In nuclear power station the nuclear energy is converted into electrical energy by the reaction of nuclear fission. In nuclear power plants heavy elements such as uranium [U-235] or thorium is subjected to nuclear fission in a special apparatus known as Reactor. The advantage of a nuclear power station is that huge amount of electrical energy can be produced from a very little amount of nuclear fuel as compared to other conventional power generating station. It has been is found that 1 kg of uranium [U-235] can produce as much energy as can produced by the burning of 4,500,000 kg of high grade coal in thermal power generating stations.
In the nuclear power stations the main principle involved is the nuclear fission. Nuclear fission is the process in which the heavy nucleus is split into small particles and releases some energy when it is bombard by certain particles. Such a reaction is possible only with heavy nuclei such as U-233,U-235 and Pu-239.
The fission of a heavy atom can be caused by bombarding with a thermal neutron. When the atom is bombarded by a neutron the nucleus splits to give nuclei of other elements.
Uranium-235 + Neutron = Barium-144 + krypton-90 + 2 free Neutrons + energy
Main Parts of a Nuclear Power Station
The main parts of the nuclear power station are as follows:
2. Heat exchanger
3. Steam turbine
Nuclear Reactor – main parts and their functions :
Reactor is the main part of the nuclear reactor where the nuclear fuel is subjected to nuclear fission and the energy released in the process is utilized to heat the coolant which may turn into generator steam. A nuclear Reactor consists of following basic components:
1. Reactor core
3. Control Rods
6. Thermal Shielding
7. Biological Shield
Reactor core :
It contains a number fuel rods diluted with non-fissionable material for better control of the reaction or to reduce the damage from fission poisoning. The size of the core just sufficient to maintain a chain reaction is the critical size. It can be brought down by using enriched uranium as fuel.
Neutrons Produced by the fission process are ejected from the nucleus at a very high velocity and therefore, have a very large kinetic energy and termed as fast neutron. Moderator is used to slow down the fast moving neutrons to for effective chain reaction in the reactor.
Boron and lithium are used as moderator in the nuclear power plants.
Control rods :
Control rods are meant for the controlling rate of fission of U-235.These are made of boron-10, cadmium and hafnium that absorbs some of the slowed neutrons. By the help of the control rods the chain reaction can be control by adjusting the control rods.
It is a medium through which the heat generated in the reactor is transferred to the heat exchanger for further utilization in the power generation. When water is used as coolant, it takes up the heat and gets converted into steam in the reactor which is directly used for the driving the turbines. A good coolant should not absorb neutrons, should be non-oxidizing, non-toxic and high chemical and stability and good heat transfer capability. The materials are used as coolants are air, helium, hydrogen, heavy water and molten sodium.
This completely surrounds the reactor core within the thermal shielding arrangement and bounds back most of the neutrons that escape from the fuel core. It is often a moderating material and some time the same material is used both for moderator and reflector.
Thermal Shielding :
The shielding is usually constructed from iron and help in giving protection from deadly alfa, beta and gamma rays and escaping neutrons by the process of fission. Coolant flows through the shielding to take away the heat.
The whole of the reactor is enclosed in a biological shield to prevent the escape or leak away of the fast neutrons, beta particles and gamma rays and these radiations are very harmful and hazardous to living beings. Lead iron or dense concrete shield are used for this purpose.
Heat Exchanger :
Heat exchanger it exchanges the heat produced in the fission reaction to the supplied water and boils the water and produces steam which is sent to the steam turbine for the production of electrical energy.
Steam Turbine :
The produced steam in the heat exchanger is sent to the steam turbine and the turbine blades are expands to the coming high pressure steam and rotates and hence produces mechanical energy.
Generator shaft is coupled to the turbine shaft, when the turbines produces mechanical energy from the steam that mechanical energy is used by the generator and produces electricity which is supplied to a step up transformer.
The exhaust steam from the turbine is sent to a condenser and the condenser converts the hot steam into hot water and the hot water is sent to the supply feed which increases the efficiency of the power plant.
Advantages and Disadvantages of Nuclear Power Station:
1.The amount of fuel required is quite small. Hence, there is a considerable saving in the cost of fuel transportation, storage etc.
2.A nuclear power station requires less space as compared to any other conventional type of power station of the same rating.
3.This type of power station is economical of producing bulk power.
4.Nuclear power station can be located near the load centers, because it does not require large quantities of water and need not be near coal mines. There , the cost of primary distribution is reduced.
5.Greater nuclear power generation leads to conservation of coal, oil etc. Which can be used for other chemical processes.
1.The capital cost of a nuclear power station is very high as compared to other types of power stations.
2.The erection and commissioning of the nuclear power station requires more technical know-how.
3.The fuel used in the nuclear power station is expensive and is difficult to recover.
4.Nuclear power stations are not well suited for varying loads, as the reactor does not respond to the load fluctuations efficiently.
5.The fission byproducts are generally radio-active and may cause a dangerous amount to radio-active pollution.
6.The disposal of the products, which are radio-active, is big problem. They have either be disposed off in a deep trench or in a sea away from sea-shore.
Installation of Nuclear Power Stations is indispensable considering the acute shortage of power in Indian- scenario and any step to step up the same should prove to be highly advantageous in the coming scenario in strengthening our electrical output. However, the main impediment behind it is the prohibitive cost of Uranium essential for the fission reaction to take place to generate power.
However, we need to evaluate some of the demerits associated with this fuel. Lat us examine a few points-
1) We need to be dependant upon other countries such as America, Russia, Germany etc for the extraction of the fuel.
2) If proper mechanism is not adhered to, the nuclear - waste would pose severe health problem because of this being a radioactive element.
3) Any lacuna in compliance of the safety rule such as explosion or escape of Neutrons, Beta - particles and Gamma rays mingling with the atmosphere may cause radio - active related diseases such as Cancer, Degeneration of body - cells, Stillbirth of the babies etc.
4) We have to train our personnel to be vigilant to avoid any mishap causing devastating results.
5) Periodical maintenance of the equipments such as turbine, compressors, condensers, generators etc are to be taken up as per scheduled.
6) The installation requires specialists to evaluate several parameters such as inspection of the each and every components of the installation, life of the generators, condensers, heat exchangers etc and at the same time the effluents ejected from the plant are being taken care of effectively so that no radio - active reaction takes place.
The author has highlighted all the salient features in an effective manner but we need to be cautious on the points listed above.