02 May, 2007

Nuclear Power Plant Operation

The below diagram shows the schematic of nuclear power plant.Nuclear power generation is much similar to that of conventional steam power generation.The difference lies only in the steam generation part i.e coal or oil boiling furnance and boiler are replaced by nuclear reactor.

Thus a nuclear power plant consists of a nuclear reactor,steam generator,turbine, generator, condenser etc. as shown in the above figure.As in a conventional steam plant, water for raising steam forms a closed feed system.However, the reactor and the cooling circuit have to be heavily shielded to eliminate radiation hazards.

A nuclear power plant uses the heat generated by a nuclear fission process to drive a steam turbine which generates usable electricity.Fission is the splitting of atoms into smaller parts. Some atoms, themselves tiny, split when they are struck by even smaller particles, called neutrons. Each time this happens more neutrons come out of the split atom and strike other atoms. This process of energy release is called a chain reaction. The plant controls the chain reaction to keep it from releasing too much energy too fast. In this way, the chain reaction can go on for a long time.

Few natural elements have atoms that will split in a chain reaction. Iron, copper, silver and many other common metals will not split, or fission. There are isotopes of iron, copper, etc. that are radioactive. This means that they have an unstable nucleus and they emit radioactivity. However, just being radioactive does not mean that they will fission, or split. But uranium will. So uranium is suitable to fuel a nuclear power plant.

As atoms split and collide, they heat up. The plant uses this heat to create steam.The heat is transfered to the water through heat exchanging tubes in steam generator in the primary loop.After extractig this heat, water is converted in to steam and collected at the top of steam generator.The pressure of the expanding steam turns a turbine which is connected to a generator in the secondary loop.After rotating turbine - generator set steam passes to the condenser.After that the function of condenser and coling towers is same as that of thermal plant.

After the steam is made, a nuclear plant operates much like a fossil fuel fired plant: the turbine spins a generator. The whirling magnetic field of the generator produces electricity. The electricity then goes through wires strung on tall towers you might see along a highway to an electrical substation in your neighborhood where the power is regulated to the proper strength. Then it goes to your home.

In the case of nuclear power plant operation the following factors must be considered

  • Control -- Keeping the nuclear reaction from dying out or exploding.
  • Safety -- If something goes wrong it can be contained.
  • Refueling -- Adding more nuclear fuel without stoping the reactor.
  • Waste production -- The byproducts of the reaction must be manageable.
  • Efficiency -- Capture as much of the heat as possible.
Control is the most important aspect to a design. When an atom of nuclear fuel (uranium) absorbs a neutron, the uranium will fission into two smaller atoms (waste) and release one to three neutrons. The kinetic energy of the waste is used to heat the water for the steam turbine. The neutrons are used to fission the next lot of uranium atoms and the process continues. If none of these neutrons are absorbed by another uranium atom then the reaction dies out. If too many neutrons are absorbed then the reaction grows extremely quickly and could explode. Current reactor designs are most usefully classified by how they ensure this nuclear reaction is kept at a level which produces power without getting out of hand.

The Nuclear Regulatory Commission (NRC), part of our government, makes sure nuclear power plants in the United States protect public health and safety and the environment. The NRC licenses the use of nuclear material and inspects users to make sure they follow the rules for safety.
Since radioactive materials are potentially harmful, nuclear power plants have many safety systems to protect workers, the public, and the environment. These safety systems include shutting the reactor down quickly and stopping the fission process, systems to cool the reactor down and carry heat away from it and barriers to contain any radioactivity and prevent it from escaping into the environment.
One of the greatest benefits of nuclear plants is that they have no smoke stacks! The big towers many people associate with nuclear plants are actually for cooling water used to make steam. (Some other kinds of plants have these towers, too.) The towers spread the water out so as much air as possible can reach it and cool it down. Most water is then recycled into the plant.
Nuclear power plants are very clean and efficient to operate. However, nuclear power plants have some major environmental risks. Nuclear power plants produce radioactive gases. These gases are to be contained in the operation of the plant. If these gases are released into the air, major health risks can occur. Nuclear plants use uranium as a fuel to produce power. The mining and handling of uranium is very risky and radiation leaks can occur. The third concern of nuclear power is the permanent storage of spent radioactive fuel. This fuel is toxic for centuries, handling and disposal is an ongoing environmental issue.

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