A nuclear reactor is a device that is mainly used in nuclear power plants to control the nuclear chain reaction of radioactive elements. The prime application of nuclear reactors lies in the production of electricity. In the current scenario, approximately 10% of the world’s electricity is obtained from nuclear power plants. In simple words, a nuclear reactor is one of the prime components of a nuclear power plant, which is used as an input source to produce a sufficient amount of energy that is required to drive the mechanism of the plant. It also helps control the electrical energy generated at the output end of the plant. Nuclear reactors are advantageous as they do not contribute to global warming. The fuel cost of nuclear reactors is quite low because a small amount of nuclear fuel is capable of generating a large amount of electrical energy. Also, the low quantity fuel requirement of the nuclear reactors reduces the mining and transportation charges. The long lifespan of a nuclear reactor serves to be yet another advantage of nuclear reactors. The energy generation process used by nuclear reactors does not lead to the emission of toxic gases or contaminants in the environment, hence there exist zero greenhouse emissions. The limitations of using nuclear reactors or nuclear power plants for the production of energy include a high risk of radioactive explosions. The waste produced by nuclear reactors is difficult to destroy and remains radioactive for a relatively long time. It is generally discharged into water bodies, which further affects marine life. The radioactive nature of the waste produced by the nuclear reactors implies that the waste has the tendency to remain radioactive for a long duration of time, which is harmful to the health of living beings and the environment. The set-up or installation cost of nuclear reactors is significantly high. A nuclear reactor does not support quick production of energy, hence cannot be used in applications that require an instant generation of energy.
Working Principle of a Nuclear Reactor
A nuclear reactor typically works on the principle of nuclear fission. Nuclear fission is the process that causes the nucleus of the atom of a radioactive element to split into two or more smaller nuclei. This reaction or splitting of the nucleus of an element leads to the production of a huge amount of energy along with the release of gamma photons in the surroundings. A nuclear reactor generally makes use of isotopes of certain radioactive elements such as uranium 238 and uranium 235. The controlled chain reaction of such elements helps produce a huge amount of energy that can be used for various purposes such as power generation etc. The controlled chain reaction is performed by slowing down the fission neutrons to thermal neutrons with the help of a moderator. The heat energy produced by the nuclear reactors is generally employed to heat a gas or a liquid that helps in the production of steam. The steam formed as a result can be used further to drive turbines or motors to produce electricity.
Parts of a Nuclear Reactor
A nuclear reactor typically consists of the following parts:
Containment is the structure that surrounds the nuclear reactor. The prime function of the containment is to protect the device from external contaminant particles or radiations. The containment of a nuclear reactor is built with the help of concrete and steel. The containment walls are about one metre thick.
2. Nuclear Fuel
Nuclear fuel is the material used in nuclear reactors that tend to undergo fission and generate energy. The radioactive elements generally used as nuclear fuel by nuclear reactors include uranium 238 and uranium 235. Isotopes of various other radioactive elements such as plutonium 239 can also be used. These radioactive elements are typically arranged in the form of cylindrical rods or tubes and are placed in the core of the active reactor.
3. Core Catchers
The core catchers installed in certain nuclear reactors are used to ensure security and safety. The core catchers are also known as core melt localisation devices that are helpful to catch the melted core material in case of a mishap or accident.
Moderator is the material that is present in the core of the active reactor. The prime function of the moderator is to slow down the neutrons that are released due to fission. For this purpose, water or elements with light nuclei can be used.
5. Control Rods or Blades
The control rods or the blades of a nuclear reactor are typically made up of materials such as cadmium, hafnium, boron, silver, indium, etc. The property of such elements is that they are capable of absorbing neutrons. The main function of control rods or blades of a nuclear reactor is to control the rate of the reaction or to completely terminate the chain reaction. This can be done by inserting or withdrawing the rods into or from the core. This helps the user attain an adaptable level of power with minimum inconvenience. The insertion or removal of the rods is done from the top, while the blade is attached to the device from the bottom. The structure of the blade resembles the shape of a cross or English alphabet ‘X’. These materials have the ability to absorb the neutrons without undergoing the fission process.
The nuclear fission process used by the nuclear reactors is a highly exothermic process that leads to the production of a huge amount of heat energy as a by-product. To avoid the excessive release of heat during the process, a fluid is circulated through the core. The main purpose of this fluid is to absorb a considerable amount of heat produced by the system to safeguard the device and the environment from high temperatures. In some of the nuclear reactors, the moderator works as the primary coolant. In nuclear reactors such as boiling water reactors or BWR, a coolant element other than the moderator known as the secondary coolant is required. The number of coolant systems tends to increase with an increase in the complexity or capacity of the nuclear reactors. For instance, a pressurized water reactor makes use of two to four steam or electricity-powered coolant systems that are attached to individual pumping mechanisms.
7. Pressure Vessel
Pressure vessels are used by the nuclear reactors to hold the fuel and to provide a passage to the coolant that enables it to travel freely through the moderator assembly. In place of pressure vessels, a network of interconnected tubes can also be used that are also simply known as pressure tubes. The material that is typically preferred to manufacture pressure vessels is robust steel.
8. Steam Generator
The steam generators are an essential part of the cooling mechanism of various nuclear reactors such as pressurized water reactors or pressurized heavy water reactors.