At around 3:40 pm (1940GMT), the stock was down 53.9 percent to $8.40.

Founded in 2013 by graduates of the Massachusetts Institute of Technology (MIT), Oklo went public by merging with AltC Acquisition Corp, a listed company.

The latter is a SPAC (special purpose acquisition company), a company whose sole purpose is to enable another firm to enter Wall Street through a merger.

Since the deal with Oklo was announced in July last year, AltC's share price has soared, gaining over 72 percent.

But transactions involving a SPAC are often highly volatile, partly because they are more exposed to speculation than traditional IPOs.

Altman is involved in several cutting-edge sectors and invested in Oklo in 2015, also becoming its chairman.

According to company documents, Altman directly controls around three percent of the capital.

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.

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.

With the merger with AltC, Oklo raised $306 million, which will be used to build the company's first fission reactor, Aurora, in Ohio.