Deep Fission is developing the Gravity reactor, a 15 MWe pressurised water reactor designed to be placed underground in an optimised borehole one mile deep. The company broke ground in December 2025 at the Great Plains Industrial Park in Parsons, Kansas. Deep Fission was selected by the US DOE for its Nuclear Reactor Pilot Program. The Gravity design places a small reactor roughly one to two kilometres underground in a drilled borehole, which simplifies siting, reduces seismic risk and eliminates the need for a conventional containment building, potentially unlocking nuclear deployment where surface siting is impossible due to land constraints, population density or regulatory requirements. Deep Fission was selected for the DOE Reactor Pilot Program in August 2025. An earlier record listed 30 MW.