A Sun on Earth

Years of scientific study of the earth’s climate, human influence on it and the impacts of a changing climate have made it clear that we have to stop using the fossil fuels that have provided the energy for the incredible technological advancement of our societies. Of course there are other, cleaner ways to make use of the energy that is ultimately provided by the Sun than using the highly concentrated chemical energy in the remains of organisms millions of years old. Wind turbines and solar panels are popular renewable alternatives, but because the energy content of the wind and Sunlight is not as concentrated as it is in fossil fuels, an incredible number of wind turbines and solar panels will be needed to supply the world’s energy needs.

Since the energy of both fossil and renewable energy sources ultimately comes from the Sun, it is interesting to look at how this distant, giant ball of plasma produces this enormous amount of energy. Our Sun was created by the gravitational collapse of the solar nebula, an enormous gaseous cloud consisting for a large part of hydrogen. During this collapse, the mass of the early Sun was increasing rapidly and so was its gravity. The huge gravitational force caused the Sun’s core to become incredibly dense and hot, until it exceeded the temperature needed for stellar nucleosynthesis: in the Sun’s case the nuclear fusion of hydrogen atoms to form helium. It is this fusion that releases enormous amounts of energy in the Sun’s core and this energy is what is preventing the Sun from collapsing under its own gravity.

nucfusion

Source: https://rampages.us/abadkea/wp-content/uploads/sites/16900/2016/05/nc3.jpg

Could humans, instead of using the Sun’s energy, find a way to directly get energy from a fusion process here on earth? Of course we already have nuclear power, but this is energy from a controlled nuclear fission1 process that mostly uses the relatively rare and heavy element uranium. There is a limited supply of uranium available on Earth and only a small part resides in conventional high-grade ores. Apart from issues with the main resource,  nuclear waste is a serious problem: radioactive contamination is dangerous to all life and so the radioactive waste products of nuclear fission have to be stored safely for very long times until all radioactive material has decayed to stable daughter elements.

Nuclear fusion is much more difficult to do here on Earth, because star-like conditions, meaning a plasma of 100 million K, have to be recreated in order for fusion to be able to take place. This is possible and it has already been seen in hydrogen bombs, which are nuclear weapons that use the energy of a nuclear fission reaction to start a nuclear fusion reaction. Successful nuclear fusion in a bomb is one thing, but creating an ongoing, safe and energy-yielding fusion reaction in the lab has not been done yet. It proved to be difficult to confine this plasma: in stars this happens because of gravity, but on earth this has to be done in a different way, for example with magnetic confinement. Also, you can probably imagine that it takes a lot of energy to heat something up to 100 million K and to date there has not been an experiment in which the energy yield of fusion exceeded the energy needed to initiate the reaction. However, nuclear fusion for energy production is still a very active area of research2 and experts believe that a successful nuclear fusion reactor will be on the grid in the coming decades. Just recently, a collaborative initiative between MIT and a private company claims that it will provide electricity from nuclear fusion within 15 years3.

fusreactornucfusion2

It is clear why countries and organizations are making huge investments in nuclear fusion research: according to Ongena (2016) the resources needed for fusion can be obtained in a cheap way, it is a nearly inexhaustible source of energy, there is no carbon involved in the process, a fusion reactor is expected to be much safer than a fission reactor and no long-term storage of nuclear waste is involved. This makes nuclear fusion a very promising option in the energy transition. It could for example complement intermittent renewables like wind and solar energy, so that energy availability is much more stable and less storage capacity is needed, addressing currently important concerns of a renewable based power grid. In my opinion, we should keep investing money in nuclear fusion research so that one day we might have plenty of clean and safe fusion energy available. However, we should not wait around and do nothing or even use the development of nuclear fusion power as an excuse to reduce our current efforts on reducing fossil fuel emission, but we should keep investing in other renewables as well.

1. You may wonder why energy can be released from fission as well as fusion processes, while these are reverse reactions (fusion means adding protons and neutrons to the nucleus, while fission is removal of protons and neutrons). This has to to with the nuclear binding energy curve:

bindenrg

Source: https://www-spof.gsfc.nasa.gov/stargaze/SnucEnerA-2.htm

The general shape of the curve is a positive slope for elements lighter than Fe56(iron) and a slight negative slope for heavier elements. This means that fusion of elements releases energy for elements lighter than Fe56(exothermic), while energy is needed for fusion of elements heavier than iron (endothermic). Conversely, fission of elements lighter than iron takes up energy, while fission of elements heavier than iron releases energy. This is the reason that the very heavy uranium is used to get energy from fission in nuclear reactors, while nuclear fusion would involve light elements, most likely hydrogen.

2. If you’re really interested in the research on this topic, since 2012 there has actually been a Master’s programme at the Eindhoven University of Technology called ‘Science and Technology of Nuclear Fusion’.

3. It should be noted that scientists have claimed that they are close to nuclear fusion energy for over 50 years. It remains to be seen whether this initiative will reinforce the stereotype of fusion scientists always saying that they are close to fusion power, but never actually getting there, or that it will finally be a success.

Sources

Gabriel S, Baschwitz A, Mathonnière G, Fizaine F, Eleouet T. 2013. Building future nuclear power fleets: The available uranium resources constraint. Resources Policy. 38(4):458-469.

Kirk A. 2015. Nuclear fusion: Bringing a star down to Earth. Contemporary Physics. 1-18.

Ongena J. 2016. Nuclear fusion and its large potential for the future world energy supply. Nukleonika. 61(4):425-432.

