To generate electric energy in power stations using nuclear energy, nuclear reactors are used. Nuclear power plants have nuclear reactors to generate electric energy. Some reactors are used to produce radio isotope for medical and industrial use, or for production of plutonium for weapons. Nuclear reactors converts the thermal energy released from nuclear fission.

Nuclear Fission

  • When a single atom is made to split into smaller atoms then, energy is released. This is called nuclear fission.

  • In nuclear power plant Uranium atom is spitted into smaller uranium atoms to produce electric energy.

  • Uranium is a mineral rock, a very dense metal that is found in the ground.

Chain Reaction

Series of nuclear fission, each initiated by the nuclei from the preceding nuclear fission is generally called as chain reaction.


What is nuclear reactor?

  • A device to initiate and control a sustained nuclear chain reaction is called as nuclear reactor.

  • A nuclear reactor is a system that contains and controls sustained nuclear chain reactions.

  • Nuclear fuel is placed into the reactor vessel along with a small neutron source. 

  • The neutrons start a chain reaction where each atom that splits releases more neutrons that cause other atoms to split.

  • Each time an atom splits, it releases large amounts of energy in the form of heat.

  • The heat is carried out of the reactor by coolant, which is most commonly just plain water.

  • The coolant heats up and goes off to a turbine to spin a generator or drive shaft. 


Components of nuclear reactor:

The main components of nuclear reactor are,

  • Core

  • Fuel

  • Moderator

  • Coolant

  • Control rods



  • The core of the nuclear  reactor contains all of the nuclear fuel and generates all of the heat.

  • It contains low-enriched uranium (<5% U-235), control systems, and structural materials.

  • The nuclear reactor  core can contain hundreds of thousands of individual fuel pins.

  • The smallest unit of the reactor is the fuel pin.

  • They are often surrounded by a metal tube (called the cladding) to keep fission products from escaping into the coolant.



  • Fuel is made of small enriched uranium oxide rods, stacked so as to form cylinders, approx. 4 metres long and with a diameter of about one centimetre.

  • These rods are wrapped in metal sheathes (steel or zirconium alloy), which allow heat to pass through while blocking the radioactive elements produced by nuclear fission.



  • It is placed in nuclear reactor to slow down the neutrons produced by nuclear  fission, in order to reach the most suitable speed allowing the chain reaction to continue.

  • Depending on the various nuclear reactor models, the moderator may consist of graphite, water or heavy water.



  • The coolant is the material that passes through the core, transferring the heat from the fuel to a turbine.

  • It could be water, heavy-water, liquid sodium, helium, or something else. In the US fleet of power reactors, water is the standard.


Control rods

  • These are rods used in specific materials (silver, indium, cadmium or boron carbide) to control fission inside the core.

  • They absorb neutrons, they are capable of controlling the chain reaction which - depending on how deep down the rods are inserted into the core - can be accelerated, slowed down or even stopped, thus changing the capacity of the reactor.

  • Indeed, if necessary, the reactor can be immediately stopped when they are fully inserted.


Types of nuclear reactors

Three types of nuclear reactors are there. They are,

  • Boiling water nuclear reactor

  • Pressurized nuclear reactor

  • Liquid metal fast breeder nuclear reactor


Boiling water nuclear reactor

  • Here the water which passes over the reactor core to act as moderator and coolant is also the steam source for the turbine.

  • A typical operating pressure for such reactors is about 70 atmospheres at which pressure the water boils at about 285 deg Celsius.


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Pressurized nuclear reactor

  • Here the water which passes over the reactor core to act as moderator and coolant does not flow to the turbine, but is contained in a pressurized primary loop.

  • The primary loop water produces steam in the secondary loop which drives the turbine.

  • It can operate at higher pressure and temperature, about 160 atmospheres and about 315 C.


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