Moderator, Coolant & Control Rod : Part II

Coolant is used to absorb the heat generated from the nuclear reactor core and transfer it to electrical generators and the environment. Since water and heavy water also can function as coolants, they can do double duty in thermal reactors. The coolant water is heated by the nuclear reactions going on inside the core. However, this heated water does not boil because it is kept at an extremely intense pressure, thus raising its boiling point above the normal 100° Celsius.

For fast reactors, water and heavy water are not suitable to be used as coolants, because they would tend to slow down the fission of neutrons as in fast reactor we needed the neutrons to be in as energetic as possible. Hence, the most fast reactors can be cooled by using liquid sodium which is very good heat transfer properties and it is not good in slowing down neutrons by elastic scattering. Besides, coolants also having chemical stability which meaning that it will not react with the neutrons, there only mall pumping requirement, irradiation stability and abundance as well as low cost.


A coolant fluid enters the core at low temperature and leaves it at higher temperature. This higher temperature fluid is then directed to conventional thermodynamic components where the heat is converted into electrical power. Different coolants are used in different purposes and some of the commonly used coolants are light water, heavy water, carbondioxide, helium, nitrogen, sodium, sodium-potassium mixture and so on. It can be seen that the coolants used vary from solids, liquids and gases and depending on the type of the reactor.