Kairos Power’s Hermes low-power demonstration unit could be operational at Oak Ridge site in 2027
Kairos Power has started construction on one of the first advanced reactors in the US in what the California-based company called a “critical milestone” on its path to commercialising advanced reactor technology.
Kairos Power said in a statement that the Hermes Low-Power Demonstration Reactor, which could be operational in 2027, is the first and only Generation IV* reactor to be approved for construction by the US Nuclear Regulatory Commission (NRC) and the first non-light-water reactor to be permitted in the US in over 50 years.
Hermes is a non-power version of Kairos Power’s fluoride salt-cooled high temperature reactor, the KP-HFR.
Kairos Power said it had recently started excavation and groundwork at the Hermes site in Oak Ridge, Tennessee, through a contract with Montana-based Barnard Construction Company.
The US Department of Energy (DOE) said in a statement that the reactor is being used to inform the development of a commercial reactor that could be deployed “next decade”.
It said Hermes is one of several projects being supported through the DOE’s advanced reactor demonstration programme, which is designed to help the domestic nuclear industry demonstrate its advanced reactor designs and ultimately help the US build a competitive portfolio of new US reactors that offer significant improvements over today’s technology.
Kairos Power has committed to invest at least $100m (€92m) to support Hermes’ construction and operation. The DOE will invest up to $303m in the project through a performance-based milestone contract funded by advanced reactor demonstration programme to support Hermes’ design, construction, and commissioning.
Hermes will use a Triso fuel pebble bed design with a molten fluoride salt coolant to demonstrate “affordable clean heat production”, the DOE said.
Kairos Power said the reactor’s novel combination of Triso coated particle fuel and Flibe molten fluoride salt coolant yields robust inherent safety while simplifying the reactor’s design.
Triso – or “tristructural-isotropic” – fuel particles contain a spherical kernel of enriched uranium oxycarbide surrounded by layers of carbon and silicon carbide, which contains fission products.
According to the DOE, Triso is essentially a “robust, microencapsulated fuel form” developed originally in the 1950s.
Perhaps Triso’s biggest benefit is that each particle acts “as its own containment system thanks to its triple-coated layers,” the DOE said. This allows them to retain fission products under all reactor conditions.
Triso particles are especially robust. “Simply put, Triso particles cannot melt in a reactor and can withstand extreme temperatures that are well beyond the threshold of current nuclear fuels,” the DOE said.
Transforming Conventional Nuclear Construction
The Hermes project was cleared for construction by the US Nuclear Regulatory Commission in December.
Kairos Power has also applied for a construction permit for Hermes 2 test reactor, which will also be built at Oak Ridge and will feature two 35 MWt units similar to the Hermes plant.
Barnard and Kairos Power have also started collaborating to build the third engineering test unit (ETU 3.0) – a non-nuclear demonstration at Oak Ridge that will generate supply chain, construction and operational experience for the Hermes project.
Both Hermes and ETU 3.0 will be built using modular construction techniques piloted at Kairos Power’s testing and manufacturing campus in Albuquerque, New Mexico.
Reactor modules will be fabricated in Albuquerque and shipped to Oak Ridge for assembly, demonstrating the potential of a factory-built small modular reactor design to transform conventional nuclear construction.
In December 2023 China’s National Energy Administration said China had begun commercial operation of the first Generation IV plant in the world, the HTR-PM (high-temperature reactor-pebble-bed modules) plant at Shidao Bay.
* No precise definition of a Generation IV reactor exists, but the term is used to refer to nuclear reactor technologies under development including gas-cooled fast reactors, lead-cooled fast reactors, molten salt reactors, sodium-cooled fast reactors, supercritical-water-cooled reactors and very high-temperature reactors. An international task force, the Generation IV International Forum (GIF), is sharing R&D to develop six Generation IV nuclear reactor technologies. GIF said goals of Generation IV reactor design include lower cost and financial risk, minimising nuclear waste and high levels of safety and reliability.
An architect’s rendering of the Hermes Low-Power Demonstration Reactor facility. Courtesy Kairos Power.
