Deep Fission Targets 2026 for First Underground 15 MW Nuclear Reactor, Poised to Revolutionize Energy Landscape

BERKELEY, CA — Deep Fission, a pioneering US nuclear energy startup, is making headlines with its ambitious plan to deploy 15-MWe small modular reactors (SMRs) a mile underground, targeting initial criticality for a pilot project by 4 July 2026. This initiative is part of the Department of Energy's (DOE) new Reactor Pilot Programme, which seeks to fast-track advanced nuclear technologies. The company envisions these subterranean reactors as a scalable solution for the rapidly growing energy demands of data centres and other industrial applications.

Advancing Underground Nuclear Technology

Deep Fission's core innovation lies in its “Borehole Reactor” design, which involves placing small modular pressurised water reactors one mile (approximately 1.6 kilometres) underground via 30-inch boreholes. This approach leverages natural geology for shielding, aiming to enhance safety and security while significantly reducing the surface footprint of nuclear power generation.

The 15-MWe Deep Fission Borehole Reactor-1 (DFBR-1)

The company's primary project, the DFBR-1, is a 15-MWe pressurised water reactor that integrates established nuclear, drilling, and geothermal technologies. This design is expected to dramatically reduce construction time and expense, potentially cutting costs by up to 80 per cent compared to traditional nuclear megastructures. Deep Fission aims for a levelised cost of electricity (LCOE) of 5 to 7 cents per kilowatt-hour for its initial commercial projects.

Strategic Timeline and DOE Partnership

Selected for the DOE's Reactor Pilot Programme, Deep Fission has gained a streamlined regulatory pathway to test and commercialise its advanced designs outside national laboratories. While the Kansas pilot project targets criticality by 4 July 2026, Deep Fission has also partnered with sustainable infrastructure firm Endeavour Energy to deploy its first commercial reactors by 2029, aiming to supply 2 gigawatts of power to Endeavour's Edged data centres.

Funding and Public Listing

Further solidifying its position, Deep Fission secured $30 million in an oversubscribed private placement offering and completed a go-public reverse merger with Surfside Acquisition Inc., which has since been renamed Deep Fission, Inc. This funding supports the construction of the pilot reactor and accelerates rapid commercialisation.

Addressing Growing Energy Demands

The push for underground nuclear reactors comes amid an explosion in demand for energy, particularly from data centres that power artificial intelligence (AI), cloud computing, and cryptocurrency mining. These facilities require vast amounts of electricity, and Deep Fission's carbon-free power source offers a compelling solution to meet this demand sustainably. Deep Fission CEO Elizabeth Muller emphasised the unique moment for the nuclear industry, stating that the company can scale its technology rapidly and profitably to address this global energy need.

Safety, Security, and Environmental Advantages

The decision to site reactors a mile underground provides several inherent advantages. The surrounding geology offers natural shielding and protection, with billions of tonnes of bedrock providing passive safety and containment. This design not only reduces the surface footprint but also strengthens security, aligning with Deep Fission's commitment to delivering safe, reliable, and affordable low-carbon power. The company utilises off-the-shelf parts and readily available, low-enriched uranium, simplifying supply chains compared to other advanced reactor designs.

Borehole Waste Isolation: How the System Seals Spent Fuel

One of the most persistent hurdles for any modern small modular reactor is the long-term management of high-level radioactive waste. Deep Fission addresses this challenge by leveraging its core borehole architecture, drawing on extensive expertise in deep borehole disposal. This method bypasses the political and logistical gridlocks associated with centralised surface repositories.

When an underground small modular reactor reaches the end of its fuel cycle, or during decommissioning, the spent fuel does not need to be transported across public infrastructure to a temporary surface pool. Instead, the engineering design facilitates a secure, in-situ isolation strategy where the system seals spent fuel canisters deep within the stable geological formations directly beneath or adjacent to the reactor zone.

The Sealing and Containment Process

To guarantee that radioactive isotopes remain isolated from the biosphere for hundreds of thousands of years, the borehole repository relies on a robust multi-barrier system:

• Corrosion-Resistant Canisters: The spent fuel is housed in heavy-walled canisters constructed from corrosion-resistant alloys, designed to withstand extreme hydrostatic pressures and aggressive chemical environments at depth.
• Bentonite Clay Barriers: The space surrounding the canisters is filled with high-density swelling bentonite clay. When exposed to deep groundwater, the bentonite expands to create an impermeable, self-healing seal that prevents fluid migration.
• Bridge Plugs and Cementitious Seals: Alternating layers of high-performance concrete, structural asphalt, and mechanical bridge plugs are positioned above the waste zone. This combination seals spent fuel assemblies permanently, preventing any upward pathway through the borehole.
• Geological Containment: At a depth of one mile (approximately 1,600 metres), the host rock—typically highly stable, low-permeability crystalline bedrock or thick shale—acts as the ultimate natural barrier, completely isolated from freshwater aquifers.

The Road Ahead

While Deep Fission's approach presents a promising future for nuclear energy, experts acknowledge that the technology still faces operational and regulatory challenges. However, the company is actively engaged with the Nuclear Regulatory Commission (NRC) in pre-application activities for the licensing of the DFBR-1. Deep Fission's co-founders, father-daughter team Richard and Elizabeth Muller, also have ties to Deep Isolation, a company focused on deep borehole disposal of spent nuclear fuel, highlighting a comprehensive approach to the nuclear fuel cycle. The Department of Energy's fast-track programme, coupled with significant private investment, positions Deep Fission to potentially achieve its ambitious 2026 target and play a transformative role in the future of clean energy.