Kairos Power has commenced construction of the low-power experimental reactor, Hermes, in Oak Ridge, Tennessee. This reactor utilizes a TRISO pebble bed design and is cooled by molten fluoride salt, enhancing operational safety.
Hermes is the first and only fourth-generation reactor approved for construction by the U.S. Nuclear Regulatory Commission, as reported by Interesting Engineering on August 1. According to Kairos Power, it is also the first non-light-water reactor licensed in the U.S. in over 50 years, with operations expected to begin in 2027. The Hermes reactor project is supported by the U.S. Department of Defense’s Advanced Reactor Demonstration Program.
Design of the Hermes low-power experimental reactor facility. (Image: Kairos Power).
According to the Office of Nuclear Energy, the Hermes reactor is being constructed as part of a commercial reactor development program that Kairos Power plans to deploy in the coming decade. Hermes will utilize a TRISO pebble bed design with molten fluoride salt as a coolant to demonstrate the ability to produce clean heat at low costs.
The U.S. Nuclear Regulatory Commission granted construction approval for the project in December of last year. The U.S. Department of Energy will invest $303 million to support the design, construction, and commissioning of Hermes through their Advanced Reactor Demonstration Program. Kairos Power is collaborating with Los Alamos National Laboratory to produce TRISO fuel for the reactor. The company has also entered into a cooperative development agreement with the Tennessee Valley Authority to provide technical support, operation, and licensing.
Kairos Power recently completed molten salt testing at the first Engineering Test Unit (ETU) at its manufacturing facility in Albuquerque, New Mexico. This system is the first of three versions being developed to assist in the design, construction, and operation of Hermes. The company is currently constructing a second ETU in Mexico and will partner with Barnard Construction on the third system located near the Hermes reactor site.
Instead of using water like conventional nuclear reactors, Kairos Power’s reactor employs molten fluoride salt as a coolant. Molten fluoride salt offers excellent chemical stability, high-temperature heat transfer capabilities, and retains fission products that can be released from the fuel. Additionally, Kairos Power’s reactor utilizes fully ceramic-coated fuel, maintaining structural integrity even at extremely high temperatures. This fuel will not be damaged even at temperatures significantly higher than the melting point of conventional metallic fuel.
The company states that their reactor features numerous passive safety characteristics, requiring no electricity to remove heat from the core once it is shut down. The reactor has a particularly large safety margin based on the combination of fuel and coolant, allowing for emergency cooling relying on fundamental physics rather than engineered systems. According to data provided by Kairos Power, the KP-FHR reactor can produce 140 MW of electricity with a net efficiency of 45%.
Recently, China has also expanded the world’s first fourth-generation nuclear power plant, the High-Temperature Gas-Cooled Reactor (HTGR) Shidaowan located in Shandong province, eastern China. Equipped with the first high-temperature gas-cooled reactor in the world, the plant has been commercially operational since December of last year. Once completed, it is expected to generate 20 billion kilowatt-hours annually, increasing the area for heating supply by an additional 20 million square meters and benefiting 600,000 local residents.
