Deep Fission shares rose after the company's nuclear safety design agreement for its gravity nuclear reactor was approved by the Energy Department.

The stock climbed 8% to $9.38 on Thursday. Shares are still down 36% this year.

The regulatory milestone confirms that the nuclear-energy company's design warrants advancement under the Energy Department's reactor pilot program, Deep Fission said.

It establishes a safety framework to guide the reactor's continued development, allowing the company to move into its next phase of authorization. The next step will be demonstrating and eventually deploying the underground nuclear-reactor technology.

Deep Fission is advancing its commercial pilot project at Great Plains Industrial Park in Parsons, Kan. It broke ground in December and is now progressing its proof-of-concept program.

Eventually, the company wants its reactor to gain a license from the Nuclear Regulatory Commission to commercially operate the unit.