The U.S. Department of Energy has approved the Nuclear Safety Design Agreement (NSDA) for the Gravity Nuclear Reactor developed by Deep Fission, a California-based startup founded in 2023 and listed on the Nasdaq under the ticker FISN. The approval, granted on August 6, 2026, confirms that the reactor design merits advancement within the DOE Reactor Pilot Program — the federal fast-track pathway for the demonstration and commercial licensing of advanced reactors.
The NSDA does not authorize reactor operation, but it establishes the safety framework that will govern all subsequent development. It is the first of four regulatory gates in the DOE authorization pathway to receive a federal sign-off. With this milestone secured, Deep Fission can move forward to the next phase of the licensing process, which includes operational demonstration and the eventual commercial deployment of the reactor. The company also made the full NSDA document publicly available — becoming the first participant in the DOE program to do so. CEO Liz Muller explicitly framed this as a deliberate commitment to building the project “in the open.”
The Gravity Nuclear Reactor is a 15 MWe pressurized water reactor designed to be lowered into a drilled borehole approximately one mile below the earth’s surface. PWR technology has a proven track record spanning seven decades; Deep Fission’s innovation lies in the underground installation, which eliminates the need for surface containment structures and aims to streamline construction by significantly reducing civil works costs. The reactor uses standard low-enriched uranium. The company argues that the overlying water column provides natural shielding, effectively replacing the conventional containment dome.
On the operational front, Deep Fission is making progress at its commercial pilot site at the Great Plains Industrial Park in Parsons, Kansas, where work began in December 2025. Since then, the company has drilled its first data-acquisition well to a depth of 1,800 meters and delivered a reactor canister prototype to the site. The Reactor Pilot Program in which Deep Fission participates was established by an executive order from the Trump administration to accelerate advanced nuclear development and meet rising energy demand. The stated goal is to convert the demonstration reactor into a fully NRC-licensed unit ready for commercial operation.
The business model targets utilities, industrial customers, and data centers. Deep Fission contends that ten Gravity reactors generate 150 MWe, while one hundred units on a single site can reach 1.5 GWe — with a land footprint far smaller than that of conventional nuclear plants. If the Kansas pilot program proceeds on schedule, this approach could become a tangible benchmark in the coming years for those seeking low-carbon baseload generation without large surface-level infrastructure.
