Analysis: a fusion energy source certainly has many attractive features, but there are immense technical challenges involved
By Brian D. Appelbe, Imperial College London
Nuclear fusion has been in the headlines in recent times, most notably when the US Department of Energy announced "fusion ignition" last year. In many ways, this is nothing new: front page headlines in 1958 promised "limitless fuel for millions of years" from an experiment that was later seen as a failure.
However, there is a growing sense in the scientific community that things are different this time. Nuclear fusion is an energy source in which nuclei of light elements (those, such as hydrogen, that are found near the beginning of the periodic table) join, or "fuse", together and undergo a nuclear reaction. This reaction is governed by Einstein's famous formula, E = mc2, and so a small fraction of the mass of the fusing nuclei is converted to energy in the form of moving particles. This is how the Sun creates its energy and scientists aim to recreate the process on Earth for electricity generation.
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From RTÉ Radio 1's Drivetime, Turlough Downes from DCU on the recent historic nuclear fusion breakthrough
A fusion energy source has many attractive features. It would not emit greenhouse gases and fusion fuel is widely available, making it a sustainable energy source. In contrast to nuclear fission, the reaction underpinning current nuclear power plants where nuclei of heavy elements are split, fusion would produce little radioactive waste and catastrophic accidents such as Fukushima and Chornobyl would be impossible.
The downside is that creating a fusion energy source is technically challenging and requires two basic tasks. First, the fuel must be made hotter than the Sun’s core (over 15 million degrees celsius). This is because fusing nuclei have positive electric charges that cause them to be repelled from each other. High temperatures force nuclei to overcome this repulsion and fuse. In contrast, nuclear fission does not require high temperatures since splitting of heavy nuclei is induced by neutrons, which have no electric charge.
Secondly, fuel must be sufficiently confined. Fuel heated to high temperatures will tend, like anything that is overheated, to blow itself apart. Therefore, the fuel must be held in place, or "confined", such that reactions can occur. The Sun solves this confinement problem by simply being so massive that its gravity keeps the hot fuel in place, but we need to be more creative on Earth.
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From RTÉ Radio 1's Morning Ireland, Dr Robbie Scott from the UK Inertial Fusion Consortium on the nuclear fusion breakthrough in California
There are two main approaches to the confinement problem. Magnetic Confinement Fusion (MCF) uses magnetic fields to confine the hot fuel for long periods of time. Because the fusing nuclei are electrically charged, their motion can be controlled by magnetic fields. This approach can be seen in ITER, currently under construction in southern France.
The second approach to the confinement problem is Inertial Confinement Fusion (ICF). Here there is a trick in that hot fuel is not actively confined. Instead the fuel is compressed to extremely high densities such that large numbers of fusion reactions happen before it blows apart. The primary example of this is located at Lawrence Livermore National Laboratory in California where the world’s biggest laser, the NIF, is used to compress small pellets of fuel.
The NIF achieved "fusion ignition" in December, meaning that the fusion energy emitted from the fuel was greater than the energy delivered by the laser to do the heating and compression. This is a significant breakthrough for fusion energy as it is a proof-or-principle demonstration that more energy can be emitted by the fuel than needs to be put in.
From BBC News, the UK-based JET laboratory has smashed its own world record for the amount of energy it can extract by squeezing together two forms of hydrogen
However, many more challenges remain to convert this result into an electricity source. The total energy produced was only enough to boil a kettle several times. It would need to be scaled up and happen several times a second in order to function as a power plant. Building a suitable laser is a vast, as yet unfunded, undertaking.
Other developments have also contributed to the current optimism about nuclear fusion. An experiment on the JET device in the UK produced a record amount of fusion energy in December 2021, although this was still less energy than was delivered to the experiment.
Another cause for excitement is the emergence of a fusion industry, comprised of start-up firms backed by private investors exploring novel designs for fusion energy. These firms are pursuing aggressive timelines for commercially viable fusion energy, in contrast to publicly funded project such as the NIF and ITER. For example, Commonwealth Fusion Systems, based in Massachusetts, has received over $2 billion funding and aims to have a commercially viable design by 2030. Meeting this ambitious target requires the rapid solution of unprecedented scientific and engineering problems.
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From RTÉ Brainstorm, is is time to give nuclear power a chance?
One such issue is conversion of energy emitted from the fuel into electricity. Energy is emitted in the form of fast-moving neutrons that can damage materials surrounding the fuel. Minimising the resulting wear and tear will require advanced engineering and regular maintenance, the costs of which are likely to determine the economic viability of fusion power plants.
Fusion energy could be a revolutionary energy source. However, the extraordinary technical challenges involved and uncertainty about when these can be resolved mean that we cannot rely on it to meet our immediate climate change goals. Instead, recent successes should give hope that persistence in scientific investigation can eventually overcome the challenges.
Dr. Brian D. Appelbe is a Research Fellow in the Faculty of Natural Sciences and Department of Physics at Imperial College London
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
