Different Types Of Nuclear Reactors & Working Principles

In this article, I will share different types of nuclear reactors and how they work. The reactor is the essential part of the nuclear power plant that results in the production of the heat needed.


It’s in the reactor core where the fission happens and the heat needed is produced.


Different nuclear power plants use different reactors due to their specific needs.


Some reactors seem to be more efficient than others.


Types of reactors used in nuclear power plants.

These are some of the nuclear power plants reactors that I will discuss in this article;

  1. Boiling water reactor (B.W.R).
  2. Pressure water reactor (P.W.R).
  3. Sodium graphite reactor (S.G.R).
  4. Fast Breeder Reactor (F.B.R).
  5. Aqueous Homogeneous Reactor (A.H.R).
  6. CANDU-reactor (Canadian Deuterium Uranium)


1. Boiling water reactor (B.W.R).

This reactor uses water as a coolant and it uses enriched uranium as a fuel.


Water is used as a moderator in this reactor.


The main components of this reactor are;

  1. Reactor core.
  2. Feed pump.
  3. Turbine.
  4. Condenser.
  5. Generator.
  6. Coolant.


If you want to know the function of these parts of the reactions, kindly check the article below.


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Working principle of boiling water reactor.

The feed pump pumps the coolant to the reactor core via the bottom pipe.


The nuclear fission that takes place in the reactor core produces heat that is needed for the energy to be produced.


The coolant enters the reactor core via the pipe and it absorbs all heat from the reactor core and gets converted into steam.


The steam leaves the reactor via the top pipe and flows to the turbine where it is used to generate electricity via the generator.


2. Pressure water reactor (P.W.R).

This reactor uses enriched uranium as fuel and water as a coolant and moderator.


The main components of a pressure water reactor are;

  1. Reactor core.
  2. Pressurizer.
  3. Turbine.
  4. Steam generator.
  5. Coolant.
  6. Condenser.
  7. Feed pump.
  8. Coolant pump.


Due to the presence of pressurizer hence the name.


Working principle of pressure water reactor.

Nuclear fission takes place within the reactor core and heat is energy is produced.


The coolant pump pumps the water into the reactor core via the bottom pipe.


Since the water has a low boiling point it is put under pressure of about 1200 p.s.i.g by the pressurizer.


The main aim of pressurizing the water is to prevent it from boiling so that it allows maximum absorption of heat within the reactor core.


After the water leaves the pressurizer it flows to the steam generator where it’s converted into steam after passing out the heat to the feed water.


The steam that loses its content energy will be pumped by the coolant pump and reused again for another cycle of heat absorption and transfer.


The steam is then taken to the turbine where it runs and produces electricity.


If you are wondering what the use of a condenser is, its main function is to condense the steam so that it allows another steam with maximum energy also to occupy the space, thus increasing the efficiency of the turbine.


3. Sodium graphite reactor.

This reactor uses two liquid metal coolants which are sodium (primary coolant) and an alloy of sodium and potassium (secondary coolant).


It uses graphite as a moderator.


It also has a heat exchanger since it uses two liquid metal coolants.


The main components of the sodium graphite reactor are;

  1. Reactor core.
  2. 2 Coolant pumps.
  3. heat exchanger.
  4. Steam generator.
  5. Feed pump.
  6. Condenser.
  7. Turbine.
  8. Generator.


Working principle of sodium graphite reactor.

Nuclear fission produces the heat needed, the coolant pump pumps the sodium coolant via the bottom pipe to the reactor core where it absorbs the heat.


After the sodium coolant has absorbed the heat it goes out of the reactor core via the top pipe.


Since the liquid metal coolant (sodium) can’t be used to transfer the heat to the steam generator, it passes through the heat exchanger where it passes its heat to the secondary coolant (sodium-potassium).


The sodium-potassium takes the heat to the steam generator via the pipes or tubes and it passes its heat to the feed water where the water is converted into steam.


The steam flows to the turbine where it is converted into kinetic energy and the electricity is produced via the generator.


These are the advantages of using a sodium graphite reactor;

  • It obtains high steam energy content since liquid metals are involved in heat transfer (they have a higher thermal conductivity).
  • There is a low pressure in the primary circuits of the coolant since the sodium coolant doesn’t need to be put under high pressure hence saving up the cost of purchasing expensive pressure vessels and pipes.


The disadvantage of using a sodium reactor is this;

  • The sodium used to transfer heat in this system becomes radioactive thus handling it becomes difficult.


4. Fast Breeder Reactor (F.B.R).

This reactor is called a fast breeder reactor simply because its fission is brought about by fast-moving neutrons, due to this fact, there is no moderator used in this reactor.



It uses two liquid coolant circuits which are sodium and an alloy of potassium and sodium.


