Tag Archive fission

Blog 3rd Jan 2023 – Nuclear power – fusion and fission

To assist our members and the general public, CiS will be listing new blogs regularly on different science topics.

Disclaimer: We will be asking top scientists in their fields to author the blogs, but the thoughts expressed are the authors.

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Nuclear power – fusion and fission.

by Dr Peter Bussey

There is an urgent need to generate more electricity in ways that do not also produce carbon dioxide, whose increasing levels in the Earth’s atmosphere are a serious threat to our habitable environment.  Many nuclear power stations have been constructed that use the heavy elements uranium and plutonium as their fuel.  Bombarding these elements’ atomic nuclei with elementary particles known as neutrons causes the nuclei to split into nuclei of lighter elements, a process known as nuclear fission which releases large amounts of energy.  The energy is carried mainly by neutrons given off in the process, and these neutrons do two things. The first is that they can induce more fissions of more uranium or plutonium nuclei in the fuel rods, making the process self-sustaining.  Otherwise, they can give up their energy to a suitable material (such as water) that is circulated into the reactor, heating it so that it can be used to drive an electricity generator.

The nuclear power stations that are in operation around the world produce very significant amounts of electricity without carbon dioxide emission.  The challenge is to dispose of their solid waste products, since many of the lighter elements that are produced are very radioactive and hazardous.  In the end, it will be necessary to store these waste materials underground for extremely long periods; however, there is no compelling reason why this cannot be done.

A different kind of process, nuclear fusion, is when nuclei of light elements combine together to form heavier elements.   Large quantities of energy can be produced by these processes too, and they are the kind of process that generates energy in stars such as our Sun.  Over many decades, research has been carried out with the aim of generating power by this means on the Earth.  Technically this is a very formidable problem.

The light nuclei that are most suitable for this purpose are two isotopes of hydrogen – deuterium,  known as “heavy hydrogen”,  and tritium, which is heavier still.  Deuterium comprises a small fraction of natural hydrogen and can be extracted from ordinary water.  Tritium is radioactive – that is, unstable – and so is not found significantly in nature.  It can be manufactured as required by bombarding the element lithium with neutrons.  There are substantial quantities of lithium in the Earth’s crust, and initially we can use neutrons from nuclear reactors.  An atom of lithium can give rise to an atom of tritium.

The deuterium and tritium nuclei must be persuaded to interact with each other.  This is not trivial, because the nuclei are positively electrically charged, and energy is needed to overcome their electric repulsion and get them close enough to interact.   Much more energy is then released in the interaction, which produces a helium nucleus and an outgoing neutron that carries most of the energy.  These neutrons can be used to make more tritium from more lithium atoms or, once again, they can heat up a circulating fluid that can be used to generate electricity.  Processes of this kind produce very low levels of hazardous waste products with no carbon dioxide, and should be capable of generating large quantities of electric power.

In trying to make this work, two approaches have been attempted.  In one, a small pellet containing deuterium and tritium is exposed to a violent burst of laser light, in order to energise it enough for the elements to interact.  At the Lawrence Livermore Laboratory in the USA, this has been achieved in late 2022, sufficiently so as to give out more energy than was put in – an important milestone!  But it is hard to devise ways to scale this prototype method into a usable power station.  More promising is to build a device containing a circular magnetic field that is able to hold deuterium and tritium ions within a fixed volume of space, even when they are very hot.  The idea is to heat the ions using electromagnetic fields, to give them enough energy to interact by nuclear fission and release usable energy, carried away by neutrons which can transfer it to circulating water (say).  This approach is known as “magnetic confinement”.

The technology and science need to be thoroughly understood in order to make this succeed.  Magnetic confinement devices of increasingly large size have been constructed to develop our understanding, and more are being built.  It is believed that with a sufficiently large device, the fission process will work and produce large amounts of power.  But it is a very complex and ambitious goal.  Governments and now private sources are putting a great deal of money into this area in the hope of success within a few decades.

Nuclear power does not exclude or sideline wind generators and solar panels, but these have their own drawbacks and limitations.  It is our human and Christian obligation to support all efforts that can provide energy that we need, but also preserve our planet for present and future generations!

 

Biographical note

Peter Bussey is an emeritus Reader in Physics at the University of Glasgow, where he taught physical science subjects over many years.  He remains actively engaged in elementary particle physics research and is a member of the ATLAS collaboration, which is based at the CERN laboratory in Geneva and co-discovered the centrally important Higgs particle.