Moderator in Fast Breeder Reactor

The moderator is a substance used in nuclear reactors to slow down fast-moving neutrons so that they can induce fission in uranium-235. In a fast breeder reactor, the moderator is used to slow down the fast neutrons produced by the fission of plutonium-239.

Heavy Water as a Moderator

Heavy water, also known as deuterium oxide (D2O), is a type of water that contains a higher concentration of the hydrogen isotope deuterium (D) than normal water. Heavy water is an excellent moderator for fast breeder reactors because it has a high neutron absorption cross-section and a low neutron capture cross-section. This means that it slows down neutrons effectively without absorbing too many of them.

Advantages of Heavy Water as a Moderator

There are several advantages to using heavy water as a moderator in fast breeder reactors. These include:

- High thermal efficiency: Heavy water has excellent heat transfer properties, which means that it can efficiently transfer heat from the reactor core to the coolant.
- High neutron economy: Heavy water has a high neutron economy, which means that it can produce more neutrons per unit of fuel than other moderators.
- Low parasitic absorption: Heavy water has a low parasitic absorption, which means that it absorbs fewer neutrons than other moderators.

Conclusion

In conclusion, the correct answer to the question is A) Heavy water. Heavy water is the most commonly used moderator in fast breeder reactors due to its excellent thermal efficiency, high neutron economy, and low parasitic absorption.