go hand in hand to successfully establish new technologies.