SSC JE Electrical Engineering 2010 Paper

There is no moderator use in fast breaker reactor because the neutron economy is such that Uranium Plutonium reactors can not bread with thermal neutrons, the neutron capture cross section for uranium 238 to produce plutonium is higher with fast neutrons. Moderator slow down neutrons and could reduce the plutonium production efficiency so that the reactor could not produce more fissile material then it used. Reader reactor producing uranium 233 out of thorium can breed with thermal neutron and do use.