The purpose of using heavy water in nuclear reactior is

Options

A. to increase the energy released in nuclear fission
B. to cool the rector to room temperature
C. to make the dynamo blades to woek wall
D. to decrease th energy of fast neutrons to the thermal energy

Explanation

### Step-by-Step Solution:

1. **Understanding Heavy Water**:
- Heavy water is chemically known as deuterium oxide (D2O), where the hydrogen atoms in regular water (H2O) are replaced by deuterium, which is an isotope of hydrogen.

2. **Role of Heavy Water in Nuclear Reactors**:
- Heavy water is primarily used in certain types of nuclear reactors as a neutron moderator.

3. **Function of a Neutron Moderator**:
- A neutron moderator slows down fast neutrons produced during nuclear fission. This is crucial because slower (thermal) neutrons are more likely to be captured by fissionable materials like Uranium-235 (U-235).

4. **Interaction with Fissionable Material**:
- When thermal neutrons collide with U-235, they can be absorbed, leading to the formation of Uranium-236 (U-236), which is an unstable isotope. This process increases the likelihood of further fission reactions.

5. **Additional Reactions**:
- Heavy water can also facilitate reactions with Uranium-238 (U-238), which can capture neutrons without undergoing fission, contributing to the overall efficiency of the reactor.

6. **Conclusion**:
- Therefore, the primary purpose of using heavy water in a nuclear reactor is to act as a neutron moderator, slowing down neutrons to enhance the probability of fission reactions with U-235.

### Final Answer:
The purpose of using heavy water in a nuclear reactor is to act as a neutron moderator, slowing down fast neutrons to thermal energies, thereby increasing the likelihood of fission reactions with Uranium-235.

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