Deep Fission, Inc., headquartered in Berkeley, California, is an advanced nuclear energy company developing a fundamentally different approach to deploying small modular nuclear reactors by installing them approximately one mile underground inside deep engineered boreholes. The company’s website is ⁠Deep Fission. Founded in 2023, Deep Fission seeks to combine proven pressurized water reactor technology with modern deep-drilling techniques developed by the oil and gas industry to produce reliable, carbon-free electricity at lower cost and with a smaller surface footprint than conventional nuclear power plants. Rather than inventing an entirely new reactor physics design or fuel cycle, the company is attempting to simplify deployment by changing where the reactor is located instead of how nuclear fission itself works. (⁠Deep Fission, Inc.)

Deep Fission was founded by the father-and-daughter team of Elizabeth “Liz” Muller and Dr. Richard Muller. Liz Muller serves as Co-Founder, President, Chief Executive Officer, and Chair of the Board. She previously co-founded Deep Isolation, a company pioneering deep borehole disposal of spent nuclear fuel and radioactive waste, where she led the company through early commercialization and regulatory engagement. Earlier in her career she co-founded Berkeley Earth, a nonprofit organization that produces independent climate and temperature research, and served as a policy advisor with the Organisation for Economic Co-operation and Development (OECD). Her career has consistently focused on combining science, engineering, environmental stewardship, and practical commercialization of complex technologies. (⁠Deep Fission, Inc.)

Her father, Dr. Richard Muller, serves as Co-Founder and Chief Technology Officer. Dr. Muller is Professor Emeritus of Physics at the University of California, Berkeley, an inventor holding more than eighty patents, author of over one hundred scientific publications, recipient of numerous scientific awards including the MacArthur Fellowship and the NSF Alan T. Waterman Award, and author of several books on physics and energy policy. He also spent more than three decades as a member of JASON, the scientific advisory organization that has long advised the United States government on advanced defense and technology issues. Together, the Mullers bring an unusual combination of nuclear engineering, physics, deep borehole technology, climate science, public policy, and entrepreneurial experience to the company. (⁠SEC)

The company’s mission is straightforward: expand access to abundant, reliable, low-carbon electricity by dramatically reducing the cost, construction time, and siting challenges associated with conventional nuclear power plants. Deep Fission believes growing electricity demand driven by artificial intelligence, hyperscale data centers, advanced manufacturing, industrial electrification, and transportation electrification will require many additional sources of dependable “firm” generation that can operate continuously regardless of weather conditions. Rather than replacing renewable energy, the company views its technology as complementary infrastructure capable of providing steady baseload electricity twenty-four hours a day throughout the year. (⁠Deep Fission, Inc.)

The underlying engineering concept is both innovative and conservative. The reactor itself is based upon familiar pressurized water reactor technology using conventional low-enriched uranium fuel and established nuclear supply chains. The innovation lies in placing the reactor approximately one mile underground inside a narrow engineered borehole. The surrounding water column naturally provides approximately the same pressure required by conventional pressurized water reactors, while the surrounding rock provides exceptional radiation shielding and physical protection. The Earth itself becomes part of the engineered safety system, reducing dependence upon massive above-ground containment structures and potentially lowering construction costs while improving protection from aircraft impacts, tornadoes, hurricanes, wildfires, and other external hazards. (⁠Deep Fission, Inc.)

Heat generated by nuclear fission would be transferred through engineered piping to the surface where conventional steam turbines and electrical generators would convert thermal energy into electricity. Surface facilities would still include turbines, condensers, switchyards, transformers, cooling equipment, control rooms, and security systems, but the nuclear reactor itself would remain approximately one mile below ground.

The company’s current reactor concept is expected to produce approximately 45 megawatts of thermal energy and roughly 15 megawatts of electrical output. That size places it well below conventional commercial reactors while making it attractive for modular deployment. Instead of constructing one very large generating station, customers could install multiple identical reactor boreholes to match their required electrical capacity.

This modular architecture may become one of the technology’s greatest strengths. A single installation could provide approximately 15 megawatts of dependable electricity for a remote industrial facility, military installation, mining operation, research laboratory, or isolated community. A cluster of ten installations could provide approximately 150 megawatts suitable for a medium-sized industrial campus. Fifty units could approach 750 megawatts, while one hundred reactor boreholes could theoretically provide approximately 1.5 gigawatts of continuous electrical generation suitable for very large industrial parks or hyperscale artificial intelligence computing campuses. The ability to add capacity incrementally rather than constructing one enormous plant allows the system to scale from relatively modest electrical loads to utility-scale generation using standardized reactor modules.

