I started in the fusion industry without a background in plasma physics or nuclear energy to serve as a reference point. This blog was written by a layman in the fusion energy business for other laypeople starting in fusion energy. It results from reading other write-ups from organizations like Helion, Commonwealth Fusion Systems, BBVA, the Fusion Industry Association, and the DOE, plus some shameless use of Perplexity AI. Each source provides numerous simple and complex comparisons, so I wanted to share a basic primer of what new folks entering the market needed to know.
The Simple Explanation - Fusion Joins and Fission Splits
When people talk of nuclear energy, it is almost always fission energy they are referring to. Fission occurs when a neutron slams into a larger atom, forcing it to excite and split into two smaller atoms, also known as fission products. Additional neutrons are also released, which can initiate a chain reaction. When each atom splits, a tremendous amount of energy is released. Uranium and plutonium are most commonly used for fission reactions in nuclear power reactors because they are easy to initiate and control.
Fusion occurs when two atoms are squeezed together to form a heavier atom, like when two hydrogen atoms fuse to form one helium atom. This process powers the sun and creates vast amounts of energy - several times greater than fission.
Here is a short video from the DOE that provides a high-level overview.
What is Nuclear Fission?
Nuclear fission is the process of splitting a heavy atomic nucleus into smaller, lighter nuclei, accompanied by the release of energy. This reaction typically involves isotopes of elements such as uranium-235 or plutonium-239. When a neutron collides with a heavy nucleus, it causes the nucleus to become unstable and split, releasing additional neutrons and a substantial amount of energy in the form of heat. This heat is then harnessed to produce electricity in nuclear power plants.
- Process - Splitting heavy nuclei into smaller fragments.
- Fuel Source - Heavy elements like uranium and plutonium.
- Waste Products - Radioactive byproducts requiring careful long-term management.
- Safety Considerations - Modern reactor designs incorporate numerous safety measures, but there is a potential for runaway chain reactions and radioactive meltdowns.
What is Fusion Energy?
Fusion energy involves combining two light atomic nuclei to form a heavier nucleus, releasing energy. This is the same reaction that powers stars, including our Sun. Earth's most common fusion reactions involve isotopes of hydrogen, such as deuterium and tritium. Achieving controlled fusion on Earth requires extremely high temperatures and pressures to overcome the electrostatic repulsion between positively charged nuclei.
- Process - Combining light nuclei to form a heavier nucleus at over 150℃.
- Fuel Source - Abundant elements like deuterium and tritium, derived from water and lithium.
- Waste Products - Primarily helium.
- Safety Considerations - Inherently safer with no risk of runaway chain reactions or significant radioactive waste.
Why Does it Produce So Much Energy?
To understand this better, we should look at Albert Einstein’s famous formula E=mc^2. E stands for energy, m stands for mass, and c is a constant that indicates the speed of light (3 x 10^8 meters per second). Einstein’s equation reveals that energy and mass are related to each other. When the speed of light squared (c^2) is multiplied by the mass of a system, one obtains the energy of that system. This reveals that a tiny mass can be converted into massive energy.
The nuclear binding energy releases a huge amount of energy related to a concept called “mass defect.” This concept tells us that the mass of an atom’s core (nucleus) is less than if the particles that the core is made of (nucleons) were separate. This might sound a bit abstract initially, but with fusion, it effectively means that deuterium and tritium together are heavier than helium and a neutron together, and the mass difference multiplied by c^2 ( the speed of light) gives the nuclear binding energy, which is the amount of energy released. Check out the illustration below:
Nuclear fusion releases massive energy due to the “mass defect.” Assuming ±2 g of deuterium and ±3 g of tritium are used as fuel, the amount of power being released in this process is E=(m tritium (3.016 g) + m deuterium (2.014 g) — m helium (4.003 g) + m neutron (1.008 g))*c^2 ≈ 450 MWh. This would power about 150 German households for a whole year. Credits: Extantia.
Differences Between Fusion and Fission
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Fusion
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Fission
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Energy Creation Process
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Combines two light atomic nuclei to form a heavier nucleus, releasing energy.
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Splits a heavy atomic nucleus into smaller nuclei, releasing energy.
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Energy Output
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Potentially releases more energy per unit mass than fission, making it a highly efficient energy source.
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While efficient, it does not match the energy density achievable through fusion.
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Fuel Sources
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Utilizes abundant light elements like deuterium and tritium. For example, just one pound of fusion fuel equals 10 million pounds of coal.
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It relies on heavy elements such as uranium-235 and plutonium-239, which are far less abundant and require extensive mining and enrichment processes.
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Waste Products
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Produces primarily helium, a non-radioactive and harmless gas, with minimal radioactive byproducts.
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Generates significant amounts of radioactive waste that must be carefully managed and stored for long periods to prevent environmental contamination.
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Safety & Environmental
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It cannot cause a runaway meltdown and produces no long-lived radioactive waste, making it a cleaner and safer energy source.
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Carries risks of meltdowns and produces hazardous radioactive waste, posing long-term environmental and safety challenges.
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Technical Challenges
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Fusion requires extremely high temperatures (over 100-150 million degrees Celsius) and precise plasma confinement, making it significantly more difficult to achieve and sustain.
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Fission is technologically mature with established methods for energy generation, though safety and waste management remain concerns.
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Regulation
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The US Congress passed the ADVANCE Act, which defines fusion machines as particle accelerators and codifies their regulation under NRC’s byproduct material framework.
