Kairos is trying to reinvent nuclear power. Its molten-salt-cooled reactor could generate safe, reliable, carbon-free electricity that’s potentially as cheap as power generated from natural gas.

The nuclear industry in much of the world can seem stuck 30 years in the past, thanks to an outdated fleet of huge fission reactors that remain expensive to build and operate and are haunted by safety concerns. Kairos wants to change that with small, safe, modular reactors that could be cost-competitive with the cheapest fossil fuel—natural gas. Ironically, it hopes to use molten-salt-cooledreactors, a technology pioneered and then abandoned in the 1950s and ’60s in favor of designs that were further along at that time.