MCQ Detailed View

A nuclear reactor is a device used to control and sustain a nuclear fission chain reaction to produce energy. During nuclear fission, heavy atomic nuclei such as uranium-235 or plutonium-239 split into smaller nuclei, releasing a large amount of energy along with fast-moving neutrons. For the chain reaction to continue efficiently, these fast neutrons must be slowed down to a moderate speed where they are more likely to be absorbed by other fuel nuclei.

This is where a moderator plays a crucial role. A moderator is a substance placed inside the nuclear reactor to slow down the speed of neutrons without absorbing them completely. Materials commonly used as moderators include heavy water (D₂O), light water (H₂O), and graphite. When high-energy neutrons collide with the light nuclei of these materials, they lose part of their energy and move slower.

Slower neutrons, known as thermal neutrons, have a much higher probability of causing further fission reactions in fuel atoms. This controlled process ensures a sustained chain reaction, allowing the reactor to operate safely and steadily while releasing heat energy that can be converted into electricity.

Without a moderator, the neutrons would remain fast-moving, making it less likely for them to trigger additional fission events, which would reduce the efficiency of the reactor. The moderator does not increase or decrease the number of electrons—it only affects the speed of neutrons.

In summary:

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  Correct answer: Slow down the speed of the neutrons (Option 2)

  
  


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  The moderator is essential for achieving the correct conditions for efficient and controlled energy production in a nuclear reactor.