U.S. Nuclear Acceleration Effort Hits Big Milestone with Second Successful Criticality Test
Ward 250’s success confirms Trump nuclear push is delivering hardware, not just headlines.
Legal Insurrection recently reported that American energy development cleared a major technical hurdle after Antares Nuclear’s Mark-0 microreactor achieved zero-power criticality under the Department of Energy (DOE) Reactor Pilot Program (RPP).
The successful test marked the first advanced reactor to meet the ambitious July 4, 2026, deadline set by President Trump’s 2025 executive order to accelerate next-generation nuclear deployment.
Now, there is another.
Valar Atomics’ Ward 250 advanced reactor is now officially the second major success under the RPP, after the reactor completed a zero‑power fueled criticality demonstration at the San Rafael Energy Lab in Emery County, Utah.
Valar Atomics announced that its Ward 250 nuclear reactor has reached self-sustaining criticality and completed zero-power testing in a Utah energy lab ahead of the July 4 deadline.
President Donald J. Trump signed an executive order in May 2025 reforming nuclear reactor testing at the Department of Energy. As part of that order, Valar Atomics was given a deadline of July 4 to have an operating reactor on United States soil. This deadline has been met.
Ward 250 reportedly reached these milestones as a complete, fully integrated system configured for power operations.
Ward 250 is a Gen IV Reactor, which is the next phase of reactor development that targets improvements in safety, sustainability, economics, and proliferation resistance beyond current Gen II/III light‑water reactors. It is a TRISO (TRI-ISOtopic)-fueled modular high-temperature gas reactor (HTGR) that uses helium coolant, graphite-moderated cores, and ceramic TRISO particle fuel to produce very high temperatures in factory-built modules, with strong inherent and passive safety characteristics.
The firm’s goal is to power operation, not merely achieve criticality, by the July 4th deadline. The systems are reported to be in place to make it happen, which would be a significant leap forward for the RPP.
Ward 250, an HTGR rated at 100 kWt initial test power and scalable to 5 MWe, uses helium coolant and TRISO fuel particles in Advanced Gas-Cooled Reactor (AGR) compacts, according to an October 2025 Valar quality-assurance program description. The document says Ward 250 incorporates passive safety features and builds on WardZero prototype technology, while the co-located Valarin Fuel Fabrication Facility is designed to manufacture TRISO-coated particle fuel embedded in graphite compacts using German HOBEG technology with modern process improvements. Kiewit Nuclear Solutions served as the project’s engineering, procurement, and construction contractor.
“Criticality proves the physics; power operations prove the engineering,” Valar said. “Power operations require cooling, instrumentation, controls, advanced shielding, and power conversion to function together as a complete system. Ward 250 went critical with those systems integrated and in place.”
Valar received preliminary DSA approval in February 2026 and final DSA approval on April 23, which cleared the last design gate before DOE’s Operational Readiness Review. The company had said in May that its July 4 target was power operations, not zero-power criticality, calling that step “a massive leap in capability and complexity.”
Built in just nine months, Valar Atomics' Ward 250 reactor reached criticality in Utah under the DOE Reactor Pilot Program.https://t.co/FLzDHQClB4#AdvancedNuclear #Ward250 #NuclearCriticality pic.twitter.com/Osu2ny8VF4
— Interesting Engineering (@IntEngineering) June 20, 2026
The DOE noted this achievement, and this unit is the first DOE-authorized reactor built outside a national laboratory.
“Today marks another historic moment for America’s nuclear renaissance,” said U.S. Energy Secretary Chris Wright. “From the first-ever airlift of a small reactor aboard a U.S. military C-17 to successful zero-power criticality testing, Valar Atomics is delivering achievements that mark a revolutionary moment for advanced nuclear in this country. The Trump administration is proud to support the rebirth of America’s nuclear industry, ensuring Americans have access to affordable, reliable and secure energy for generations to come.”
In June, Antares Nuclear’s Mark-0 reactor achieved criticality at Idaho National Laboratory.
Beyond making Ward 250 the second advanced reactor to reach criticality under the federal timeline, DOE said the demonstration marks the first DOE-authorized reactor built outside a national laboratory.
