Deep Fission Is Burying Its Nuclear Reactors a Mile Underground

The most expensive real estate for a nuclear reactor is not the land itself. It is the acres of concrete, the security perimeter, and the political capital required to build on the surface. Deep Fission has a simple, if audacious, counter-proposal: go down. A mile down.

The borehole wedge

Deep Fission's bet is that by placing its small modular pressurized water reactor underground, it can sidestep the surface-level costs and controversies that have hamstrung traditional nuclear. The company's Gravity Nuclear Reactor uses low-enriched uranium and gravity for passive safety [Deep Fission, Dec 2025]. The pitch is that this approach, using standard drilling rigs, can cut construction timelines to as little as six months and deliver power for 5-7 cents per kilowatt-hour [Business Wire, Jan 2025]. Their primary targets are utilities, industrial parks, and the data centers powering the AI boom.

A father-daughter team with nuclear form

Leading the charge is a father-daughter founding team with a track record in the subsurface. CEO Elizabeth (Liz) Muller was previously CEO of Deep Isolation, a nuclear waste disposal company. Her co-founder and father, Richard Muller, is a Professor Emeritus of Physics at UC Berkeley [UC Berkeley Physics, Unknown].

Traction and a curious SPAC

The company's momentum is a mix of solid regulatory steps and aggressive commercial claims. On the tangible side, Deep Fission is in pre-application engagement with the Nuclear Regulatory Commission for its DFBR-1 reactor design and has secured a site at the Great Plains Industrial Park in Kansas for a Department of Energy-backed pilot, with groundbreaking planned for December 2025 [NRC.gov, May 2024] [KCUR / ANS, Dec 2025]. It has also raised a total of $114 million across several rounds, the most recent being a $30 million financing tied to a go-public transaction via a SPAC in September 2025 [TechCrunch, Sep 2025] [Crunchbase, Aug 2024].

On the more speculative side, the company claims a pipeline of signed Letters of Intent for 12.5 gigawatts of power [Deep Fission, Inc., Unknown]. The SPAC move itself, while providing capital, introduces a layer of financial complexity and public market scrutiny not typical for a hardware company at this stage.

The risks are geological

For all its intriguing geometry, Deep Fission faces a steep climb. The nuclear industry is a graveyard of optimistic cost estimates, and a 5-7 cent kWh target remains an unproven claim on a spreadsheet. The regulatory path for a novel underground design, while started, is long and fraught. And while borehole drilling is routine in oil and gas, marrying that technology with nuclear fission at an industrial scale is untested.

• The cost claim. The 5-7 cent per kWh target is the linchpin of the business case but lacks third-party validation.
• The timeline. A six-month build is a radical departure from the decade-long timelines of traditional nuclear.
• The SPAC structure. Going public via a SPAC brings cash and attention, but also the pressures of quarterly reporting [Latitude Media, Sep 2025].

Deep Fission's ultimate test is not against other advanced nuclear startups like Oklo or Last Energy, but against the incumbent it must beat: the natural gas peaker plant. It must prove its buried reactors can be built faster and operated more cheaply than a gas plant can be permitted and fueled. If it can, it will have dug itself a very deep moat.

Sources

1. [Deep Fission, Dec 2025] Nuclear Company Deep Fission Announces Site for Department of Energy Pilot | https://www.deepfission.com/media-center/press-releases/detail/100/nuclear-company-deep-fission-announces-site-for-department-of-energy-pilot-at-great-plains-industrial-park-in-kansas
2. [Business Wire, Jan 2025] Deep Fission and Endeavour Partner to Speed Delivery of Low-Cost Nuclear Power | https://www.businesswire.com/news/home/20250107219029/en/Deep-Fission-and-Endeavour-Partner-to-Speed-Delivery-of-Low-Cost-Nuclear-Power-for-Hyperscalers-Targeting-5-7-Cents-Per-kWh
3. [NRC.gov, May 2024] Deep Fission pre-application activities | https://www.nrc.gov/reactors/new-reactors/advanced/who-were-working-with/pre-application-activities/deep-fission
4. [TechCrunch, Sep 2025] Nuclear startup Deep Fission goes public in a curious SPAC | https://techcrunch.com/2025/09/08/nuclear-startup-deep-fission-goes-public-in-a-curious-spac/
5. [Crunchbase, Aug 2024] Pre Seed Round - Deep Fission | https://www.crunchbase.com/funding_round/deep-fission-pre-seed--fb70957e
6. [Deep Fission, Inc., Unknown] Deep Fission Expands Customer Pipeline to 12.5 Gigawatts | https://ir.deepfission.com/news-events/press-releases/detail/98/deep-fission-expands-customer-pipeline-to-12-5-gigawatts
7. [Latitude Media, Sep 2025] Deep Fission’s SPAC deal raises questions | https://www.latitudemedia.com/news/deep-fissions-stock-market-debut-comes-with-questions/