X-energy
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X-energy, Inc. is an American advanced nuclear reactor and fuel company based in Rockville, Maryland. Founded in 2009 by entrepreneur Kam Ghaffarian, it develops the Xe-100, a high-temperature gas-cooled small modular reactor (SMR), together with a proprietary pebble fuel called TRISO-X. The company is one of the most prominent players in the United States advanced nuclear industry, in large part because of a partnership with Amazon, which led a roughly $500 million financing round in 2024 and committed to buying as much as 5 gigawatts of X-energy nuclear capacity by 2039. X-energy went public on the Nasdaq on April 24, 2026 under the ticker symbol XE, raising about $1.02 billion in what was described as the largest nuclear initial public offering on record. The surge of investor interest reflects a wider bet that SMRs can supply the firm, carbon-free electricity that AI data centers increasingly require.
X-energy was founded by Kam Ghaffarian, an Iranian-born American engineer and serial founder who also started or co-founded the space-services contractor Stinger Ghaffarian Technologies (SGT, sold to KBR for $355 million in 2018), Intuitive Machines, Axiom Space, the investment firm IBX, and Quantum Space. Ghaffarian serves as X-energy's founder and executive chairman. Day-to-day leadership is held by chief executive Clay Sell, a former United States Deputy Secretary of Energy, who joined the company in 2019. By the time of its IPO, X-energy had grown to nearly 1,000 employees and was operating design, testing, and training facilities in Maryland alongside its fuel operations in Tennessee.
The company sells two linked products: the Xe-100 reactor and the TRISO-X fuel that powers it. That vertical integration, owning both the reactor design and the fuel supply chain, is one of the features X-energy uses to distinguish itself from other SMR developers such as TerraPower, Oklo, and Kairos Power.
The Xe-100 is a high-temperature gas-cooled reactor (HTGR) of the pebble-bed type. It is moderated by graphite and cooled by inert helium gas, which leaves the core at over 750 degrees Celsius. That heat is passed through a helical-coil steam generator to produce superheated steam at about 565 degrees Celsius and 16.5 megapascals, conditions high enough to drive a conventional steam turbine or to serve industrial processes directly.
Each Xe-100 module produces about 200 megawatts of thermal power (MWth), which converts to roughly 80 megawatts of electricity (MWe), or it can instead deliver up to 200 megawatts of process heat in the form of steam. X-energy designs the reactor to be deployed in groups: a standard "four-pack" plant of four independently operating units generates about 320 MWe, and a single site can be scaled to as many as 12 units, or about 960 MWe. The company targets a 60-year operating life and a 95 percent capacity factor, and says the design can ramp between 40 percent and full power in roughly 12 minutes, allowing it to follow load on a grid with variable renewable output.
A central safety claim is that the Xe-100 cannot melt down. The reactor relies on passive physics rather than active intervention: as temperature rises, the nuclear reaction naturally slows, and the fuel itself is engineered to retain its radioactive material at temperatures well above normal operating conditions. The United States Department of Energy has described X-energy's design as a "pebble-bed reactor that they say can't melt down."
| Parameter | Specification |
|---|---|
| Reactor type | High-temperature gas-cooled, pebble-bed (HTGR) |
| Coolant | Helium |
| Moderator | Graphite |
| Thermal output, per unit | 200 MWth |
| Electrical output, per unit | about 80 MWe |
| Process heat option, per unit | up to 200 MW of steam |
| Helium outlet temperature | over 750 degrees Celsius |
| Steam conditions | about 565 degrees Celsius, 16.5 MPa |
| Standard plant | four units, about 320 MWe |
| Maximum site | up to 12 units, about 960 MWe |
| Fuel | TRISO-X pebbles, HALEU (under 20% U-235) |
| Pebbles per core | about 220,000 |
| Design life | 60 years |
| Load following | 40% to full power in about 12 minutes |
| Refueling | online, continuous, multi-pass |
The Xe-100 runs on TRISO-X, X-energy's version of TRISO (tri-structural isotropic) fuel. Each spherical fuel "pebble" is about 6 centimeters across and contains roughly 19,000 poppy-seed-sized kernels of enriched uranium, each individually coated in layers of carbon and ceramic silicon carbide that act as a miniature pressure vessel. A single Xe-100 core holds about 220,000 of these pebbles, which circulate through the reactor and pass the core several times before they are spent, so the reactor refuels continuously while running rather than shutting down for batch reloads.