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The Nuclear Regulatory Commission (NRC) regulates nuclear fission under Part 50 of the Code of Federal Regulations (CFR). The NRC is an independent agency that licenses and regulates the civilian use of atomic energy to protect the public, the environment, and national security.
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Applications
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Fusion is primarily in the experimental stage, with projects like ITER aiming to demonstrate feasibility. Commercial fusion energy has not yet been realized.
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Fission is widely used in current nuclear power plants globally, providing a substantial portion of low-carbon electricity.
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Fusion vs Fission Frequently Asked Questions (FAQ)
- Why is fusion energy called “the power of the Sun?”
Fusion energy is the process of producing heat and power within the Sun and countless stars across the universe.
- Is fusion the same as nuclear power or fission?
While fusion is a type of nuclear power, it is the opposite process of fission, which is what we commonly refer to as nuclear power.
- What is Q>1?
A fusion energy gain factor, usually expressed with the symbol Q, is the ratio of fusion power provided to a fusion machine versus the power produced by said machine. Q>1 indicates that a fusion machine creates more energy than it consumes.
- What is the main difference between fusion and fission?
Fusion involves combining two light atomic nuclei to form a heavier nucleus, releasing energy. Fission consists of splitting a heavy atomic nucleus into smaller nuclei, which also releases energy, though much less than fusion.
- Why are they called “fusion machines” versus reactors?
The NRC coined the term “fusion machine” in the ADVANCE ACT to distinguish fusion devices from nuclear fission reactors used to split atoms.
- What is an Interial Confinement Fusion Machine (Laser)?
In inertial confinement, nuclear fusion is triggered by focusing high-power laser beams onto a fuel capsule containing a mixture of deuterium and tritium.
- What is a Tokamak Fusion Machine (Magnetic)?
A tokamak is a machine that confines a plasma using magnetic fields in a donut shape that scientists call a torus. The term "tokamak" comes from a Russian acronym for "toroidal chamber with magnetic coils."
- What is a Stellarator Fusion Machine (Magnetic)?
Stellarator fusion machines use magnetic fields to confine plasma like a tokamak. However, they use two magnetic field coils to confine the plasma. One set produces the toroidal component of the magnetic field, while the other is wound around the plasma in a helix.
- What is a Z-Pinch Fusion Machine?
A Z-pinch fusion machine is a compact device that uses an electrical current to compress and heat plasma to create fusion conditions. The Z-pinch effect is an electromagnetic phenomenon where electric currents create powerful magnetic fields that compress matter. If you run a powerful enough current through plasma, a Z-pinch can create conditions hot and dense enough for fusion.
- Why is fusion considered a cleaner energy source compared to fission?
Fusion primarily produces helium, a non-radioactive gas, as a byproduct, whereas fission generates significant radioactive waste that requires long-term management. Fusion cannot cause a runaway meltdown, enhancing its safety profile.
- What are the main technical challenges in achieving nuclear fusion?
The primary challenges include reaching and maintaining the extremely high temperatures (over 100 million degrees Celsius) and pressures required for fusion and effectively confining the plasma to sustain the reaction. Additionally, materials must withstand the intense conditions within a fusion reactor.
- What is Hydrogen, Deuterium, and Tritium?
Hydrogen is the most abundant substance in the universe. Hydrogen consists of a positively charged proton surrounded by a negatively charged electron, deuterium’s core contains one additional neutron (neutrally charged particle), and tritium’s core has two neutrons.
- How does the fuel availability compare between fusion and fission?
Fusion fuel, such as deuterium, is abundantly available from seawater, and lithium used for tritium breeding is also plentiful. In contrast, fission relies on heavy elements like uranium and plutonium, which are less abundant and require extensive mining and enrichment processes.
- What is the current status of commercial fusion energy?
Fusion energy remains experimental, with significant research projects like ITER aiming to demonstrate its feasibility. Due to the considerable technical and financial requirements and challenges involved, commercial fusion power plants are expected to be operational in 2035 at the earliest.
- Are there any existing nuclear fusion reactors?
As of now, there are no commercial nuclear fusion reactors. Experimental reactors, such as tokamaks and inertial confinement facilities, are used to research and develop the technology necessary for future commercial applications.
- How does the safety of fusion reactors compare to fission reactors?
Fusion reactors are inherently safer as they cannot experience runaway chain reactions or meltdowns. If any containment breaches occur, the reaction simply stops. In contrast, fission reactors have the potential for severe accidents and require robust safety measures to prevent radioactive releases.
- What regulatory frameworks exist for fusion energy?
Currently, fusion machines are regulated under frameworks similar to those for particle accelerators and medical facilities rather than nuclear reactors. The Nuclear Regulatory Commission (NRC) in the U.S. has recognized the differences and is regulating fusion separately from fission.
- Why is fusion energy yet to be commercially viable despite decades of research?
Fusion requires achieving and sustaining conditions that are extraordinarily difficult to maintain, such as extremely high temperatures and precise plasma confinement. The engineering challenges and high costs associated with building and operating fusion reactors have also delayed commercial viability.
- Can fusion energy help combat climate change?
Yes, fusion energy has the potential to provide a vast, low-carbon energy source that could significantly reduce greenhouse gas emissions. Its high energy output and minimal radioactive waste make it an attractive option for sustainable energy. However, realizing this potential depends on overcoming current technical and financial challenges.
- How is fusion vs. fission energy regulated?
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. In the US, fusion energy is regulated like a particle collider, similar to the CERN facility. The NRC regulates both fusion and fission facilities based on the ADVANCE ACT.
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