Question

Heavy water is used in a nuclear reactor as:
A) Coolant
B) Moderator
C) Both coolant and moderator
D) Catalyst

Answer 1

Hint: In nuclear reactors, the neutrons must be slowed down to ensure an effective fission chain reaction occurs. This process of slowing neutrons down is done by moderators. And a coolant is used to remove the heat from the nuclear reactor and transfer it to electrical generators and the environment.


Complete step by step answer:
(i)Deuterium oxide is called heavy water. Heavy water absorbs fewer neutrons than hydrogen, which is extremely important as nuclear fission reactions require neutrons to carry out their chain reactions.
(ii)The heavy water is kept under pressure which increases its boiling point so that it can operate at high temperatures without boiling.
(iii)Heavy water also used a coolant because it has identical properties as normal water.
From the above points, we can say that heavy water can be used as both coolant and moderator.

So, the correct answer is “Option C”.

Additional Information:
(i)Many nuclear reactors use normal light water under pressure as a coolant. Those are called light water reactors. And there is another type of reactor called heavy water reactors which uses heavy water as a coolant.
(ii)The cost of production of heavy water takes a significant part in the cost of the nuclear reactor project. But it is very cheap when it comes to usefulness. The process of producing deuterium oxide is big and has to do a very long process.
(iii) Heavy water is produced under the process called the Girdler Sulphide process. This process is based on an exchange of deuterium between Hydrogen Sulphide and light water.
${H_2}S + HDS \rightleftharpoons HDO + {H_2}O$

Note:
There is no catalyst used in the nuclear reactors. In India, the majority of reactors are Pressurised Heavy Water Reactors (PHWR). And Heavy water is produced prominently in India.