by Sebastian Hettrich
Technical aspects and environmental issues
What is nuclear fission and how does it work?
The visible matter in our world is built up out of atoms which are the core composed of neutral particles (neutrons) and positive particles (protons), surrounded by a cloud of negative particles (electrons). These particles are stuck together by two different basic physical forces: the electrons are attracted to the core by the electromagnetic force and the core (neutrons and protons) is kept together by the strong interaction, as known as strong nuclear force. Both these forces find exploitation in energy production. The electromagnetic force comes to play in chemical reactions such as fire, the strong interaction finds application in nuclear energy production.
Now there are actually three totally different nuclear processes: nuclear fission; nuclear fusion; and nuclear decay, all of which can be used for gaining energy. In fact the two latter ones are the two processes that naturally occur every day, but when thinking of nuclear energy, most people have in mind nuclear fission.
To explain them with an analogy, let’s imagine a raspberry. A raspberry, like a nuclear core, is builts up of several smaller pieces. Nuclear fusion in that analogy would be taking single little pieces of that raspberry and ‘gluing’ them together to become one finished raspberry. Nuclear decay is if we take that raspberry apart little piece by little piece.
Nuclear fission is somewhat more violent; we shoot a little piece of raspberry with high speed onto another raspberry to split it into two larger and several smaller pieces. During each of these three processes, a fraction of the raspberry is directly put into energy.
Advantages and disadvantages of nuclear fission energy
As this article focuses on nuclear fission, we would like to briefly describe the advantages and disadvantages that come with this particular sort of generating usable energy. As mentioned, during nuclear fission, the core of an atom larger than iron is shot at with an energetic projectile, usually a neutron. When splitting the core, two large pieces and several (usually 2-3) free neutrons are produced, and some of the material is — using Einstein’s famous mass-energy equivalence E=mc² — transformed entirely into energy . This energy output is proportional to the weight of nuclear cores, which is why Uranium, the heaviest natural element, found its way into nuclear fission reactors. Uranium generates, when split, on average 200 MeV (Mega electron volts) of thermal energy , out of which around 190 are usable in fission reactors . Therefore one kilogram of Uranium could theoretically produce 78 Terajoule of energy. For comparison, that is 2.3 million times more energy than in one kilogram of the best anthracite coal. Or put in another way: we can get the energy of 2300 tonnes of coal with just one kg of Uranium, but without the carbon dioxide emissions of it. But that is about all that can be listed under advantages.
Nuclear fission comes with disadvantages many of which are caused by the physics of the process:
As each reaction is producing more of the energetic neutrons, which again split more cores, the process goes quickly into a chain reaction if a certain mass of Uranium is present. It therefore needs constant steering (via control rods) and moderation (many reactor designs use water) of the free neutrons . The produced amount of heat needs to get constantly transported out of the reactor, even if the reactor is not in operation . Therefore a constant supply of fresh water is necessary. If the cooling cycle is interrupted, heat will pile up and evaporate the coolant leading to an increase in pressure. Consequently, the fuel elements will run dry, leading – as the coolant also acts as moderator to slow down the chain reaction – to an increase in heat, melting the fuel element . Ultimately, escaping hydrogen may explode and further destroy the reactor while releasing large amounts of radioactive material into the atmosphere, such as happened during the Chernobyl or the Fukushima Daiichi disasters. This dependency on water cooling makes nuclear fission reactors also vulnerable to climate change, as the extreme heat summers of 2018 and 2019 in central Europe have shown; several reactors in Germany, France, and Switzerland had to be throttled down or even entirely taken off-grid due to low water levels and rising river temperatures [5,6,7,8].
Because of the nature of the fission process, nuclear fission reactors cannot quickly switch on  and even less switched off quickly (in fact, if an old reactor is taken off the grid, entirely shutting down its reactions takes up to years) , therefore they can not flexibly adapt to peaks in energy demand.
Unfortunately the list of disadvantages does not quite end here. Nuclear fission energy, despite often being portrayed as sustainable or renewable, in fact is neither of the two. As during nuclear fission the material is using up, it is not renewable, and in order to be sustainable, Uranium, or better fissionable Uranium, is too rare. While Uranium is relatively abundant on Earth, the best Uranium ores hold only a few percent of Uranium, located in only a few places on Earth, and 99,27% of it is Uranium 238, which cannot be used for fission. Only Uranium 235 is fissionable, but makes up only 0,72% of the natural abundant Uranium .
