Atomic Criticality

The Dawn of Critical Fission Abundance

In the high desert of Idaho on June 4, an advanced reactor quietly achieved “criticality”; the moment a nuclear chain reaction sustains itself for the first time. Just two weeks later, on June 18 in the red-rock country of Utah lit up another fission core and it was the first ever built completely outside a national lab. These aren’t dusty government projects from the 1970s. They are built by nimble private teams racing against an ambitious national deadline, and they are ahead of schedule.

This is America’s fission future arriving faster than almost anyone expected.

The Machines That Are Changing the Game

Each company is attacking the old challenges of nuclear energy from a different angle, making reactors smaller, safer, faster to build, and more useful than ever before.

Antares Nuclear proved you can test the heart of a microreactor in record time. Their sodium heat-pipe design is like a super-efficient, self-regulating radiator that can’t easily overheat. It hit criticality at Idaho National Lab and is now on a clear path to start generating electricity next year perfect for powering a military base or a remote town without needing a massive power line.

Valar Atomics took it one step further: they built their helium-cooled Ward 250 reactor in Utah, airlifted parts across the country, and flipped it critical on June 18 at a brand-new site. These high-temperature reactors can produce both electricity and the intense heat factories need for steel, chemicals, or hydrogen. And because they’re compact and transportable, they can go where the need is.

Aalo Atomics is thinking like an iPhone factory: build modular sodium-cooled units in a gigafactory, ship them, and click them together on site. They’ve already unveiled their critical test hardware at Idaho and are sprinting toward the July 4 deadline so they can start powering hungry AI data centers with plug-and-play reactors.

Deep Fission has the coolest safety trick yet: drop the entire small reactor a mile underground. The earth itself becomes the ultimate shield. They just went public to fund the first borehole pilot and are partnering with data-center developers who need rock-solid, always-on power.

Meanwhile, bigger players are scaling up fast. Kairos Power broke ground in Tennessee on a salt-cooled reactor that runs so safely it can basically look after itself. TerraPower (backed by Bill Gates) just got the first-ever green light from regulators for its sodium reactor paired with giant molten-salt “batteries” that store heat for when the sun isn’t shining or demand spikes. Oklo is teaming up with Meta to build a 1.2-gigawatt campus in Ohio that will recycle old nuclear fuel so nothing goes to waste. X-energy is working with chemical giant Dow in Texas to deliver both electricity and the high-temperature steam factories crave. And NuScale is signing up for multi-gigawatt projects with utilities in Tennessee and Romania.

Even thorium and molten-salt designs, the ones that can run on an element three times more abundant than uranium and produce far less long-lived waste are getting attention. China is already breeding fuel inside a working reactor, while Western startups are racing to build factory-produced versions that could power entire communities with minimal refueling.

The fissile excitement isn’t just technical. These reactors can be built in factories like cars, delivered by truck or plane, and switched on in years instead of decades. They produce steady power 24/7, create high-paying jobs, strengthen energy security, and give us the clean abundance we need to run AI, desalinate water, make hydrogen, some tritium, and lift living standards everywhere.

Real Projects, Real Places, Real Timelines

Right now the map is lighting up:

• Idaho and Utah host the breakthrough test reactors (Antares and Valar) already running this month.

• Ohio will see Meta’s giant 1.2 GW campus with Oklo (pre-construction 2026, first power early 2030s).

• Wyoming’s Kemmerer site is preparing for TerraPower’s Natrium plant (construction ramping now, commercial power in the early 2030s).

• Texas is getting four 80-megawatt high-temperature units from X-energy for Dow’s chemical plant (late 2020s).

• Tennessee’s Oak Ridge is home to Kairos’s next demo, while NuScale plans are advancing for up to six gigawatts with the Tennessee Valley Authority — the largest single SMR commitment in the U.S.

Partnerships are everywhere: Meta and other tech giants are writing big checks and signing power contracts directly; chemical companies want the heat; the military wants portable, resilient micro-power; and utilities are teaming up for gigawatt-scale clean replacements for coal plants. Timelines have compressed from “maybe in the 2040s” to “first electricity in 2027, multiple plants online before 2030.”

The People and Policies Making It Happen

None of this velocity would exist without leadership that decided to stop waiting. President Trump’s May 2025 executive order created the Reactor Pilot Program with a visible deadline: get at least three new test reactors critical by America’s 250th birthday on July 4, 2026. Energy Secretary Chris Wright and the DOE team turned that order into action approving safety plans, releasing fuel, and cheering every milestone like coaches on the sidelines. Their message is simple: America can still do hard things fast.

Private leaders like the founders of Antares, Valar, Aalo, and the established teams at TerraPower, Oklo, Kairos, and X-energy are executing with urgency and transparency. They’re the ones turning regulatory green lights into actual steel and neutrons.

What Comes Next: A Fantastic Fission Future

Expect more “we did it” announcements before Independence Day. Then watch the first electricity flow in 2027, commercial plants multiply in the late 2020s, and thorium and advanced designs join the mix in the 2030s. Data centers will get their own dedicated clean power plants. Factories will run on high-temperature heat instead of fossil fuels. Remote towns and military bases will gain unbreakable energy independence. And the compounding effect will kick in: each success makes financing easier, supply chains stronger, and public confidence higher.

We stand at the beginning of an era where energy isn’t a constraint — it’s an engine of human progress. Cleaner air, more jobs, stronger security, and the power to dream bigger about everything from desalination to space colonization.

The reactors are waking up. The future is waking up with them. And it feels fantastic.