What is Nuclear Power Plant?
A nuclear power plant (sometimes abbreviated as NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces electricity.
Nuclear power plants are a type of power plant that uses the process of nuclear fission in order to generate electricity. They do this by using nuclear reactors in combination with the Rankine cycle, where the heat generated by the reactor converts water into steam, which spins a turbine and a generator.
Nuclear power provides the world with around 11% of its total electricity, with the largest producers being the United States and France. As of 2018, the International Atomic Energy Agency reported there were 450 nuclear power reactors in operation in 30 countries around the world.
Nuclear plants are usually considered to be baseload stations since fuel is a small part of the cost of production and because they cannot be easily or quickly dispatched. Their operations, maintenance, and fuel costs are at the low end of the spectrum, making them suitable as base-load power suppliers. However, the cost of proper long-term radioactive waste storage is uncertain.
How does Nuclear Power Plant work?
Nuclear power plants to heat water to produce steam. The steam is used to spin large turbines that generate electricity. Nuclear power plants use the heat produced during nuclear fission to heat water.
In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Fission takes place inside the reactor of a nuclear power plant. At the center of the reactor is the core, which contains uranium fuel.
The uranium fuel is formed into ceramic pellets. Each ceramic pellet produces about the same amount of energy as 150 gallons of oil. These energy-rich pellets are stacked end-to-end in 12-foot metal fuel rods. A bundle of fuel rods, some with hundreds of rods, is called a fuel assembly. A reactor core contains many fuel assemblies.
The heat produced during nuclear fission in the reactor core is used to boil water into steam, which turns the blades of a steam turbine. As the turbine blades turn, they drive generators that make electricity.
Nuclear plants cool the steam back into water in a separate structure at the power plant called a cooling tower, or they use water from ponds, rivers, or the ocean. The cooled water is then reused to produce steam.
Components of a Nuclear Power Plant
1. Nuclear Reactor
The reactor is a key component of a power plant, as it contains the fuel and its nuclear chain reaction, along with all of the nuclear waste products. The reactor is the heat source for the power plant, just like the boiler is for a coal plant.
Uranium is the dominant nuclear fuel used in nuclear reactors, and its fission reactions are what produce the heat within a reactor. This heat is then transferred to the reactor’s coolant, which provides heat to other parts of the nuclear power plant.
Besides their use in power generation, there are other types of nuclear reactors that are used for plutonium manufacturing, the propulsion of ships, aircraft, and satellites, along with research and medical purposes. The power plant encompasses not just the reactor, but also cooling towers, turbines, generators, and various safety systems. The reactor is what makes it different from other external heat engines.
2. Steam Generation
The production of steam is common among all nuclear power plants, but the way this is done varies immensely.
The most common power plants in the world use pressurized water reactors, which use two loops of circling water to produce steam. The first loop carries extremely hot liquid water to a heat exchanger, where water at a lower pressure is circulated. It then heats up and boils to steam, and can then be sent to the turbine section.
3. Turbine and Generator
Once the steam has been produced, it travels at high pressures and speeds through one or more turbines. These get up to extremely high speeds, causing the steam to lose energy, therefore, condensing back to cooler liquid water. The rotation of the turbines is used to spin an electric generator, which produces electricity that is sent out to the electrical grid.
4. Cooling Towers
They work to reject waste heat to the atmosphere by the transfer of heat from hot water (from the turbine section) to the cooler outside air. Hot water cools in contact with the air and a small portion, around 2%, evaporates and rises up through the top.
Moreover, these plants do not release any carbon dioxide the primary greenhouse gas that contributes to climate change. Click here to see how a cooling tower works.
Many nuclear power plants simply put the waste heat into a river, lake, or ocean instead of having cooling towers. Many other power plants like coal-fired power plants have cooling towers or these large bodies of water as well.
This similarity exists because the process of turning heat into electricity is almost identical between nuclear power plants and coal-fired power plants.
5. Pressurizer
A component of the primary cooling circuit where the liquid and vapor stages are balanced in conditions of saturation, so as to control the pressure.
6. Reactor Vessel
Steel vessel that houses the nuclear reactor, the main component of the nuclear power plant where the fission chain reactor is produced. Its nucleus is composed of fuel elements.
7. Fuel
The material where the fission reactions take place. The most common material used is enriched uranium oxide. It is used simultaneously as a source of energy and neutrons in order to maintain the chain reaction. It is presented in the solid state, in the form of cylindrical pellets encapsulated into metallic rods around 4 meters tall.
8. Control Rod
These are the reactor’s control elements, acting as neutron absorbents. They are made up of indium-cadmium or boron carbide, which makes it possible to control at all times the neutron population and the reactor reactivity, making it critical during its operation and subcritical during the stops.
9. Containment building
A building that houses the reactor’s cooling system as well as several auxiliary systems. It functions as shielding in normal operation and prevents the leakage of polluting products to the exterior. Along with other safeguarding systems, it has the functional responsibility to avoid the release of fission products into the atmosphere in case of an accident.
10. Alternator
A device that produces electricity by converting mechanical rotation energy from the turbine into medium-power and high-intensity energy.
11. Transformer
A device that raises the tension of the electricity produced in the alternator, in order to minimize losses during its transport to the consumption points.
12. Cooling Water
Water is taken from a river, reservoir, or sea and used to liquify the water vapor in the condensator. It can be directly returned to its origin (open cycle) or be reused via the cooling tower (closed cycle).
13. Condensator
Heat commuter composed of a set of tubes where cooling water circulates. The water vapor going inside the condensator from the turbine is liquified. This conversion produces a vacuum that improves the turbine’s performance
Efficiency
The efficiency of a nuclear power plant is determined similarly to other heat engines—since technically the plant is a large heat engine. The amount of electric power produced for each unit of thermal power gives the plant its thermal efficiency, and due to the second law of thermodynamics, there is an upper limit to how efficient these plants can be.
Typical nuclear power plants achieve efficiencies around 33-37%, comparable to fossil-fueled power plants. Higher temperature and more modern designs like the Generation IV nuclear reactors could potentially reach above 45% efficiency.
Advantages of Nuclear Power Plant
Following are the advantages of nuclear power plants:
- It requires less space compared to other plants.
- Well suited for large demands.
- It gives better performance at high load factors (80 to 90%).
- Less fuel consumption and no fuel handling.
- Transportation cost of the fuel is very less.
- Increased reliability of operation.
- These are not affected by adverse weather conditions.
- Less water is required.
- The higher capacity of the plant can be installed.
- Compact and simple in maintenance.
Disadvantages of Nuclear Power Plant
Following are the disadvantages of nuclear power plants:
- High initial cost.
- The danger of radioactivity hazards is always persisting.
- Not suitable for varying load conditions.
- The disposal of fission products is a big problem.
- The maintenance cost is always high.
- Skilled operators are required.
- Working condition is always detrimental to the health of the workers.
