Oklo Cleared for Test Reactor Startup as DOE Program's July Deadline Arrives
Antares and Valar Atomics hit criticality in June; Oklo's startup clearance completes the three-reactor July 2026 target set in Trump's March 2025 executive order.
The U.S. Department of Energy has authorized Oklo to proceed with its pilot reactor startup, the third company to reach that milestone under a March 2025 executive order that set July 2026 as the deadline for at least three advanced reactors to achieve criticality. The order's longer objective is to grow U.S. nuclear capacity from roughly 100 gigawatts to 400 GW by 2050, a goal that makes early-stage test successes essential groundwork.3,1
Getting three reactors to criticality by a specific date is one kind of milestone. Converting that into commercial operating capacity is another, and the gap between them is where most advanced reactor programs have historically stalled. Oklo's clearance puts it past the first gate; everything from this point is about speed and cost on the path to actual power generation.3
Antares Nuclear went first. Rigzone reported on June 10 (2026-06-10) that Antares had achieved initial criticality in a TRISO-fueled microreactor design, the first under the Trump administration program. The company said the result confirmed "the reactor can operate as designed." Valar Atomics followed on June 19 (2026-06-19), according to Power Magazine, when its Ward 250 high-temperature gas reactor reached self-sustaining criticality at Utah's San Rafael Energy Lab. Ward 250 is rated at 100 kilowatts thermal, scalable to 5 megawatts electric, with Kiewit Nuclear Solutions as engineering, procurement and construction contractor.3,4
Oklo has secured outside technical expertise for its pilot. Under a March 2026 agreement, Swedish nuclear firm Blykalla committed between $100 million and $200 million and 30 to 40 engineers to joint workstreams that include neutronics and thermohydraulics support for Oklo's DOE-authorized project, Power Magazine reported in May 2026. Blykalla is simultaneously seeking approval for up to 1.7 gigawatts of its own lead-cooled SEALER reactors in Sweden, and the U.S. collaboration gives it regulatory exposure that Sweden cannot yet provide domestically.1
Fuel supply was the harder problem. Oklo's reactor design runs on high-assay low-enriched uranium, known as HALEU, a fuel for which no commercial enrichment supply chain existed until recently. The National Defense Authorization Act of 2024 directed the DOE to help seed that market, and in January 2026 Centrus Energy secured a $900 million DOE contract to begin commercial HALEU production. When the deal was confirmed, Oklo shares rose 4 percent on Thursday (2026-06-18), while Centrus shares surged more than 12 percent, Yahoo Finance reported. Markets were closed Friday (2026-06-19) for Juneteenth. The asymmetric reaction reflected that HALEU enrichment capacity unlocks Centrus's core business model, while for Oklo it removes a supply constraint rather than generating revenue.5
Oklo's commercial case rests on AI data center demand. The company has signed partnerships with major operators in that sector, positioning its small reactors as baseload power for facilities where uptime carries a significant premium, according to reporting from June 2026. Whether those partnerships convert to firm power purchase agreements that support project financing has not been established by available data.2
The United States has accumulated nearly 100,000 metric tons of used nuclear fuel over six decades without a permanent disposal site, a Motley Fool analysis noted on July 15 (2026-07-15). Oklo's Aurora design is intended to eventually run on recycled spent fuel as feedstock, turning a stranded waste liability into reactor input. The economics of that closed cycle are not demonstrated at commercial scale, and the regulatory path for recycled fuel adds another layer of complexity to an uncertain development timeline.7
Nuclear equity performance in 2026 has been muted relative to 2025 highs. The Global X Uranium ETF was trading at $39.87 on Monday (2026-07-27), down 0.31 percent on the day. The sector broadly underperformed in the first half of the year after strong 2025 gains, per a July 8 (2026-07-08) market review. Test criticality events have registered positively but have not reversed the equity drift.6
The gap between test criticality and reliable grid power is where reactor programs stall. The $900 million HALEU supply investment and Blykalla's engineering commitment are both premised on Oklo bridging that gap faster than predecessors managed. Until a signed commercial offtake agreement appears, the next concrete signal worth watching is how quickly the company moves from startup authorization to measurable power output.3,5,1