Today the company remains in the advanced development and regulatory engagement stage rather than commercial operation. Deep Fission has been selected to participate in the U.S. Department of Energy Reactor Pilot Program and has maintained active pre-application engagement with the U.S. Nuclear Regulatory Commission. The company has completed conceptual reactor design work, submitted conceptual design documentation to the NRC, initiated geological investigations, begun borehole drilling activities at its demonstration location in Parsons, Kansas, and recently delivered a full-scale prototype reactor canister for non-nuclear installation testing. These are significant engineering milestones, but they should not be confused with commercial operation. The recently delivered prototype contains no nuclear fuel and is intended to validate installation procedures, handling methods, and large-scale mechanical systems rather than produce electricity. (⁠Deep Fission, Inc.)

Several important milestones remain before commercial deployment becomes possible. The company must complete geological characterization of its demonstration site, validate large-borehole construction techniques, demonstrate reliable installation and retrieval of the reactor canister, complete thermal and hydraulic testing, finalize engineering designs, continue extensive engagement with the Nuclear Regulatory Commission, obtain the necessary construction and operating licenses or other applicable regulatory authorizations, demonstrate safe long-term operation, and ultimately prove that its projected economic advantages can be achieved under commercial operating conditions.

One of the most interesting engineering questions concerns maintenance and refueling. Because the reactor operates approximately one mile underground, technicians cannot simply walk into a containment building and perform routine maintenance. Instead, the reactor is expected to function as a modular unit that can be retrieved from the borehole when significant maintenance or refueling becomes necessary. This means major service activities would likely involve disconnecting the reactor module, lifting the entire canister to the surface using specialized equipment, performing maintenance within shielded facilities, and then lowering the reactor back into the borehole.

For an individual installation containing only one reactor, this specialized maintenance equipment could represent a significant capital expense. Much of the required lifting equipment, shielding systems, fuel handling equipment, and radiological support infrastructure might need to be brought to the site only when major maintenance or refueling becomes necessary. If those activities occur only every several years, maintaining dedicated permanent equipment at every small installation could prove economically inefficient.

By contrast, a larger campus containing ten, twenty, fifty, or even one hundred reactor boreholes could share a centralized maintenance facility. Such a site could justify permanent heavy lifting systems, shielded maintenance buildings, spent fuel handling equipment, inspection facilities, trained maintenance personnel, and specialized service equipment. Individual reactor modules could then be serviced sequentially while the remaining reactors continue supplying electricity. This type of shared infrastructure may become an important economic advantage for larger multi-reactor installations.

Based upon the publicly available information released to date, Deep Fission has not yet published definitive commercial refueling intervals. Conventional pressurized water reactors often operate between approximately eighteen months and several years between refueling outages depending upon fuel enrichment, reactor design, operating strategy, and fuel management practices. Because Deep Fission’s reactor geometry differs substantially from conventional commercial reactors, and because detailed core design information has not yet been released publicly, it is not presently possible to determine an accurate refueling interval. That operating characteristic will likely become clearer as licensing documents and detailed engineering information become available through the regulatory process. At present, any precise estimate would be speculative rather than technically supported.

Like every advanced reactor concept currently under development, Deep Fission faces important engineering challenges. Long-term reliability of mile-deep piping systems, inspection of underground components, retrieval of reactor modules after many years of operation, groundwater protection, borehole integrity, corrosion management, and demonstration of practical maintenance procedures all remain subjects requiring successful engineering validation. None of these challenges appear fundamentally impossible, but each must be demonstrated through careful testing before widespread commercial adoption becomes realistic.

Nevertheless, Deep Fission represents one of several promising directions now emerging within the advanced nuclear industry. Other companies are pursuing conventional small modular reactors enclosed within traditional containment buildings, high-temperature gas reactors, molten salt reactors, sodium-cooled fast reactors, microreactors for remote installations, and other advanced concepts. Some designs emphasize simplicity and proven technology. Others emphasize higher operating temperatures, different fuel cycles, or greater electrical efficiency. Deep Fission distinguishes itself by using largely conventional reactor technology while fundamentally changing the physical environment in which the reactor operates.

The coming decade is likely to provide governments, utilities, industrial companies, and large electricity consumers with an increasingly diverse portfolio of firm generation technologies. Some will continue using conventional containment structures. Others may employ underground borehole deployment. Some will serve large regional electrical grids, while others will provide dedicated power for industrial facilities, military installations, artificial intelligence computing centers, advanced manufacturing campuses, and remote communities. Together with improvements in energy storage, transmission, and renewable generation, these emerging nuclear technologies may significantly expand society’s ability to provide the continuous, reliable electricity required to support artificial intelligence, advanced computing infrastructure, semiconductor manufacturing, robotics, electrified transportation, and the homes, businesses, hospitals, schools, factories, and critical infrastructure that will define the next generation of economic growth. Whether Deep Fission ultimately becomes one of the industry’s long-term success stories will depend upon its ability to successfully complete the engineering demonstrations, regulatory approvals, operational validation, and commercial scaling that still lie ahead, but its concept illustrates the growing diversity of approaches now being pursued to provide dependable, weather-independent electrical generation for the future.