Question

Which one of the following is used as a moderator in nuclear reactors?
a.Uranium
b.Thorium
c.Lithium
d.Beryllium oxide

Answer 1

Hint: Generally, nuclear reactors are used to set a nuclear chain reaction in motion and control the reaction in a self-sustained manner. They are used at nuclear power plants for the purpose of generating electricity.

Complete Step by Step answer: The main work of a nuclear reactor is to control the process of the occurring nuclear fission, a process in which atoms split and release energy. These reactors use uranium for nuclear fuel and the fuel rods immersed in water act as both a coolant and moderator.
The neutrons produced by fission are slowed down by the moderator in order to sustain the chain reaction. Pressurized water reactors are commonly used and make up for about 65% of US nuclear reactors.
The most commonly used moderator is light water. It is also referred to as deuterium-depleted water. Beryllium and hydrocarbons are also used in some of the experiments. The moderators which are free of neutron-absorbing impurities are considered to be good, such as boron. Hydrogen, deuterium, carbon, beryllium and Lithium -7 are the materials used.
Looking at the options given:

Option a: The deuterium-moderated reactors use unenriched natural uranium. This is not the appropriate answer.
Option b: Thorium fuel is used to breed fissile uranium-233 in various kinds of nuclear reactors. This is an incorrect answer.
Option c: Lithium-7 is often used in a molten salt reactor. But, this is not the correct answer.
Option d: Beryllium oxide is an ideal option as a moderator in nuclear reactors as nuclei with low mass numbers are most effective. Hence, this is the correct answer.

Note: Don't get confused with the other nuclear moderators such as Lithium-7 while answering. Li-7 is used in the primary water circuit of pressurized water reactors in order to control the pH level of the coolant.