Difference between Nuclear fission and Nuclear fusion

Let’s start with a detailed explanation of the Difference between Nuclear fission and Nuclear fusion.

Nuclear Fission

Nuclear Energy is produced by the conversion of a small amount of the mass of the nucleus of an atom into energy. The amount of energy released in nuclear fission is equivalent to the energy content of over three million metric tons of coal. Heavy atoms such as uranium or plutonium can be split by bombarding them with the neutron.

Nuclear Fission


Fission Reaction of U235

 92U235 + 0n192U23656Ba141 + 36Kr92 + 30n1 + Q

Some other 92U235 fission reactions are:

 92U235 + 0n1 → 54Xe140 + 38Sr94 + 20n1


                        →  57La148 + 35Br85 + 30n1

Neutrons produced here are called fast neutrons and their energy is about 2 MeV. These fast neutrons can escape from the reaction so as to proceed the reaction they are requirement to slow down.

The aspect of energy and mass in nuclear fission

The energy and mass aspects of the fission reaction:

  • Let the total energy of the heavy nucleus and the two fission products be Bh, Bf1, and Bf2
  • Amount of energy released per emission,

Er = (Bf1+Bf2) – Bh

  • Amount of mass converted to energy

Er/c2 = {(Bf1+Bf2) – Bh}/c2

  • The kinetic energy of the neutrons, the vibration energy of the fission fragments, and gamma radiation. All of these forms of energy are converted to heat by absorption with the surrounding media in the reactor, mainly the coolant and the moderator.


Nuclear Reactor

It is a device in which nuclear fission can be carried out through a sustained and controlled chain reaction.

The nuclear reactor involves the splitting of the nucleus of uranium-235 when it is struck by a neutron. The uranium-235 first absorbs the neutron to yield uranium-236, and most of these U-236 nuclei split into two fission fragments. Fission reaction releases two to four neutrons. One of these neutrons triggers another fission for a sustained chain reaction.

Uranium-236 nucleus does not split evenly into equal fission fragments. Rather, the tendency, especially with fission induced by thermal neutrons, is for one fragment to be considerably lighter than the other.


Parts of Nuclear Reactor

  1. Fissionable material: It is the fuel of the reactor. Uranium isotope (U235), Thorium isotope (Th232), and Plutonium isotopes (Pu239, Pu240, and Pu241).


  1. Protective shield: Shield is in the form of a concrete thick wall that surrounds the core of the reactor to save the persons working around the reactor from hazardous radiations.



  1. Control Material: It controls the chain reaction. This material controls the number of neutrons available for fission. Cadmium rods can absorb neutrons.


  1. Coolant: It is a cooling material that removes the heat generated due to fission in the reactor. Commonly used coolants are water, CO2nitrogen, etc.


Neutron Reproduction Factor

The chain reaction once started will remain regular, accelerate, or retard depending upon, a factor called neutron reproduction factor (k).

K = rate of production of neutrons/rate of loss of neutrons

  • when k = 1, the chain reaction will be regular.
  • If k > 1, the chain reaction accelerates, resulting in an explosion.
  • If k < 1, the chain reaction gradually comes to a halt.


Reactions for plutonium-239 

      92U238 + 0n1 → 92U239

        92U239 → 93Np239 + 0e-1

    93Np239 → 94Pu239 + 0e-1


Reactions for uranium-233

   90Th232 + 0n1 → 90Th233

    90Th233 → 91Pa233 + 0e-1

    91Pa233 → 92U233 + 0e-1


Nuclear Fusion

In nuclear fusion, two or more than 2 lighter nuclei combine to form a single heavy nucleus. The mass of the single nucleus so formed is less than the sum of the masses of parent nuclei.

nuclear fussion

Now,  1H2 + 1H2 → 1H3 + 1H1 + 4.0 MeV

1H3 + 1H2 → 2He4 + 0n1 + 17.60 MeV

1H2 + 1H2 → 2He4 + 24 MeV

The difference in mass results in the release of a tremendous amount of energy.

Fission bombs was known as the primary produces a flood of radiation including a large number of neutrons. This radiation impinges on the thermonuclear portion of the bomb, called the secondary. The secondary consists largely of lithium deuteride. The neutrons react with the lithium in this chemical compound, producing helium & tritium.

3Li6 + 0n1 à 2He4 + 1H3


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