Deep Fission drills in Kansas for a 1,800-metre-deep nuclear reactor

Far beneath the Midwest prairie, drilling crews are cutting a slim shaft through ancient stone that could soon cradle a miniature sun.

In a still patch of Kansas, a California start-up is staking its future on an unusual idea: the most secure place for a nuclear reactor may be not inside vast concrete fortresses, but nearly two kilometres underground-sealed within rock that has scarcely shifted for millions of years.

A nuclear plant that disappears below ground

Deep Fission, a California-based newcomer, has begun drilling test wells for what it says will become the first commercial nuclear reactor installed at extreme depth. The work is being carried out near the city of Parsons in south-eastern Kansas, selected for its stable geology and well-characterised subsurface strata.

On 11 March, teams started drilling the first of three exploratory wells. Each borehole is planned to reach about 6,000 feet (roughly 1,830 metres) and measures just 20 centimetres across. The company is relying on standard oil-and-gas drilling rigs-the same type used widely across US shale regions.

"The aim: slide a 15‑megawatt thermal reactor down a narrow shaft, and let the surrounding rock act as its natural shield."

These first wells will not generate electricity. Instead, they function as a geological “check-up”. Engineers will record the rock sequence in detail, assess how dense and impermeable each layer is, and evaluate how drilling tools perform at that depth. That evidence is intended to validate whether the location can safely accommodate the reactor module.

If what they find aligns with the company’s modelling, Deep Fission plans to drill a fourth well designed specifically to hold the reactor. The unit would be lowered straight down and hung on a cable within a water-filled cavity at the base of the shaft.

How a deep borehole reactor works

Deep Fission’s concept is derived from conventional pressurised water reactors, reconfigured to suit a borehole. The core is far smaller, built as a sealed module, and designed so it can be installed or retrieved using dedicated lifting equipment.

At around 1,800 metres below ground, the column of water above the reactor would exert pressure of about 160 atmospheres. In surface-based stations, comparable pressures are handled by thick steel pressure vessels and extensive reinforcement; in this approach, depth and gravity provide the pressure naturally.

"The water column doubles as coolant, pressure vessel and part of the safety system, reducing the need for massive steel structures at ground level."

Heat produced in the core is passed to water, which then circulates up the well to heat exchangers. At the surface, that thermal energy is converted into electrical power. The initial unit is planned to deliver roughly 15 megawatts of heat, which equates to around 5 megawatts of electricity-enough to supply a small industrial site, a group of rapidly expanding data centres, or a remote community.

Using the Earth as a containment structure

Today’s nuclear plants typically depend on huge concrete containment buildings intended to keep radioactive material confined in extreme accident scenarios. Deep Fission’s proposal assigns that containment role largely to the surrounding bedrock.

The chosen Kansas location sits over dense rock with low permeability. Such formations are sought because liquids move through them only very slowly and because they show limited tectonic disturbance. If a major failure were to occur, the concept is that radioactive products would remain trapped almost two kilometres below ground, separated from the surface by thick geological barriers.

"The rock becomes a biological shield, replacing the multi‑metre concrete shells that dominate the skyline of traditional nuclear facilities."

Placing the system underground also reduces the surface presence. Above ground, the site would resemble an oil well pad more than a conventional nuclear power station: a compact spread of equipment, power-conversion hardware and control rooms, without prominent cooling towers or domed structures.

Costs, timelines and the promise of fast build‑out

Deep Fission maintains that its underground approach can cut both build time and upfront cost. Large nuclear projects in the US and Europe are frequently late and over budget, often because of complex civil construction and one-off engineering.

The company, by contrast, says that standard drilling rigs, modular reactor hardware and limited surface works could allow a single unit to be installed in about six months once permitting and site preparation are complete. It also argues that the cost per installed megawatt could fall by a factor of around five compared with existing large reactors.

• No massive reactor buildings or cooling towers
• Standardised drilling equipment from the oil and gas sector
• Small, repeatable reactor modules designed for serial production
• Reduced land use and visual impact on surrounding communities

Backers have taken notice. Deep Fission has raised close to $80 million to advance the idea from paper studies to the Kansas pilot. It has also agreed a fuel supply deal with Urenco USA for low-enriched uranium-the same category of fuel used in many current reactors, adapted for the smaller core.

