US-based Deep Fission Completes Full-Scale Reactor Vessel Deployment and Retrieval Demonstration Using Commercial Drilling Equipment

On September 3, 2026, advanced nuclear energy development company Deep Fission, Inc. (stock ticker: FISN) announced that it had completed a deployment and retrieval demonstration of a full-scale non-nuclear prototype reactor vessel using standard commercial drilling and hoisting equipment. The company is developing a technology pathway that deploys small modular pressurized water reactors in boreholes approximately 1 mile deep underground.

In this demonstration, a commercial drilling and hoisting team lowered a 20-foot-long prototype reactor vessel into a 34-inch-diameter, 100-foot-deep borehole, and after completing alignment, retrieved it to the surface. Deep Fission stated that the equipment used in the demonstration was all standard equipment already in commercial use in the drilling industry, with no specially invented, custom-built, or modified nuclear equipment.

Deep Fission CEO and co-founder Liz Muller stated that the focus of this demonstration was that no entirely new specialized equipment needed to be developed. She said the company used commercially available equipment already on the market, and the reactor technology basis comes from pressurized water reactor technology that the nuclear industry has operated for decades. Deep Fission's innovation is primarily reflected in the way mature components are combined, rather than reinventing systems that have never been built.

Deep Fission's technology pathway is built on two mature industrial foundations: commercial drilling and pressurized water reactors. As envisioned by the company, the drilling industry has the capability to drill boreholes of the required diameter and depth, and to place and retrieve loads within boreholes; its Gravity™ nuclear reactor adopts pressurized water reactor technology and uses standard low-enriched uranium fuel. The company states that what it changes is the reactor installation location, not the fundamental reactor physics or fuel cycle.

According to Deep Fission's plan, the reactor will be deployed in a water-filled borehole approximately 1 mile deep underground, using the water column and surrounding rock formations to provide safety barriers, operating pressure, heat transfer, and emergency cooling conditions. The company believes this approach helps simplify plant structures, reduces some of the surface infrastructure required by traditional nuclear facilities, and may improve safety margins, shorten construction timelines, and lower construction costs.

The prototype vessel used in this demonstration is a full-scale non-nuclear replica designed to house the Gravity™ reactor core, and contains no nuclear fuel. Deep Fission stated that this demonstration is part of its commercial validation program, and subsequent work also includes drilling, system integration, regulatory approval, and preparation for commercial operation.

Deep Fission recently received approval from the U.S. Department of Energy (DOE) for its Nuclear Safety Design Agreement (NSDA) for the Gravity™ nuclear reactor. Currently, the company is advancing its deployment arrangements under the U.S. Department of Energy's reactor pilot program, and is developing its first reactor project in Parsons, Kansas.