Engineers in Parsons, Kansas, are preparing to test an unusual small modular reactor concept developed by California-based Deep Fission. Known as the Gravity Reactor, the design places the reactor canister roughly one mile underground inside a water-filled borehole.

 

Engineers in Parsons, Kansas, are preparing to test an unusual small modular reactor concept developed by California-based Deep Fission.

Known as the Gravity Reactor, the design places the reactor canister roughly one mile underground inside a water-filled borehole. Instead of relying on the massive concrete containment structures and steel pressure vessels used at conventional nuclear facilities, the concept uses the surrounding geology and the weight of the water column as part of its containment and cooling system.

At that depth, the water above the reactor creates substantial natural pressure. Deep Fission says the pressure could reach around 160 atmospheres, reducing the need for some of the large surface structures associated with traditional nuclear plants.

The company also expects the underground design to reduce construction and operating costs, with estimates suggesting potential savings of up to 80 percent. Those figures remain projections and will need to be demonstrated through engineering tests and future operation.

A full-scale, non-nuclear prototype reactor canister has already arrived at the Kansas site. The prototype is part of the project's proof-of-concept phase and will be used to test installation procedures, equipment, and engineering assumptions before any nuclear fuel is introduced.

The approach is attracting attention at a time when electricity demand is rising rapidly. Artificial intelligence, cloud computing, manufacturing, and large data centers are placing additional pressure on power grids, increasing interest in reliable sources of electricity that can operate around the clock without direct carbon emissions.

Deep Fission's concept is still at the demonstration stage. The Kansas testing program will be important in determining whether an underground reactor can deliver the safety, reliability, and cost advantages its developers envision.

If the technology works as intended, it could offer a very different approach to nuclear power: smaller reactors installed deep underground rather than large facilities built around enormous surface structures.

Source: World Nuclear News, 2026. Deep Fission receives prototype reactor canister.— in New York

Neil Degrasse Tyson

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