Safety logic: passive cooling and seismic resilience

Burying the reactor in a deep borehole changes several assumptions about nuclear safety. A major claim is that the system can depend less on active equipment and emergency electricity supplies.

In most existing plants, pumps constantly force coolant through the core. If the grid goes down, generators and batteries must take over to prevent temperatures from rising dangerously. In Deep Fission’s design, the water column above the core is intended to enable passive flow through natural convection: warmer water rises while cooler water sinks, creating circulation that removes heat without mechanical pumping.

"In an emergency shutdown, the system is designed so that gravity and buoyancy handle the job that diesel generators normally perform."

The narrow, vertical geometry could also behave differently in an earthquake compared with broad surface structures. Set within stable rock, the reactor module sits in a slim, symmetric cavity that is less exposed to lateral shaking than large concrete buildings above ground.

Who might use a 5‑megawatt underground reactor?

The first customers being pursued are not typical utility-scale power buyers. Deep Fission is aiming at distributed, energy-intensive operations that need continuous electricity but do not have straightforward access to dependable grid supply.

They include:

• Data centres supporting AI training, cloud services and streaming platforms
• Remote mines and industrial sites in need of stable off‑grid power
• Military or government facilities requiring secure, independent supply
• Isolated communities where long transmission lines are expensive or fragile

Because the reactor and much of the associated risk would sit underground, the company believes opposition linked to appearance and land take could be less intense than for surface nuclear plants. A multi-reactor site of boreholes could look more like a small industrial compound than a traditional power station.

Key concepts worth unpacking

What “15 megawatts thermal” really means

Reactor capacity is commonly stated in megawatts thermal (MWt), which refers to heat output rather than electrical generation. Only a fraction of that heat becomes electricity. In this case, 15 MWt is expected to convert to roughly 5 megawatts electric (MWe) after losses in the power-conversion process.

For context, a large modern nuclear station might generate 3,000 MWt and deliver about 1,000 MWe-around two hundred times the electrical output of Deep Fission’s first unit. The smaller scale makes an underground pilot more feasible, but it also implies that many units would be required to match the output of one large plant.

What happens at the end of life?

Decommissioning and spent fuel are among the most sensitive issues for any nuclear project of this kind. Deep Fission presents its reactor as a sealed module. When the unit reaches the end of its service life, the plan is to haul the entire module back up the same shaft and, if the location continues operating, lower a replacement module into place.

The spent core would then be sent for long-term storage or reprocessing, in much the same way as fuel from conventional plants. The borehole itself could then be closed using engineered plugs and cement, effectively adding another barrier. Before any long-term rollout, regulators are likely to examine these steps closely as part of the licensing process.

Risks, regulatory hurdles and wider implications

Even with ambitious claims, the proposal will face intense examination. US nuclear regulators must decide how to license a design that does not fit comfortably into frameworks written for large, surface-based reactors. Emergency planning zones, inspection practices and liability arrangements may all need to be revised.

Environmental organisations may also challenge the assumption that deep burial removes contamination risk, especially over long timescales or in areas with complicated groundwater behaviour. Critics may point to the difficulties encountered by deep geological repositories for nuclear waste as evidence that rock is not a perfect seal.

"The Kansas wells will act as a real‑world test of whether drilling technology, nuclear engineering and geology can truly work together at scale."

If Deep Fission achieves its stated goal of reaching “criticality”-when the chain reaction becomes self-sustaining-by July 2026, it could mark a significant milestone for small nuclear technologies. A successful demonstration could also prompt oil and gas firms to redirect drilling expertise towards energy generation that produces no carbon dioxide during operation.

Conversely, setbacks, rising costs or engineering difficulties could deepen doubts about next-generation nuclear approaches. A large part of the argument about climate-friendly power turns on whether nuclear can overcome a reputation for slow, expensive delivery. An operating reactor 1,800 metres underground in Kansas would be a compelling data point in that debate, followed closely not only in the US but also by policymakers and investors elsewhere.