ANS:A - uses molten sodium as moderator.

Using molten sodium as a moderator is not a typical practice in nuclear reactor designs. Moderators are materials that slow down fast neutrons to thermal speeds so that they are more likely to cause fission in fissile materials. Common moderators include water, heavy water (deuterium oxide), and graphite. However, molten sodium is commonly used as a coolant in some types of fast breeder reactors. These reactors use fast neutrons without a moderator to breed fissile material (such as plutonium-239) from fertile material (such as uranium-238). The fast neutrons produced during fission are absorbed by fertile material, converting it into fissile material. The molten sodium coolant transfers heat away from the reactor core to generate electricity. So, while molten sodium is used as a coolant in fast breeder reactors, it is not used as a moderator.