Nuclear Fusion: A Necessary Gamble?

What is nuclear fusion? What is needed to achieve it? What actually happens inside the reaction chamber - the donut-shaped tokamak - when fusion occurs? What is the basic chemical equation that describes the process? Is it true that temperatues need to be hotter than those at the sun's core? What are the main benefits and risks of fusion? Will it give us unlimited low carbon energy, or is it just an expensive gamble? We explain all you need to know.
Close up picture of the sun
The Sun is powered by nuclear fusion. Photo: NASA

Fusion Energy Could Become a Reality by 2050

The big joke about nuclear fusion energy is that it’s 30 years away and always will be. But according to experts, recent advances in fusion science might actually see the first fusion power on the grid by 2050. 1

Several cutting-edge fusion projects are up and running. One is the International Thermonuclear Experimental Reactor (ITER) in southern France, where China, the EU, India, Japan, South Korea, Russia and the United States are collaborating to build the world’s largest magnetic fusion reactor, or tokamak. 2 ITER hopes to conduct its first experimental runs in 2025, and aims eventually to produce 500 megawatts of power – 10 times more than is needed to run it.

Another is a prototype fusion reactor called Sparc, designed by Commonwealth Fusion Systems (CFS), a spin-off out of the Massachusetts Institute of Technology. According to CFS. its high-temperature superconducting magnets are 10 times smaller than those used by ITER, with a similar performance spec. 3 4

Both these projects use a process known as magnetic confinement. Meantime, other scientists at the National Ignition Facility (NIF) of Lawrence Livermore Laboratory in the United States are developing a second process known as inertial confinement. More about this later.

Benefits of Nuclear Fusion

In a nutshell, nuclear fusion holds out the promise of limitless low-emission nuclear power without any long-term radioactive waste. It is comparable in greenhouse gas emissions with renewable energy like wind power. What’s more, nuclear fusion can theoretically be made entirely non-radioactive. If so, it would represent the perfect type of sustainable energy to help us combat climate change without compromising growth. It would have all the benefits of renewable energy, without any worries about intermittency or continuity of supply.

Fusion is the Opposite of Fission

In simple terms, nuclear fusion is the opposite of nuclear fission, the process used to produce nuclear energy today. In fusion, lighter nuclei are fused into a heavier nucleus, instead of splitting a heavy nucleus into smaller nuclei – the process used in fission.

See also: Is Nuclear Energy A Replacement For Fossil Fuels?

Nuclear Fusion is Used by Stars

Nuclear fusion occurs continuously inside stars. In the sun, for instance, around 620 million metric tons of hydrogen (consisting of four isotopes of hydrogen-1) are fused together to make 616 million metric tons of helium (helium-4), every second, in a continuing nuclear reaction which releases huge amounts of energy.

The Sun makes use of its massive gravitational forces to maintain the fusion process in its core, but down here on Planet Earth the necessary conditions are much harder to create.

What is ‘Nuclear Fusion’ Exactly?

Nuclear fusion takes place when two light atoms bond together (fuse), to make a heavier one. As a result of the fusion process, the total mass of the new heavier atom is less than that of the two atoms that made it. The “lost” mass is given off as energy, as laid down in Albert Einstein’s famous E=mc2 equation.

What is Needed for Nuclear Fusion?

There are a number of different formulas for creating nuclear fusion, which rely on differing combinations of atoms. Most involve isotopes of hydrogen such as protium, deuterium and tritium.

One of the most hopeful combinations involves the fusion of two isotopes of hydrogen: a deuterium atom (H-2) and a tritium atom (H-3). Deuterium is a less common isotope of hydrogen, but it’s still fairly abundant and it’s not radioactive. It can be extracted from seawater.

In contrast, Tritium does not occur naturally but is made in nuclear reactors by bombarding lithium with neutrons. Tritium is radioactive.

What Are Isotopes Exactly?

Isotopes are atoms of the same element that have the same number of protons and electrons but a different number of neutrons.

What is the Equation for Nuclear Fusion?

The fusion reaction is shown in the following formula:

Equation for nuclear fusion
Diagram shows the basic chemical equation involved in the fusion of two isotopes of hydrogen: deuterium and tritium. One atom of deuterium (H-2) and one atom of tritium (H-3) join together to form one helium-4 atom and a neutron. Most of the energy generated is in the form of the high-energy neutron. The energy is expressed in MeVs (million electron volts of electricity). The D-T fusion process, which requires temperatures of approximately 72 million degrees Fahrenheit (39 million degrees Celsius), produces 17.6 million electron volts of energy. Image: Public domain/ Wiki.

Fossil Fuels: The Facts.
What Are The Environmental Effects Of Fossil Fuels?

Engineering the Nuclear Fusion Concept

While the concept of nuclear fusion holds out the tantalizing prospect of an almost inexhaustible supply of carbon-free energy based on the same principle that powers our Sun and stars, it also poses a number of fiendishly complex engineering challenges.

Problem 1. The Need for Ultra High Temperatures

For hydrogen atoms to fuse, the nuclei must come together. However, the protons in each nucleus will naturally repel each other because they have the same charge (positive). The only way to overcome this issue and get them to fuse, is to infuse the atoms with enough energy so that they collide with each other at great speeds.

To achieve and sustain this process, different isotopes of hydrogen must be heated to extremely high temperatures and must be kept stable and confined for long enough to permit the atomic nuclei to fuse.

Martin Greenwald, senior scientist at MIT’s Plasma Science and Fusion Center, says that commercial fusion reactors would need to generate temperatures of up to 200 million degrees Celsius: that’s about 12 times hotter than the sun. 5

At this sort of temperature, hydrogen is no longer a gas but a plasma – a high-energy state of matter in which all electrons are torn away from their parent atoms and move about freely.

