Probably we all know the dark side of nuclear energy. In reality, the bright side of it exceeds the dark side in many folds. In this article we will learn about nuclear detectors, their types and different constituents of nuclear reactors.
What is a nuclear reactor?
A nuclear reactor is a device that is designed to maintain a nuclear chain reaction producing a steady flow of neutrons generated by the fission of heavy nuclei. In terms of purpose, they are classified as research reactors and power reactors.
Nuclear research reactors
Nuclear Research reactors are mostly used for research and medical purposes. In many countries, the universities and research centers operate these research reactors including many nations where no nuclear power reactors are operated. These reactors generate neutrons for multiple purposes, including producing radiopharmaceuticals for medical diagnosis and therapy, testing materials, and conducting basic research.
Nuclear power reactors
As the name signifies these reactors are used for the generation of electric power. These reactors are bulkier than research reactors and generally found in nuclear power plants. According to Statista, there are about 30 countries with nuclear power reactors in operation.
There are many different types of power reactors. However, they have one common feature; they produce thermal energy. This thermal energy can be used to convert into mechanical energy or electrical energy.
In nuclear power reactors, the fission of heavy atomic nuclei produces heat that is transferred to a fluid which acts as a coolant. During the fission process, bond energy is released and this first becomes noticeable as the kinetic energy of the fission products generated and that of the neutrons being released. Since these particles undergo intense deceleration in the solid nuclear fuel, the kinetic energy turns into heat energy.
In the case of reactors designed to generate electricity, the heated fluid can be gas, water or a liquid metal. The heat stored by the fluid is then used either directly (in the case of gas) or indirectly (in the case of water and liquid metals) to generate steam. The heated gas or the steam is then fed into a turbine driving an alternator.
Since, according to the laws of nature, heat cannot fully be converted into another form of energy, some of the heat is residual and is released into the environment. Releasing is either direct – e.g. into a river – or indirect, into the atmosphere via cooling towers. This practice is common to all thermal plants and is by no means limited to nuclear reactors which are only one type of thermal plant.
Table 1 summarize the list of power reactors with their fuel, coolant and moderator
| Reactor Type | Fuel | Coolant | Moderator |
| Pressurised water reactors | Enriched uranium | Light water | Light water |
| Boiling water reactors | Enriched uranium | Light water | Light water |
| Pressurised heavy water reactor | Natural uranium | Heavy water | Heavy water |
| Gas-cooled reactors | Natural or enriched uranium | CO2 | Graphite |
| Light water graphite reactors | Enriched uranium | Pressurised boiling water | Graphite |
Constituents of nuclear reactor
A Nuclear Reactor mainly consists of
a) Fuel
b) Moderators
c) Control rods
d) Shielding
e) Coolant
f) Turbines
g) Generator
h) Cooler Pipes
i) Water Supply
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Core – It’s the focal point of the reactor, where fuel is contained and nuclear fission reactions take place.
Fuel: The fissionable material used in the reactor is called as fuel. The commonly used fuels are Uranium, Plutonium or Thorium. It can be U-235, U-238, Pu-236 or Th-232. Uranium is mostly preferred as it has high melting point.
Moderators: Only neutrons of a fairly low speed should be used to have controlled chain reaction. To slow down the speed fast moving neutrons produced during the fission process, moderators are used. Moderator reduces the speed of the neutron by absorbing its energy but not absorb neutron. Graphite, Heavy water and Beryllium are common moderators.
Rods:These rods absorb neutrons and stop the chain reaction to proceed further.
Control Rods: These rods absorb neutrons and stop the chain reaction to proceed further. These are made up of steel containing a high percentage of material like cadmium or boron which can absorb neutrons. When control rods are completely inserted into the moderator block then all the neutrons is absorbed and reaction comes to halt.
Shielding: Shielding prevents radiations to reach outside the reactor. Lead blocks and concrete enclosure that is strong enough of several meters thickness are used for shielding.
Coolant: The coolant is substance in a pipe to the steam generator where water is boiled. This is where heat-exchange process occurs. Heat is absorbed by the coolant that is produced in the reactor. Typical coolants are water, carbon dioxide gas or liquid sodium.
Turbines: Steam produced in the boiler is now passes to a turbine. The force of the steam jet causes the turbine to rotate. Heat energy (steam) is converted to mechanical energy (moving turbine).
Generator: The generator consists of coils that change the mechanical energy into electric energy. The turbine moves and the change in magnetic flux cause electricity. This is transmitted to substations for distribution of electric power.