US-backed Ward 250 nuclear reactor achieves criticality under DOE program in Utah | Aamir Khollam, Interesting Engineering
Valar Atomics achieved criticality with its advanced reactor just nine months after construction began at the Utah site.
The United States has reached… pic.twitter.com/n1N9semPoZ
— Owen Gregorian (@OwenGregorian) June 20, 2026
Valar Atomic CEO Isaiah Taylor and the firm’s Nuclear Officer Mark Mitchell offered a video introduction to their company, for those who are interested in more background:
Ward 250’s success underscores that Trump’s ambitious nuclear acceleration order is not just visionary rhetoric but an emerging reality, as next‑generation reactors move from paper designs to powered hardware on American soil.
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Comments
Excellent. I want one in my basement please.
I’d also like to know what the safety considerations are for each. Any one have any expertise with the technologies being employed?
I HEART Nuclear Power!!!
However, it uses graphite moderated cores, not water moderated. The Chernobyl RCMB-type reactors used graphite moderation which gave them a positive void coefficient which helped generate the explosion. However, it also states the core is helium-cooled, not water-cooled.
I’m not an expert here, and I’m sure they fully understand graphite moderation thingy. Let’s hear it for American engineers!!!!
Yeah the graphite part caught my attention. Besides Chernobyl there was another graphite fire at Windscale in UK. Much earlier though.
I just hope that these projects will be far enough along by 12/2028 so that they cannot be cancelled by the next administration. That is the typical fate of these sorts of things, just like at NASA.
Watch the vile, stupid and evil Dhimmi-crats suddenly ignore their decades of costly, irrational, infantile, fact-avers, energy independence-undermining and national security-undermining anti-nuclear power demagoguery, histrionics, agitprop and obstructionism, to suddenly try to claim credit for the American revival in nuclear power and Small Modular Reactor developments that are being advanced and funded by #47, the GOP and Big Tech.
Yeah, they will undoubtedly start singing the praises of narwal gas and coal fired plants.
natural gas, there’s no edit feature for fat fingers. LOL
Narwal gas? That’s a byproduct in the refining of whale oil, correct?
How far along would we have been if even a fraction of the 100s of Billions/Trillions(?) of dollars pi**ed away in the Green scams had been directed toward Nuclear and Clean Coal power?
When can I get one?
I have a small island on order, with contractors lined up for my Fortress, and a couple of CIWS for placement on the highest towers, and this is exactly what I need to power it all.
Barring that, it would be really nice to have one in my section of town to make our grid reliable and independent.
Fortress of Solitude? It’s been done.
This stuff should’ve been done thirty years ago.
All these wasted years the US had been hampered by the losers who want to stop all technology.
We should absolutely be ahead of the world in everything and yet weee playing catch up with China.
What a load of shit.
Evolutionary, not revolutionary. We need thorium fluoride molten salt reactors (MSRs). Inexpensive fuel, passive no-power emergency shutdown, small, operating a very high temperature (best for powering turbines) and low pressure (don’t require an over-built pressure vessel), and it produces a variety useful (and marketable) radionuclides.
I also see tech bros really love them some Tolkien. Palantir, Anduril (awesome), and now Valar. The first is magic communication device, the second a weapon, the last are Tolkien’s archangels.
This article is word salad. “Tri-isotopic light water” is an oxymoron. What idiot wrote this? Where is the propulsion? How do they define “criticality”?
Since this program is a Trump initiative be prepared for rogue judges and loony TDS Leftists trying to sabotage it.
Who would trust the Democratic Socialists of America with anything nuclear?
That’s just nuts.
I was born in the 1950’s and absorbed all the promises and terrors of the nuclear age. I literally was taught to hide under my school desk in case of nuclear attack. However I was also promised “electricity too cheap to meter.”
Now, an interesting parallel (interesting to me anyhow) is that telephone service and especially long distance telephone used to be very expensive (a dollar a minute when that was two and a half gallons of gas). Now even international calls actually are “too cheap to meter.”
I hope to live long enough to see the approach of “universal unmetered electricity” on the same line of unlimited data for the internet. You would pay a flat fee for access of course.
Of course it may not happen in my lifetime… I’m kind of resigned to the fact that I won’t ever get my flying car.
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