26 April, 2007

Nuclear Power Plant,Types, Advantages and Disadvantages

Nuclear Power Plant
Nuclear power is generated using Uranium, which is a metal mined in various parts of the world.
The structure of a nuclear power plant in many aspects resembles to that of a conventional thermal power station, since in both cases the heat produced in the boiler (or reactor) is transported by some coolant and used to generate steam. The steam then goes to the blades of a turbine and by rotating it, the connected generator will produce electric energy. The steam goes to the condenser, where it condenses, i.e. becomes liquid again. The cooled down water afterwards gets back to the boiler or reactor, or in the case of PWRs to the steam generator.


The great difference between a conventional and a nuclear power plant is how heat is produced. In a fossile plant, oil, gas or coal is fired in the boiler, which means that the chemical energy of the fuel is converted into heat. In a nuclear power plant, however, energy that comes from fission reactions is utilized.
How it works


  • Nuclear power stations work in pretty much the same way as fossil fuel-burning stations, except that a "chain reaction" inside a nuclear reactor makes the heat instead.
  • The reactor uses Uranium rods as fuel, and the heat is generated by nuclear fission. Neutrons smash into the nucleus of the uranium atoms, which split roughly in half and release energy in the form of heat.
  • Carbon dioxide gas is pumped through the reactor to take the heat away, and the hot gas then heats water to make steam.
  • The steam drives turbines which drive generators. Modern nuclear power stations use the same type of turbines and generators as conventional power stations.
In Britain, nuclear power stations are built on the coast, and use sea water for cooling the steam ready to be pumped round again. This means that they don't have the huge "cooling towers" seen at other power stations.
The reactor is controlled with "control rods", made of boron, which absorb neutrons. When the rods are lowered into the reactor, they absorb more neutrons and the fission process slows down. To generate more power, the rods are raised and more neutrons can crash into uranium atoms.
Nuclear Power Plant TypesSeveral nuclear power plant (NPP) types are used for energy generation in the world. The different types are usually classified based on the main features of the reactor applied in them. The most widespread power plant reactor types are:
  • Light water reactors: both the moderator and coolant are light water (H2O). To this category belong the pressurized water reactors (PWR) and boiling water reactors (BWR).

  • Heavy water reactors (CANDU): both the coolant and moderator are heavy water (D2O).

  • Graphite moderated reactors: in this category there are gas cooled reactors (GCR) and light water cooled reactors (RBMK).

  • Exotic reactors (fast breeder reactors and other experimental installations).

  • New generation reactors: reactors of the future.
Advantages
  • Nuclear power costs about the same as coal, so it's not expensive to make.
  • The amount of fuel required is quite small ,therfore there is no problem of transportation, storage etc.
  • Does not produce smoke or carbon dioxide, so it does not contribute to the greenhouse effect.
  • Produces huge amounts of energy from small amounts of fuel.
  • Produces small amounts of waste.
  • The output control is most flexible.
  • Nuclear power is reliable.
Disadvantages

  • The fuel used is expensive and is difficult to recover.
  • The fission by-products are generally radio active and may cause a dangerous amount of radio active pollution.
  • Although not much waste is produced, it is very, very dangerous. It must be sealed up and buried for many years to allow the radioactivity to die away.
  • The initial capital cost is very high as compared to other power plants.
  • Nuclear power is reliable, but a lot of money has to be spent on safety - if it does go wrong, a nuclear accident can be a major disaster. People are increasingly concerned about this - in the 1990's nuclear power was the fastest-growing source of power in much of the world. In 2005 it was the second slowest-growing.
  • The cooling water requirements of a nuclear power plant are very heavy.

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