TerraPower Natrium: A Full Guide to the Kemmerer Reactor, Molten Salt Storage, HALEU Fuel and Limits

On March 9, 2026, the NRC issued construction permit CPAR-1 for Kemmerer Power Station Unit 1 in Wyoming, the first construction permit it has ever issued for a commercial non-light-water power reactor. Six weeks later, TerraPower started building it.

That plant is TerraPower Natrium, a sodium-cooled fast reactor wired to a tank farm of molten salt. It's backed by Bill Gates, half-funded by the Department of Energy and already pre-sold to Meta as a fleet of up to eight units. It also just lost its lead contractor.

This full guide covers how Natrium works, the Kemmerer timeline, the licensing path, fuel, money, the Meta and Hyundai deals, how it compares with Oklo Aurora, and the honest limits, all as of October 24, 2026.

Last updated: October 24, 2026.

Key Takeaways

• TerraPower Natrium pairs a 345 MWe sodium fast reactor with molten salt storage that boosts output to 500 MW, per TerraPower.
• Kemmerer Unit 1 got the first NRC construction permit for a commercial non-light-water power reactor in March 2026.
• The project costs about $4 billion, with up to $2 billion in federal cost-sharing; completion is targeted for 2030.
• Meta signed for up to eight Natrium units, 2.8 GW of baseload and 4 GW with storage, from 2032.
• Honest limit: Bechtel exited the EPC role in September 2026, and first-core HALEU depends on a new South African plant.

What TerraPower Natrium actually is

Natrium is a reactor and a storage plant sold as one product. TerraPower and GE Vernova Hitachi Nuclear Energy co-developed the technology, according to TerraPower's Meta announcement.

The reactor is a 345 MWe sodium-cooled fast reactor. Its heat runs into a molten salt storage system, which lets the plant boost output to 500 MW when demand peaks while the reactor itself runs steady.

The design traces back to two older programs. POWER magazine reports that the 2020 Natrium debut blended TerraPower's Traveling Wave Reactor work with GEH's PRISM sodium reactor.

The first plant sits near the retiring Naughton coal plant outside Kemmerer, Wyoming. It's a coal-to-nuclear swap, and it's the reason Natrium's first customer is a grid, not a data center.

TerraPower Natrium specs at a glance

Here are the headline numbers, each tied to a TerraPower, DOE or trade-press disclosure.

Source: TerraPower's construction-start release, DOE Office of Nuclear Energy and POWER's Kemmerer timeline.

TerraPower says the 500 MW peak is enough to power around 400,000 homes. That's a marketing equivalence, not a measured figure, so treat it as scale, not a forecast.

How Natrium makes power: sodium, salt, then steam

Most U.S. reactors boil or pressurize water. Natrium doesn't. That single choice drives almost everything else about the plant.

The sodium fast reactor

Liquid sodium cools the core at low pressure. TerraPower says the reactor runs above 350 degrees Celsius and far below sodium's boiling point, and it relies on gravity and natural convection for passive cooling.

Fast reactors don't slow neutrons down the way water does. That's why Natrium needs high-assay low-enriched uranium (HALEU) in metallic form, which is the supply chain problem covered below.

The molten salt storage tank

Here's the bit that makes Natrium different. The sodium loop heats molten salt, the salt goes into tanks, and a conventional steam plant draws on the tanks when the grid needs power.

PacifiCorp's 2021 planning, as reported by POWER, modeled ramping at 8% per minute across roughly 100 to 500 MWe, at a 92.5% capacity factor. The reactor stays at constant power while the turbine follows the grid.

Nuclear island vs energy island

TerraPower physically separates the reactor from the salt tanks and turbines. The company says this decoupling lets non-nuclear teams run the turbines and salt tanks outside the nuclear control area.

That split also helped the schedule. The NRC granted an exemption in May 2025 that let TerraPower build the energy island while the reactor permit was still under review.

Why the salt tank matters for AI data centers

AI campuses want firm power around the clock, and grids want power that shows up at the evening peak. Natrium is designed to sell both from one site.

The reactor delivers a steady 345 MWe. When prices spike, the stored heat lets the plant run at 500 MW for over five hours, then recharge from the reactor once demand falls.

That's the pitch Meta bought. Its agreement counts 2.8 GW of baseload plus 1.2 GW of built-in storage across eight potential units, and the power is meant to feed the grids that serve its data centers.

Of course, none of this helps a campus that needs power in 2027. For that window, gas turbines, fuel cells and batteries still do the work, as Inside Deep Tech's behind-the-meter generation guide lays out. Natrium is a 2030s answer.

