Kairos Power announced July 15, 2025, that it has installed the reactor vessel for its third Engineering Test Unit, designated ETU 3.0, at its Oak Ridge, Tennessee site. The 14-foot vessel is a non-nuclear prototype and was fabricated using electron beam welding technology in partnership with Cambridge Vacuum Engineering and the University of Sheffield AMRC. Construction of the ETU 3.0 facility around the vessel is being managed with Barnard Construction. The project is supported through the U.S. Department of Energy’s Advanced Reactor Demonstration Program under a milestone-based agreement with DOE.
What it means
ETU 3.0 will function as a testing and operator training platform for Kairos Power’s Hermes reactor, which is also under construction at the Oak Ridge site. The facility will be used to pilot new manufacturing techniques and construction processes aimed at lowering the cost of building Kairos Power’s commercial reactor, and will support staging, assembly, and testing of Hermes plant equipment modules before installation. ETU 3.0 will also serve as a test platform for Hermes remote handling and maintenance equipment. Kairos Power’s CEO Mike Laufer said the ARDP structure allows the company to “move quickly through progressively sophisticated iterations” toward commercial deployment.
Hermes, the low-power reactor under construction alongside ETU 3.0 in Oak Ridge, is the first Generation IV reactor to receive a construction permit from the U.S. Nuclear Regulatory Commission. It uses a TRISO fuel pebble bed design with a molten fluoride salt coolant. Kairos Power’s commercial KP-FHR technology draws in part on DOE-sponsored Integrated Research Projects led by universities, national laboratories, and international partners, with commercial deployment targeted for the 2030s.
Key facts
- Reactor vessel height: 14 feet
- Unit designation: Engineering Test Unit 3.0 (ETU 3.0), the company’s third such prototype
- Location: Oak Ridge, Tennessee
- ETU 3.0 is non-nuclear; it will serve as a training center and test platform for Hermes equipment
- Vessel fabricated using electron beam welding with Cambridge Vacuum Engineering and University of Sheffield AMRC
- Construction partner: Barnard Construction
- Funding program: DOE Advanced Reactor Demonstration Program (ARDP), milestone-based agreement
- Commercial reactor deployment target: 2030s (according to the company)
Source: U.S. Department of Energy (energy.gov), reporting a Kairos Power release