One of Silicon Valley's leading figures since OpenAI released ChatGPT, Altman became an early backer of nuclear startup Oklo in 2015, and is also its chairman.

Altman has explained that his investment in nuclear power is closely linked to the artificial intelligence revolution he champions, which will require massive amounts of energy.

"I'm all-in on energy. I think there's urgent demand for tons and tons of cheap, safe, clean energy at-scale," Altman told CNBC on Tuesday.

Oklo plans to build small modular reactors (SMRs), which are theoretically quicker to build than conventional power plants and less complicated to construct in remote areas. Oklo also wants to offer nuclear fuel recycling.

Conventional nuclear reactors are hugely expensive and take a long time to construct, with major projects having become notorious for their budget and schedule overruns.

"Our long-term goal is to build a wide range of advanced fission power plants, including small and large designs and designs that are economically competitive," said Jacob DeWitte, Oklo's co-founder and CEO.

The startup does not yet have a site of its own, and in January 2022 was refused a license to build an SMR in Idaho by the Nuclear Regulatory Agency (NRC).

The NRC rejected the application on the grounds that there was a lack of information on the risks of accidents and the responses planned in such cases.