Every Nuclear Plant Under Construction in the US in 2026

NNN's tracker currently shows one U.S. nuclear unit under construction: TerraPower's Natrium Demonstration (Kemmerer), a 345 MW net sodium-cooled fast reactor with molten-salt storage. The tracker milestone log records the NRC construction permit on March 4, 2026, TerraPower says nuclear construction began on April 23, 2026, and the current completion expectation is February 2031. That makes Kemmerer the only live U.S. build in the tracker right now.

Key facts

• NNN's tracker currently lists one U.S. unit under construction: Natrium Demonstration (Kemmerer) at Kemmerer Power Station in Wyoming.
• The unit is a 345 MW net sodium-cooled fast reactor with molten-salt storage.
• The tracker milestone log records the NRC construction permit on March 4, 2026, the first modern commercial non-light-water U.S. power reactor permit in more than 40 years.
• TerraPower says nuclear construction officially began on April 23, 2026.
• TerraPower's latest public completion expectation is February 2031, which matches the tracker's 2031 estimate.

What happened

The U.S. build list is not broad. It is a single row: Natrium Demonstration (Kemmerer). That row exists because TerraPower moved from permit to site work, and NNN's tracker turns those milestones into a current-state record instead of a press-release stack.

The March 4, 2026 permit matters because the DOE described it as the first construction permit ever issued by the NRC for a commercial non-light-water power reactor. The April 23, 2026 construction start matters because it moved the project out of the planning-only lane and into actual build mode.

That combination is why Kemmerer sits at the top of the U.S. tracker story in 2026. It is not just an advanced-reactor announcement. It is the one U.S. project where the paperwork, the site, and the construction status all line up in the same row.

The underlying hardware is straightforward to describe and hard to deliver: 345 MW net from a sodium-cooled fast reactor paired with molten-salt storage. TerraPower says the storage lets the plant ramp delivered power when the grid needs it, which is why Kemmerer has become the reference point for the coal-to-nuclear transition conversation.

Why it matters

A lot of nuclear commentary sounds like a pipeline when the reality is a pinch point. The U.S. new-build pipeline is tiny, and the tracker makes that visible. In mid-2026, the answer to "what is actually under construction in the U.S.?" is one project, one unit, one site.

That matters for suppliers, lenders, utility planners, and state policymakers because the difference between "supported" and "under construction" is everything. Support is cheap. Concrete is not. The tracker helps separate future possibility from present reality.

It also matters because the U.S. market still lacks a broad fleet of builds to compare against. If you want to know whether advanced reactors are becoming an industry instead of a talking point, count the sites that move from permit to nuclear work. Right now, Kemmerer is the clearest signal on the board.

For context, see Natrium, explained for the design itself and SMRs, explained for the broader category debate. The comparison piece BWRX-300 vs AP300 vs Natrium shows why Natrium is not a standard water-cooled SMR even though it sits in the same deployment conversation.

Background

This article is unit-level on purpose. NNN's tracker tracks reactor units, not plant-wide headlines, so the question is not "is there a nuclear site in the U.S.?" It is "which unit is actually under construction right now?" In 2026, the answer is Kemmerer Unit 1.

That distinction keeps the dataset honest. A site can be announced, permitted, licensed, or even in the middle of early work without being an active nuclear construction project. The tracker only moves a unit into under_construction when the build has crossed that line.

Kemmerer is also useful because it shows how the modern U.S. buildout is likely to unfold: one project at a time, with licensing, supply chain, and financing all needing to line up before a second domestic row appears. Until another project makes that jump, the U.S. construction map stays thin.

The image on this page shows the project as the DOE presented it, which is appropriate here because the story is about a public, visible build rather than a hidden design study. The broader lesson is simple: the nuclear industry is easier to talk about than to build, and the tracker is there to show which projects have crossed the line.

What's next

The next checkpoints are more site work, long-lead procurement, and supply-chain execution, with HALEU remaining the obvious watch item for Natrium. If TerraPower holds its current schedule, Kemmerer should remain the only U.S. unit under construction until another project clears licensing and starts nuclear work.

That is the real test for 2026 and 2027. Not whether the sector can announce more projects, but whether it can convert another one into a live construction row.

FAQ

How many nuclear plants are under construction in the US in 2026?

NNN's tracker shows one U.S. nuclear unit under construction: TerraPower's Natrium Demonstration at Kemmerer, Wyoming.

Is Kemmerer Unit 1 the same as a plant?

The tracker records units, not site-wide aggregates. Kemmerer Unit 1 is the live U.S. construction row tied to the Kemmerer Power Station site.

Why use the tracker instead of headlines?

Because headlines can lag the permit and the site work. The tracker shows what is actually under construction right now, which is the number that matters.