Current Research in Nuclear Fusion Power and Its Place in Future Electricity Production.

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Current Research in Nuclear Fusion Power and Its Place in Future Electricity Production

Introduction

Nuclear fusion is a process where two lighter atomic nuclei fuse, forming a heavier nucleus and releasing energy.

The type of nuclear fusion currently being researched most vigorously in the context of forming a future source of power is the fusion of two isotopes of hydrogen - deuterium and tritium, forming helium and a neutron and releasing large amounts of energy.

= Neutron = Proton

Deuterium Nucleus Neutron (+14.1 MeV)

Tritium Nucleus Helium Nucleus (+3.5 MeV)

Figure 1

This can be described by the equation H + H ==> He + n, yielding 17.6 MeV per fusion. Another fusion reaction which is possible is the fusion of two deuterium nuclei, though this yields less energy and is not generally being pursued as a source of power in future reactors. It is described by the equation H + H ==> He + n, yielding 3.3 MeV per fusion.

A central concept in understanding the origin of this extra energy is the equivalence of mass and energy.

The strong nuclear force binds together protons and neutrons in the nucleus, it is very strong over short distances hence it overcomes the electromagnetic repulsion of protons in the nucleus. The energy that is required to hold to hold the nucleus together can be thought of as adding to its mass. Hence the mass of a deuterium nucleus is higher than the mass of its individual components when isolated - one proton and one neutron, and hence energy must be put in for them to bind together by the strong nuclear force. Hence also energy is released when they are taken apart. When considering the fusion reaction, the total mass of the deuterium and the tritium nuclei before the reaction is more than that of the helium nucleus and neutron formed. This is because the neutron that is emitted is no longer held by the strong nuclear force, the forces have been rearranged at the end of the reaction ending up with a lower potential energy. This energy that once held the neutron is carried away as translational kinetic energy, which does not affect the particles' mass, largely by the neutron. The typical values of this extra kinetic energy are shown on the diagram above, 14.1 MeV on the neutron, 3.5 MeV on the helium.

However the energy required for this to occur is staggeringly high, and the deuterium and tritium gas must be heated to such high temperatures that they forms a plasma - the fourth state of matter. It is only at such high energy states that the deuterium and tritium will collide with enough energy to overcome the strong force binding the protons and neutrons together in the nucleus. A plasma state occurs when atoms become so energetic that the nucleus and the electrons overcome the electromagnetic forces holding them together and separate and a 'sea' of charged particles, the negative electrons and the positive nuclei, is formed. Temperatures around and above 100 million degrees Celsius are required for fusion to occur.

Fusion and Current World Energy Production

This is the reaction which powers stars, and international research has been progressing for around fifty years to try to make it possible to perform this reaction in a controlled and sustainable manner to provide electricity in a clean and practically limitless way.

Fossil fuels, by far the main source of electricity globally, cause incredible damage to the environment and could lead to extreme climate change unless action is taken in the immediate future. More alarming for governments worldwide, fossil fuels are running out.

At current consumption levels reserves of oil are likely to be exhausted within 50 years, natural gas within 80 years and coal lasting around 250 years. Oil especially is used in the production of other industrial products such as plastics, and the exhaustion of its reserves is certainly an uncomfortable thought.

Nuclear fission, involving the splitting of uranium-235 into smaller elements and releasing large amounts of energy, has been used in power plants since 1954. However it suffers many drawbacks including the production of radioactive waste which must then be disposed of, the waste remains radioactive for thousands of years and exposure can cause damage to cells as radiation sickness, cancer, and eventually death. There is also the risk of meltdown should the reactor become unstable, this occurred in 1986 in Chernobyl in the Ukraine. Dozens of people died instantly or within days, countless others have been affected by the movement of radioactive particles in the wind causing increased cases of cancer in the region. The region is still irradiated and will be for thousands of years. These factors have led to poor public opinion of fission, and whilst many hundreds of reactors around the world remain functional, the construction of new reactors has slowed to a virtual standstill since Chernobyl.
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Power from renewable resources often requires large areas of land to be dedicated to it, solar and wind power for example need large areas to produce the same power as one fossil fuel power plant, and there are few areas suitable for large-scale geothermal power or hydroelectric dams.

Fusion power on the other hand, has only helium as a by-product and cannot suffer any kind of meltdown as if the plasma becomes unstable it will collapse and the nuclear reaction will cease. Any future fusion power plants would occupy roughly the same area as a fossil fuel ...

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