Deep Fission is a nuclear start-up developing small underground reactors that sit roughly a mile below the surface in narrow boreholes, using pressurized water reactor (PWR) technology to generate low‑carbon electricity.

What Deep Fission Is

  • Deep Fission is an advanced nuclear energy company founded to rethink how reactors are built and sited, focusing on cost, speed, and safety.
  • Its core idea is to place relatively small PWR-based “Gravity Reactors” in a deep vertical borehole instead of building large surface nuclear plants.

How the Technology Works

  • Each reactor is installed in a borehole about one mile (around 1.6 km) underground, in a hole on the order of 30 inches in diameter, leveraging oil and gas drilling know‑how.
  • The reactor core operates similarly to a conventional PWR at roughly 315°C, using low‑enriched uranium fuel and water as coolant and moderator.
  • At that depth, the weight of the water column provides on the order of 150–160 atmospheres of pressure, so the geological setting itself supplies the pressure that standard reactors need huge vessels and systems to maintain.

Power Output and Deployment

  • A single Deep Fission Gravity Reactor is designed for about 15 megawatts electric (MWe) output, which is small compared with gigawatt‑scale nuclear plants but large enough for industrial or grid‑support roles.
  • Sites can host many boreholes: concepts describe up to 10 reactors (150 MWe) or even around 100 reactors on a few acres providing about 1.5 gigawatts electric (GWe).
  • On the surface, the plant looks more like a compact industrial facility or chemical plant, with steam turbines and power equipment above ground and the radioactive components mostly below.

Claimed Advantages

  • Cost and construction : By avoiding massive pressure vessels, containment domes, and sprawling structures, the company argues it can cut capital costs, since much of traditional nuclear expense is concrete and steel rather than fuel.
  • Safety : Burying the reactor deep underground leaves roughly billions of tons of rock between the core and the surface, which should isolate it from events like plane crashes, tornadoes, or tsunamis and reduce the risk of large releases.
  • Supply chain : Because it uses familiar PWR fuel and components, Deep Fission aims to lean on existing nuclear supply chains instead of needing entirely novel fuel cycles.

Challenges and Open Questions

  • Engineers note the idea is technically feasible but faces design challenges, including drilling, long‑term maintenance, inspection, and eventual decommissioning of underground reactors.
  • Regulatory pathways for such deeply buried reactors are still emerging, and real‑world costs, timelines, and community acceptance remain uncertain as of the latest public information.

TL;DR: Deep fission here refers to Deep Fission’s concept of small PWRs buried about a mile underground in boreholes, using natural hydrostatic pressure and rock shielding to promise cheaper, safer, and faster‑to‑deploy nuclear power, though it is still in early stages with significant engineering and regulatory hurdles.

Information gathered from public forums or data available on the internet and portrayed here.