How is reaction rate controlled in a nuclear reactor?

Explanation

To control the reaction rate in a nuclear reactor, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Nuclear Fission**:
- In a nuclear reactor, a heavy nucleus (like Uranium-235) undergoes fission when it absorbs a neutron. This process splits the nucleus into smaller nuclei and releases energy along with additional neutrons.

**Hint**: Remember that fission not only releases energy but also produces more neutrons, which can lead to a chain reaction.
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