California-based startup Kairos Power has been granted permission by the US Nuclear Regulatory Commission (NRC) to construct its Hermes demonstration reactor in Tennessee. This marks the first time in over 50 years that the US has approved a novel nuclear reactor, indicating a growing openness among regulators to alternative methods of generating power from nuclear fission. Unlike traditional commercial reactors that use water for cooling, Kairos Power’s technology utilizes molten fluoride salt as a coolant.
The function of a nuclear reactor revolves around controlling nuclear fission, a process in which atoms split and release energy. The fuel in a reactor consists primarily of uranium, processed into ceramic pellets and enclosed in sealed metal tubes called fuel rods. These rods, bundled together, form a fuel assembly, and a typical reactor core houses hundreds of these assemblies. Within the reactor vessel, the fuel rods are submerged in water, which serves as both a coolant and a moderator. The moderator slows down the neutrons produced by fission, sustaining the chain reaction. The heat generated by fission converts water into steam, which drives turbines to generate electricity.
Currently, all commercial nuclear reactors in the US are light-water reactors that use ordinary water as both a coolant and a neutron moderator. Over 65% of these reactors are pressurized-water reactors (PWRs), which circulate water at high pressure within the core to prevent boiling. However, regulatory processes have historically hindered the approval of new reactor designs, despite the global push to accelerate nuclear power deployment in the fight against climate change.
Kairos Power is one of several companies striving to market designs that can be manufactured in facilities and set up on-site, claiming that their approach is faster and more cost-effective than conventional large-scale reactors. Their innovative reactor uses molten fluoride salt as a coolant, which offers remarkable chemical stability and exceptional heat transfer capabilities at high temperatures. Studies have confirmed the compatibility of these salts with standard high-temperature structural materials, ensuring reliability and a prolonged service life.
The Kairos Power reactor employs fully ceramic fuel that maintains its structural integrity even under extremely high temperatures. By using pebble-type fuel, the reactors enable online refueling for reliability and operational availability. Additionally, the company adopts a model-to-learn approach to optimize the transition to clean energy, promising cost reduction and the development of innovative nuclear technologies.
Kairos Power’s advanced reactor falls under the category of small nuclear reactors (SMRs), defined by the International Atomic Energy Agency (IAEA) as having a capacity under 300 MWe. In contrast, present-day large conventional reactors typically have around 1,000 megawatts of capacity. The development of SMRs is driven by private investment, signaling a shift from public-led and -funded nuclear research and development to private-led initiatives aimed at deploying affordable clean energy sources without harmful carbon emissions.
In 2020, the US Department of Energy announced $30 million in initial funding support for five US-based teams developing affordable reactor technologies, including Kairos Power for their Hermes Reduced-Scale Test Reactor. This scaled-down version of their fluoride salt-cooled high-temperature reactor (KP-FHR) is set to begin construction next year, with completion expected by the end of 2026. The objective is to demonstrate the viability of Kairos Power’s design and molten salt technology, which potentially offers safety advantages over water-cooled systems.
While the Hermes demonstration reactor will not generate electricity, it serves as a precursor to the Hermes 2 project. This next phase involves two similar reactors capable of producing a combined output of approximately 28 megawatts of electricity. The NRC is currently evaluating Kairos Power’s application for a construction permit for this venture. The company’s ultimate vision includes a commercial endeavor featuring two larger reactors with a capacity exceeding 100 megawatts.
With the approval of its Hermes demonstration reactor, Kairos Power ushers in a new era of cleaner, safer, and scalable nuclear power. This innovative approach holds promise for addressing climate change by leveraging efficient, affordable, and sustainable energy sources.