![]() ![]() ![]() Nuclear Fusion is the process by which two elements collide to form a new element, releasing a tremendous amount of energy much greater than that of a fission reaction. If the coolant pumps do not work, emergency cooling methods must be used to remove decay heat to prevent damage to the core, possible meltdown or release of highly radioactive fission products to where they should not be. Therefore, coolant pumps must continue to be run for many hours after the reactor is shutdown to remove the decay heat, which over the course of hours eventually decreases. However, about 7% comes from heat of decay of highly radioactive fission products, which cannot be stopped by shutting down the reactor, and must continue to be removed from the reactor to prevent overheating and damage to the reactor core. Most of the power from nuclear fission reactors comes directly from the fission, which can be rapidly stopped by a shutdown of the reactor. Another type of reactor used in civilian power plants in the former Soviet Union called an RBMK reactor used graphite (carbon) as a moderator, but is considered insufficiently safe. In a BWR, water also functions as both a coolant and moderator. A boiling water reactor (BWR) is another common design of current nuclear reactor plants in commercial use. A moderator is usually water however, graphite and heavy water can also be used. A moderator slows down the neutrons, because slower moving neutrons are better at causing fission to occur. In a PWR, water functions as a coolant and as a moderator. A pressurized water reactor (PWR) is a common design of a nuclear reactor. Generally speaking, water is used, however helium gas and liquid sodium can be used as substitutes. This steam spins a turbine, which then powers an electric generator. The heat carried away causes incoming cooler water to turn into steam. Since the process of fission produces large amounts of heat, the coolant is used to carry away the heat. By raising or lowering the control rods in the reactor, the concentration of neutrons, called the neutron flux, in the core increases or decreases respectively. The control rods, usually made of cadmium metal, absorb neutrons in order to control the rate of fission. The region inside the nuclear reactor where the fuel elements undergo fission to generate heat is called the nuclear reactor core. The moderator and coolant flows between the fuel elements (or rods) moderating the neutrons and carrying away the heat. The fissile material is encased in a solid cladding, made of Zircalloy (alloy of zirconium, having low capacity to absorb neutrons), to contain both the fuel and the resulting fission products and keep then from escaping into the moderator, coolant, or anywhere outside the cladding. The fuel elements contains the fissile material, typically uranium or plutonium, which is used as the fuel to undergo fission and provide the nuclear energy. To produce energy, a nuclear reactor contains several major components: fuel elements (or rods), control rods, and coolant/moderator, besides the vessel itself containing everything. They serve the purpose of converting “nuclear energy” to heat. The opposite of a nuclear explosion, nuclear reactors are the controlled release of fission energy. However, in a nuclear reactor, energy is being produced at a controlled, constant rate a nuclear explosion is unlikely to occur. This rapid release of nuclear energy causes an explosion. In uncontrolled reactions, neutrons escape too quickly to maintain a chain reaction. A great example of this phenomenon would be a nuclear bomb. When one mass of U-235 exceeds the mass of U-235 that is large enough to hold down a chain reaction, also known as critical mass, an explosion occurs. An explosion could only occur if the reaction becomes uncontrolled. Note here Uranium 235 is used because it has a fairly large nucleus which facilitates the process of fission. During each U235/92 fission, 2.5 neutrons are released on average. In today's nuclear reactors, Uranium-235 is commonly used. According to Einstein's equation \(E=mc^2\), the small amount of missing mass is converted into a large amount of energy.Ī chain reaction occurs when the neutrons released in fission collide with at least one other nuclei, causing the fission of another nuclei. The mass of these products is less than the original mass. Nuclear fission is the process in which the nucleus of an atom is split, forming nuclei of lighter atoms and neutrons. ![]()
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