Atoms and Nuclear Energy: The Underlying Science
Atoms to Energy: Producing Electricity with Nuclear Energy
Electricity is produced in power-generating plants and transmitted through high-voltage power lines.
             
All About Nuclear
Some large plants use dams, rivers, or other water (hydro) sources to generate electricity; however, the majority of non-hydro power plants use coal, fuel oil, or natural gas to boil water to produce steam. The steam pressure turns large turbine blades, which then turn a generator. A generator is a rotating machine that converts mechanical energy into electrical energy by creating relative motion between a magnetic field and a conductor. After the steam passes through the turbines and begins to cool, it changes back to water. The water is cooled further in a separate structure, called a "cooling tower," at the power plant. The water can be used again and again. Nuclear power plants do not use coal, fuel oil, or natural gas to boil water, but instead, they capture the heat released during fission in the nuclear reactor to heat water to make steam. Capturing Heat during FissionNuclear energy is energy in the nucleus of an atom. Before nuclear energy can be used to make electricity, it must first be released from the atoms. This can happen in two ways: nuclear fusion and nuclear fission. In nuclear fusion, energy is released when atoms are combined together to form a larger atom. This is how the sun produces energy. In nuclear fission, atoms are split apart to form smaller atoms, a process that releases the energy that binds the atoms together. Nuclear power plants use nuclear fission. The intense heat released during fission is captured and used to make steam. Most nuclear power plants use uranium for nuclear fission. Uranium is a common metal found in rocks all over the world. The best type of uranium for nuclear chain reactions is U-235 because its atoms are easily split during fission. Although uranium is a common metal-about 100 times more common than silver-U-235 is relatively rare. Most uranium in the United States is mined in the western states. A nuclear reactor uses pellets of uranium that are approximately the size of a dime and an inch in length, or about the size of your fingertip. These energy-rich pellets are stacked end-to-end in 12-foot metal fuel rods. The rods are collected into bundles called the “fuel assembly.” Each uranium pellet produces the same amount of energy as 150 gallons of oil. A pound of uranium is smaller than a baseball, and it is roughly equivalent to a million gallons of gasoline. Typically the fuel assembly is submerged in water, which acts as a coolant, inside a pressure vessel. Left uncontrolled, the uranium would overheat and melt. To prevent the bundles from overheating, operators insert control rods into them. The control rods, which are made of a material that absorbs neutrons, are raised and lowered to control the rate of the nuclear reaction. When the rods are raised out of the uranium bundle, the uranium core produces more heat. When the rods are lowered into the bundles, the rods produce less heat. The rods can also be lowered completely into the uranium bundles to shut the reactor down for repairs or to change the fuel. A nuclear reactor's pressure vessel typically is surrounded in a concrete liner that acts as a radiation shield. That concrete liner is housed in a much larger steel containment vessel that holds the reactor core and the cranes and hardware needed to refuel and maintain the reactor. The steel containment vessel prevents radioactive gases or fluids from leaking from the plant. The steel containment vessel is protected by an outer concrete building that is strong enough to survive a crashing jet airliner or an earthquake. These secondary containment structures prevent the escape of radiation and radioactive steam. Like all industrial processes, nuclear power generation has by-product wastes-used fuels, other radioactive waste, and heat. Most nuclear waste is low-level radioactive waste that consists of ordinary tools, protective clothing, wiping cloths, and disposable items that have been contaminated with small amounts of radioactive dust or particles. These materials are subject to special regulations that govern their disposal so they will not come in contact with the outside environment. Compared with electricity generated by burning fossil fuels, nuclear energy is extremely clean. Nuclear power plants produce no air pollution or carbon dioxide. Only a small amount of emissions results from processing the uranium that is used in nuclear reactors. Nuclear Power Plants Information
Source: International Atomic Energy Association. Links for more information.. |
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