Top SMR developers in 2026, ranked by what they've actually built

The best SMR developer of 2026 is the one pouring concrete: GE Vernova Hitachi, whose BWRX-300 is in construction at Darlington with an operating licence application already filed. TerraPower and Rolls-Royce SMR complete the podium. This ranking scores the 127-design field on hard evidence only — construction starts, licences in hand, and firm, funded orders — not renderings or memoranda of understanding.

Key facts

• The NEA counts 127 SMR designs worldwide; fewer than a dozen have steel in the ground or an application in formal regulatory review
• Ranking criteria, in order of weight: nuclear construction underway, licences granted, licence applications docketed, firm funded orders, fuel-supply readiness
• Two Western SMR-class plants are in nuclear construction: Darlington's BWRX-300 and TerraPower's Natrium
• Four DOE-authorized microreactors reached first criticality by July 4, 2026
• Data as of August 5, 2026; every status below links to a primary source

1. GE Vernova Hitachi — BWRX-300

The only developer with a Western SMR in construction and an operating licence application on file. Unit 1 of four at OPG's Darlington site in Ontario is in civil construction with first power targeted for the end of 2030, and OPG has applied to the CNSC for a 20-year operating licence. The order book is the deepest in the field: TVA's Clinch River construction permit cleared its NRC safety evaluation in June 2026, and Poland's Orlen Synthos has applied for state backing for 14 units across three sites — the first phase of a program targeting 26. The BWRX-300 also cleared UK GDA Step 2 in December 2025. Its edge is boring on purpose: standard fuel, boiling-water heritage, and repetition.

2. TerraPower — Natrium

The most advanced advanced reactor. Natrium — a 345 MWe sodium-cooled fast reactor with molten-salt storage that flexes to 500 MWe — holds the NRC's first modern commercial fast-reactor construction permit (March 2026) and began nuclear construction at Kemmerer, Wyoming on April 23, 2026. The pipeline hardened this year: a January agreement with Meta covering up to eight plants for data centers, PacifiCorp expansion units in its resource plan, and UK GDA entry. The watch item remains HALEU fuel, which TerraPower is chasing down four parallel supply tracks. It ranks behind GVH only because first-of-a-kind risk still sits between Kemmerer and a fleet.

3. Rolls-Royce SMR

The biggest balance sheet behind any Western SMR program. In April 2026 Rolls-Royce SMR signed the delivery contract with Great British Energy - Nuclear for three 470 MWe units at Wylfa in Wales, backed by over £2.5bn of UK government commitment and a National Wealth Fund loan facility. It is the only design in active Step 3 of the UK's Generic Design Assessment, and ČEZ signed early-works contracts in April for up to six units at Temelín in Czechia. No nuclear construction yet — which is the only reason it isn't higher.

4. Oklo

Nobody has moved faster from dirt to authorization. Oklo's Groves Isotope Test Reactor in Lockhart, Texas received DOE startup authorization on July 23, 2026 — fuel loading and first criticality cleared just over ten months after groundbreaking (NNN's coverage). Its Aurora-INL plant broke ground in September 2025, and the NRC approved its principal design criteria in half the usual review time in May 2026. The caveat that keeps Oklo at four: everything built so far runs under DOE authorization on federal or private land, and the NRC combined licence for commercial Aurora plants is still ahead of it.

5. X-energy

The quiet supply-chain leader. The Xe-100 construction permit for Dow's Seadrift, Texas site cleared its environmental review in May 2026 with the final NRC safety evaluation due in November — and X-energy's TRISO-X subsidiary holds the first-ever NRC Part 70 licence for HALEU fuel fabrication, a 40-year licence for its Oak Ridge plant granted in February 2026. Amazon anchored a ~$700m raise targeting more than 5 GW of Xe-100 projects, including the Cascade project with Energy Northwest in Washington state. Owning your fuel plant is a moat nobody else in this list has.

6. Kairos Power

The iteration machine. Hermes 1 has been in safety-related construction at Oak Ridge since May 2025, and Kairos broke ground on the two-unit Hermes 2 plant in April 2026 — the first power-producing Gen IV reactor with an NRC construction permit, and the first deployment under its 500 MW master agreement with Google, delivered via TVA's grid. Kairos builds test hardware in-house and treats each unit as a learning cycle; its NRC reviews keep finishing early. What it lacks is a commercial-scale order book.

7. NuScale / ENTRA1

Still the only company with NRC-approved SMR designs — the 50 MWe module certified in 2023 and the uprated 77 MWe US460 approved in May 2025. The long-awaited first project finally firmed up in February 2026 when Romania's RoPower took a final investment decision on the six-module, 462 MWe Doicești plant. ENTRA1, its commercialization partner, is working with TVA on planning for up to 6 GW. The gap between paper leadership and construction leadership is the story of NuScale's decade; Doicești is its chance to close it.

8. Holtec

A licensing two-track. Holtec filed the first phase of its SMR-300 construction permit for the Palisades site in Michigan on the last day of 2025, and the NRC opened the environmental review in June 2026 — on the same campus as the restarted Palisades large reactor. In the UK it completed GDA Step 2 in March 2026 and is pursuing the ~$11bn privately-financed Cottam project. Holtec's differentiator is the restart-plus-newbuild combination; its constraint is that no SMR-300 construction has started anywhere.

9. Westinghouse — AP300

Still the field's biggest paper tiger, honorably. The AP300 packages proven AP1000 passive safety into 300 MWe, but it remains in NRC pre-application three years in, and its once-stated 2027 design-certification target has not been reaffirmed. An August 2026 pact with Amentum aims squarely at accelerating NRC approval. Westinghouse's nuclear muscle is currently pointed at AP1000s — including the DOE-backed 10-unit program — which is rational, and exactly why the AP300 ranks ninth. See how it stacks up in BWRX-300 vs AP300 vs Natrium.

10. The microreactor insurgents — Aalo, Antares, Valar, Radiant, Last Energy

The DOE Reactor Pilot Program produced 2026's most startling stat: four test reactors reached first criticality by July 4 — Antares' Mark-0, Valar Atomics' Ward 250, Deployable Energy's Unity and Aalo's Aalo-X, months from groundbreaking to neutrons. These are zero-power test units under DOE (not NRC) authorization, so they aren't yet commercial plants — but as a class they compressed the build-learn cycle from a decade to a year. Radiant's Kaleidos is fueled and awaiting full-power testing at Idaho's DOME test bed; Last Energy is piloting at Texas A&M. One of these names will be on next year's top five.

Side by side

How to read this ranking

Construction beats certification, and certification beats announcements — that's the whole methodology. It is why NuScale, with the field's only approved US designs, sits below five companies with fewer approvals and more concrete. For the broader context — what counts as an SMR, and why serial production is the entire economic bet — start with the complete SMR guide, then the running list of every US nuclear plant under construction. This page is refreshed quarterly; statuses above are dated August 2026.