Sunday, November 28, 2010

Nuclear Technology Basics: Introduction (Fun With Fission)

Well, I have just returned from Thanksgiving break. As promised, I will begin a series of posts concerning nuclear reactor technology and how different types of nuclear reactors differ from one another. In the near future, I will also include a glossary entry on my blog that people can reference at a later date in case they come across terminology that is not clear to them.

At the most basic level, all thermally-based power plants share the same mechanics of how they generate electrical energy. A heat source is used to generate steam, which causes a turbine to spin from the pressure provided by the steam which is being used as a working fluid. The action of the spinning turbine is connected to a generator which converts mechanical energy into electrical energy by the rotation of the turbine. Coal, oil, biomass and natural gas facilities use the combustion of these fuels to provide heat to create steam while solar thermal power stations use light from the sun and convert it into a source of heat. Geothermal energy is also thermally-based because it relies on heat from under the ground in geologically active regions in order to operate. Non-thermally based methods of electricity generation such as wind, hydroelectric, and wave energy turbines are directly spun by the movement of wind or water. Photoelectric solar stations generate electricity from solar cells using the photoelectric effect.

In the case of nuclear energy, heat is harnessed from a sustained nuclear chain reaction to drive a steam turbine. Nuclear reactions concern the interaction of an atom's nucleus with the nuclei of other atoms. Heat and subatomic particles are often produced as a result of a nuclear reaction, depending on what type of nuclear reaction it is and what elements are involved. A nuclear chain reaction is when the products of one nuclear reaction trigger additional nuclear reactions within a whole group of nearby atoms in a positive feedback loop. There are two main types of nuclear chain reactions, nuclear fission and nuclear fusion.

Nuclear fusion is when the nuclei of a pair or more of atoms become fused together. The fusion of the atoms releases large amounts of energy. Nuclear fusion is what powers stars in space and has also been achieved within a human laboratory. While nuclear fusion could hypothetically be used as a source of terrestrial power, this has proven to be quite difficult. Surrounding each atom is a positively charged field known as the electrostatic force that tends to repel other atoms away before a pair of atoms can become close enough for their nuclei to fuse. It requires massive amounts of energy to overcome the repulsion of the electrostatic forces between neighboring atoms. Although the development of a nuclear fusion reactor has been a high priority for many governments around the world for many decades, nuclear fusion reactions being carried out in a laboratory have yet to result in a sustainable fusion chain reaction as it seems to require more energy to cause atoms to fuse than what is actually released during the fusion process when attempted on Earth. Because of this, it is likely that a working fusion reactor is still many years away from being a reality.

Nuclear fission is the second type of nuclear chain reaction. It is basically the process of causing atomic nuclei to fragment by ramming them with subatomic particles, which in turn causes the subatomic particles that result from the fragmented nuclei to crash into the nuclei of other atoms and repeat the process. Fission reactions produce heat and other forms of radiation depending on what the products of the fission reaction are. Since the successful operation of the first fission reactor in 1942 at the University of Chicago, all reactors that have been built by humans have been fission-based. Interestingly enough, the existence of naturally occurring fission reactors has also been observed in nature such as the Oklo fossil reactors in Gabon, Africa where the isotopic ratio of uranium deposits within the area allowed nuclear fission to sustain itself. In addition, the georeactor theory in the geological field postulates that the Earth's magnetic field and the heat that is produced from its core might arise from the activities of a naturally occurring reactor in its interior similar to what has been seen at Oklo. However, the georeactor theory has little in the way of evidence that supports it at this time although this may change in the future.

That is enough for now, as I do not want to get too long-winded with each post. The next part of this series will be a look at the basics of nuclear fuel, reactor design, and the fuel cycle itself. Feel free to ask any questions that you might have.


Joffan said...

Good idea, and a great start.

I'd say that all thermal generating plants share the same mechanics you describe - including solar thermal and geothermal. Then you can mention wind and water turbines (including, importantly, hydro) and solar PV after that.

The georeactor hypothesis is poorly supported. Radioactive decay produces enough heat for the observed effects as I understand it.

Neurovore said...

I fixed a few of the things that might not have been clear based on your suggestions. On a different note, I do not know much about the history of non-power generating (research) reactors. Do you know of a book or website that you would be able to recommend of that nature?