ABSTRACT
The task of controlling in thermal reactors has hitherto been widely accomplished by materials that are strong neutron absorbers. The three primary control methods used in power reactors are movable control absorbers, burnable neutron poisons, and chemical shim. The term control rods is frequently applied in a very general way to any mechanical device which permits a change of the reactor reactivity. The rates of neutron generation and loss are directly related to the effects of reactivity and control of a nuclear fission reactor. The most effective control materials for the fission reactor are strong neutron absorbers. Shielding materials are meant to reduce the radiation and heat flows generated in the core of a nuclear reactor low enough to protect personnel and equipment from the damaging effects of radiation. The design of a nuclear reactor and its associated equipment must take into consideration the provision for the attenuation of escaping nuclear radiations by some form of shielding.
