Nuclear fission

Nuclear fission

Introduction

Nuclear fission is the process of bombarding a piece of radioactive material with neutrons in order to cause it to radioactively decompose, emitting smaller particles and energy. In a power plant this takes place with a tank of water, which is heated and is converted to steam, which turns turbines which are connected to a generator- which forms electricity, and recycles the water.

Nuclear fusion is the process of doing the opposite- combining small hydrogen particles into larger helium particles and tapping the energy formed in the process. Fusion reaction produces a much larger amount of energy than fission, however, it is much harder to produce and at the current time, it is purely experimental, as at this time it is not economically viable- more energy is put in to combine the atoms than is produced.

The fusion process

Nuclear fusion is the reaction process which occurs in stars and is therefore the basic energy of the universe, upon which all life relies. The fusion reaction in the sun occurs at

15 000 000° C, however the conditions at the core of the sun are impossible to mimic on earth, as they include pressures which no substance known to humanity could contain, so to compensate the cores of fusion reactors on earth must be heated to ten times that of the sun (150 000 000° C). Also, on earth Deuterium and Tritium (isotopes of hydrogen) are reacted instead of two hydrogen atoms as is done in the sun, because deuterium and tritium can produce the highest energy at the lowest temperatures.

According to theories of conservation, energy or mass cannot be made or destroyed. This is not entirely accurate- energy and mass are interchangeable, as shown in Einstein's equation ΔE=Δmc2. As such, and in the knowledge that combining two hydrogen atoms (or a deuterium and a tritium) does not have the same mass as a helium atom and a neutron then it is possible to see that energy will be produced in the reaction.

In 1968 the Soviet Union created a “doughnut-shaped magnetic confinement device” (ITER information leaflet for New Scientist) called a “Tokamak” which allowed the high temperature and plasma (electron gas cloud) to be confined within the core. The tokamak is the current design for all viable fusion generators. There are several fusion research projects currently underway, including the “Joint European Torus” (JET) which has been operational in Culham, UK, since 1983 and set the current world record in 1997 for the amount of power produced in a fusion generator- 16MW for a limited period of time, and 5MW for 5 seconds. At the moment a new international research project is being built- the “ITER”. It is a new tokamak fusion generator being built in the south of france and will utilise superconducting magnets to allow better confinement and higher energy levels to be achieved and will be able to produce 500MW of output power for 1000 seconds, for every 50MW input- meaning that ten times more power is output than is input. The ITER's constituent members represent more than half of the worlds population, and is therefore a project that could potentially be fuelling most of the world by 2040.

The fission process

Nuclear fission is the opposite of nuclear fusion and is a lot easier to achieve. In fission a radioactive element or radioactive isotope is irradiated with neutrons, one is absorbed by a nucleus within the substance and causes it to be further unstable, making it decompose into two products and three neutrons, which then also collide with nuclei, which also decompose creating further products and more neutrons, creating a chain reaction.

Fission is ethically questioned as the products from the reaction are radioactive and cannot be used in fission so they must be disposed of, however there is no safe way of disposing of radioactive waste. Because of this it can be irresponsibly dumped, which leads to leaks into the environment. Usually it is stored in sealed concrete bunkers with the idea being to wait for it to complete radioactive decomposition so that it can be disposed of safely. Furthermore fission has caused some of the greatest man-made atrocities of the modern era, including the atomic bombs which were dropped on the Japanese cities of Hiroshima and Nagasaki on the 6th and 9th of August 1945. Estimates of the number of people killed vary, however, at least 214,000 people were killed by the bombs- either instantly or they were killed by radiation poisoning within a year after the bombs were dropped. Also, the Chernobyl disaster, in which a fission power station exploded killed approximately 50 deaths among the workers and fire fighters, however it is impossible to calculate how many people died from cancer contracted by the explosion- but there was also enormous environmental impact.

Since the Chernobyl disaster, there have been safety procedures put in place to try to make fission power safer, including making the base of the power station out of a material with a lower melting point than the walls and base. This is so that if the station starts to meltdown and overheats then the radioactive material will sink into the ground instead of escaping into the atmosphere.

In fission reactors carbon control rods are lowered into the core. These absorb neutrons without radioactively decaying, which means that the rate of reaction can be slowed down. This is necessary, as an uncontrolled fission reaction in a power station would be comparable to a large nuclear bomb exploding, and is similar to what happened at Chernobyl.

Conclusion

I feel that as effective as fission power is, it is a force that is far too powerful to ever be safely tapped. Furthermore the radioactive waste will continue to pollute the earth for hundreds of years- meaning that by using fission power we are ruining the world for our grandchildren too.

I think fusion power is a viable energy source, as it is much cleaner- however at this time it is only science fiction so other energy sources are needed.

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