Paleja reported in later November 2024 that the Nuclear Regulatory Commission (NRC) has approved the construction of the first-ever molten-salt reactor that will power the grid in the US. The approval was granted to Kairos Power, which is currently building the Hermes Low-Power Demonstration Reactor at the Heritage Center Industrial Park in Oak Ridge, Tennessee.
Artist's rendering of molten salt reactor to be built by Kairos Power in the US.
Kairos Power
As the world looks for carbon-free approaches to meeting its energy demands, nuclear fission technology is poised for a comeback. Even before the 2011 Fukushima disaster, work was underway to improve the safety features of nuclear reactors. Generation IV nuclear power is the umbrella term for nuclear fission technology, which is designed to avert the leak of radioactive material even in extreme scenarios such as earthquakes and generates energy with much higher fuel efficiency.
Molten-salt reactors are one of the many different approaches that scientists are using to achieve Gen IV nuclear power. Here, the nuclear fuel is either mixed in molten salt or embedded in graphite, while the molten salt is used as a coolant, and the operation proceeds at high temperatures. Kairos Power uses the latter approach for its Hermes reactors.
Kairos’ approach to nuclear energy
Tennessee-based Kairos Power’s nuclear plant design features a graphite-moderated pebble-bed reactor with fluoride salt as its coolant. It uses tri-structural ISOtropic (TRISO) particle fuel, which is “randomly packed” in pebble form inside the reactor. The reactor has a high-assay low-enriched uranium (HALEU) enrichment of nearly 20 percent.
Founded in 2016, Kairos Power uses a rapid iterative development approach. It uses iterative hardware demonstrations to clear regulatory hurdles and develop in-house manufacturing capability to de-risk its technology and supply chain.
As part of its iterative process, the company has built Engineering Test Units (ETUs) at its Albuquerque and Oak Ridge facilities. Under controlled conditions, these units use non-nuclear tests to validate their critical system components, such as coolant flow and heat transfer rates.
The next step in the company’s development approach is building the Hermes reactors. 
Schematic of the molten salt reactor Hermes to be used by Kairos Power to
supply energy to the grid. Image credit: Kairos Power
To power the gridIn December 2023, Kairos Power received the NRC nod for building the Hermes Low-power Demonstration Reactor (Hermes 1), the first Gen IV reactor to receive construction approval in the US. This non-power reactor will be built only to demonstrate system integration and operational safety. With the recent approval, the NRC has given Kairos the go-ahead to build a power plant that will eventually supply power to the grid. Dubbed Hermes 2, the power plant will be sited next to Hermes 1 and will feature two 35-MWth reactors with a combined generation capacity of 20 MWe. Hermes 2 will replicate complete plant architecture at a reduced scale while supplying carbon-free energy to the grid.
Not only has Kairos succeeded in getting approvals from the NRC for Hermes 2, but it has also achieved this in 16 months. The company attributes this to extensive pre-application engagement with the NRC dating back to 2018.
The NRC is also looking to simply its regulatory approvals for future projects. “While keeping safety at the forefront, the permitting process was quite efficient, and we issued these permits in less than 18 months,” said Christopher Hanson, NRC Chair, in a press release.
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“This shows we can rapidly apply relevant conclusions from earlier reviews to promptly reach decisions on new reactors.”
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