Kairos Power says it has finished the first phase of testing on Engineering Test Unit 3 (ETU 3) at its Oak Ridge, Tennessee campus. The unit is a non-nuclear mockup built to test two things for the company’s planned Hermes 2 plant: precast concrete radiation shielding and remote maintenance with robotic tools.
ETU 3 at a glance
| Item | Detail |
|---|---|
| What it is | Reduced-scale, non-nuclear replica of the Hermes 2 reactor cavity |
| Location | Oak Ridge, Tennessee |
| Status | Phase one complete (announced September 4, 2026); later phases not described |
| Shielding | 12 modular precast wall elements in four designs, per Kairos |
| Maintenance test | Robotic arms connected and disconnected process lines without anyone entering the enclosure, per Kairos |
| After testing | Training platform for future operators |
What Kairos tested
ETU 3 includes a reactor vessel and a precast concrete shielding structure on steel frames. Joints between the wall elements use stepped and sinusoidal geometries, which are meant to stop radiation from leaking through the seams. Each panel has steel-framed openings for testing shielding plugs, the pieces that let process lines pass from the reactor through the shield.
The robotic arms sit above the cavity. A company team called SPEED (Salt Process Equipment Execution and Delivery) is developing this kind of servicing for Kairos’s fluoride salt-cooled high-temperature reactor, known as the KP-FHR. The goal is lower operating cost and less worker exposure in a real plant.
How the shielding was made
Oak Ridge National Laboratory’s Manufacturing Demonstration Facility helped design and produce 3D-printed polymer composite forms for the precast panels. Tindall Corporation cast the panels and Barnard Construction installed them, per Kairos. Printed forms can let designers change geometry faster than conventional formwork. It’s a different technique from the metal printing of reactor pressure vessels at ORNL and Idaho National Laboratory.
Where ETU 3 fits
Kairos broke ground on the Hermes 2 Demonstration Plant in April 2026 on the former Oak Ridge Gaseous Diffusion Plant site, according to World Nuclear News. Hermes 1, a scaled low-power demonstration reactor that will not produce electricity, is also under construction there. It is the first non-light-water reactor the NRC approved for construction. Earlier test units covered other ground: ETU 1.0 ran more than 2,000 hours of pumped salt operation, and ETU 2.0 tested modular construction methods.
Co-founder and CTO Ed Blandford said that demonstrating the interfaces between modular shielding structures and reactor equipment helps Kairos decide which design features to standardize in commercial plants. Austin Clark, the senior engineer who led ETU 3 development, said “Delivering real hardware is central to Kairos Power’s mission to enable safe and affordable commercial deployment.”
Why It Matters to You
- This is a test rig, so nothing here reaches consumers or customers today.
- If remote maintenance works in a real plant, the stated goals are lower operating cost and less worker exposure. No source gives a savings figure.
- Plant operators and workers would see any benefit first, and only after Hermes 2 and later commercial plants are built.
What this does not show
This was a non-nuclear, reduced-scale mockup. It shows that the hardware fits and the robots can handle the interfaces, but not how the system performs under radiation, heat or salt contamination. The reported results are Kairos’s own, and neither Kairos nor World Nuclear News published test data, radiation measurements or maintenance times. Kairos has not said what later phases will cover or when they will finish. Hermes 2 is a demonstration plant, not yet a commercial-scale plant, so standardization lessons apply to later commercial fleets.
Quick answers
Is ETU 3 a working reactor? No. It is a non-nuclear mockup of the Hermes 2 reactor cavity used to test shielding and remote handling.
Does this prove robots can maintain a real reactor? Not yet. It shows the approach works in a mockup. Real reactors add radiation, high temperatures and salt chemistry that the mockup does not reproduce.
What is the difference between Hermes 1 and Hermes 2? Hermes 1 is a scaled low-power demonstration reactor that will not produce electricity. Hermes 2 is a demonstration plant whose design will draw on Hermes 1 and ETU 3 results.
What should readers watch next? Later ETU 3 phases and how Kairos folds the findings into the Hermes 2 cavity design.
Sources
- Kairos Power: Kairos Power Completes First Phase of ETU 3 Hardware Demonstration (Sep 4, 2026)
- World Nuclear News: Kairos completes first phase of testing in ETU 3 reactor mockup (Sep 7, 2026)