Wednesday, June 29, 2011
7:45 AM | Posted by
Anonymous |
In nuclear power plants such as the one shown in above figure, a controlled nuclear reaction is used to make heat to produce steam needed to drive a steam turbine generator.
the Question now is What is Nuclear Energy?
Atoms are the building blocks from which all matter is formed. Everything is made up of atoms. Atoms are made up of a nucleus(with protons and neutrons) and orbiting electrons. The number of atomic particles (sum of neutrons, protons, and electrons) determines the atomic weight of the atom and type of element in the periodic table. Nuclear energy is contained within the center of atoms (nucleus) where the atom’s protons and neutrons exist. Nature holds the particles within the atom’s nucleus together by a very strong force. If a nucleus of a large element (such as uranium 235) is split apart into multiple nuclei of different element compositions, generous amounts of energy are released in the process.
The heat emitted during this process (nuclear reaction) is used to produce steam energy to drive a turbine generator. This is the foundation of a nuclear power plant.
There are basically two methods used to produce nuclear energy in order to produce heat to make steam.
The first process is called fission. Fission is the splitting of large nuclei atoms such as uranium inside a nuclear reactor to release energy in the form of heat to be used to produce steam to drive steam turbine electrical power generators.
The second process is called Fusion.
Fusion is the combining of small nuclei atoms into larger ones, resulting in an accompanying release of energy. However, fusion reactors are not yet used to produce electrical power because it is difficult to overcome the natural mutual repulsion force of the positively charged protons in the nuclei of the atoms being combined.
In the fission process, certain heavy elements, such as uranium, are split when a neutron strikes them. When they split, they release energy in the form of kinetic energy (heat) and radiation. Radiation is subatomic particles or high-energy light waves emitted by unstable nuclei.
The process not only produces energy and radiation, it also provides additional neutrons that can be used to fission other uranium nuclei and, in essence, start a chain reaction.
The controlled release of this nuclear energy using commercial grade fuels is the basis of electric power generation. The uncontrolled release of this nuclear energy using more highly enriched fuels is the basis for atomic bombs.
The reactor is contained inside an obvious containment shell. It is made up of extremely heavy concrete and dense steel in order to minimize the possibility of a reactor breach due to an accidental.
Nuclear power plants also have an emergency backup scheme of injecting boron into the reactor coolant. Boron is an element that absorbs neutrons very readily. By absorbing neutrons, the neutrons are not available to continue the nuclear reaction, and the reactor shuts down.
The most widely used design for nuclear reactors consists of a heavy
steel pressure vessel surrounding the reactor core. The reactor core contains the uranium fuel. The fuel is formed into cylindrical ceramic pellets about one-half inch in diameter, which are sealed in long metal tubes called fuel tubes.
The tubes are arranged in groups to make a fuel assembly. A group of fuel assemblies forms the reactor core.
Controlling the heat production in nuclear reactors is accomplished by using materials that absorb neutrons. These control materials or elements are placed among the fuel assemblies. When the control elements, or control rods as they are often called, are pulled out of the core, more neutrons are available and the chain reaction increases, producing more heat.
When the control rods are inserted into the core, more neutrons are absorbed, and the chain reaction slows down or stops, producing no heat. The control rod drive system controls the actual output power of the electric power plant.
Most commercial nuclear reactors use ordinary water to remove the heat created by the fission process. These are called light water reactors. The water also serves to slow down or moderate the neutrons in the fission process. In this type of reactor, control mechanisms are used such that the chain reaction will not occur without the water to serve as a moderator.
In the United States, there are two different types of light-water reactor designs used, the pressurized water reactor (PWR) and the boiling water reactor (BWR).
we will discuss two types in details in next lessons.
Do you feel confused confused about this lesson? Leave your question now in a comment.
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