California-based start-up Deep Fission, which plans to place small modular pressurised water reactors in boreholes one mile underground, has begun drilling its first data acquisition well in Parsons, Kansas. The well is the first of three planned wells and represents the initial phase of site characterisation and engineering validation. It will be drilled to a depth of approximately 6,000 feet and will have a diameter of roughly eight inches.
Construction of the drilling pad at the Parsons site has also been completed, preparing the location for drilling operations marking a key infrastructure milestone on the path from planning and engineering to active field development.
The data acquisition well will make it possible to gather critical geological, hydrological, and thermal data to inform final engineering design, safety analysis, and regulatory planning. The drilling campaign and subsequent testing programme will support a series of technical evaluations aimed at accelerating progress to commercial deployment.
Deep Fission’s approach integrates proven pressurised water reactor (PWR) technology with advanced drilling methods developed in the oil and gas industry and geothermal heat-transfer techniques. Each 15 MWe Gravity Reactor, using low enriched uranium fuel, is designed to be installed deep underground in a sealed borehole, leveraging stable bedrock for natural shielding and containment. Its small footprint and dense power output means it will need a fraction of the land needed for traditional surface nuclear: ten reactors on the same site would deliver 150 MWe, while 100 reactors would produce 1,500 MWe.
Deep Fission broke ground in December at the Great Plains Industrial Park in Parsons, Kansas, for its pilot project and plans to build a full-scale commercial plant there following the test reactor demonstration.
In August 2025, Deep Fission was one of 10 companies selected by the US Department of Energy (DOE) to receive support under its Nuclear Reactor Pilot Program, which aims to see at least three designs achieve criticality by 4 July 2026. This was authorised under the May 2025 Executive Order 14301, which allows reactor testing and deployment on sites outside of national laboratories.
The three-well drilling programme is expected to provide the subsurface data necessary to advance reactor demonstration and future commercialisation efforts. “Drilling our first borehole is a major step forward for Deep Fission,” said Liz Muller, CEO and Co-Founder of Deep Fission. “It represents the shift from concept to construction and begins the process of demonstrating a fundamentally new approach to nuclear energy deployment.”
Deep Fission was founded in 2023 by father-daughter team Elizabeth and Richard Muller, who also co-founded Deep Isolation in 2016 to develop the concept of placing canisters of radioactive waste hundreds of metres underground via a borehole.
