Essay: Nuclear Power Plants – advantages, disadvantages & environmental Impact

a) Description

Nuclear energy is the usable energy extracted from atomic nuclei using a controlled nuclear reactions, and nuclear power plants have been used for several years. Uranium was first discovered in 1789 by Martin Klaproth who was a German chemistry. Nuclear energy was discovered as the one of the most energy source that produce electrical energy at a large quantity. In this type of station heavy elements such as uranium and thorium are exposed to nuclear fission in the equipment called reactor. The heat energy released is then utilised in a raising steam at a high temperature and pressure. The steam is then runs the steam turbine which converts steam energy to mechanical energy.

The most important thing about the nuclear power station is that it produced large amount of electrical energy at a small scale of a nuclear fuel, yet it is most expensive but it is preferable to be used due to production scale compared to other power stations.

Figure 1: Nuclear Power Station [4]

Technologies and type of nuclear power station

• Small modular reactor technologies
• Light Water Reactor Technologies
• Advanced Reactor Technologies

Work principle of nuclear power station

All convenient nuclear power plant simply used the reactor as a nuclear boiler to increase the steam which is then used to drive the conventional steam turbine driven by generators. The basic operation of the nuclear power station is based on a Ranking Steam Cycle, it operate in the same way as the steam power plant by using the same equipment. Instead of burning of fossil fuels to provide the heat in the boiler, heat is generated in the nuclear reactor by the process of nuclear fission of an unstable isotopes of uranium. The ranking cycle explains how the heat exchanger used to turn on the turbine and as the turbine turns it is connected to a generator that will convert the mechanical energy to electrical energy. And then water has to be condensed for the purpose of reused but this can’t be done without the help of external source in a form of pump to help the condensed water to reach the steam generator. [3]

Most of the modern engines and generators are steam based because steam is more efficient than water. [3]

b) Schematic Layout of a Nuclear Power Station

Figure 2: Nuclear Power Station Schematic Layout [4]

• Fission fuels (uranium) – usually bits of uranium oxide (UO2) are arranges in tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core. [3]
• Moderator – material in the core which slows down the neutrons released from fission so that they cause more fission. [3]
• Control rods – that is the major safety system in the nuclear reactors provided by control rods of Boron, Cadmium or Graphite which absorbs neutrons created by the process of fission by removing them from active mass to prevent further fission from taking place. [3]
• Containment building – reactors are contained inside a huge reinforced concrete casing with a steel inner structure which acts as a radiation shield and is designed to prevent the release of radioactivity into the surroundings. In the case of an accident in the reactor it protect the reactor from external events which may be earthquakes, aircraft impacts and deliberate acts of sabotage. [3]
• Pressure vessel or pressure tubes – it is robust steel containing the reactor core and moderator or coolant, it may be series of tubes holding the fuel and the conveying the coolant through the surrounding moderator. [3]
• Coolants – the reactor core acts as a heat exchanger in which the coolant which may be either liquid or a gas, surrounding the fuel rods and capture the heat generated by the nuclear reaction. Coolant also acts as a thermal working fluid which is used either directly or indirectly to raise steam to drive a turbine generator. [3]
• Nuclear reactor – is a device in which nuclear fuel (uranium) is subjected to a nuclear fission by controlling the chain reaction that starts once the fission is done. [3]
• Heat exchanger – the coolant gives up heat to the heat exchanger which is utilised in the rising steam, after giving up heat the coolant is then fed to a reactor. [2]
• Steam turbine – the steam produced in the heat exchanger is then fed to a steam turbine through valve, the steam is then exhausted to a condenser. The condenser condenses the steam which is fed to a heat exchanger through feed water pump. [2]
• Alternators – the steam turbine drives the alternator which converts mechanical energy to electrical energy. [2]

