Class 12 > Unit # 27: Nuclear Physics > Nuclear Reactor

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Nuclear Reactor & Its Main Components

Nuclear Reactor

A nuclear reactor is a device in which a controlled fission chain reaction takes place. A nuclear reactor is also known as a nuclear pile or atomic pile.

Such a system was first achieved with uranium as the fuel in 1942 by Enrico Fermi. He used the uranium-235 isotope that releases energy through nuclear fission.

Figure 27.10: Schematic diagram of a nuclear reactor showing the reactor core, heat exchanger, turbine, and cooling tower.

The following are the main components of a nuclear reactor:

1. Fissionable Substance:

Nuclear reactors use fuel, typically enriched uranium or plutonium, to sustain the fission chain reaction. The $\text{U-235}$ is fissionable, but uranium from ore typically contains only about $0.7\%$ of $\text{U-235}$, with the remaining $99.3\%$ being the $\text{U-238}$ isotope. Because uranium-238 tends to absorb neutrons, reactor fuels must be processed to increase the proportion of $\text{U-235}$ so that the reaction can sustain itself. This process is called enrichment.

2. Moderator:

The function of the moderator is to slow down the highly energetic neutrons produced in the process of fission of $\text{U-235}$ to thermal energies. Heavy water ($\text{D}_2\text{O}$), graphite, beryllium, etc., are used as moderators. Ideally, moderators have low atomic weight and low absorption cross-section for neutrons.

3. Control Rods:

Control rods are made of materials like boron or cadmium that absorb neutrons, regulating the rate of the fission chain reaction. By adjusting the position of control rods within the reactor core, operators can control the power output and maintain stability.

4. Coolant:

Coolant circulates through the reactor core to transfer heat away from the fuel and other reactor components. Common coolants include water, heavy water, or gases like helium or carbon dioxide. The heated coolant then transfers its thermal energy to a secondary loop containing water, which turns into steam. This steam drives turbines connected to generators, producing electricity.

5. Protective Shield:

In a nuclear reactor, there are many types of harmful radiations emitted which are dangerous for all living things. In order to protect from these radiations, the reactor is surrounded by a massive biological shield.

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