Deep Fission, Inc. (Nasdaq: FISN), a company developing small modular pressurized water reactors installed one mile underground, announced that the U.S. Department of Energy has approved its Nuclear Safety Design Agreement for its Gravity Nuclear Reactor.

The approval establishes the safety framework for the reactor's continued development and confirms the design warrants advancement under the DOE's Reactor Pilot Program. Deep Fission said the company will move to the next phase of the DOE authorization pathway, advancing toward demonstration and eventual deployment.

"This approval is a major step forward for Deep Fission," said Liz Muller, co-founder and CEO. "We believe our mile-deep design gives us the ability to move faster in the stages ahead."

The announcement comes as Deep Fission advances its commercial pilot project at the Great Plains Industrial Park in Parsons, Kansas. Since breaking ground in December 2025, the company has drilled its first data acquisition well to 6,000 feet and delivered a prototype reactor canister to the site. The company said it is progressing a proof-of-concept program that includes large-diameter well drilling and prototype installation milestones before a full-scale demonstration.

Deep Fission stated that its Parsons demonstration reactor is intended to become a fully Nuclear Regulatory Commission-licensed, commercially operating unit following initial testing and DOE authorization, consistent with Executive Order 14301 and the Reactor Pilot Program.