c) Criteria for Selection of Site

• Availability of water – sufficient water is required for cooling purpose, hence the plant should be located near the source of water. For instant, across the river or by side-sea. [2]
• Disposal of waste – the waste that is produced by fission in the power station is basically radioactive and it is hazardous towards the human health. Waste should be either buried in the deep trench or disposed in the sea but deeply in the sea shore. Therefore site selection should favours the disposal of radioactive waste.[2]
• Distance from polluted areas – site selection for nuclear power plant should be far away from the polluted areas as there’s a large possibility of radioactivity in the atmosphere. For safety precautions, dome is used in the plant which stops radioactivity to spread by the wind or by underground waterways. [2]
• Transportation facilities – site should have sufficient facilities for transportation of heavy equipment during erection, and also to facilitate the movement of employees to the plant. [2]

d) Advantages and Disadvantages of a Nuclear Power Station

Advantages

• Less amount of uranium needed to produce the same amount as coil or oil can produce, that lowers the production cost of energy. It is considered as a saving in the of fuel transportation. [1]
• It requires a less space compared to other type of power stations. [2]
• It is reliable as it can operate up to 540days without any interruptions. [1]
• It does not associate with any greenhouse gases.[1]
• It can be located near the load centre because it does not require any large quantity of water. [1]

Disadvantages

• Raw material (uranium) used in the process of fission it’s naturally unstable element, meaning that safety precautions should be taken during the mining, transportation and storage of uranium as well as other waste product to prevent  hazardous level of radiation. [1]
• The capital cost of nuclear power station is quite high compares to other type of station.
• The overall efficiency is quite too low (about 20%) because of the gases from the turbine which contains sufficient heat. [2]

Nuclear fission chambers is cooled by water then thus water is turned to a steam which is used by power turbines, this water is no longer used again due radiation but before pumped outside to the wetland it ensures that there is no radiation on it. [1]

e) Efficiency and Environmental Impact

Efficiency of the Nuclear Power Station

Nuclear power station have more efficiently compared to the burning of fossil fuels. However, this station is the one that produce electricity of a large quantity with a small scale of uranium used. There is far less uranium reserves in the world compared to the fossil fuel reserves, energy generated still the greatest energy produced. Even though nuclear power is not renewable, but it still the one that produce a lot of energy. [2]

Environmental Impact of a Nuclear Power Station

Nuclear power plant starts disturbing the environment during the plant construction. Thermal discharges of the unused heat from the fossil fuels or from the fission in the nuclear fuel also has the impact on the environment. Water that is released during heat discharges from the power plants prevent catastrophic kills that may be occurs, and this also have the effect on the marine species. Nuclear power plant has the highly visible transmission lines in linked with the generation and distribution of electricity. Disposal of radioactive waste is hazardous towards the environment and it may also cause natural disaster. [5]

References

1. Advantages and Disadvantages of Nuclear Energy. 2016. Advantages and Disadvantages of Nuclear Energy. [ONLINE] Available at:http://greenliving.lovetoknow.com/Advantages_and_Disadvantages_of_Nuclear_Energy. [Accessed 24 March 2016].
2. MEHTA, V.K. ‘Principles of Power System’, 3rd Edition, S. Chand & Company PVT. LTD, New Delhi, 2005.
3. Electrical Energy Supplies – Conventional and Sustainable Energy Comparisons. 2016. Electrical Energy Supplies – Conventional and Sustainable Energy Comparisons. [ONLINE] Available at:http://www.mpoweruk.com/electrical_energy.htm. [Accessed 24 March 2016].
4. nuclear power stations – Google Search. 2016. nuclear power stations – Google Search. [ONLINE] Available at: https://www.google.co.za/search?q=nuclear+power+stations&espv=2&biw=1366&bih=659&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiL8_SujtnLAhUIlxoKHZ4XDisQ_AUIBigB#imgrc=HL3srApq658Q5M%3A. [Accessed 24 March 2016].
5. Ibrahim Dincer, ‘EXERGY: Energy, Environment and Sustainable Development’, 2 Edition. Elsevier Science,2012.