Kemmerer Unit 1 timeline, 2020 to 2026

The program has moved from a slide deck to a construction site in about six years. Here are the dated milestones.

• October 2020: DOE picks Natrium as one of two Advanced Reactor Demonstration Program flagships, alongside X-energy, with $80 million in initial funding each.
• November 2021: Kemmerer is named the preferred site, a 1,120-acre parcel near the Naughton coal plant.
• 2023: the completion target slips from 2028 to 2030, mainly over HALEU availability.
• March 2024: TerraPower files its construction permit application; NRC dockets it in May, the first non-light-water commercial docket in more than 40 years.
• June 2024: non-nuclear construction begins on the Kemmerer site.
• December 2025: NRC completes its safety review ahead of schedule and 11 percent under budget.
• January 9, 2026: Meta signs for up to eight Natrium plants.
• March 4 and 9, 2026: the Commission votes, then staff issue Construction Permit CPAR-1.
• April 23, 2026: TerraPower officially starts construction on Kemmerer Unit 1.
• August 14, 2026: Hyundai E&C is named EPC contractor for up to eight future Natrium reactors.
• September 2026: Bechtel and TerraPower part ways on the next EPC phase.
• October 14, 2026: Curtiss-Wright installs the Stage 1 training simulator on site.

The licensing path: the first permit of its kind

TerraPower's subsidiary US SFR Owner applied under the NRC's two-step Part 50 process: a construction permit first, an operating license later. The Federal Register notice confirms the permit was issued on March 9, 2026 and is immediately effective.

The review was fast by nuclear standards. TerraPower says the NRC set a 27-month schedule and finished in 18 months, helped by pre-application work and federal pressure to speed advanced reactor licensing.

POWER reports that the permit was the first to use a fully risk-informed, performance-based licensing basis and that it carries four exemptions, including ones on HALEU fuel handling and emergency core cooling analysis.

Construction status in October 2026

Kemmerer is a real construction site now. TerraPower said it was mobilizing roughly 1,600 workers when it started building in April.

Then the contractor changed. Bechtel told a Virginia agency it could cut approximately 200 positions because the two companies couldn't agree on the next phase of the project. Bechtel will stay to finish the Sodium Test and Fill Facility, and TerraPower will rebid the EPC contract.

TerraPower says the schedule holds. ENR, which pegs the project at an estimated $4 billion, reports the company still targets completion in 2030 and has named no replacement or procurement timetable.

The ripple effects are local. Kemmerer's plans to house as many as 1,600 construction workers were left in limbo because Bechtel had been running the housing solicitation.

Other work kept moving. Curtiss-Wright installed a full-scope Stage 1 training simulator in October and is also building the plant's distributed control and reactor protection systems. On October 15, Bill Gates toured the site, and Wyoming Governor Mark Gordon said the project had absorbed a two-year delay driven by federal policy decisions.

Fuel: HALEU decides the schedule

Natrium needs metallic HALEU fuel. When TerraPower and GNF-A announced the fuel plant in 2022, POWER notes that commercial metallic HALEU of this form was available only from Russia's state-owned TENEX.

TerraPower has built a four-track supply chain to fix that. Each track is a separate bet.

• Enrichment (South Africa): ASP Isotopes signed to supply the first fuel core plus up to 150 metric tons of HALEU from 2028 through 2037, from a new Pelindaba plant financed partly by a TerraPower loan.
• Enrichment (Ohio): Centrus's Piketon demonstration, tied to a $115 million, 80/20 cost-shared contract from 2020, produced roughly 900 kilograms of HALEU by mid-2025.
• Metallization (Washington): Framatome produced its first metallic uranium pucks in Richland in November 2025, using depleted uranium.
• Fabrication (North Carolina): the Natrium Fuel Facility at GNF-A's Wilmington site is a joint investment of more than $200 million.

TerraPower's own 2024 release frames these deals as a way to secure HALEU from the U.S. and allied countries rather than Russia. None of the four tracks has delivered a commercial HALEU core yet.

Money: ARDP, private rounds and the $4 billion price tag

Natrium is a public-private build. The DOE's Advanced Reactor Demonstration Program authorizes a 50/50 cost share of up to $2 billion, and TerraPower and partners match it dollar for dollar.

The private side has come in rounds. TerraPower raised $750 million in August 2022, including $250 million from SK, then a $650 million round in June 2025 that added NVentures, NVIDIA's venture arm, alongside Gates and HD Hyundai.

POWER puts total private capital since 2022 at more than $2.2 billion, and Korea Hydro and Nuclear Power joined the investor base in January 2026. TerraPower remains private.

That's enough to fund one first-of-a-kind plant. It isn't enough to fund a fleet, which is where Meta and Hyundai come in.

