What is the role played by the moderator in a nuclear reactor ?

Explanation

**Step-by-Step Solution:**

1. **Understanding Nuclear Reactions**: In a nuclear reactor, two primary types of nuclear reactions occur: fission and fusion. Fission is the process where heavy, unstable nuclei split into smaller nuclei, releasing energy and neutrons.

2. **Role of Neutrons in Fission**: During the fission process, fast-moving neutrons are produced. These neutrons are essential for sustaining the chain reaction, as they can collide with other fissile nuclei (like Uranium-235) to induce further fission.

3. **Need for Moderation**: Fast neutrons are less likely to cause fission in heavy nuclei. To increase the likelihood of these neutrons inducing further fission reactions, their speed must be reduced.

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