TRISO-X uses high-assay low-enriched uranium (HALEU), meaning uranium enriched to less than 20 percent uranium-235, a higher level than the roughly 5 percent used in conventional light-water reactors. To make the fuel, X-energy's TRISO-X subsidiary is building a commercial fuel-fabrication plant, designated TX-1, on the 110-acre Horizon Center site in Oak Ridge, Tennessee. The company says the roughly 215,000-square-foot facility will employ around 500 people and produce about 700,000 pebbles per year, enough to fuel about 11 Xe-100 reactors.
In February 2026 the Nuclear Regulatory Commission (NRC) issued TRISO-X a special nuclear material license (SNM-7007) authorizing it to possess and process HALEU at the Oak Ridge plant. The 40-year license, which the NRC said runs to 2066, was the first Category II fuel-fabrication license the agency had ever issued and the first new commercial fuel-fabrication license it had granted in roughly 50 years. X-energy and the Department of Energy both described it as a milestone for establishing a domestic HALEU fuel supply chain.
In October 2020 the U.S. Department of Energy (DOE) selected X-energy, alongside TerraPower, as one of two winners of its Advanced Reactor Demonstration Program (ARDP), a flagship federal effort to get a commercial-scale advanced reactor operating before the end of the decade. Each company received $80 million in initial funding. X-energy signed its ARDP cooperative agreement on March 1, 2021; under it, the company is eligible for up to roughly $1.23 billion in federal cost-shared funding over seven years to design, license, build, and demonstrate an Xe-100 plant together with a commercial TRISO fuel facility. The total demonstration project has been valued at around $2.5 billion, with X-energy and its partners covering the balance beyond the federal share.
X-energy originally planned to site the ARDP demonstration plant with the public utility Energy Northwest in central Washington. In 2023 it instead reached agreement with the chemical maker Dow to build the first Xe-100 plant at a Dow site on the Gulf Coast, and that project, the Long Mott Generating Station in Texas, became the program's lead demonstration.
Dow is developing the Long Mott Generating Station through a wholly owned subsidiary, Long Mott Energy LLC, at its UCC Seadrift Operations chemical complex in Seadrift, Texas. The plant is planned as four Xe-100 units that would supply both electricity and industrial steam to the site, replacing aging gas-fired energy and steam assets. X-energy and Dow describe it as the first grid-scale advanced nuclear facility built to serve an industrial site in North America. In late March 2025 the two companies submitted a construction permit application to the NRC, which docketed it for review. The NRC later completed an environmental assessment and issued a Finding of No Significant Impact, an early regulatory step ahead of any decision to grant a construction permit.
X-energy and Energy Northwest signed a joint development agreement in 2023 for the deployment of up to 12 Xe-100 modules in central Washington, capable of generating up to about 960 megawatts. In October 2024 Amazon anchored that effort: through its Climate Pledge Fund, Amazon led X-energy's roughly $500 million Series C-1 round and agreed to support an initial four-unit, 320 MWe project with Energy Northwest, with an option to expand to 12 units. Amazon and X-energy said they aimed to bring more than 5 gigawatts of capacity online in the United States by 2039, which they characterized as the largest commercial SMR deployment target announced to date.
In 2025 X-energy partnered with the British energy company Centrica to develop a fleet of up to 6 gigawatts of Xe-100 reactors in the United Kingdom. By late 2025 the company reported an orderbook and commercial pipeline of more than 11 gigawatts, equivalent to roughly 144 Xe-100 reactors.
| Partner | Project and location | Scope | Status |
|---|---|---|---|
| Dow (Long Mott Energy) | Long Mott Generating Station, Seadrift, Texas | four Xe-100 units for power and industrial steam | construction permit application submitted to NRC in March 2025; NRC reached Finding of No Significant Impact |
| Energy Northwest | central Washington | joint development agreement for up to 12 Xe-100 units (about 960 MWe) | signed 2023 |
| Amazon | United States deployment | up to 5 GW by 2039; initial four-unit, 320 MWe project via Energy Northwest | announced October 2024 |
| Centrica | United Kingdom | fleet of up to 6 GW of Xe-100 reactors | announced 2025 |
X-energy raised capital through a series of private rounds before listing publicly. It finalized a $235 million Series C in December 2023, anchored by funds affiliated with Ares Management and by Ghaffarian himself, with earlier participation from Ontario Power Generation, Curtiss-Wright, DL E&C, and Doosan Enerbility. The Amazon-led Series C-1 of about $500 million followed on October 16, 2024, joined by Citadel founder Ken Griffin, Ares, NGP, and the University of Michigan. On November 24, 2025 the company closed an oversubscribed Series D of roughly $700 million led by the trading firm Jane Street, with new investors including ARK Invest, Point72, XTX Ventures, Galvanize, Hood River Capital Management, and Reaves Asset Management, plus existing backers such as Ares, Emerson Collective, NGP, and Segra Capital Management. In total the company raised more than $1.4 billion privately before going public.