See also: Hydrogen Energy: Tomorrow’s Clean Fuel.

Problem 2. The Need for Ultra High Pressure

Heat alone is not enough to secure nuclear fusion. We must squeeze the atoms together to get them to fuse. This compression is only possible by using incredibly powerful magnets, lasers or ion beams.

At present, we can only generate enough temperature and pressure to make deuterium-tritium fusion possible. In future, when technology allows us to generate higher temperatures and pressures, it may be possible to achieve deuterium-deuterium fusion. The point is, it is easier to extract deuterium from seawater than to produce tritium from lithium. It also produces more energy.

There are two basic technologies to achieve the temperatures and pressures required for hydrogen fusion: magnetic confinement and inertial confinement. 6

How Nuclear Fusion Works
Cutaway image of the International Thermonuclear Experimental Reactor (ITER) the world’s largest tokamak (toroidalnya kamera ee magnetnaya katushka), which is projected to begin full operation in 2035. For a sense of scale, see the standing human figure (in blue) at bottom. Source: U.S. Department of Energy.

Magnetic Confinement

This fusion method uses microwaves, electricity and neutral particle beams from accelerators to heat a stream of hydrogen gas, turning it into plasma. The plasma is then compressed magnetically by huge super-conducting magnets placed around the vessel, which forces fusion to occur. The entire fusion process takes place inside a reactor vessel called a tokamak. The fusion energy is absorbed as heat in the walls of the vessel and turned into steam. The steam then drives turbine generators to produce electricity.

Inertial Confinement

This method, developed at the Lawrence Livermore Laboratory, uses lasers to ignite the fusion process. Up to 200 laser beams are beamed at a one-centimeter hollow cylinder, known as a hohlraum. Inside the cylinder is a capsule containing fuel in the form of a pellet consisting of a mixture of deuterium and tritium. The fuel pellet is about the size of a pinhead and contains about 10 milligrams of hydrogen gas.

The aim is to implode the capsule and energize the isotopes. If all goes according to plan, the outer layer of the hohlraum explodes, producing a shockwave that compresses and heats the fuel capsule to such an extent that the hydrogen plasma reaches 20 times the density of lead and ignites at 100 million degrees Celsius. A self-sustaining thermonuclear reaction will then set in yielding many times the input energy. Fusion begins.

Similar to the magnetic-confinement process, the heat produced from inertial-confinement fusion will be channeled to a heat exchanger to make steam for the generation of electricity. As of 2020, no fusion has actually occurred using inertial confinement, although scientists are getting closer. 7

What Are the Benefits of Nuclear Fusion?

On paper, nuclear fusion offers the prospect of unlimited low carbon energy. Controlled fusion releases almost four million times more energy than a chemical reaction like the burning of coal, or petroleum or natural gas. It produces the kind of ‘always-on’ baseload energy needed to provide electricity for industry and other constant demand sectors, without adding to global warming in any significant way.

Fusion fuels are abundant and nearly inexhaustible. Deuterium can be distilled from all forms of water, while tritium can be produced during the fusion reaction as fusion neutrons react with lithium. Alternatively, land-based reserves of lithium are sufficient to drive fusion power plants for more than a thousand years, while oceanic reserves are sufficient for millions of years.

Nuclear fusion releases no air pollution, no forms of particulate matter or other harmful pollutants like carbon dioxide or other greenhouse gases into the atmosphere. Its only significant by-product is helium: an inert, non-toxic gas.

What Are the Risks of Nuclear Fusion?

Unproven Concept
The main disadvantage of fusion is that – as of January 2021 – it remains an unproven concept. Plasma has been created, but the temperatures needed for fusion have not been achieved, and neither of the two containment methods have been fully realized.

High Cost
Moreover, the cost is staggering. The US Department of Energy now says the cost of ITER is likely to exceed $65 billion, which would make it the world’s most expensive science project, ever. ITER headquarters in France sticks by its original costing of $22 billion. (In 1998 the budget was $3 billion.) Either way, it’s a lot of money for an unproven theory.

Radioactive Waste
The final issue concerns radioactivity and nuclear waste. Fusion is not fission, but some materials used in the process will become radioactive during the lifetime of a reactor, due to bombardment with high-energy neutrons.

The amount of this short- to medium-term radioactive waste would be similar to the corresponding volumes from fission reactors. Fusion does not create long-term nuclear waste.

Health Concerns
There are also health concerns regarding the possible release of tritium into the environment. Tritium is radioactive and very difficult to contain. It can penetrate concrete, rubber and some types of steel.

Although a fusion reactor will only contain a few grams of tritium, leaks are inevitable even with the best containment systems. With a half-life of 12.3 years, tritium remains a threat to health for roughly 125 years after it is created.

All this is why scientists are hoping long-term to be able to create deuterium-deuterium fusion, thus dispensing with the need for tritium. 8

References

  1. “Fusion Energy Is Coming, and Maybe Sooner Than You Think.” Power. June 1, 2020. []
  2. “What is ITER?” []
  3. “Validating the physics behind the new MIT-designed fusion experiment.” []
  4. “Scientists present a comprehensive physics basis for a new fusion reactor design.” []
  5. “MIT Validates Science Behind New Nuclear Fusion Reactor Design.” []
  6. “How Nuclear Fusion Reactors Work.” []
  7. “Pursuing Fusion Ignition.” []
  8. “Nuclear Fusion Power.” World-nuclear.org. Nov. 2020. []
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