2 Responses

1. the moderators slow down neutrons and control rod slow the rate of fission or stop it completely

2. the moderator changes the energy level and speed of the neutrons released to better suit the absorption of the neutrons by the fuel atoms (called “Thermalizing the neutrons). In many types of light and heavy water reactors, the moderator is also the reactor coolant. in some cases the moderator is graphite or a gas

   Control Rods are used to maintain a constant power across the various sections of the axial and radial power densities of the reactor core. This ensures even fuel burnup and prevents hot spots from becoming created in the fuel areas. They are also used to ensure enough negative reactivity when fully inserted to allow for the core to be maintained shutdown and enough positive reactivity when withdrawn to overcome the negative reactivity caused by the build up of gasseous poisons in the moderator (Xenon mostly)