Beyond Kemmerer: Meta, Hyundai E&C, the UK and Korea

The Meta agreement

Meta's January 2026 announcement splits the deal in two. Meta funds early development of two Natrium units, up to 690 MW of firm power from as early as 2032, and holds rights to energy from six more units totaling 2.1 GW by 2035.

In total that's 2.8 GW of baseload and 4 GW with storage. TerraPower said the companies would identify a site for the first dual unit "in the coming months." As of October 24, 2026, TerraPower's newsroom shows no site announcement.

For data center buyers, the dual-unit figure matters most: a pair of Natrium reactors gives 690 MW firm and up to 1 GW dispatchable. That's a campus-scale block, not a microreactor.

Hyundai E&C and SK Innovation

In August 2026, TerraPower picked Hyundai Engineering & Construction as EPC for up to eight future Natrium reactors, with completion, price and performance guarantees meant to unlock conventional project finance. SK Innovation signed a term sheet for Korea's first Natrium plant.

The UK, Utah and Kansas

Natrium entered the UK's Generic Design Assessment in February 2026, and TerraPower has exploratory deals in Utah and Kansas. During the October 15 site tour, Levesque said a second or third Kemmerer reactor depends on data centers moving close enough to use the power.

TerraPower Natrium vs Oklo Aurora

Both are sodium-cooled fast reactors on metallic fuel, and both count Meta as a customer. They're built for different jobs.

Source: DOE on the Natrium permit, TerraPower's Meta release and Inside Deep Tech's Oklo Aurora full guide, which has the Oklo sources.

Natrium is a grid-scale plant with a turbine that follows load. Aurora is a smaller unit that scales by count. If you need a gigawatt, Natrium gets there in two pairs; Aurora needs more than a dozen units.

Honest limits: where the Natrium story can break

Natrium has cleared more hurdles than any U.S. advanced reactor rival. These are the five things that can still move the date or the price.

1. No lead EPC contractor today

TerraPower is rebidding the EPC contract for Kemmerer Unit 1 after Bechtel's exit. Hyundai E&C's framework covers future units, and no one has announced who takes over the first. Changing builders mid-stream is a classic way for first-of-a-kind nuclear projects to slip.

2. HALEU is still mostly a promise

The first core depends on a new enrichment facility at Pelindaba, South Africa that TerraPower is helping finance with a loan. The Framatome line has so far proven metallization with depleted uranium, not HALEU. Until one of these tracks delivers a full core, fuel is the critical path.

3. The schedule has slipped before

The original target was 2028; it moved to 2030 in 2023, and commercial operation is now set for 2031. Governor Gordon called it a two-year delay. Another slip would push Meta's 2032 units too.

4. Sodium adds engineering burden

Sodium doesn't need high pressure, and it reacts with water and air. Every sodium plant needs leak detection and fire protection that light-water plants don't. That's why TerraPower built a dedicated Sodium Test and Fill Facility to prove first-of-a-kind equipment.

5. Cost is not proven

About $4 billion for 345 MWe is a first-of-a-kind price, and nobody has published an nth-of-a-kind figure. The Hyundai guarantees are the first real test of whether later units get cheaper.

What TerraPower Natrium means for you

• If you plan AI data center power: Natrium is a 2032+ option for 690 MW blocks, not a fix for 2027 load. See Inside Deep Tech's behind-the-meter generation guide for the near-term stack.
• If you compare nuclear vendors: weigh permits, fuel contracts and EPC guarantees over press-release capacity. The small modular reactor guide covers the wider field.
• If you invest: TerraPower is private, so watch partners' disclosures: ASP Isotopes, Curtiss-Wright, Hyundai E&C and Meta.
• If you work in grid planning: the salt tank makes Natrium a firm, dispatchable resource, closer to a peaker than a classic baseload plant.

For how the AI power race compares across energy sources, see Inside Deep Tech's Commonwealth Fusion Systems SPARC guide and the OpenAI Stargate guide.

Oklo Aurora: A Full Guide to the Powerhouse Fast Reactor

Oklo's 75 MWe sodium fast reactor, the Aurora-INL path, Meta and Switch deals, HALEU fuel and the honest limits.

Inside Deep Tech

FAQ

What to watch next

Three signals will tell you whether Natrium keeps its lead. First, who replaces Bechtel on Kemmerer Unit 1. Second, whether ASP Isotopes' Pelindaba plant starts producing HALEU on time. Third, the site TerraPower and Meta pick for the first dual unit.

If you're planning power for a 2030s campus, put Natrium on the shortlist now and ask for fuel and EPC terms before you ask for a price.