Kairos Power Completes ETU 2 Vessel Assembly with Successful Top Head Closure

Highlights:

• Kairos Power installed the top head on its second Engineering Test Unit (ETU 2) in Albuquerque, New Mexico.

• The assembly marks the completion of the first reactor vessel produced entirely in-house by Kairos Power.

• Data from the heavily instrumented unit will validate thermal-hydraulic models and inform the design of Hermes and future reactors.

Kairos Power successfully sealed the top head on to the Engineering Test Unit 2 reactor vessel at its Manufacturing Development Campus in Albuquerque, New Mexico.  

This is the first completed reactor vessel manufactured and assembled in-house by the Kairos Power team, and a product of the company's vertical integration and rapid iterative development strategies to deliver advanced nuclear hardware with cost and schedule certainty.

Precision Assembly

Closing the ETU 2 top head was a highly precise operation that required managing gaps as tight as 30,000ths of an inch to ensure perfect alignment between the vessel's head and its internal components.

The team routed a massive, complex network of internal instrumentation through consolidated nozzles in the vessel head that will collect high-fidelity data on internal pressures, temperatures, and flow rates during operations.

While the first Engineering Test Unit focused on basic system operations and molten salt handling, ETU 2 represents a significant step forward in complexity by integrating sophisticated sensing technology required for the Hermes Low-Power Demonstration Reactor.  

The data generated will help confirm how the molten salt, pebble bed, and graphite internals interact within the vessel.

"ETU 2 as a test unit is heavily instrumented," said Jae Choi, manager of reactor systems for Kairos Power. "These test units are going to provide us the extra measurements—not simulation-based estimates—to provide the data to confirm our design and models."

"By successfully executing this assembly in-house, we are proving that we can maintain rigorous quality control while significantly accelerating our project timelines," said Ed Blandford, Kairos Power co-founder and chief technology officer.  “We aren't just waiting for a supply chain to catch up—we are actually creating it. This allows us to identify integration challenges early and refine our manufacturing muscle memory, ensuring that the proficiency gained today can support the rapid deployment of the Hermes reactor."

Path to Hermes  

ETU 2 is Kairos Power's second major, large-scale hardware demonstration serving as a physical precursor to Hermes.

The non-nuclear prototype is the company’s first modular design that will help clear technical hurdles and refine manufacturing procedures for the Hermes reactor series.

With the vessel installation complete, several integration steps remain to transform the system into a fully operational loop.  

In the coming weeks, the team will begin Argon leak testing to ensure the integrity of the primary boundary, which serves as the "engine" of the system and houses the pump that circulates the molten salt.

Before those operations can begin, the team must also complete the installation of the pebble-handling and reactivity-control systems.

Looking Ahead

ETU 2 commissioning is expected to start later this summer in Albuquerque.

The operational experience gained from ETU 2 will directly inform the construction, commissioning, and operation of Hermes in East Tennessee and carry forward to the future commercial fleet.