Inevitable (an MCJ Podcast)

Episode: Underground Nuclear Reactors? Inside Deep Fission’s Energy Solution

Date: April 10, 2025
Host: Cody Sims
Guest: Liz Muller, CEO & Co-founder, Deep Fission

Episode Overview

This episode explores Deep Fission’s ambitious plan to revolutionize nuclear energy by moving reactor cores one mile underground. Host Cody Sims interviews Liz Muller, whose prior company, Deep Isolation, focused on nuclear waste disposal deep underground. They discuss how lessons learned from nuclear waste management, conventional oil and gas drilling, and the economics of civil construction for nuclear plants inform Deep Fission’s innovative approach. Key topics include cost reduction, safety, fuel supply, regulatory challenges, the changing energy landscape, and the future of nuclear innovation.

Key Discussion Points

1. Deep Isolation: The Waste Problem as a Precursor

• Background: Liz recaps her previous venture, Deep Isolation, which tackled nuclear waste disposal using deep boreholes and techniques borrowed from oil and gas.
  • Key Insight: “We’re talking about a mile underground. You don’t need humans underground… You can do it both faster and more flexibly, but also significantly cheaper.” (Liz Muller, 01:37)
  • Differentiator: Unlike oil and gas, no pressurization or fracking is involved—just drilling.
• Waste Recycling: France and others reprocess nuclear waste but still require permanent disposal solutions (03:48).

2. Deep Fission’s Core Innovation

• ‘Aha’ Moment: Customer inquiry into what happens if fresh fuel is accidentally placed underground led to the realization that boreholes provide both pressure and containment needed for nuclear reactions.
  • Quote: “…about 80% of the cost of nuclear power is in this physical construction… What is the construction to do? Well, it’s really two things: it’s to create 160 atmospheres of pressure… and it’s also for containment… Here we were in a borehole a mile underground, and we know we have amazing containment.” (04:19–05:30)
• Technical Layout: Reactors are housed in 30-inch diameter boreholes, with each hole holding a small modular reactor (~15 MW). Multiple holes can be arrayed to scale up, ideal for data centers’ high demand (07:44–08:32).
  • Memorable Visual: “If you use nothing but nuclear power… the waste that you would generate would fit inside one soda can.” (Liz Muller, 09:03)
• Drilling Cost: Around $6–8M per borehole, with costs dropping in bulk (09:45).

3. Safety, Fuel, and Regulatory Approach

• Fuel Choice: Deep Fission favors conventional 5% enriched uranium (“pressurized water reactor fuel”) because of a robust, established supply chain, avoiding HALEU or unproven fuels (10:55).
  • “We already have a mature supply chain… not trying to do anything new at this stage.” (Liz Muller, 10:55)
• Comparison with SMRs:
  • Above-ground SMRs still require significant construction for containment; Deep Fission’s underground model removes this major cost factor (12:17).
  • Advanced (non-light water) reactors try to avoid high-pressure needs but face supply chain and licensing challenges.

4. Enhanced Geothermal vs. Underground Nuclear

• Versus Geothermal: Geothermal’s limited heat extraction and slow replenishment contrast with placing an active nuclear heat source at depth, providing higher output per borehole.
  • “Sometimes I refer to Deep Fission as enhanced geothermal… but we’re putting a small nuclear reactor at the bottom of the borehole…” (14:33)
• Resilience & Safety: Underground siting offers exceptional protection from surface disasters, including wildfires or airplane impacts—“When you’re a mile underground… it’s not going to have any sort of impact on the actual nuclear technology.” (16:14)

5. Land Use, Security, and Operations

• Physical Footprint: Extremely small surface area needed (3 acres for 100 reactors); surface infrastructure is primarily turbines (18:04).
• Security: Physical security requirements may be reduced, but specifics await regulatory clarity—“It’s hard to come up with a scenario in which even if the worst case scenario were to happen, that it would have an impact on humans or the environment.” (18:42)
• Maintenance: Reactors have short (~2-year) fuel cycles. After completion, modules can be lowered to pre-drilled deeper sections of the borehole for permanent storage, minimizing handling and above-ground waste (19:52–22:08).
• Safety Design: Borehole and surrounding rock, not containers (canisters), provide the primary safety function—“The borehole and the rock really is the safety.” (21:38)

6. Commercial Progress and Cost Projections

• Customer & Commercialization: Deep Fission is working with Endeavour Data Centers, with an initial order for 2GW. First deployment will likely use moderate arrays (~75MW per module) (23:24–24:41).
• Cost Savings: Targeting total costs at roughly 20% of traditional nuclear. First-of-a-kind reactors predicted at $25M for 15MW—5–7 cents per kWh, with strong potential for reductions (25:07).
  • Quote: “We are expecting to be about 20% of the cost… $25 million per reactor… that’s a remarkably good price.” (25:07)
• Containment Assurance: Leverages deep isolation and oil/gas industry expertise to assure water table safety and effective containment (26:44–28:22).
• Funding: Raised a $4M pre-seed led by 8VC; seeking more capital to complete design, hire engineers, and secure first site (28:31).

