Question:
In a nuclear reactor, heavy water (D_2O) is used as a moderator. Its main function is to:
In a nuclear reactor, heavy water (D_2O) is used as a moderator. Its main function is to:
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Moderator ≠ absorber.
Control rods absorb neutrons; moderator only slows them.
Updated On: Jun 10, 2026
- absorb neutrons to stop reaction
- accelerate neutrons to sustain reaction
- slow down fast neutrons to thermal energies
- cool the reactor core
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The Correct Option is C
Solution and Explanation
Concept:
In nuclear fission, fast neutrons are produced with very high kinetic energy. These neutrons must be slowed down to thermal energies to increase probability of further fission in U-235.
Heavy water acts as a moderator because it slows neutrons via elastic collisions without absorbing them significantly.
Step 1: Role of moderator Fast neutrons collide with deuterium nuclei and lose energy gradually.
Step 2: Why slowing is important Thermal neutrons have higher fission cross-section, sustaining chain reaction. Thus, correct option is (C).
Step 1: Role of moderator Fast neutrons collide with deuterium nuclei and lose energy gradually.
Step 2: Why slowing is important Thermal neutrons have higher fission cross-section, sustaining chain reaction. Thus, correct option is (C).
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