A nuclear power plant (nuclear power station) looks like a standard thermal power station with one exception. The heat source in the nuclear power plant is a nuclear reactor. As is typical in all conventional thermal power stations the heat is used to generate steam which drives a steam turbine connected to a generator which produces electricity.
A steam turbine is a common feature of all thermal power plants. Steam Turbine was invented in 1884 by Sir Charles Parsons, whose first model was connected to a dynamo that generated 7.5 kW (10 hp) of electricity. An exceptional feature of the nuclear power plant is the nuclear reactor and its safety and auxiliary systems.
How is Heat Generated In Nuclear Power Plants?
In a nuclear power plant, heat energy is generated by a nuclear reaction called nuclear fission. Nuclear fission of heavy elements such as Uranium or Thorium is carried out in a special apparatus called a nuclear reactor. A large amount of heat energy is generated due to nuclear fission. The rest parts of a nuclear power plant are very similar to conventional thermal power plants. It is found that the fission of only 1 Kg of Uranium produces as much heat energy as that can be produced by 4,500 tons of high-grade coal. This considerably reduces the transportation cost of fuel, which is a major advantage of nuclear power plants. Also, there are large deposits of nuclear fuels available all over the world and, hence, nuclear power plants can ensure a continued supply of electrical energy for thousands of years. About 10% of the total electricity of the world is generated in nuclear power plants.
How Does A Nuclear Power Plant Work?
Heavy elements such as Uranium (U235) or Thorium (Th232) are subjected to nuclear fission reactions in a nuclear reactor. Due to fission, a large amount of heat energy is produced which is transferred to the reactor coolant. The coolant may be water, gas or a liquid metal. The heated coolant is made to flow through a heat exchanger where water is converted into high-temperature steam. The generated steam is then allowed to drive a steam turbine. The steam, after doing its work, is converted back into the water and recycled to the heat exchanger. The steam turbine is coupled to an alternator which generates electricity. The generated electrical voltage is then stepped up using a transformer for the purpose of long-distance transmission.
Basic Components And Layout Of Nuclear Power Station
Components Of Nuclear Power Plant
Nuclear Reactor
A nuclear reactor is a special apparatus used to perform nuclear fission. Since nuclear fission is radioactive, the reactor is covered by a protective shield. The splitting up of nuclei of heavy atoms is called nuclear fission, during which a huge amount of energy is released. Nuclear fission is done by bombarding slow-moving neutrons on the nuclei of a heavy element. As the nuclei break up, it releases energy as well as more neutrons which further cause the fission of neighbouring atoms. Hence, it is a chain reaction and it must be controlled, otherwise, it may result in an explosion. A nuclear reactor consists of fuel rods, control rods, and a moderator. A fuel rod contains small round fuel pallets (uranium pallets). Control rods are of cadmium which absorbs neutrons. They are inserted into a reactor and can be moved in or out to control the reaction. The moderator can be graphite rods or the coolant itself. The moderator slows down the neutrons before they bombard the fuel rods.
Heat Exchanger
In the heat exchanger, the primary coolant transfers heat to the secondary coolant (water). Thus water from the secondary loop is converted into steam. The primary system and secondary system are a closed-loop, and they are never allowed to mix up with each other. Thus, a heat exchanger helps in keeping the secondary system free from radioactive stuff. A heat exchanger is absent in boiling water reactors.
Steam Turbine
Generated steam is passed through a steam turbine, which runs due to the pressure of the steam. As the steam is passed through the turbine blades, the pressure of steam gradually decreases and it expands in volume. The steam turbine is coupled to an alternator through a rotating shaft.
Steam Generator Or alternator
The steam turbine rotates the shaft of an alternator thus generating electrical energy. The electrical output of the alternator is delivered to a step-up transformer to transfer it over distances.
Pressurizer
Pressure in the primary circuit is maintained by a pressurizer, a separate vessel that is connected to the primary circuit (hot leg) and partially filled with water which is heated to the saturation temperature (boiling point) for the desired pressure by submerged electrical heaters. The temperature in the pressurizer can be maintained at 345 °C (653 °F), which gives a subcooling margin (the difference between the pressurizer temperature and the highest temperature in the reactor core) of 30 °C.
Reactor Coolant Pumps
Reactor coolant pumps are used to pump primary coolant around the primary circuit. These pumps are powerful, they can consume up to 6 MW each and they can be used for heating the primary coolant before a reactor start-up.
Condenser
The steam coming out of the turbine, after it has done its work, is then converted back into water in a condenser. The steam is cooled by passing it through a third cold water loop.
Condensate Feed Water System
Condensate-Feedwater Systems have two major functions. To supply adequate high-quality water (condensate) to the steam generator and to heat the water (condensate) to a temperature close to saturation.
