In a nuclear reactor, what is the function of the moderator (like heavy water or graphite)?
A. To act as the nuclear fuel.
B. To absorb excess neutrons to stop the chain reaction.
C. To slow down the fast-moving neutrons so they can cause further fission.
D. To transport heat away from the reactor core.
Answer: Option C
Solution (By JKExamLibrary)
Uranium-235 undergoes fission most efficiently when struck by slow-moving (thermal) neutrons. However, fission reactions release very fast-moving neutrons. The moderator (like graphite or heavy water) collides with these fast neutrons to slow them down without absorbing them, sustaining the controlled chain reaction. Control rods (cadmium/boron) are used to absorb excess neutrons.
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