Earlier, X-energy had attempted to reach the public markets through a special purpose acquisition company. In December 2022 it agreed to a business combination with Ares Acquisition Corporation that valued the combined company at about $2 billion and was expected to close in 2023. The two sides mutually terminated the merger on October 31, 2023, citing difficult market conditions and weak trading by comparable companies; an Ares-affiliated vehicle then made a private investment to support X-energy's operations instead.
The company finally completed a conventional IPO in April 2026. It priced an upsized offering of 44,254,659 shares of Class A common stock at $23 each, above the initial marketed range of $16 to $19, and the shares began trading on the Nasdaq Global Select Market on April 24, 2026 under the ticker XE. The sale raised about $1.02 billion. The stock closed roughly 27 percent above the offering price on its first day, valuing X-energy at around $11.5 billion. In its first results as a public company, reported on June 4, 2026, X-energy posted first-quarter 2026 revenue of about $43 million, up roughly 109 percent year over year, while continuing to operate at a loss as it scaled up.
| Round | Date | Amount | Lead and notable investors |
|---|---|---|---|
| Series C | December 2023 | $235 million | Ares Management, Kam Ghaffarian; earlier OPG, Curtiss-Wright, DL E&C, Doosan |
| Series C-1 | October 16, 2024 | about $500 million | Amazon Climate Pledge Fund (lead); Ken Griffin, Ares, NGP, University of Michigan |
| Series D | November 24, 2025 | about $700 million | Jane Street (lead); ARK Invest, Point72, XTX Ventures, Galvanize, Hood River, Reaves |
| IPO (Nasdaq: XE) | April 24, 2026 | about $1.02 billion | 44,254,659 Class A shares at $23 |
X-energy's rise has been propelled by the electricity demands of artificial intelligence. Training and serving large models has pushed AI energy consumption sharply higher, and operators want power that is both round-the-clock and carbon-free, a profile that fits nuclear better than intermittent renewables. Hyperscale cloud providers have responded with a wave of nuclear deals: Amazon's investment in X-energy is one example, Microsoft contracted with Constellation Energy to restart a reactor at Three Mile Island, and Google agreed to buy capacity from Kairos Power. The Xe-100's modular four-pack format, relatively small land footprint, and ability to supply high-temperature steam as well as electricity are pitched as advantages for siting near data centers and industrial loads.
Coverage of X-energy's Series D and its IPO repeatedly tied the company's valuation to this trend. Technology and financial press described the listing as a "data center-driven IPO," and analysts pointed to the surge in AI-related power demand, together with Amazon's offtake commitment, as the reason a pre-revenue-scale reactor developer could raise more than a billion dollars in a single sitting. The company itself markets advanced nuclear as a way to power the AI buildout, while cautioning, as does most of the sector, that its first reactors will not begin operating until around the end of the decade.
| Date | Event |
|---|---|
| 2009 | X-energy founded by Kam Ghaffarian |
| October 2020 | Selected by DOE for the Advanced Reactor Demonstration Program, alongside TerraPower |
| March 1, 2021 | ARDP cooperative agreement signed (up to about $1.23 billion federal cost share) |
| December 2022 | Agrees to a SPAC merger with Ares Acquisition Corporation |
| 2023 | Dow and X-energy agree to build the first Xe-100 plant at Dow's Gulf Coast site |
| October 31, 2023 | SPAC merger with Ares Acquisition Corporation terminated |
| December 2023 | $235 million Series C finalized |
| October 16, 2024 | Amazon-led Series C-1 of about $500 million |
| March 2025 | Dow and X-energy submit Long Mott construction permit application to the NRC |
| November 24, 2025 | Series D of about $700 million closed |
| February 2026 | NRC issues TRISO-X fuel-fabrication license (SNM-7007) |
| April 24, 2026 | X-energy completes its Nasdaq IPO (ticker XE) |