In the world today, there are 441 nuclear power reactors producing approximately 10% of the global electricity. Nuclear power has constantly been an important topic of debate regarding its potential of becoming a future utopian source of energy. How exactly does this technology work?
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Nuclear Fission
An atom is made of a nucleus at the center, with electrons orbiting around the nucleus. The nucleus consists of protons and neutrons held together with a strong force. Certain atoms can undergo nuclear fission, which is the splitting of a nucleus when bombarded with neutrons. Fission releases nuclear energy and neutrons from the nucleus. These neutrons cause a chain reaction by striking other atoms’ nuclei.
Uranium-235 is one example of a fissionable isotope, and nuclear power plants mostly use U-235 as their fuel. However, natural uranium is composed mostly of U-238 (99.2%), with only a small amount of U-235 (0.7%). Therefore, in order to be used as fuel, mined uranium ores must be processed and enriched in levels of U-235. These uranium fuels are then shaped as small pellets, made into long rods (fuel rods), and bundled into assemblies.
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Nuclear Power
In nuclear power plants, the fission process of the uranium fuel assemblies takes place in the reactor core. Energy released from fission is captured as heat. For most reactors, a coolant fluid (usually water) is used to transfer heat from the reactor core. This heat is used to produce steam, which drives a turbine to generate electricity. The steam is then condensed and cooled by natural water sources or by water from cooling towers.
The fission chain reaction in the reactor core is controlled with moderators and control rods. Moderators, usually water, slow down the released neutrons so that the uranium fuel can capture the fast-moving neutrons. Without moderators, neutrons would be too fast for a nucleus to absorb, so the chain reaction may not continue. Control rods slow down the rate of fission by absorbing the released neutrons. Control rods can be inserted or withdrawn from the reactor core to control the chain reaction. These control rods are made with substances such as cadmium, hafnium, or boron, which are effective in absorbing neutrons.
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Nuclear Waste
Nuclear reactors produce radioactive wastes, such as spent fuel rods. Spent fuel is classified as high-level radioactive waste because it contains radioactive fission products (lighter isotopes formed by fission) and leftover fuel. Due to economic reasons and security risks, spent uranium fuels are mostly stored rather than being reprocessed into new fuel. Spent fuel rods are usually stored in cooling pools, where the water cools the fuel rods and shields radiation. These pools are often located at the nuclear plants where the fuel rods were used. Some old fuel rods later get transferred into dry casks.
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