Hermes is scaled version of Generation IV fluoride salt-cooled nuclear plant
US-based advanced nuclear reactor developer Kairos Power has completed the first installation of nuclear safety-related concrete for the Hermes Low-Power Demonstration Reactor, marking the start of “nuclear construction” on the project in Oak Ridge, Tennessee.
Hermes is a scaled demonstration of Kairos Power’s Generation IV* fluoride salt-cooled high-temperature reactor (KP-FHR) technology and is the first advanced nuclear reactor to receive a construction permit from the US Nuclear Regulatory Commission (NRC).
Kairos Power first broke ground at the Hermes site in July 2024 and completed excavation in October.
Safety-related construction activities, which are subject to oversight by the NRC and can only be performed with a construction permit, started on 1 May with a focus on the building’s foundation.
To ensure structural soundness, Hermes will have 51 drilled piers, each almost two metres wide, to anchor the building to bedrock.
Kairos said the first safety-related concrete pour was the culmination of several months of preparation. Two earlier projects at the Oak Ridge site served as proving grounds to test the drilled pier installation process and refine Kairos Power’s nuclear quality assurance programme.
Hermes will use Triso pebble fuel with a mixture of lithium fluoride and beryllium fluoride salts known as Flibe as its coolant. It will have thermal power output of 35 MWth and no electric capacity.
Molten salt reactors are said to have advantages over more traditional water-cooled plants, including improved safety and higher efficiency. Molten fluoride salts have excellent chemical stability and tremendous capacity for transferring heat at high temperature and retaining fission products.
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 Department of Energy (DOE), Triso is essentially a “robust, microencapsulated fuel form” developed originally in the 1950s.
Background: DOE Backing, Google Commitment
Hermes is one of several projects being supported through the US 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.
In October tech company Google announced it would back the construction of seven small modular nuclear reactors (SMRs) from Kairos Power, becoming the first tech company to commission new nuclear power plants to provide low-carbon electricity for its energy-hungry data centres.
Google and Kairos said that under the terms of the deal, the first of its kind, Google committed to buying power generated by seven reactors to be built by Kairos.
Kairos is one of four companies chosen by Texas A&M University System to explore developing advanced nuclear power reactors on its Rellis research campus.
It is also one of eight companies chosen to potentially demonstrate their ability to deliver nuclear power for defence installations in the US.
* 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.
To ensure structural soundness, 51 drilled piers will anchor the reactor building to bedrock. Courtesy Kairos Power.
