US DOE Approves Nuclear Safety Design Agreement for Deep Fission Underground SMR

Deep Fission, a US advanced nuclear energy company, announced on August 6 that the US Department of Energy (DOE) has approved the Nuclear Safety Design Agreement (NSDA) for its Gravity reactor. The company stated that this milestone means its reactor design meets the requirements for continued advancement under the DOE's Reactor Pilot Program.

Deep Fission is developing a small modular pressurized water reactor concept, with plans to place the reactor in a borehole approximately 1 mile, or about 1.6 kilometers, underground. The approved Nuclear Safety Design Agreement will serve as the safety framework for subsequent reactor development work. According to the company's plans, the project will proceed to the next phase of the DOE authorization process, preparing for technology demonstration and subsequent deployment of the underground nuclear reactor.

Liz Muller, co-founder and CEO of Deep Fission, stated that this approval marks an important step for the company. She noted that the company believes its approximately 1-mile-deep underground deployment design will help accelerate progress in subsequent phases.

Currently, Deep Fission's commercial pilot project at the Great Plains Industrial Park in Parsons, Kansas, continues to advance. Since site construction began in December 2025, the project has completed drilling of the first data acquisition well, reaching a depth of 6,000 feet, approximately 1,829 meters. The company has also recently delivered a prototype reactor pressure vessel to the project site and is advancing its proof-of-concept plan, which includes large-diameter well drilling and prototype installation, laying the groundwork for subsequent full-scale demonstration.

Deep Fission stated that the Parsons project is not a one-time criticality test. Under its plan, the demonstration reactor will be used for power generation after completing initial testing and receiving DOE authorization, and will further be developed into a commercially licensed facility under a full NRC license. The company said this pathway is designed to directly link the demonstration project with commercial deployment.

Deep Fission's Gravity reactor concept combines proven pressurized water reactor technology with an underground deployment model, aiming to establish a new pathway for simplifying construction processes, enhancing safety, and supporting scalable commercial deployment. The company stated that its technology targets growing electricity demand scenarios such as utilities, industrial users, and data centers, providing low-carbon baseload power.