Yes. Kairos Power announced a $643 million Series D financing round in February 2024 to support development of its advanced nuclear technology, including construction of its Hermes demonstration reactors in Oak Ridge, Tennessee. The funding was not a $643 million grant earmarked solely for a single reactor called “Hermes 2”; it was company financing intended to advance a broader program.
What the $643 million raised means
The financing was a private investment round, not a government award or a final construction budget for one facility. Kairos said the capital would help it progress its commercial development plans, build out its engineering and manufacturing capabilities, and advance the Hermes demonstration project. Investors in a financing round provide money to the company in exchange for an ownership interest or related investment rights; that differs from a grant, a loan, or a project-specific public appropriation.
That distinction matters because headlines can make the figure sound like the exact cost of Hermes 2. The announcement described funds raised by Kairos Power, not a verified total cost for one reactor. A company may use financing across several connected activities, and project costs can change as designs, licensing, construction schedules, and supply needs develop.
What Hermes and Hermes 2 are
Hermes is Kairos Power’s demonstration reactor program in Oak Ridge, Tennessee. The U.S. Nuclear Regulatory Commission (NRC) issued a construction permit for the first Hermes demonstration reactor in December 2023. Kairos has described the project as a step toward demonstrating its fluoride salt-cooled high-temperature reactor technology and building experience relevant to a future commercial plant.
Hermes 2 is a planned follow-on demonstration facility at the same general project site. It is not the same thing as the first Hermes reactor, and the two names should not be treated as one unit. Kairos has described Hermes 2 as a larger demonstration effort intended to produce electricity, while the first Hermes unit is a non-power demonstration reactor. Regulatory reviews and approvals are required for the applicable project stages; a construction permit for Hermes does not itself authorize every later reactor or operation.
The “2” in Hermes 2 identifies a separate planned project, not a claim that it is a second commercial power station already operating. At the time of the 2024 financing announcement, neither Hermes nor Hermes 2 was generating electricity.
How Kairos Power’s reactor concept works
Kairos Power is developing a high-temperature reactor that uses TRISO fuel and a molten fluoride salt coolant. TRISO fuel consists of small uranium-bearing particles surrounded by multiple protective layers and embedded in graphite pebbles. The pebble form allows fuel to be handled and moved through a reactor system designed around that fuel type.
In broad terms, fission in the fuel releases heat. Fluoride salt carries heat away from the reactor core; a separate heat-transfer system can then use that heat for an application such as electricity production. The design differs from conventional light-water reactors, which use water as both coolant and moderator. Different technology does not mean that nuclear regulation or safety oversight disappears: reactor design, construction, fuel use, and operation remain subject to regulatory requirements.
Hermes is intended to test technology and systems at a demonstration scale, rather than immediately serve as a large commercial power station. Demonstrations can provide operating and engineering information, but they do not by themselves prove that a technology is commercially competitive or ready for widespread deployment.
Why the financing matters
Advanced reactor development demands substantial work before electricity can be sold. Funding can support activities such as detailed design, component development, production planning, testing, licensing work, and construction. The 2024 round therefore represented a significant commitment to the company’s long-term program, but it should not be read as evidence that all costs have been covered or that a commercial reactor is guaranteed.
Kairos announced the financing as a Series D round. The company said the round was led by existing investor Google, with participation from other investors. Google’s involvement drew attention partly because large technology companies have been exploring ways to obtain dependable, low-carbon electricity for energy-intensive operations. That association does not mean Google owns Hermes 2, has purchased its output, or has secured an operating reactor through the financing announcement.
For readers tracking the project, the most informative milestones are not just funding announcements. They include NRC decisions, construction progress, completion of testing, fuel-related approvals, and any later authorization needed to operate a facility and produce power.
What the announcement does not establish
The $643 million figure does not establish a final project cost, a completion date, a guaranteed electricity price, or an operating date for Hermes 2. Nor does it mean the NRC approved Hermes 2 simply because it had issued a construction permit for the first Hermes reactor. Each project and phase must be understood according to its own regulatory record and status.
It is also useful to distinguish a demonstration reactor from a commercial plant. A demonstration project is built to test systems and gain practical experience. A commercial plant would need to meet its own design, licensing, construction, operational, and economic requirements. Success at one stage may inform later work, but it does not automatically settle those questions.
Frequently Asked Questions
Did Kairos Power raise $643 million for Hermes 2?
Not exclusively. Kairos raised $643 million in a company-wide Series D financing round announced in 2024. The funding supports its broader development program, including its Hermes demonstration work.
Where is the Hermes project?
The demonstration project is in Oak Ridge, Tennessee, a city with a long history of U.S. nuclear research and development.
Is Hermes 2 operating?
No. The financing announcement did not mean Hermes 2 was operating or producing electricity. It was a planned follow-on demonstration project.
Is Hermes 2 the same as the first Hermes reactor?
No. Hermes and Hermes 2 refer to separate demonstration projects. The first Hermes reactor is a non-power demonstration unit; Hermes 2 has been described as a larger follow-on intended to generate electricity.
Did the NRC approve Hermes 2 when it approved Hermes?
No. The NRC’s construction permit for the first Hermes reactor is not blanket approval for Hermes 2. Regulatory decisions apply to specific projects and stages.
Does the $643 million represent the cost to build the reactor?
No. It is the amount Kairos announced raising in a financing round, not a confirmed final construction cost for Hermes or Hermes 2.
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