Insider Brief
- Proxima Fusion has announced its reactor design based on increasing fuel vessel size and magnetic field strength to achieve net energy gain, drawing significant interest.
- While breakeven is a key milestone, the overlooked challenge of tritium fuel sustainment poses a major obstacle to commercial fusion viability.
- Investors should evaluate fusion startups beyond breakeven claims, considering whether they have credible plans for tritium production and long-term fuel sustainability, along with other considerations.
Proxima Fusion, a startup aiming to develop a fusion power plant, recently announced its reactor design, generating significant interest. The company emphasized that its approach is based on proven principles of increasing fuel vessel size and magnetic field strength to achieve net energy gain.
Proxima’s leadership reports that their design is grounded in science. However — and this isn’t meant to pick on Proxima — the fusion industry faces other factors, as well as difficult challenges, that go beyond the highly touted breakeven — producing more energy from fusion than is consumed — milestone. Investors and analysts are debating whether some of these announcements that focus on breakeven reflect genuine technical progress or are simply “fuel” for of a broader trend of enthusiasm around fusion startups.
And, as fusion energy startups begin to attract attention and investment interest, how can investors and policymakers weigh the ambitious claims of commercial viability and separate reality from hype?
In this article, we’ll look at other factors investors should consider to measure the progress of fusion.
Net Energy Gain
Most fusion efforts focus on a simple but critical goal — producing more energy from fusion than is consumed to maintain the reaction. This aforementioned “breakeven” point is a milestone has long been the industry benchmark. The standard strategy to achieve this is increasing the size of the reaction chamber and the strength of the magnetic fields that contain the hot plasma where fusion occurs. This approach has already been validated by decades of experiments.
Many startups and government-backed projects are pursuing designs that leverage this well-established principle. Their reactors use fuel vessel sizes and magnetic field strengths that far exceed those of past experiments, such as JET in the UK and TFTR in the U.S. This gives them a high probability of producing net fusion power without requiring new physics.
The Overlooked Barrier: Tritium Fuel Supply
Achieving net energy gain does not automatically translate into a practical power plant, writes Michael Cole, of ColeFusion, in a LinkedIn post. One of the most critical and often overlooked challenges in fusion is the fuel supply. Most fusion projects, including government-funded reactors, rely on tritium, a rare isotope of hydrogen.
Tritium is preferred because it produces the most efficient fusion reaction, generating the most energy output per reaction. However, the global supply is extremely limited—only about 20 kilograms exist today, sourced from the nuclear fission industry. This is barely enough to start a single fusion plant.
For fusion to be commercially viable, reactors must not only burn tritium but also generate new tritium internally to sustain operations. Without this, even a successful reactor will run out of fuel.
The Missing Piece: Tritium Sustainment Technology
Despite its importance, tritium sustainment technology remains underdeveloped, according to Cole, author of Fusion’s Fading Star. Fusion research has focused primarily on achieving breakeven rather than ensuring a stable fuel cycle. Only two reactors — JET in the UK and TFTR in the U.S. — have ever run on tritium, and neither attempted to replace the fuel they consumed.
Estimates of tritium breeding — where a reactor produces more tritium than it burns — appear in many fusion proposals. However, these projections lack experimental validation and often ignore key losses. Data from past experiments indicate that tritium losses could be orders of magnitude higher than what would be required for a self-sustaining fusion cycle.
Lessons from the 1980s
The tritium problem is not new. In 1988, the Next European Tokamak (NET) project proposed a reactor that assumed breakeven as a given but struggled with tritium sustainment. Even with optimistic projections, the design would have suffered a 20% net tritium loss per reaction cycle. Worse, since fusion plants do not operate continuously, tritium losses from radioactive decay during downtime would further deplete fuel reserves.
NET was never built, and in the decades since, no successor has demonstrated a viable tritium replacement system. The fundamental problem remains unsolved.
The Risk for Investors
Despite its central importance, tritium sustainment is rarely highlighted in fusion marketing materials, according to Cole. Most fusion companies are founded by plasma physicists rather than specialists in tritium chemistry or nuclear fuel cycles. Investors evaluating fusion startups should consider whether the company has a credible plan to address this issue.
If a company claims it can sell energy from fusion, its real challenge is not just achieving breakeven but ensuring a stable tritium fuel supply. Without this, fusion remains an expensive experiment rather than a viable energy source.
A Different Fuel Approach?
Some researchers suggest moving away from tritium entirely. The original vision for fusion—using fuel extracted from seawater—relied on a different reaction involving deuterium and helium-3 or boron. However, these reactions require significantly higher temperatures and more advanced technology, making them even further from practical implementation.
The Importance of a Fusion Startup Team
While technological milestones like breakeven and tritium sustainment are critical for commercial fusion viability, another factor that must be considered is the composition and expertise of a startup’s team are just as important. Fusion is a complex, multidisciplinary challenge requiring expertise beyond plasma physics. A successful company would most likely integrate knowledge from nuclear engineering, materials science, tritium chemistry, and large-scale energy systems.
Historically, most fusion startups have been founded by plasma physicists, which makes sense given the field’s focus on achieving and maintaining high-energy reactions. However, as the industry shifts from proving concepts to building viable power plants, the expertise needed expands dramatically. Startups must recruit specialists in tritium breeding and handling, nuclear fuel cycles and power plant engineering—areas that have received less attention in fusion research but are essential for long-term success.
For investors evaluating fusion companies, the team’s composition can serve as an indicator of a startup’s ability to address critical commercialization challenges. A company focused solely on plasma physics breakthroughs but lacking expertise in fuel supply or reactor engineering may struggle to translate its scientific advances into an operational power plant. On the other hand, teams that include experts in nuclear fuel cycles, supply chain logistics, and large-scale energy infrastructure may have a stronger foundation for overcoming the hidden barriers to fusion commercialization.
Ultimately, investors looking at fusion energy should move beyond the sole focus of breakeven announcements. While generating net energy is an essential milestone, the true bottleneck for commercial fusion is fuel sustainment. Without a viable tritium cycle and a multidisciplinary team, no fusion power plant will operate for long.
Understanding this distinction will help separate meaningful progress from speculative hype for investors.