7. The Future of Nuclear Innovation

• Trends & Drivers: Climate change, energy security (post-Ukraine), and rapid data center/AI growth are all increasing demand for reliable power (29:10).
  • “We need really big things… nuclear is one of the big things that we can do that will actually have significant impact.” (Liz Muller, 29:10)
• Industry Shift: Modular nuclear enables rapid “learning-by-doing,” more akin to solar deployment, aiding cost-downs and scalability.
  • “If you can be profitable on your first implementation… you will find more people who are willing to move forward.” (32:29)
• Consolidation Likely: The industry will likely see shakeouts based on market segment fit and profitability. Portable nuclear (like Radiant’s work) or ultra-low cost, high-reliability applications will coexist, but not all designs will survive (33:49).
  • “I think we are going to see a consolidation. I think not all technologies are going to make it through. I think it’s going to come largely down to who can be profitable, which is why there’s so much focus on cost.” (Liz Muller, 34:06)

Notable Quotes & Memorable Moments

• On Underground Containment:
  “One of the scenarios you have to consider in the nuclear industry is what happens if an airplane crashes into your facility. When you’re a mile underground… it’s not going to have any sort of impact on the actual nuclear technology.” (Liz Muller, 16:14)
• On Nuclear Waste Density:
  “If you use nothing but nuclear power to power everything… the waste… would fit inside one soda can.” (Liz Muller, 09:03)
• On Cost Savings:
  “80% of the cost of nuclear power is in this physical construction. What we’re doing is removing the need for surface construction.” (Liz Muller, 04:19)
• On Industry Outlook:
  “There’s tremendous excitement in the nuclear industry right now. It started with climate change… accelerated by the war in Ukraine… and now, data centers and AI.” (Liz Muller, 29:10)
• On Innovation Through Modularity:
  “It is both the first of a kind and the hundredth of a kind. And you’re learning as you go. That’s huge. That’s what we do right now for solar.” (Liz Muller, 31:46)

Segment Timestamps

• 00:00 – Introduction and Liz’s background in nuclear waste
• 04:19 – Inspiration for Deep Fission’s underground reactor concept
• 07:44 – Reactor size, modularity, and applications for data centers
• 09:45 – Drilling logistics and costs
• 10:55 – Fuel choice and supply chain rationale
• 12:17 – Cost and construction comparisons to SMRs and advanced reactors
• 14:33 – Comparison to/enhancement over geothermal
• 16:14 – Disaster resilience and underground safety advantages
• 18:04 – Surface footprint and land use
• 19:10 – Security, safety, and maintenance protocol
• 21:36 – On-site waste management by lowering spent reactors
• 23:24 – Commercial progress with first customer (data centers)
• 24:41 – Cost breakdown and economic outlook
• 25:07 – Detailed cost and price-per-kWh expectations
• 29:10 – Broader trends driving nuclear’s resurgence
• 31:46 – Modularity, first-of-a-kind vs. nth-of-a-kind innovation
• 33:49 – Future industry consolidation and segments

Takeaway Summary

Liz Muller and Deep Fission are pioneering a fundamentally new way to make nuclear energy safer, cheaper, and more rapidly deployable by leveraging deep borehole containment and lessons from both the oil/gas and nuclear waste management sectors. With a practical focus on standard fuel and proven technology, the company is well-positioned to serve the booming demand for reliable data center power and beyond. Regulatory engagement has begun, initial customer commitments are in place, and—if successful—this could mark a significant transformation in how the world produces and thinks about nuclear energy.

For More Information

• Deep Fission is seeking connections with potential customers and interested observers.
• To learn more or get in touch: visit Deep Fission’s website or reach out to Liz Muller directly.
• Stay tuned for licensing and deployment progress in 2026–2029.

This summary was prepared to provide a detailed and engaging overview of the “Inevitable” podcast episode featuring Liz Muller.