What is Nuclear Reactor : Working & Its Applications

The first nuclear reactor was designed to use in bombs to generate 239Pu. After that, these reactors are used for different purposes like electricity generation and also used in propelling ships for generating radioisotopes and supply heat. There are different types of nuclear reactors available in different designs where the power generation in these reactors mainly depends on the nuclear fission. The frequently used reactors are the PWR (Pressurized Water Reactor), BWR (Boiling Water Reactor) & PHWR (Pressurized Heavy Water Reactor). This article discusses an overview of a nuclear reactor, components, and types.

What is a Nuclear Reactor?

Definition: The nuclear reactor is an essential system in a nuclear power plant. They include nuclear drain reactions to generate heat using a method called fission. The heat which is generated can be used to make steam for spinning a turbine. So that electricity can be generated. In global, there are hundreds of commercial reactors are there, in that above 90 reactors are located in the USA. So nuclear power is one of the largest energy sources for reliable and carbon-free electricity.

How Does a Nuclear Reactor Work?

The main function of the nuclear reactor is to control nuclear fission. The nuclear reactor working principle is nuclear fission and it is one kind of method used for splitting the atoms to generate electricity. Nuclear reactors use uranium that will process into tiny ceramic pellets & stacked jointly into fuel rods. A fuel assembly can be formed by a bunch of above 200 fuel rods. Usually, a reactor core can be fabricated through these assemblies based on the level of power.

In the vessel of a nuclear reactor, the fuel rods are placed within the water. So that it can act like a coolant as well as mediator to assist while reducing the speed of the neutrons. These neutrons can be generated through fission to maintain the chain reaction.

After that, control rods can be placed into the reactor core for reducing the rate of reaction. The generated heat through the fission process can make the water into steam to rotate a turbine for generating carbon-free electricity.


The essential components of the nuclear reactor mainly include the following. The nuclear reactor diagram is shown below.

Nuclear Reactor Block Diagram
Nuclear Reactor Block Diagram
  • Core
  • Reflector
  • Control Rods
  • Moderator
  • Coolant
  • Turbine
  • Containment
  • Cooling Towers
  • Shielding


The core in the reactor includes nuclear fuel to generate the heat. It includes uranium with less enriched, control systems & structural materials. The shape of the core is a circular cylinder with a diameter of 5 to 15meters. The core includes a number of individual fuel pins.


The reflector is arranged around the core to replicate the back of the neutrons that overflow from the surface of the core.

Control Rods

Nuclear reactor control rods are designed with heavy mass elements. The main function of this is to soak up the neutrons. So that it can continue or stop a reaction. The main examples of these rods are lead, cadmium, etc.
These rods are mainly used for starting the reactor, maintain the reaction at a constant level, and shut down the reactor.


The main function of the moderator in a nuclear reactor is to slow down the neutrons from high energy levels as well as high velocities. So that there is a chance for the neutron to hit the fuel rods will e increased.

The modern moderators used at present mainly include water H2o, heavy water D2o, Beryllium, and Graphite. The properties of the moderator are the stability of thermal is high, radiation & chemical stability, non-corrosiveness, etc.


The material that is used to transfer the heat from fuel to a turbine through the core like water, liquid sodium, heavy-water, helium, or something else is known as coolant. The characteristic of coolant mainly include melting point is low, the boiling point is high, non-toxicity, less viscosity, the stability of radiation & chemical, etc. The commonly used coolants are Hg, He, Co2, H2o.


The main function of the turbine is to transfers the heat energy from the coolant device to electricity.


The containment separates the nuclear reactor from the surroundings. Generally, these are available in dome-shaped and designed with high-density and steel-reinforced concrete.

Cooling Tower

These are used by some types of power plants to put the surplus heat that cannot be changed to heat energy because of the thermodynamic laws. These towers are the hyperbolic symbols for nuclear energy. These towers can generate simply freshwater vapor.


It protects the working men from the radiation effect. In the fission process, particles like alpha, beta, gamma, fast & slow neutrons can be formed. So to give safety from them, concrete or lead thick layers are used around the reactor. The alpha & beta particles can be stopped by using thick layers of plastics or metals.

Types of Nuclear Reactors

Worldwide, there are different types of nuclear reactors available. Based on its design, it uses Uranium with different concentrations used for fuel, moderators to delay the process of fission and coolants to heat transfer. The PWR or pressurized water reactor is the most common type of reactor.

PWR/Pressurized Water Reactor

These types of reactors are most frequently used in worldwide. It uses normal water like both moderator as well as coolant. In this, the coolant can be rushed to discontinue it from flashing into vapor to maintain during the process. Powerful pumps move the water using pipes, transfers the heat from boil water in a secondary loop. The resultant vapor drives the turbine generator to generate electricity.

BWR/Boiling Water Reactors

In these reactors, light war performs like both coolant as well as moderator. The coolant is set aside at a low pressure to boil the water. The vapor can be supplied directly to the turbine generators to generate electricity.

Pressurized Heavy Water Reactors

These are also known as CANDU type reactors. These reactors signify about 12% of the nuclear reactors globally. These are mainly used at all Canadian nuclear stations. These reactors use heavy water like both coolant & moderator. As a fuel, it uses natural uranium because, in a pressurized water reactor, the coolant can be used for boiling normal water in a different loop.

Gas-cooled Reactors

These reactors are used only in the UK. These are available in two types namely the Magnox and the AGR (advanced gas-cooled reactor). These reactors use C02 like the coolant & graphite like the moderator. The fuel used in the Magnox is natural uranium whereas, in the AGR, it uses enhanced uranium.

Light Water Graphite Reactors

These reactors are used in the country Russia. So these reactors use ordinary water as the coolant & graphite like the moderator. In boiling water reactors, the coolant boils when it supplies throughout the reactor. The generated steam will be supplied directly toward turbine generators. Early LWG type reactors’ designs were frequently operated without security characteristics.

Fast Breeder Reactors

These reactors use quick neutrons to change the materials like U238 and Thorium232 into fissile materials to fuel the reactor. This process is united with recycling, which has the capacity to enhance accessible nuclear fuel resources. These reactors operate in Russia.

Small Modular Reactors

The modern SMR is mainly designed economically. These reactors are growing to supply electricity to small electricity grids & probably to supply heat for resource industries. These reactors can also be used in larger grids when demand grows.

Some SMR type reactors are in difficult stages of development like fully underground, reducing the usage of land, staffing & security requirements. Some of these reactors contain passive safety systems which work for up to 4 years without refilling

Some other types of reactors are CANDU, Fast breeder, Thorium, Boiling water, Pressurized water, Prismatic, Molten salt, Small modular, Radioisotope thermal generators, Fusion reactors, RBMKs, Magnox, Pebble bed, Supercritical water-cooled, AES-2006/VVER-1000, VHTR, HTGR, and Research type reactors.

Uses of Nuclear Reactor

The applications of nuclear reactor include the following

  • These are used at nuclear power plants to generate electricity & also used in nuclear marine propulsion.
  • Nuclear power plants supply the required energy to produce electrical energy.
  • These drive the propellers of ships otherwise to turn the shafts of electrical generators.

Thus, this is all about an overview of a nuclear reactor. Similarly, there are different types of commercial nuclear reactors available around the world like Gas-cooled, Fast Neutron & Light Water Graphite, Pressurized water, Boiling water, Pressurized heavy water, and Fast breeder reactor. Here is a question for you, what is the fuel used in PHWR?