Deep Fission, a US advanced nuclear energy company developing small modular reactors installed one mile underground, announced that the US Department of Energy (DOE), has approved the company’s nuclear safety design agreement (NSDA) for its Gravity nuclear reactor.

The California-headquartered company, founded in 2023, said the approval marks a major regulatory milestone, confirming that the reactor design warrants advancement under the DOE’s Reactor Pilot Program, which establishes a fast-track pathway for advanced reactor demonstration and commercial licensing.

The NSDA approval establishes the safety framework that will guide the reactor’s continued development.