Moderator

Moderator

The moderator of a nuclear reactor is a substance that slows down the speed of neutrons produced from fission. By slowing the neutrons down the probability of a neutron interacting with uranium-235 nuclei is greatly increased thereby maintaining the chain reaction.
₉₂U²³⁵ + ₀n¹ → ₅₆Ba¹⁴¹ + ₃₆Kr⁹² + 3₀n¹ + Energy
₉₂U²³⁵ + ₀n¹ → ₃₈Sr⁹⁵ + ₅₄Xe¹⁵⁹ + 2₀n¹ + Energy
In traditional nuclear reactors, the moderator is the same thing as the coolant. When fast neutrons strike the hydrogen atoms in H₂O, they slow down a lot. Graphite, heavy water and beryllium are good moderators. When graphite is used as moderator, the reactor is called atomic pile and when heavy water is used as moderator, the reactor is called swimming pool reactor. In atomic piles, a huge block of specially graphite containing holes in which U-rods are inserted, acts as moderators. The absorption of neutrons may occur by Th-232 in atomic piles. It produces fissionable U-233 isotope-
₉₀Th²³² + ₀n¹ → ₉₀Th²³³ → ₉₁Pa²³³ + _-1e⁰ → ₉₂U²³³ + _-1e⁰
In the swimming pool reactor, heavy water is used in tank in which the U-rods are suspended.

 Share