Three advanced nuclear reactors have now reached criticality on U.S. soil under a federal pilot program that compressed what typically takes years of regulatory review into a matter of months. Deployable Energy’s Unity became the third unit to hit the milestone, joining Antares Nuclear’s Mark-0 and Valar Atom in meeting a White House deadline that gave the Department of Energy (DOE) until July 4, 2026, to deliver at least three working experimental reactors. The speed of the effort raises a pointed question: whether the DOE-only authorization path can sustain safety standards while bypassing the traditional Nuclear Regulatory Commission (NRC) licensing process, and what happens to these machines after their initial startup.
An executive order set the July 4 deadline, and DOE just cleared it
The race traces back to Executive Order 14301, which directed DOE to bring at least three advanced reactors to criticality by Independence Day 2026. The order created the Reactor Pilot Program, a framework that lets DOE authorize experimental reactor startups at its own national laboratories without routing each project through the NRC’s multi-year licensing pipeline. That distinction matters because NRC reviews for new reactor designs have historically stretched across half a decade or longer, and the executive order explicitly sought to prove that small, experimental units could be tested faster under DOE’s existing safety authority.
Antares Nuclear’s Mark-0 was the first to cross the line. The reactor completed a zero-power fueled criticality demonstration at Idaho National Laboratory, making it the first advanced reactor startup recorded under the pilot program. Valar Atom followed as the second. Then Deployable Energy’s Unity achieved criticality as the third, which DOE announced as direct fulfillment of the executive-order target in a statement that it had met the presidential goal for three advanced reactors. Together, the trio allowed DOE to declare success against the numerical requirement laid out in the executive order.
All three demonstrations were zero-power or near-zero-power experiments, meaning the reactors sustained a controlled chain reaction but did not generate electricity. That is a standard early step in reactor commissioning, but it is far from the finish line. Generating usable heat or power requires additional testing phases that can take months or years, depending on the design and the safety case built around it. For now, the reactors are proof-of-principle machines that show their cores can go critical under tightly constrained conditions.
DOE’s test bed and safety approvals reveal the infrastructure behind the sprint
The physical infrastructure enabling this push sits at Idaho National Laboratory, where DOE operates the Demonstration of Microreactor Experiments facility, known as DOME. The test bed is a repurposed EBR-II containment structure originally built for the Experimental Breeder Reactor-II, and it supports experiments up to 20 MW thermal. That capacity is small by commercial power-plant standards but large enough to host the microreactor prototypes that the pilot program targets. Using an existing shielded building and support systems has allowed DOE to focus engineering effort on the reactors themselves rather than on greenfield infrastructure.
A parallel project at the same laboratory, the MARVEL microreactor, illustrates how DOE stages these startups. DOE approved a Preliminary Documented Safety Analysis (PDSA) for MARVEL’s initial criticality, authorizing a dry configuration that functions as a near-zero-power experiment. The PDSA process is DOE’s internal equivalent of an NRC safety review, but it is conducted under the department’s own regulatory framework rather than under the independent commission’s rules. That procedural split is the core tension in the current sprint: DOE can move faster precisely because it is both the project sponsor and the safety regulator, a dual role that critics of the approach have flagged as a structural weakness, even as supporters argue it is appropriate for contained, noncommercial tests at federal sites.
The NRC, for its part, tracks advanced reactor licensing activity on a separate timeline. Its 2026 advanced reactor highlights summary emphasizes design certifications, construction permits, and other milestones for reactors that are pursuing full commercial approval. That process runs on a different clock than DOE’s experimental authorizations. The two tracks will eventually need to converge if any of these pilot reactors, or their commercial successors, are to connect to the power grid and serve paying customers. Until then, the pilot units remain research assets, not power plants.
Post-criticality testing gaps and the road to actual power
Reaching criticality is a binary milestone: either the reactor sustains a chain reaction or it does not. But the steps that follow are graduated and less predictable. Each reactor must demonstrate safe operation at progressively higher power levels, prove that its cooling systems and fuel perform as designed under sustained conditions, and build a safety record sufficient to justify commercial deployment. None of the three pilot reactors have publicly disclosed detailed power-ramp schedules or target dates for generating electricity, and DOE has not published a unified test plan that would tie the experiments to specific performance benchmarks.
The absence of integrated NRC review during the experimental phase could extend these post-criticality stages. Any company that wants to commercialize a design tested under DOE authority will still need to obtain an NRC license before selling power. That means the safety data collected during DOE-supervised testing must eventually satisfy NRC standards, and if the two agencies’ requirements diverge on key points, developers could face rework. For example, a thermal-hydraulic limit that DOE deems acceptable for a short-duration test might not align with the conservative margins NRC expects for decades-long commercial operation.
Developers also face practical questions about fuel supply, remote monitoring, cybersecurity, and emergency planning that fall outside the narrow scope of initial criticality tests. A microreactor that operates safely at a DOE site with on-call experts and extensive backup systems may still need design modifications before it can be deployed at an industrial facility or remote community. Those changes, in turn, can trigger new rounds of safety analysis and potentially new licensing submissions.
What happens to the pilot reactors next?
The executive order set a clear numerical target, and DOE met it. Three reactors reached criticality before the July 4, 2026, deadline. What the order did not specify, and what no public DOE document has yet detailed, is how long the post-criticality testing phases will take, what metrics will define success beyond initial startup, or when these experimental machines might inform commercial reactor designs that the NRC can license for the grid.
In the near term, the pilot units are likely to remain in an experimental loop: short runs at low power, pauses for inspection and analysis, incremental hardware and software tweaks, and then repeat. That iterative cycle is normal for first-of-a-kind reactors, but it sits uneasily beside the political narrative of rapid deployment. Policymakers can point to the criticality milestones as evidence that advanced nuclear is moving, while the more technical work of qualifying materials, refining safety cases, and aligning with NRC regulations continues largely out of public view.
Longer term, the value of the program will depend on how effectively DOE and NRC translate experimental findings into licensable designs. If the agencies coordinate closely, data from the Mark-0, Valar Atom, and Unity could shorten future licensing reviews by resolving technical questions in advance. If they do not, developers may discover that their hard-won test results answer the wrong questions, forcing them to revisit key design choices just as they seek to scale up.
For now, the three advanced reactors at Idaho stand as both achievement and challenge. They demonstrate that, under DOE’s internal framework and with existing national lab infrastructure, new nuclear concepts can reach criticality on a compressed schedule. They also underscore how much work remains before any of these machines-or their descendants-can deliver reliable, regulated power to the grid. The next phase of the experiment will be less about racing a calendar and more about reconciling speed with the slow, methodical culture of nuclear safety that ultimately determines whether advanced reactors move from laboratory curiosities to everyday infrastructure.
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*This article was researched with the help of AI, with human editors creating the final content.