Currently, the world’s nuclear fission reactors consume 63000 tonnes of fissionable Uranium per year, while producing 375GW or 14% of the world’s electric energy . At the current rate, the known Uranium reserves are estimated to last roughly until the end of this century . Doubling or even tripling the amount of nuclear power would significantly lower the remaining reserves, while only contributing around 6% in global CO2 reductions (comparable to the amount emitted by air traffic) . So in the foreseeable future, prices for Uranium will go up – affecting the price of electricity – and due to the uneven distribution, global supply dependencies will grow, and with more than 70% of the known reserves lying on indigenuous land , mining those comes with social issues. More advanced fuel cycles could potentially extend the duration of already available Uranium, however, it would require entirely replacing many of the existing ~ 440 reactors in addition to building the 1000 new reactors to reach the tripling . Not only are nuclear reactors already expensive and take some years to build, they also require thick concrete and steel walls to shield the radiation, both of which materials are CO2-intensive in their production (~500 to 600 kg of CO2-emissions per tonne of cement [12,13] and 1500 to 1800 kg CO2-emissions per tonne of steel ).
Further environmental issues arise in the mining and processing of Uranium. In 2014, an EU-funded report  reflects in detail on the negative environmental impact Uranium mining has. Due to the low concentration of Uranium in the ore, large amounts of soil have to be mined and processed. The use of a variety of highly toxic and acidic chemicals to clean out the Uranium inside the rock often results in measurable pollution of soil and water in the vicinity of the mines . Also the open waste rock piles, often with radioactive doses several times higher than maximum annual dose limits, release Uranium and toxic heavy metals into the surrounding soil and could be measured in nearby rivers . Interestingly, this report also mentions that in 2012, the extraction of 1 tonne Uranium 235 dioxide came with the emission of roughly 78 tonnes of CO2 , with only 0,72% fissionable material within this tonne, making around 11 tonnes of CO2 per 1 kg of fissionable material.
But not only the beginning of the nuclear fuel production causes issues, also the end-of-life disposal of spent nuclear fuel and a zoo of nuclear byproducts , as well as the highly radioactive reactor material after decommissioning is a hot topic. In the years prior to the ban from 1994, nuclear waste material has simply been dumped into the oceans . Lesser known is that nuclear waste material is up to now still being sold to totalitarian countries like Equatorial Guinea, where the unprofessional storage of millions of barrels of nuclear material on the Island of Annobón already is already threatening the environment and the health of its population [18, 19]. Waste from nuclear fuel production, particularly spent fuel elements are highly radioactive with long half-life times of thousands to millions of years and radiation 20 to 25 times higher than the lethal dose , meaning that it would have to be safely be stored away for at least 300 to 1000 years to decay to safe levels . Currently no country in the world has yet any established facility for the safe long-term storage of these high-level radioactive waste which just for European reactors amounts to roughly 6.6 million cubic metres . The costs for the disposal of spent fuel and the decommissioning of nuclear reactors are not — as should be — covered by the plant operators but are mainly carried by taxpayers and often amount to several billion € . As there is always the danger of nuclear material getting into the wrong hands and causing damage, proliferation or terrorism, e.g. via dirty bombs, has to be considered for site-selection and future safe-guarding of storage facilities .
To summarise, while nuclear fission energy has always been promoted as unlimited, clean, and safe energy for the future, at least on the paper, a look behind the scenes uncovers that the physics do not allow failures, that nuclear material is all but unlimited, that the way it is produced is not as clean as it seems, and that costs and responsibility for the legacy has been sold to future generations. Due to the above-mentioned limitations and long commission times, nuclear fission power is not a suitable option to fight climate change, and rather exchanges one global problem with a whole bunch of different problems.
During the research for this article it became apparent that there seems to be a discrepancy between the search results depending on the language you search in. English literature and media seem to have a bias towards seeing nuclear fission energy as a clean source of energy, while it is hard to find english sources critically describing the disadvantages, environmental and social impacts of nuclear fission.
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