Final answer:
Moderators slow down fast neutrons so they can induce more fission in the fuel, while control rods absorb excess neutrons to finely regulate the rate of the nuclear chain reaction. The correct option is A.
Step-by-step explanation:
In normal operation of a nuclear reactor for energy production, both a moderator and control rods are necessary components. The moderator serves to slow down the fast neutrons produced during fission, making them more likely to induce further fission events in the fuel (usually uranium).
This is essential because fast neutrons tend to bounce off the uranium nuclei rather than inducing fission. The most commonly used moderators are light water or heavy water, although other materials like graphite can also be used.
On the other hand, control rods are used to absorb excess neutrons. By adjusting the position of the control rods within the reactor core — inserting them to absorb neutrons or withdrawing them to allow more neutrons to cause fission — operators can control the rate of the nuclear chain reaction.
This prevents the reaction from becoming too intense, which would overheat the water and potentially damage the reactor. Common materials for control rods include boron and cadmium, which are very effective at capturing neutrons.
The correct option that describes the functions of the moderator and control rods is: a) Moderators slow down neutrons; control rods absorb excess neutrons to regulate the reaction rate.