Why fusion is not “nuclear”

Fusion is not fission.  

 

That may seem to be a simple statement but given that only nuclear fission has been commercially used for power generation, there can be considerable confusion in how people associate the two. From a fundamental physics standpoint, both are nuclear processes. But in an important way, they are opposites.  

 

Fusion combines two light nuclei (e.g., hydrogen, helium) into a heavier nucleus. Fission, on the other hand, splits a heavy nucleus (e.g., uranium, plutonium) into two lighter nuclei. That difference results in very distinct public safety, regulatory, and societal implications for the two processes. 

 

Over the past 70 years, public understanding of “nuclear energy”—reinforced in part by the language and structure of laws and regulations—has come to equate “nuclear” with the fission process and “nuclear power” with the large light water reactors currently in operation in the United States.  

 

For us at Helion, and others aiming to deliver clean fusion energy as quickly as possible, it is important to distinguish fusion machines from nuclear reactors.

 

Regulatory approach 

 

The Nuclear Regulatory Commission (NRC), the agency responsible for regulating the civilian use of radioactive materials in the U.S., acknowledged the difference last year with its decision to regulate fusion machines separately from nuclear reactors. That decision was the result of an NRC initiated study to review which of the agency’s regulatory frameworks, established by the Atomic Energy Act (AEA) of 1954 and contained in Title 10 of the U.S. Code of Federal Regulations (10 CFR), could best apply to commercial fusion energy. 

 

Of the options, three were clearly not fit for fusion:  

 

> The special nuclear material framework refers specifically to plutonium, uranium-233 and enriched uranium, none of which are required to produce fusion energy. 

> The source material framework is for thorium and isotopes of uranium that could be used to generate special nuclear material. None of these are needed for commercial fusion energy.  

> The production facility framework is for facilities that generate, separate, or process special nuclear material. This category also doesn’t apply in any practical way to the purposes or outputs of a fusion power plant.  

 

Two frameworks remained part of the discussion: 

 

> The utilization facility framework was created for, generally, any fission reactor that’s not a production facility.* 

> The byproduct material framework covers materials that have been made radioactive through the use of radiation, including by particle accelerators.  

 

After investigating each of these options for fusion, the NRC concluded in 2023 that fusion machines should be regulated under the byproduct material framework: the same framework that generally applies to hospitals and other medical facilities, universities, and factories across the country that use radioactive material.  

 

Then this year, Congress passed the ADVANCE Act, which defines fusion machines as particle accelerators and codifies their regulation under NRC’s byproduct material framework. With the NRC decision and the ADVANCE Act, now is the time to ensure that communities understand the decision and the differences between fusion and fission.  

 

More on the reasoning behind this important distinction:  

 

Pursuit of fusion energy

 

It took only four years after the discovery of fission in 1938 for Enrico Fermi and his group to build the world’s first human made nuclear reactor. And just 13 years for the Experimental Breeder Reactor-I (EBR-I) to become the first nuclear power plant to produce usable electricity. Fission was quickly harnessed by humanity, using 1940s technology, to become a viable energy source. 

 

In contrast, Ernest Rutherford and Mark Oliphant reported the first instance of human induced fusion reactions in 1934. Here we are, nearly a century later, and only now are we on the verge of deploying fusion energy for power generation.  

 

Fusion is hard to turn on

 

Fusion is difficult to initiate, much more difficult than fission. 

 

To initiate meaningful amounts of fusion energy, we must actively heat the fuel to at least 100 million degrees (hotter than the sun) while confining it long enough (keeping the nuclei close enough together) to sustain fusion reactions. This is extremely difficult, and to date, no one has done so for commercial power generation. 

 

Fusion is easy to shut off

 

Fusion has no possibility of a chain reaction, a defining feature of nuclear reactors. Unless actively maintained, a fusion machine turns itself off.  

 

In comparison, all it takes to sustain a light water reactor, the type in use at every commercial nuclear power plant in the U.S., is neutrons from other fissions and the water that is always present. Those neutrons then cause more fission reactions that produce more neutrons. Nuclear reactors have specific control mechanisms to maintain the right number of neutrons initiating reactions, ensuring the machine doesn’t become supercritical. 

 

So, while fusion is difficult to start and sustain, it also makes the safe shutdown of the machine simple.  

 

When fusion is off, it’s off

 

A fusion machine begins to cool as soon as the switch is flipped. Once a fusion machine is turned off, it does not continue to create new radioactive materials, it has no possibility of turning itself back on, and it does not require active/large-scale cooling once powered down.  

 

No free lunch

 

I don’t mean to imply that the commercial deployment of fusion energy has no risks. For instance, fusion machines are expected to produce tritium and neutrons. 

 

Tritium emits a relatively weak form of radiation and it poses no danger when kept external to the body. Precautions must still be taken to ensure workers are not exposed to it in ways that enable it to enter their body. 

 

For most concepts, tritium will be an integral part of the fuel cycle and considered a valuable commodity, it is either used directly as fuel or decays into helium-3, Helion’s fusion fuel. Good tritium processing and storage solutions will be a commercial and safety necessity.  

 

Neutrons and thus activated materials will also be produced by fusion machines. Sufficient shielding and careful monitoring of activated materials and radiation damage to components are other musts for ensuring worker safety.  

 

Shielding is a very well-known and understood concept; concrete and water provide excellent protection from neutrons and other forms of radiation. For our materials, we are working to refine alloys and increase purity from our suppliers to minimize activation products, enhancing safety for our team members and minimizing low-level waste production. 

 

Fusion is not “nuclear.” 

 

And so, while I understand that fusion is indeed physically a nuclear process, I want to make clear that common preconceived notions about nuclear power simply do not apply to commercial fusion energy.  

 

If we want to be serious about deploying the clean, reliable, abundant power that fusion can deliver, we must all do our part to ensure our communities and decision-makers approach fusion with an open mind and evaluate it on its own merits.  

 

 

*The AEA does leave room to include other devices or equipment that use “atomic energy in such quantity as to be of significance to the common defense and security, or in such manner as to affect the health and safety of the public.”