Richter J. 2017. Energopolitics and nuclear waste: Containing the threat of radioactivity. Energy Research & Social Science. 30:61-70.

https://www.theguardian.com/environment/2018/mar/09/nuclear-fusion-on-brink-of-being-realised-say-mit-scientists

6 thoughts on “A Sun on Earth

  1. Thank you for the article! I was wondering if you know, whether we could use the nuclear waste from fission in order to do fusion? This could help us to reduce the burden of nuclear waste and have a carbon free source at the same time..

    Like

  2. Thank you for your blogpost! You mentioned some advantages of nuclear fusion. However, I was wondering what exactly the disadvantages of nuclear fission are (such as safety issues, high costs, nuclear waste etc.)? Also, how would you compare the potential of nuclear fusion to that of renewable energy? Do you think it could eventually, despite its disadvantages, surpass the potential of renewable energy and become our main energy source?

    Like

  3. @laurianenoi Thank you for your comment! Combining fission and fusion in the way you describe does indeed sound like optimal use of nuclear waste. Unfortunately this is not realistic. As I mentioned in the article, fusion is done with very light elements, while fission requires very heavy elements. There are a number of dangerous fission products that have to be stored for a very long time, but all of these are still heavier than iron, meaning that they require energy to be fused instead of releasing energy. Fission also produces some lighter elements, but there is no reason for us to use them for fusion since ‘normal’ fusion fuel is widely available and these fission products are not the ones with slow and dangerous radioactive decay.
    So the dangerous radioactive fission products can unfortunately not be used for fission.

    Like

  4. @simionauc Thanks for your comment! The most important disadvantages of nuclear fission power are:
    – Nuclear waste: fission in nuclear power plants in the end always produces a number of radioactive isotopes, some of which have half-lives of around 30 years, but the 7 long-lived fission products have half-lives between 200.000 to 16 million years. This waste has to be stored somewhere safely for an incredibly long time and this is dangerous, expensive and requires serious long-term management.

    – Accidents: Although a nuclear power plant will never explode like a nuclear bomb, serious accidents can occur that cause the radioactive fission products inside the reactor to be spread in the area around the reactor. Events like the Chernobyl disaster show that this has a large impact on the environment and people living in the area around the reactor and that this area will not be safe to live for humans for thousands of years. This also makes nuclear power plants vulnerable to (terrorist) attacks.

    – Social resistance: Because of the reasons above, there is social resistance against nuclear power. Even if we think it is a good solution for climate change, the people would need to be convinced first.

    – Nuclear weapons: Technologies and materials used for nuclear power plants are very similar to the technologies and materials used for the production of nuclear weapons. If more countries decide to research and experiment with nuclear power, other countries might not agree with this, fearing the development of nuclear weapons in that country. This would be a great challenge for international politics. Of course, this is also partly the case with fusion technology, which is not as similar to nuclear weapons production, but still requires a lot of knowledge of nuclear physics that could potentially lead to nuclear weapons production.

    – Fuel: There is a limited supply of uranium available on Earth and only a small part resides in conventional high-grade ores. Estimates say that the world’s measured resources of uranium that are economically recoverable are enough to last for between 70 and 100 years. This is of course difficult to predict: if there is a huge transition to nuclear energy, this uranium will be depleted much earlier, but then there will also be a lot of research into unconventional uranium resources. However, it is clear that fission fuel is not as easily accessible as fusion fuel.

    As for the potential of nuclear fusion compared to renewable energy, naturally, this is very difficult to predict. It very much depends on the upcoming research and experiments whether we will be able to do fusion with acceptable energy yields and at what price. However, I have heard the likes of Elon Musk predicting that the future energy production will be a combination of conventional renewables and fusion power, so I am definitely hopeful. It would certainly be helpful in coping with the intermittency of renewable energy.

    Like

  5. Thank you very much for your reply, however I mean to ask what the disadvantages of nuclear fusion are. Nevertheless, thank you for letting me know about the known disadvantages of nuclear fission. Are the disadvantages for nuclear fission similar? There could be some major differences due to the fact that fusion is based on a different process.

    Like

  6. @simionauc Haha it’s unfortunate that the two words are so similar…

    Anyway, good question. The disadvantages of nuclear fusion are indeed quite different from those of nuclear fission.

    – Accidents: Accidents in a fusion plant would not be like fission plant accidents. While fission needs active cooling, fusion needs active heat, pressure and magnetic field management in order for it to continue. If for some reason this management stops, the reaction and heat generation would simply stop, so a ‘meltdown’ will not occur. Accidents can occur in fusion plants, but they mostly seem to have to do with explosions caused by the magnets that are used to keep the plasma dense and hot enough. While explosions in a fusion reactor would be dangerous to the people working there, no large scale spreading of radioactive material is involved.

    – Radioactive waste: This depends a bit on the exact fusion reaction that takes place (there are multiple possibilities), but a fusion reactor is not entirely free of radioactive waste. In one type of nuclear fusion reaction, Tritium will continually be released. This is a radioactive isotope of Hydrogen and it is volatile and biologically active. However, its half-life is only 12 years and it does not bioaccumulate: it is removed from the body as water with a biological half-life of about two weeks. Still, the Tritium will need to be contained and stored safely for some time. Apart from this, the structural materials of the fusion reactor itself become radioactive, so when a plant shuts down, it will need to be dismantled and the radioactive parts have to be stored safely, just like nuclear fission power plants.

    – Money: Research into fusion power is very expensive and has already cost us a lot of money (billions of euros). We don’t know the price of a future fusion plant, but it will probably not be cheap given the highly advanced technologies involved.

    – Weapons: Like with fission, the development of fusion reactors can lead to the development of nuclear weapons because the technologies involved are similar.

    Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s