Deep Fission Targets 2027 Debut for Underground Nuclear Reactors

Key Points

• Underground reactor model: Deep Fission plans to deploy existing pressurized water reactor technology in boreholes roughly one mile underground, using surrounding rock and the water column for containment, pressure, heat transfer and emergency cooling. The company says this could reduce construction costs and timelines compared with conventional nuclear plants.
• Commercial target and regulatory path: The company is targeting a first 5-megawatt commercial reactor in late 2027, followed by 15-megawatt units from 2028. It has received DOE approval for a Nuclear Safety Design Agreement and is pursuing NRC authorization under the proposed Part 57 framework, though approval timing remains uncertain.
• Kansas launch site and expansion plans: Deep Fission selected Great Plains Industrial Park in Parsons, Kansas, for initial development and is testing larger boreholes that could improve fuel economics. It cites an 18.5-gigawatt customer pipeline and envisions projects scaling to roughly 1 gigawatt across 100 acres.

Deep Fission NASDAQ: FISN is pursuing an underground approach to advanced nuclear power, with plans to place pressurized water reactors in boreholes roughly a mile below the surface, Co-Founder and CEO Liz Muller said at Canaccord Genuity’s 46th annual growth conference.

Muller said the company’s model is designed to reduce the construction complexity, time and cost associated with conventional above-ground nuclear plants. Rather than developing a new reactor physics concept, Deep Fission is using existing pressurized water reactor technology in a different environment, she said.

“We are taking existing, available pressurized water reactor technology, but we are deploying it in a new model that is much faster and much, much less expensive,” Muller said.

Using Geology as Part of the Plant Design

According to Muller, locating reactors underground allows Deep Fission to use the surrounding rock and water column for functions that normally require major plant systems and structures. The company’s concept uses a mile of water in the borehole to provide pressure, transfer heat and serve as an emergency cooling resource, while the surrounding rock would serve a containment function.

Muller said the company therefore does not need components including a conventional containment dome, a separate pressurizer or a large reactor pressure vessel. She contrasted the company’s reactor canister with above-ground reactor pressure vessels, which she said can cost about $1 billion and have limited manufacturing availability.

Deep Fission plans to use drilling technology developed in the oil-and-gas sector and heat-transfer practices used in geothermal power. Muller described the concept as “nuclear-assisted geothermal,” noting that an operating site would resemble a geothermal facility from the surface because the reactors would be underground.

While geothermal projects depend on naturally hot rock formations, Deep Fission’s heat would be generated principally by the nuclear reactor, Muller said. This could provide greater geographic flexibility than conventional geothermal development, she added.

Commercial and Regulatory Timeline

The company is participating in the U.S. Department of Energy’s Reactor Pilot Program and is targeting its first commercial reactor for late 2027, with larger-scale commercial deployment beginning in 2028, according to Muller. She said the company is pursuing a full commercial reactor rather than a test reactor or criticality experiment.

Deep Fission recently received approval from the Department of Energy for its Nuclear Safety Design Agreement, Muller said, describing the agreement as a framework for presenting the company’s safety case to the agency.

The company is also pursuing Nuclear Regulatory Commission authorization in parallel with the DOE process. Muller said Deep Fission expects to use the NRC’s proposed Part 57 regulatory framework, which she said is expected to be finalized by the end of 2026. She said the framework is intended to focus more on a reactor’s safety case than on requirements tailored to traditional above-ground facilities.

Still, Muller acknowledged uncertainty around approvals while expressing confidence that the company could generate electricity from its first commercial reactor next year.

Kansas Site, Supply Chain and Project Pipeline

Deep Fission has selected a location at Great Plains Industrial Park in Parsons, Kansas, for its initial development work. Muller said the industrial park has been zoned for nuclear and industrial uses for more than 20 years and includes infrastructure such as roads, a security perimeter and rail access.

The company is currently working on a proof-of-concept effort focused on drilling larger-diameter boreholes. Deep Fission expects to begin with boreholes about 40 inches in diameter and ultimately move toward diameters closer to 60 inches. A larger borehole could accommodate nine fuel assemblies rather than four, improving fuel economics, Muller said.

For 2027, the company expects an initial 5-megawatt electric installation, a size Muller said could support a faster grid-interconnection process. Beginning in 2028, it is targeting 15 megawatts electric per reactor. Muller said a site with roughly 70 reactors could provide about 1 gigawatt across 100 acres.

Deep Fission estimates drilling a well would take about 60 days and said total build time would be measured in weeks rather than years. It has already received a prototype reactor canister at its site and expects the next version to require about six months to manufacture and deliver.

• Deep Fission said it has an 18.5-gigawatt customer pipeline.
• The company plans to use standard low-enriched fuel already used in conventional pressurized water reactors.
• Muller said potential fuel suppliers include Framatome and Westinghouse.
• The company cited supply-chain relationships including Halliburton, Day & Zimmermann, Urenco and RWB Industries.

Operations and Safety Approach

Deep Fission intends to operate under a build-own-operate model, at least for its first project. Muller said the company sees the model as responsive to customer demand for a proven operating facility and said it expects project payback periods of less than five years.

On maintenance, Muller said the company plans to replace an entire reactor canister rather than refuel it at the surface. Used reactor units could be lowered into additional space at the bottom of the borehole for storage before eventual removal to a disposal facility, or potentially left in the borehole for disposal.

Addressing questions about groundwater and potential reactor incidents, Muller said the borehole would be steel-cased and cemented in place. She said the company views a loss-of-coolant scenario as unlikely because the water column has no apparent route to escape, while the depth of the facility would provide separation from the surface.

About Deep Fission (NASDAQ:FISN)

Deep Fission Inc develops and deploys small modular nuclear reactors placed deep underground to generate electricity. Deep Fission Inc is based in Berkeley, California.

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