At a glance of Nuclear reactor

In our previous blog, we discussed the basics of nuclear power plants about fission processes, chain reaction, and nuclear fuels, so moving forward, we will discuss the Nuclear reactor their main parts and functions. Such as Reactor core and Moderator also good moderator material properties, Moderator material.

So let’s discuss first what nuclear reactor. The nuclear reactor is the main part of a nuclear power plant where fuel is subjected to nuclear fission. The energy released in the process is utilized t heat the coolant, which may generate steam?. Later on, this steam expands on a turbine to generate electricity.

In short, the reactor is used to control the emission and absorption process of neutrons.

The main components of a nuclear reactor are:

1. Reactor core
2. Moderator
3. Control rod
4. Coolant
5. Reflector
6. Thermal shielding
7. Reactor vessel
8. Biological shield

We will discuss each part of the reactor in this blog.

Reactor core of Nuclear reactor

The reactor core is the part of the nuclear reactor that contains the nuclear fuel components with which the nuclear reaction is taking place. About this process, we will discuss it down here.

The reactor core contains several fuel rods made of fissile material diluted with non-fissionable material for better reaction control. Therefore, we can say that it reduces the dame from fission product poisoning.

Poisoning of the reactor is like a parasite that absorbs the neutrons and due to this rate of fission reduces.

A core is generally of cylindrical or cubical shape rather than spherical shape because it facilitates the refueling operation and simplifies the process of coolant circulation through the core.

The core contains parallel fuel elements in thin plates or small-sized rods with coolant flowing axially. Additional Moderator or reflector material surrounds the assembly.

Basically, the reactor converts fertile material into fissionable material. The material to be converted is put around the core so that neutrons (which try to escape the core) would utilize for conversion. So this arrangement simplifies the process of separation of converted material during fueling.

Moderator of Nuclear reactor

The main function of the Moderator is to moderate or reduce the neutron speed to a value that increases the probability of fission occurrence.

Neutrons produced by the fission process are ejected from the nucleus at a very high velocity of 1.5× 107 m/s which produces a large amount of kinetic energy and are named fast neutrons.

The neutrons that undergo a fission reaction with fast neutrons are U-235, U-233, and Pu- 239.

Fast neutrons should be slowed down to speed corresponding to the speed of molecules in a gas at normal temperature; such neutrons that are slowed down are known as slow or thermal neutrons.

It is desirable to slow down the neutrons for the effective use of a nuclear reactor. The absorption properties of U-238b are very much reduced with the help of slow neutrons.

So if the uranium is bombarded by using slow neutrons, the chain reaction can be maintained, which is accomplished with the help of a Moderator, which is suitably mixed with fissile material.

When the fast neutron collides with the nuclei of moderator material, they lose their energy and slow down.

So to understand this assumption, if neutrons collide with a nucleus of equal mass, it will lose all its energy. It will come standstill, whereas if it collides with a heavier nucleus, it will lose very little energy. There will be not much change in the magnitude of velocity, but its direction will change. It is all as per the simple law of mechanics.

good moderator material properties

1. For every system to become economical, the first factor we always consider is the cost so that it should not be costly.
2. To not absorb the neutrons as it collides, Moderator should always have a light nucleus.
3. The moderator material should be chemically inert. It should neither corrode nor erode (gradual destruction of Moderator by natural force).
4. Moderator must not react with neutrons because neutrons captured in a nuclear reaction are lost to the fission process, making the reactor inefficient.
5. The neutrons moderator material should not undergo any harmful physical or chemical changes when bombarded by the neutrons.
6. The average neutron nucleus collision should lead to large neutron energy loss.

Moderator material used in Nuclear reactor

The material used for Moderator is only the elements at the top of the periodic table or the compounds with small nuclear weights.

Such elements are:

• Hydrogen
• Deuterium
• Helium
• Lithium
• Beryllium
• Boron
• Carbon
• Nitrogen
• Oxygen

Graphite is simple to fabricate and handle; it does not pose any containment problem. However, a disadvantage of using graphite is that if we continue the bombarding, it may create some stress.

Generally, ordinary water is cheap, but it has a high neutron absorption capacity. So we can only use it with enriched uranium. So this can be used as a coolant to moderate the temperature and pressure of the core.

There is another option for moderator material that is heavy water. Still, heavy water is costlier per unit weight than graphite or ordinary water. And also, there is a containment problem while using heavy water. Still, for the same power output, the size of a reactor using heavy water is compact compared to ordinary water and graphite. Also, it can be used with ordinary uranium. So in most power plants, heavy water is preferred regardless of its high cost.

The Moderator and the fuel can either be intimately mixed, or the fuel may be scattered throughout the Moderator in discrete lumps. These two arrangements of Moderator are commonly known as homogenous and heterogeneous arrangement respectively.

So today, we have discussed Moderator and reactor core. In our upcoming blog, we will discuss other nuclear reactor components. So stay tuned for more information.