The Fourth of July this summer marks not only the 250th anniversary of the United States, but also the deadline for 10 nuclear companies vying to develop small and more advanced reactors to reach what the industry calls “criticality.”
Criticality — more on that below — is a key step in the development of any nuclear reactor, and is being used by the Trump administration as a milestone for the development of more advanced nuclear energy technologies that could change the energy sector.
Unlike the decades-old reactors now operational, advanced nuclear reactors use fewer components, employ alternative cooling systems to run at higher temperatures, and can be built on a much smaller scale for rapid deployment.
The Trump administration is hoping to utilize these quick-to-power reactors as it looks to shore up energy security and meet the surging demand caused by advancements in artificial intelligence and defense operations, in order to get ahead of China in the AI race.
With a slew of nuclear energy-focused executive orders last May, President Donald Trump called for at least three reactors to reach criticality by Independence Day of this year.
But what does mean for a reactor to hit criticality?
Defining criticality
Reaching criticality means a reactor is perfectly stable and its nuclear chain reaction is self-sustaining.
This means the atoms splitting in the core of the nuclear reactor are able to produce enough neutrons to continue sustaining additional reactions that produce energy.
As a reactor is built and commissioned for demonstration or commercial purposes, achieving criticality is crucial to prove that the reactor can operate and is safe.
There are approximately five main stages a reactor must reach before it can be fully operational, starting with what is called “subcritical.” In this stage, the reactor’s chain reaction is not self-sustaining, the atoms are not splitting constantly, and control rods are still fully inserted to the reactor.
The Idaho National Laboratory has compared this stage to when a car is parked with the parking brake fully engaged.
The second stage is “approaching critical,” meaning the control rods are withdrawn in a careful manner, the nuclear fission reaction is triggered, and the reactor moves closer to a steady sustaining reaction.
In the car analogy, this would be when the vehicle has the brake pedal released and ignition turned, but the engine has not yet begun to run.
Zero-power criticality marks the third stage. Minimal heat is generated during this step, meaning no coolant is needed for the reactor. Think of it like a car running with a cold engine.
Next, a reactor moves to “low-power criticality.” Cooling systems are brought in and the reactor hits near-normal, if not normal, operating temperatures for the self-sustained reaction needed to produce energy.
The Idaho National Laboratory compares this stage to when a car is running idle, with a fully warm engine.
Finally, the fifth stage is when the nuclear reactor is at full power and able to produce energy under controlled conditions. In other words, the car is driving on the road as it should.
Supported by the Department of Energy
Last year, Trump set a highly ambitious timeline for three small modular reactors to achieve criticality within one year. It is a part of the administration’s broader goal of rapidly expanding nuclear energy in the U.S., with the aim of quadrupling nuclear energy capacity by 2050.
Many within the industry were unsure if developers would be able to deliver, as there are no SMRs operational in the U.S.
Advanced reactors such as SMRs traditionally have a smaller footprint, generating around 300 megawatts of power. For comparison, one megawatt can usually produce enough electricity to power 400 to 900 homes.
The smaller footprint, in theory, allows SMRs to be built closer to local grids on an accelerated timeline.
Given how reliable nuclear energy is compared to alternative resources, SMRs and other advanced reactors have become an extremely attractive option for the administration as it seeks to meet surging electricity demand associated with the AI race.
To accelerate the innovation of these advanced nuclear technologies, the Department of Energy launched its Reactor Pilot Program.
This program leverages the Energy Department’s authority to approve nuclear reactor authorizations for research, development, and demonstration purposes.
The idea is that, by streamlining and simplifying the agency’s approval process for test reactors, the administration will be able to provide information to the Nuclear Regulatory Commission that is needed for federal approvals of SMRs and other reactors meant to operate commercially — such as reactor criticality.
Last August, 10 companies and 11 projects were selected to participate in the pilot program. And as of mid-June, the industry is on track to hit Trump’s ambitious timeline.
Who’s achieved criticality so far
The first small modular reactor being developed under the pilot program hit criticality one month before the deadline.
The Department of Energy announced on June 4 that an advanced reactor being built by Antares Nuclear achieved criticality.
The agency said at the time that Antares’s design, known as Mark-0, successfully completed a zero-power fueled demonstration at the Energy Department’s Idaho National Laboratory.
Antares expects to have its advanced reactors producing electricity by 2027, and plans to deploy the reactors at U.S. military installations in 2028.
A second advanced reactor achieved criticality on June 18.
The reactor, known as the Ward 250, is also being developed under the administration’s pilot program and is being built by Valar Atomics.
THE MAN LEADING TRUMP’S NUCLEAR RENAISSANCE
Valar Atomics successfully completed a zero-power fueled criticality demonstration at the Utah San Rafael Energy Lab, marking the first reactor authorized by the Department of Energy to be built outside of a national lab.
Several other developers that are part of the pilot reactor program are hopeful they too will hit the July 4 deadline, including Aalo Atomics.
