Unraveling Safe and Practical Fusion – New Insights into Trapped Fuel Shared

Fusion & Fuel Efficiency

Nuclear Fusion is potentially the ultimate green energy source, producing no dangerous byproducts, radioactivity (the only “waste” is helium), or greenhouse gases. And it could be powered by a fuel so abundant that it is a significant percentage of the entire Universe: deuterium, an isotope of hydrogen.

But this is also a very difficult to achieve form of energy generation. It requires replicating on Earth the conditions in the core of the Sun, with tremendous pressures and tens or hundreds of millions of degrees.

Nuclear fusion has been achieved in physics laboratories for decades, but a net energy-positive fusion reaction is still to be reached. This is what many are racing to accomplish, from the international megaproject ITER to commercial fusion projects like Commonwealth Fusion Systems and Proxima Fusion.

Commercial viability will depend not only on achieving stable and energy-positive plasma generation, but also on the general efficiency of the process.

One open question is the fuel efficiency. Deuterium is known to be partially absorbed by the walls of the tokamak fusion reactors. Researchers at Princeton University, University of California, University of Tennessee, Sandia National Laboratory, and General Atomics are figuring it out.

They published their results in Nuclear Materials and Energy¹, under the title “Deuterium retention behaviors of boronization films at DIII-D divertor surface”.

Deuterium, Tritium & Fusion

The lighter an atom is, the more potential energy is released when it undergoes nuclear fusion. So it makes sense that most nuclear fusion projects focus on merging together variants of hydrogen, with the most popular option being deuterium-tritium fusion.

Source: Nature

Deuterium-deuterium fusion is also possible, but for technical reasons, it is assumed to be even more difficult to achieve commercially. This is why almost all commercial projects or prototypes of commercial projects like ITER are planning to use deuterium-tritium as a fuel.

One issue with tritium is that it is radioactive, contrary to deuterium. So you do not want to accumulate too much tritium in the reactor, nor do you want to lose track of it. This is not only a safety issue but also a regulatory one.

“There are very strict limitations on how much tritium can be in a device at any given time. If you go above that, then everything stops, and the license is removed.

So, if you want to have a functioning reactor, you need to make sure that your accounting of tritium is accurate. If you go over the limit, that’s a showstopper.”

Alessandro Bortolon – Managing principal research physicist at PPPL (Princeton Plasma Physics Laboratory)

As deuterium-tritium fuel will likely be used in commercial nuclear fusion reactors, knowing what happens to the fuel is very important. And we already know that part of it gets absorbed by the walls of the reactor.

Deuterium Absorption

Nuclear fusion reactors’ walls are made of graphite and coated with boron. The boron helps reduce the plasma impurities such as oxygen, carbon, and tungsten.

Source: Nuclear Materials and Energy

It has been known for a while that these boron-coated walls are absorbing some deuterium out of the plasma. However, the mechanism and quantity involved were not clear.

To understand it, they performed tests on DIII-D, a tokamak fusion reactor at General Atomics.

They discovered that the culprit for deuterium absorption was actually not boron but carbon.

Source: Nuclear Materials and Energy

The carbon and the boron together can bind so tightly to deuterium that it would take temperatures around 1,000 degrees Fahrenheit to break the bond, making it very challenging to remove the fuel without damaging the fusion system.

“Carbon must be minimized. While we cannot get it to zero, we use all the means we have to reduce the amount of carbon as much as possible.

We want to get rid of all the carbon and have clean tungsten walls to ensure the calculations are even closer to what will be experienced in ITER.”

Florian Effenberg – PPPL Staff Research Physicist

Finding Solutions

Digging deeper, the researchers found that exposure to a plasma with small amounts of carbon contamination increased the amount of trapped deuterium significantly.

For every five units of boron trapped in a sample, two units of deuterium were trapped.

The phenomenon is also temperature-dependent. Above 600,000°K (1 million °F), the retention of deuterium is limited, and the wall releases back the deuterium at 900,000°K.

However, such temperatures touching the wall coating are best avoided for the long-term stability of the material, so it is not a practical solution to avoid fuel accumulation in the reactor walls.

