https://iceberg-research.com/2026/09/24/deep-fission-fisn-a-money-pit/

Deep Fission ($FISN): a Money Pit

September 24, 2026

Please refer to our disclaimer at the bottom of the report.

Main findings

• Nasdaq-listed Deep Fission (FISN) is developing a small modular reactor (SMR) with a capacity of 5MWe-15MWe. The company plans to bury a miniature version of the widely used pressurized water reactor (PWR) one mile deep, inside a 40-60-inch water-filled borehole drilled into hard rock. 

• Like other SMR developers, FISN pitches itself as an AI data-center power solution. But data centers have turned to natural gas to accelerate deployment. Almost all of the roughly 75GW of booked data center on-site generation is natural gas-based. FISN has no regulatory approval and remains years away from commercialization.

• Before its June 2026 IPO, FISN guided to a levelized cost of energy (LCOE) of just $50-70/MWh. Then the company dropped the reference. Using figures disclosed in its June 2026 prospectus, we calculate an LCOE of $289/MWh for the first-of-a-kind (FOAK) reactor and $148/MWh for the nth-of-a-kind (NOAK) reactor, about 200% above prior guidance. This is not competitive with behind-the-meter gas solutions.

• Even this NOAK estimate is too optimistic, as capital cost is understated. Using figures from independent third parties, we estimate NOAK capital cost to be $112mn, 34% above FISN’s estimate, raising our estimated NOAK LCOE to $170/MWh. 

• FISN claims it can secure Nuclear Regulatory Commission (NRC) approval in less than a year. Yet it has already struggled with the less demanding Department of Energy (DOE) process, missing the program deadline while at least four peers have already completed it. Even if NRC approved, commercialization is far from assured: NuScale, which has a much more conventional design, has yet to sell a reactor three years after receiving its NRC license.

• FISN targets deploying its reactor in just six months versus 3-4 years for other advanced SMRs, citing fewer safety-related systems. Yet its own filing states a two-year development timeline. Peers pursue the same simplification strategy, but FISN adds a major step: drilling a one-mile borehole.

• FISN touts the industry’s largest customer pipeline. Most counterparties are undisclosed. Of those identified, one is an undeveloped industrial park with doubtful demand for a nuclear reactor. The other two (Endeavour Energy and Blue Owl) have signed only non-binding agreements. 

• FISN has less than twelve months of cash runway and faces ~$350mn of unfunded capital needs, potentially implying ~43% dilution to its existing shareholders. At the same time, the competition for SMR funding is intensifying: publicly traded SMR names have risen from three before October 2025 to nine today, with three more coming to the market, including a far more established player, Westinghouse.

• FISN is largely a repackaging of the founders’ prior venture, Deep Isolation, a deep-borehole nuclear waste disposal company that has failed to commercialize its concept after a decade.

Background and bull case

Deep Fission (NASDAQ: FISN) is a California-headquartered company founded in 2023. The company is developing a nuclear reactor called Gravity. The reactor is intended to be a miniature version of the conventional pressurized water reactor (PWR), using low-enriched uranium (LEU) as fuel. The company’s key innovation is that its reactor would be buried in a 40-60-inch water-filled borehole one mile (~1.6 km) underground. The reactor is designed with a power generation capacity of 5–15MWe.

Source: Deep Fission

Management claims that its reactor is cheaper to build because its innovative borehole design eliminates certain components required in above-ground PWR reactors. For example, the depth and surrounding geology provide natural containment, potentially eliminating the need for the reinforced concrete and steel containment structures typical of above-ground reactors.

FISN was founded by Richard Muller, a UC Berkeley physics professor, and his daughter Elizabeth, who serve as CTO and CEO of the company, respectively. The company became an unquoted public company in September 2025 through a reverse merger with shell company Surfside Acquisition, before listing on Nasdaq in June 2026.

FISN is participating in the Department of Energy’s (DOE) pilot reactor program. The company is seeking DOE authorization to build a pilot reactor at a site in Parsons, Kansas, by 1H 2027. Then, FISN plans to submit license applications to the Nuclear Regulatory Commission (NRC) to convert the pilot reactor into a commercial facility by the end of 2027, with high-volume deployment targeted to begin in 2028. Because its reactor is based on well-established PWR technology, its licensing pathway would be simpler than for novel advanced reactor designs. 

The company claims that its reactor can then be commercially deployed in as little as six months, compared with three to four years for other small modular reactors (SMR). 

FISN expects the surge in power demand from AI data centers will drive demand for its reactors and claims the largest pipeline of potential customers, representing 18.5GW of prospective capacity.

It’s time for small modular reactor supporters to admit it: natural gas, not SMRs, is the undisputed winner of the AI data center build-out

In early 2024, the market realized that AI would consume enormous amounts of energy. This kicked off a trading frenzy from conventional nuclear, to gas-turbine manufacturers, to the speculative (and often sketchy) SMR companies. Every player, including the most exotic concept, was supposed to win.

Fast forward two years, and the verdict is in. Gas-fired generation is the clear preferred solution for powering AI infrastructure. Data centers have booked 75GW of onsite generation capacity so far. Almost all of them will rely on natural gas.

Source: Semianalysis

While the largest and most efficient combined-cycle gas turbines face multi-year lead times, data centers have turned to smaller engines or aeroderivatives with lead times as short as twelve months. Gas generation is a proven technology and can meet AI power demand quickly, with the added advantage of cheap natural gas in the US. SMRs, on the other hand, sit at exactly the opposite end of the spectrum: they remain unproven, with commercialization not expected before the 2030s. 

The political environment has also become more favorable to fossil-fuel-based generation, removing one of the key roadblocks to new gas development.

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