reflector

A reflector in a nuclear reactor is a layer of unfueled material surrounding the core. Its primary purpose is to scatter neutrons that escape the core, returning some of them back into the core to help sustain the chain reaction. This allows for a smaller core size and helps to create a more even distribution of power within the reactor by utilizing neutrons that would otherwise be lost.1

Reflectors are especially important in research reactors, where they often house experimental apparatus. In some designs, reflectors are even placed inside the core as central islands to achieve high neutron intensities for experiments. For most power reactors, reflectors are less critical due to their larger size, which minimizes neutron leakage. However, in liquid-metal reactors, reflectors can be designed as a "blanket" to capture leaking neutrons and breed new fissile material from fertile material.1