A more likely solution is to try to limit to the absolute maximum any carbon impurities to make their way into the reactor walls, something that was not known until now to matter that much.

This will have a direct practical impact on the final design and manufacturing of ITER reactor walls.

“ITER and future devices should be careful to minimize C impurity contamination to reduce deuterium retention.”

It is also likely to limit the practicality or commercial viability of any nuclear fusion engine using graphite tiles on the walls (graphite being made of carbon atoms), like the DIII-D fusion used in this experiment, as this design will likely accumulate too much tritium over time to be authorized to operate as a powerplant.

Conclusion

Nuclear Fusion is progressively becoming a well-understood technology, with the record for stable plasma duration beaten regularly, the latest being 22 minutes in a French-Chinese collaboration.

With the help of AI, it is likely that fusion will keep getting more efficient over time, up to the point where net energy is achieved.

As the technology inches closer to commercialization, new challenges are emerging, like following regulations regarding fuel accumulation and radioactivity, something experimental reactors had less to be concerned about.

Luckily, these issues are also being ironed out, and optimizing the quality of materials used for the reactors will help.

Combined with constant improvements in our understanding of superconductivity, this could help make our trouble generating green energy a thing of the past in the next 1-2 decades.

Fusion Companies

Currently, none of the companies dedicated solely to making nuclear fusion commercially viable are publicly listed. These include Helion, General Fusion, Commonwealth Fusion, TEA Technologies, ZAP Energy, and NEO Fusion.

You can find an extensive list of startups in the nuclear fusion space on the dedicated page of Dealroom.

Still, one publicly-listed company has been active in the field of fusion, with a redirection of its concept from energy production to space propulsion: Lockheed Martin.

Lockheed Martin Corporation

One notable exception to privately-listed startups dominating the field is the publicly traded company Lockheed Martin Corporation, a giant of the defense industry.

Lockheed has been working since the early 2010s on Compact Fusion, a nuclear fusion reactor that is expected to be ready by the 2020s. However, it has since been announced that the work on the project was stopped in 2021.

The company has been very discreet about this project since the 2021 public announcement. To this day, it is unclear what could have prompted the company to abandon the idea.

At the same time, it seems that it did not fully abandon the concept, notably with investments in 2024 in Helicity, a startup developing a fusion engine.

The idea is to propel spacecraft with short bursts of fusion. Helicity plans to use a plasma gun, the same approach as General Fusion. Potentially, Lockheed’s internal results have shown that its design could not sustain fusion in a way that is compatible with energy production.

But maybe, at the same time, are short bursts enough for the need for propulsion in space and much closer to becoming an actual product? It would also be a better fit with the company’s overall aerospace and defense-focused profile.

Besides fusion projects, Lockheed Martin is one of the world’s largest aerospace & defense companies, which we covered in detail in November 2025 in “Lockheed Martin (LMT) Spotlight: A Leader In Defense and Aerospace”.

In short, this is the company behind aircrafts like the Black Hawk helicopters or the F-16, as well as advanced equipment like the F-35, flying radar planes, or logistical aircrafts like the C-5 Galaxy & C-130J Super Hercules.

Source: Lockheed Martin

It is also the producer of some of the US military’s most important missile systems like the JAASM, Javelin, ATACMS, and HIMARS, in extremely high demand following the depletion of stockpiles by the conflict in Ukraine.

Lockheed is the lead contractor for the design, development, testing, and production of the Orion spacecraft, which may be the least controversial part of the entire Artemis program.

The company is active in other space programs, like the GOES-R weather satellites, the collection of asteroid samples by OSIRIS-REx, Jupiter probe JUNO, a wearable radiation-shielding vest AstroRad,

Overall, from key military systems to equally important space and nuclear fusion programs, Lockheed Martin is at the forefront of American innovation and seems to have kept its edge a lot sharper than many of its large defense contractor competitors.

Latest on Lockheed Martin Corporation

Study Reference:

^{1. Shota Abe et al. (2025) “Deuterium retention behaviors of boronization films at DIII-D divertor surface”. Nuclear Materials and Energy Volume 42, March 2025, 101855.}