Nuclear Fission and Fusion

Nuclear Fission

The process of splitting of a heavy nucleus into two nuclei of nearly comparable masses with liberation of energy is called nuclear fission.

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Neutron reproduction factor is defined as the ratio of the rate of production of neutrons to the rate of loss of neutrons. Thus,

A fission reaction will be steady, in case k = 1. In case k > 1, the fission reaction will accelerate and it will retard, in case k < 1.

Nuclear Reactor

Main parts and their functions:

Fuel:

It is a fissionable material mostly U-235.

Moderator:

It is used to slow down the neutrons released during the fission. The most common moderators are water, heavy water and graphite.

Control Rods:

These rods are cadmium or boron, which control the chain reaction by absorbing neutrons.

Coolant and Heat Exchange:

The coolant takes away heat from the reactor core and in turn heats the water in the heat exchanger to produce steam. The commonly used coolants are liquid sodium and heavy water.

Radiation Shielding:

These are thick concrete walls, which stop the radiations from going out.

Nuclear Fusion

It is the process in which two or more small nuclei fuse together to form a single heavy nucleus.

The mass of the single heavy nucleus formed is less than the total initial mass of the mass of the parent nuclei.

This difference in mass appears in the form of energy (as per, E = mc²).

Example: ₁H² + ₁H² → ₂He⁴ + Enormous amount of energy

Enormous amount of energy produced by the sun is due to the phenomenon of nuclear fusion.

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