THURSDAY, 4 JANUARY 2024What comes to mind when you see the word “nuclear”? Is it a post-apocalyptic hellscape engulfed by the flames of war, or an advanced civilisation fuelled by limitless energy? What, then, about the phrase “nuclear fusion”? Does that repaint the image in deeper shades of red or green? Nuclear energy has been heavily stigmatised in the wake of the Cold War-era nuclear arms race and the haunting tales of Fukushima, Chernobyl, and Three Mile Island. This has not only hindered the development of nuclear plants, but also cast a shroud of mystery, fear, and misinformation over adjacent technologies – technologies like nuclear fusion. It is more important, now than ever, to dispel the myths surrounding fusion, for it will eventually form the bedrock of our energy landscape.
THE DEFINITION OF FUSION
Nuclear energy, as people have come to know and fear, most commonly refers to nuclear fission – the splitting of heavy elements into lighter ones to produce energy. In contrast, nuclear fusion alludes to the binding of light elements into heavier ones while also releasing energy. Superficially, fusion and fission seem to be two peas in a pod with pedantic differences. But in practice, they cannot be more different.
Fusion is a process typically associated with stars like our Sun, and the endeavour to build fusion reactors is nothing less ambitious than to create a miniature Sun. In the Sun, hydrogen nuclei collide with astounding speed and under immense pressure, while in fusion experiments, hydrogen isotopes (the same element with a different number of neutrons) are subjected to temperatures 7 times hotter than the Sun’s core. The result is a helium nucleus and an inconceivable amount of energy. Here’s a useful analogy: picture a rock sitting precariously atop a hill. Push it, and it will roll down the slope, slamming onto a tree. Likewise, the conversion from multiple hydrogen nuclei into one helium nucleus is a downhill journey, and the sorry state of the tree reflects the associated energy release.
However, this process doesn’t occur spontaneously. Instead, there is an intricate interplay between two fundamental forces of nature. The electromagnetic force keeps two positively charged nuclei apart, and its effect extends ad infinitum. Conversely, the strong nuclear force binds nucleons tightly together, but only works over very short distances. Hence, only when the nuclei come very close together under extreme temperature or pressure, will they then fuse. This is like having a wall between the rock and the valley – some work needs to be done to raise the rock over the wall for it to begin its descent.
THE ULTIMATE SOLUTION
Compared to conventional energy sources, the benefits of fusion sound almost fictional. Fusion is the most fuel-efficient process humanity can harness yet. One kilogram of fusion fuel is equivalent to ten million kilograms of fossil fuels, or four kilograms of fission fuel. Fusion reactors also utilise abundant resources. The major ingredient of fusion is deuterium, a hydrogen isotope which can be obtained by purifying seawater. The other reactant is tritium, a different isotope that exists in trace amounts in nature, but research is underway to integrate its production into the fusion process. Conversely, non-renewable sources like coal, natural gas, and oil are estimated to deplete within the next hundred-odd years. Perhaps the greatest advantage of fusion is the clean and safe waste. A fusion reaction produces none of the pollutants and greenhouse gases plaguing our Earth today, but only helium – an inert and harmless gas. The only radioactive material involved is tritium, with a lifespan of 12.3 years, as opposed to fission reactions that leave a cocktail of radioactive wastes lasting up to billions of years for future generations to inherit.
THE CURRENT SITUATION
As amazing as it sounds, fusion is still a work in progress. There are currently two prominent methods to achieve fusion: magnetic confinement, where fuels are injected and circulated within a doughnut-shaped magnet as white-hot plasma, and inertial confinement, where powerful lasers focus their beams onto a small fuel pellet to cause an implosion. A crucial threshold to measure the success of fusion reactors is the break even point, where the useful energy produced matches the energy required to run the reactor. This is quantified by the Q-value, such that exceeding Q=1 means more energy output than input. Thus far, the best result comes from the National Ignition Facility (NIF) in the USA, reporting a Q=0.70 from its inertial confinement reactor.
Looking forward, the highly anticipated International Thermo-nuclear Experimental Reactor (ITER), a magnetic confinement reactor currently being built by the European Union, will be completed in 2025 and can potentially achieve a staggering Q=10. Developments for commercial fusion are also underway: DEMO, a class of prototype reactors, will be operational by 2050 around the world; the UK has plans to build one in Nottinghamshire by 2040; and ARC, a compact reactor developed by MIT, will begin construction as early as 2025. Experts believe that with an optimistic outlook in funding and technological advancement, the second half of the century will witness the rise of fusion power in electricity generation.
CAVEATS AND COMPLICATIONS
The possibility of fusion energy manifesting within our lifetime is a great cause for celebration. However, the road ahead is not only fraught with difficult scientific and technical problems, but also myriads of political, social, and economic challenges. Scientists and engineers face off against the four horsemen of fusion:
- Attaining and regulating temperatures over 100 million °C.
- Developing materials capable of withstanding the steep temperature gradient and merciless particle bombardment.
- Breeding and handling the scarce tritium fuel.
- Maintaining the reactor remotely with robots.
Therein lies the crux of the matter: fusion is expensive – really expensive. The ITER collaboration, with an initial budget of €6 billion, is currently rocking a price tag of €22 billion. For perspective, the James Webb Space Telescope costs $10 billion, while CERN’s Large Hadron Collider goes for a measly $4.75 billion.
The hardest part is convincing people that fusion is worthwhile and safe. This requires dissociating fusion from the nuclear anxiety that stems from the histories of nuclear meltdowns, and the fear of nuclear warfare, especially in a knee-jerk reaction to Putin’s nuclear threats amidst the ongoing Russo-Ukrainian War. Indeed, the debate on nuclear power is on an unfortunate trajectory deviating from evidence-based reasoning and driven by the fear-mongering of anti-nuclear organisations. But the facts are difficult to contest, if only they were rationally considered: fusion plants will not melt down, and cannot be weaponised. A fusion reactor does not operate on chain reactions, and any slight disruption will halt the reactor in seconds. Furthermore, a fusion-powered warhead cannot be made with the limited fuel present in a reactor, and will also require an additional fission bomb to detonate.
THE FUSION CONVERSATION
At present, nuclear fusion remains an obscure subject that most people know little about, and it is certainly not a major topic on the government agendas. But as scientific progress accelerates in the coming decades, political and social conversations ought to keep up. And when the technology is ready for the world, the world needs to be ready for it. There is a running joke that fusion energy is 30 years away and always will be, but let its delay be the fault of scientists and engineers, not politicians and protesters.
Xavior Wang is a third year Physics student at St Edmund's College. His interests span the spectrum of length scales, from nuclear fusion and quantum computation to astrophysics and cosmology. Illustration by Pauline Kerekes.