Question

The purpose of a moderator in a nuclear reactor is

Answer 1

A nuclear reactor, also known as an atomic pile, is a device that is used to start and control nuclear chain reactions or nuclear fusion reactions. Nuclear reactors are used to generate electricity at nuclear power plants and for nuclear marine propulsion.

Complete step-by-step solution:
Nuclear fission heat is transferred to a working fluid (water or gas), which then drives steam turbines. These either turn the shafts of electrical generators or drive the propellers of a ship. In principle, nuclear-generated steam can be used for industrial process heat or district heating.
Some reactors produce isotopes for medical and industrial purposes, while others produce weapons-grade plutonium. According to the International Atomic Energy Agency (IAEA), there are 454 nuclear power reactors and 226 nuclear research reactors in operation around the world as of early 2019.
Fast neutrons (produced by splitting atoms in fissile compounds like uranium-235) are slowed down by neutron moderators in nuclear reactors, making them more effective in the fission chain reaction. The neutrons are slowed or moderated, allowing them to be absorbed more easily by fissile nuclei, resulting in more fission events.
A fission neutron normally travels at nearly the speed of light. At this speed, the chances of being captured by the $92{{U}^{235}}$ nucleus are slim. As a result, a moderator slows down the neutrons, allowing them to cause more fission.

Note: The number of neutrons capable of inducing further fission events can be controlled to control the rate of fission reactions within a reactor core. To adjust the reactor's power output, nuclear reactors typically use a variety of neutron control methods. Some of these techniques are based on the physics of radioactive decay and are simply accounted for during reactor operation.