Let’s Go Fusion

Okay, I admit that the title does not work as well as it did here, but I’m out of ideas. I am here to present to you nuclear fission’s even more powerful (although currently industrially unviable) partner, nuclear fusion.

Fission is a very powerful process. With a simple splicing of the atom comes a great deal of energy, an amount not even closely matched by fossil fuels. Sadly, nuclear fission comes with a variety of downsides – the connotations of radioactive waste and Chernobyl are all real life risks posed by fission reactors. Thus relying on only fission when fossil fuels are exhausted is not a good enough plan for the future of humanity. Nuclear fusion is a promising solution.

Fusion merges two atomic nuclei together, as opposed to fission which splits one apart. But why is fusion superior? One key advantage of fusion reactions is that they release far more energy per reaction that fission reactions do, and delving into some physics can help explain this.

Where does the energy released by a nuclear reaction actually come from? Contrary to common sense, there is not strictly a conservation of mass during a nuclear reaction. The mass of an atomic nucleus is ever so slightly lower than the combined mass of its constituent nucleons (protons and neutrons). How could this be, though, since the laws of physics dictate a conservation of mass? This difference in mass, called the mass defect, is converted into energy, or the binding energy. The amount of energy released is governed by one of the most famous equations in physics, E = mc2.

These mass defects are microscopic; they generally account for less than a hundredth of the total mass. But due to the extremely high value of c2, a tiny amount of mass can release heaps of energy.

By calculating the binding energy per nucleon for each element of the periodic table and plotting this on a graph in order of nucleon number A, it becomes clear which elements have the potential to release the most energy as a fuel. This graph is commonly known as the curve of binding energy.

Curve of Binding Energy

In a nuclear reaction we must start with reactants and finish with products. The reactants must have a lower binding energy than the products or else the reaction would require energy rather than release energy. A viable fission reaction would involve elements to the right of the peak at iron (A = 56). A common fission reaction used in commercial reactors is uranium (A = 235) and one neutron to form barium (A = 139) and krypton (A = 94) and three neutrons.

On the other hand, fusion reactions involve elements to the left of the peak. A common fusion reaction used in experiments is deuterium and tritium (both isotopes of hydrogen with (A = 2 and A = 3) to helium (A = 4). The difference in binding energy per nucleon between the reactants and products in this reaction is clearly much higher than those in the fission reaction – the curve of binding energy shows us why fusion reactions inherently tend to release more energy.

Keep an eye out for my following posts, in which I will explore deeper into this potential solution to our future energy demands.

Yanhao

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4 thoughts on “Let’s Go Fusion

  1. I’m totally not a science person, but I recall a couple of researchers in Utah in the 80s claimed to have developed cold fusion, then quickly retracted their claims. Have scientists now found a way to achieve cold fusion? Isn’t that like the Holy Grail in terms of ultra-safe and powerful energy? Or are fusion and cold fusion two different things?

    Liked by 1 person

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