Much of the funding and industrial activity in advanced reactors is centered in the US, where several companies are close to demonstrating their technology.

Kairos Power is building reactors cooled by molten salt, specifically a fluorine-containing material called Flibe. The company received a construction permit from the US Nuclear Regulatory Commission (NRC) for its first demonstration reactor in late 2023, and a second permit for another plant in late 2024. Construction will take place on both facilities over the next few years, and the plan is to complete the first demonstration facility in 2027.

TerraPower is another US-based company working on Gen IV reactors, though the design for its Natrium reactor uses liquid sodium as a coolant. The company is taking a slightly different approach to construction, too: by separating the nuclear and non-nuclear portions of the facility, it was able to break ground on part of its site in June of 2024. It’s still waiting for construction approval from the NRC to begin work on the nuclear side, which the company expects to do by 2026.

A US Department of Defense project could be the first in-progress Gen IV reactor to generate electricity, though it’ll be at a very small scale. Project Pele is a transportable microreactor being manufactured by BWXT Advanced Technologies. Assembly is set to begin early this year, with transportation to the final site at Idaho National Lab expected in 2026.

Advanced reactors certainly aren’t limited to the US. Even as China is quickly building conventional reactors, the country is starting to make waves in a range of advanced technologies as well. Much of the focus is on high-temperature gas-cooled reactors, says Lorenzo Vergari, an assistant professor at the University of Illinois Urbana-Champaign. These reactors use helium gas as a coolant and reach temperatures over 1,500 °C, much higher than other designs.

China’s first commercial demonstration reactor of this type came online in late 2023, and a handful of larger reactors that employ the technology are currently in planning phases or under construction.