Kairos Power Tests Mockup to Prepare Next-Generation Nuclear Reactor
Kairos Power has completed the first phase of testing on a non-nuclear mockup of the reactor cavity planned for its Hermes 2 demonstration plant in Oak Ridge, Tennessee. The Engineering Test Unit 3 (ETU 3) project is being used to test modular concrete shielding, remote handling equipment and maintenance procedures before those systems are incorporated into the reactor.
The reduced-scale mockup includes a reactor vessel surrounded by precast concrete shielding supported by steel frames. By testing the hardware without nuclear fuel, Kairos can identify construction and maintenance problems in a controlled environment before applying the lessons to its nuclear reactor projects.
Testing the Hermes 2 Reactor Cavity
Kairos installed 12 modular wall elements in the ETU 3 mockup, using four different designs with stepped and sinusoidal joint geometries. The configurations are intended to prevent radiation from escaping through seams between the concrete panels once a reactor is operating.
The team also tested different shielding plugs for openings where pipes and other process lines need to pass through the reactor cavity. These connections must provide radiation protection while still allowing equipment to be accessed and maintained.
Remote Maintenance Is a Key Part of the Design
Kairos is also using ETU 3 to test remote systems for connecting and disconnecting process lines and handling reactor components. The aim is to reduce the need for workers to enter areas where radiation could be present and make future maintenance operations more efficient.
The company says the testing will help establish a repeatable maintenance approach for its planned reactor fleet. ETU 3 will also serve as a training platform for future operators, allowing procedures to be practised before they are required at an operating nuclear facility.
3D Printing Helps Build the Shielding
The project also includes an advanced manufacturing element. Kairos worked with Oak Ridge National Laboratory’s Manufacturing Demonstration Facility to develop 3D-printed polymer-composite forms used to produce the precast concrete panels.
The panels were manufactured by Tindall Corporation in South Carolina and installed at the Oak Ridge site by Barnard Construction. Kairos is using this approach to test whether modular construction methods can make future reactor projects easier to manufacture, transport and assemble.
ETU 3 Feeds Into Hermes 2
The ETU programme is part of Kairos Power’s broader strategy of testing reactor-scale hardware before deploying nuclear systems. Its first Engineering Test Unit completed more than 2,000 hours of pumped molten-salt operations, while ETU 2 has focused on modular construction and system assembly.
Kairos broke ground on the Hermes 2 Demonstration Plant in April 2026. The 50-megawatt reactor is designed to build on lessons from the company's earlier testing and eventually produce electricity for the grid.
A Step Toward Commercial Reactor Deployment
Kairos is developing a fluoride salt-cooled high-temperature reactor (KP-FHR), a Generation IV reactor design that uses molten fluoride salt as its coolant. The company is pursuing the technology as a potential route to safer and more flexible nuclear power generation.
The ETU 3 results will now feed into further iterations of the Hermes 2 reactor cavity design. While the mockup itself is not a nuclear reactor and does not generate electricity, the testing gives Kairos an opportunity to resolve construction and maintenance issues before they become part of a commercial-scale plant.
