Skip to content
FusionBenchmark
Deep Fission — image published by the organisation
Picture published by Deep Fissionsource ↗
Deep Fission

Deep Fission

🇺🇸 Berkeley, US · Founded 2023 · Active

Deep Fission is a Berkeley, California company founded in 2023 that plans to place small pressurised water reactors at the bottom of boreholes about one mile (1.6 km) deep. It calls the design the Gravity Reactor and aims for up to 8 MWe per reactor at first, with several reactors clustered at one site. In August 2025 the Department of Energy selected it for the Reactor Pilot Program, and in December 2025 it broke ground at a pilot site in Parsons, Kansas, where it began drilling a first data well in March 2026. It listed on Nasdaq as FISN in June 2026, disclosing that it had no revenue and that its auditors had raised substantial doubt about its ability to continue as a going concern. It had not built or licensed a reactor as of 2026.

Website ↗LinkedIn ↗X ↗YouTube ↗
Sector
Fission
Technology
Pressurised water reactor
Fuel
Low-enriched uranium
Role
Reactor developer

Its recorded equity, $137m, is the 15th largest of the 25 organisations with a priced round here. Not every round is on record, so this is not its total raised.

Terms

Pressurised water reactor
Ordinary (light) water kept under high pressure so it heats without boiling, transferring heat to a separate steam loop; the water is both coolant and moderator. Fuel is low-enriched uranium oxide pellets in zirconium-alloy rods. The most common reactor type in service worldwide.
Low-enriched uranium
Uranium enriched to 5% uranium-235 or less, typically 3 to 5%: the range almost all power reactors use. Formally, anything below 20% is low-enriched; this site holds the band from 5% to just under 20% separately as HALEU, with its 5 to 10% part also tagged as LEU+. A fuel above 5% uranium-235 belongs in one of those, never here, whatever a developer's own materials call it.

Funding

$137m
equity in the 3 rounds recorded here
  1. 2026-06-22
    IPO
    Public offering the company calls its initial public offering: 2,500,000 shares at $16.00, completed 22 June 2026: $40.0 million gross, $34.3 million net after $3.2 million underwriting and $2.5 million other expenses.
    $34m
  2. 2026-02-05
    Equity round
    Private placement of 5,333,333 shares at $15.00 on 5 February 2026: $80.0 million gross, $75.1 million after $4.851 million of offering costs.
    $75m
  3. 2025-09-05
    Equity round
    Private placement of 10,000,000 shares at $3.00, closed 5 September 2025 alongside the reverse merger that made Deep Fission public: $30.0 million gross, $27.1 million after $2.91 million of offering costs.
    $27m

Designs

Design Developer Approach Electrical output per unit Size class Licensing stage
Gravity Nuclear Reactor Gravity reactor, Deep Fission Borehole Reactor Deep Fission Pressurised water reactor 15 MWe planned Small modular reactor No milestone recorded

People

  • Liz MullerCo-Founder & CEO, Board Chair · founder
  • Jonathon AngellCEO of Angell Investments, Board Member
  • Thomas GlanvilleManaging Partner, Eschelon Advisors, LP, Board Member (Audit Committee Chair)
  • Leslie Goldman TepperManaging Partner of LGT Seven Enterprises, Board Member (Nominating & Governance Committee Chair)
  • Blake JanoverChairman and CEO of J2 Labs, Board Member (Compensation Committee Chair)

Related companies

Sources