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Overview
In general, a power plant uses the chemical energy released when expending some fuel to produce mechanical energy, movement, which in turn is used to produce electrical energy. Our first example is the most common energy source: the coal power plant. The coal plant burns coal to boil water. The steam, in turn, has a great amount of energy, is at a high pressure and is at a high velocity. The steam’s energy is converted to electrical energy by traveling through turbines which produce electricity by a moving magnetic field around conducting wire. Coal plants have been around for a long time and have worked out well; however, have several drawbacks. Burning coal greatly increases the greenhouse gases; which leads to global warming, and coal is not a renewable energy source; once we burn a ton of coal, there is a ton of coal that ton of coal is gone for another several million years until fossilized plants form into it again. Nuclear power from fission, by its nature, works around both of these.
Where does the energy come from?
An atom consists of three main components: electrons, neutrons and protons. The neutrons and protons are contained in the nucleus in the center and the electrons encircle the nucleus at some distance, depending on the nature of the atom. The neutrons and protons are held together in the nucleus by the so called strong force. The strong force acts only up to a distance, unlike the electromagnetic force which has an unlimited range. In a large nucleus, the protons are held together by the strong force attractions of the neighboring nucleons, but are repelled by the electromagnetic force of the protons further from them. Most nuclear reactors use Uranium-235, which is an extremely large atom, one of the most massive found naturally on Earth. This leads our conversation to binding energy per nucleon.
Binding Energy per Nucleon vs. Mass Number (BE/A)
The BE/A curve reaches a maximum value of 8.79 MeV at A = 56 and decreases to about 7.6 MeV for A = 238. The binding energy is the amount of energy required to add or break off a single nucleon from any particular element. For any element which is fissionable and has more protons than lead would be a good fuel for a fission reactor. U-235 is chosen because it readily decays, after capturing a neutron, by fission and it is relatively abundant on earth. When a nucleus of Uranium 235 is hit by a neutron, it forms U-236 for about 10-14 seconds, and decays by fission (it breaks up into two smaller atoms). These two atoms have a smaller mass combined than the original U-236 atom did, so this extra mass is converted directly to energy by Einstein’s famous equation:
ΔE = Δm * c2
The constant c is the speed of light, ΔE is the change in energy, and Δm is the change in mass. The difference in mass between the original U-236 atom and the two fission fragments the energy released by the U-236 fission reaction. On average, this reaction releases 215 MeV of energy and 2.4 neutrons to continue the chain reaction. If a nuclear reactor is said to be critical, then the number of neutrons from this reaction causing another fission reaction must be one, on average. If it is less than one, there are not enough neutrons around to keep break apart more uranium, and is considered subcritical. If there are more than 1 neutron causing fissions, then the reactor can quickly get out of control, and is considered supercritical. Most reactors are “slow neutron” reactors so that the number of reactions may best be controlled. These less energetic neutrons are just common enough in the core to sustain the reaction. Without this control, the reaction would get out of hand and the amount of energy produced would be more than could be removed by the coolant, causing the reactor pressure to increase up until the reactor core ruptures.
The reaction is regulated by control rods. In most cases, the control rods are made of either boron or cadmium. These are both good neutron absorbers and therefore can easily regulate a nuclear reactor. When withdrawn, less neutrons are absorbed by the control rods, therefore more are available to produce fission in the fuel. Eventually, for each fission there is another fission caused by one of the neutrons released, the reactor is then said to be critical.
Public stigma
The public believes that nuclear power is a bad form of power production. This has spurred the Department of Energy to not issue any permits to build new nuclear power plants since the late 1970s. We have determined the public to be incorrect in this assumption. When the fission reaction occurs, high energy photons are released as well. These high energy photons are ionizing; they can cause atoms in one’s body to lose electrons which causes biological damage beyond the scope of this paper. Also, there is potentially dangerous waste produced by the reactor which must be disposed of. For the former problem, the reactor is shielded by enough lead and steel to stop most of the radiation released. The coolant water is generally not released for public consumption or for wildlife because it retains quite a bit of radioactivity. The radioactive waste is another problem; it has been proposed that the waste from reactors may be buried in the Yucca mountain range in Nevada, where it can be stored until the waste has depleted to safe levels. This project of the Department of Energy has been halted several times by those in Nevada worried that it may harm them.
What does this all mean?
For an equivalent amount of uranium and coal, much more energy is released in the nuclear fission reaction of uranium (about 2 x 109 kWh/ton), than of coal (about 6150 kWh/ton). Therefore, less uranium is needed for he same amount of energy production. In addition nuclear power plants do not add to the greenhouse gases in the atmosphere. Despite the public’s dislike for nuclear power, it is the best option available until alternative solutions, such as wind or solar power, become viable.