In this reactor, the core containing U235 is surrounded by a blanket layer of fissionable material U238.


The main function of the blanket layer of U238 is to absorb the neutrons and form more fissionable material that will keep the chain reaction going to produce the required heat energy.


The fissionable material formed in this reactor is Pu239.


Fast breeder reactors are better when it comes to the point of safety and thermal efficiency.


Working principle of the fast breeder reactor.

The fast-moving neutrons produce heat due to fission with other nuclei of U235 which causes some other neutrons to be absorbed by U238 hence resulting in more fissionable material formed thus sustaining the chain reaction.


The coolant is pumped to the reactor core by the coolant pump, it absorbs the heat in the reactor core and it goes out of the reactor core via the top pipe.


Since the primary coolant can’t be used to transfer heat to the steam generator, it passes its heat to the secondary coolant (sodium-potassium) via the heat exchanger.


The secondary coolant flows through the tube of the steam generator and passes heat to the feed water.


The water in the feed water gets converted into steam which flows to the turbine via the tubes, it will then drive the turbine and result in electricity production via the generator.


5. Aqueous Homogeneous reactor (A.H.R).

This reactor uses heavy water as a coolant and a moderator.


It also makes use of the fertile material which circulates with the coolant.


The soluble nuclear salts are dissolved in heavy water.


They are the type of reactors that handle very large increases in reactivity thus making them very sufficient and safest.


Fissionable material (U238) is contained in one point and a slurry of Thorium oxide and deuterium oxide is contained in another zone of the pressure vessel.


The main component of a homogeneous reactor are;

  1. Pressurizer.
  2. Heat exchanger.
  3. Steam turbine.
  4. Pressure vessel.
  5. Condenser.
  6. Canned rotor pumps.
  7. Blanket heat exchanger.
  8. Gas separator.


Working principle of the homogeneous reactor.

Since the fuel is mixed with the coolant, the water seems to be boiling as it moves along the tubes and this is due to the production of hydrogen and oxygen as the radiation and fission particles dissociate in water in the process known as radiolysis.


The gas separator is used to separate the gasses from the coolant which are hydrogen and oxygen.


The pressurizer keeps the coolant under pressure to prevent it from boiling to facilitate maximum heat transfer.


From the gas separator, the coolant flows to the heat exchanger when the coolant passes its heat to the heavy water that will be converted into steam and sent to the steam turbine.


The heavy water that will be in the secondary circuit does not contain dissolved uranium components, and thus is used to generate the steam needed since there is no steam generator in this reactor.


So, it uses a direct circuit system in the secondary circuit of the coolant.


The blanket heat exchanger takes heat from the pressure vessel and transfers it to the tube that takes its steam into the steam turbine, which is also used to increase the energy content of the steam.


You might like this: Types Of Nuclear Reactor Coolants, Cycles And Their Properties


Advantages of using an aqueous homogeneous reactor;

  • It’s economical since it uses heavy water.
  • There are no problems associated with solid wastes since the fuel is dissolved in the coolant.


The disadvantage of using an aqueous homogeneous reactor;

  • There is a very large usage of fuel.
  • The circulation of the coolant within the system makes the external components of the reactor radioactive thus making it hard to handle it.
  • There is high vapour pressure of water since there is an increase of air dissolving within the water i.e hydrogen and oxygen.


6. CANDU-reactor (Canadian Deuterium Uranium).

The reactor uses heavy water (99.8%) and deuterium oxide as a moderator and coolants.


The reactor vessel is a steel cylinder that contains several tubes running within it and is subjected to high pressure.


The tubes are subjected to high pressure to prevent water from boiling since it has low boiling, this is to improve the energy absorption process by water.


Natural uranium-235 is used as a fuel in this reactor.


Working principle of CANDU-reactor.

The tubes contain fuel elements and the pressurized coolant flows along and around the fuel tubes to absorb the heat liberated by fission.


The coolant flows in opposite direction to increase the energy transfer rate.


Since the fuel in this reactor is fed while the reactor is still operating control rods are provided to provide control and protection during operation.


The coolant then flows to the steam generator via the tubes where the heat is transferred to the feed water.


The water gets converted into steam and then sent to a steam turbine to lead to the production of electricity via the generator.


The cool coolant returns to the reactor to absorb heat again and the process repeats itself.


This is the working principle of the above reactors.


Thanks for reading, if you have any questions leave your comment. See you in my next article.


Related articles to check.

  1. Advantages & Disadvantages of Nuclear Power Plant
  2. Different Types Of Nuclear Reactors & Working Principles
  3. Boilers: Components, Types & Working Principle
  4. Steam Condensers: Components, Types & Working Principle
  5. Design Of Water Distribution Systems

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