AUXILIARY CONTROL ROD FOR NUCLEAR REACTORS

An auxiliary control rod for fine-setting the reactivity of a nuclear reactor including closely-packed zirconium-oxide pellets in cladding of stainless steel. The zirconium-oxide pellets prevent the collapse of the cladding. The stainless steel cladding controls the reactivity of the reactor to a substantially smaller extent than the main control rods which are of conventional structure and operation. With the cooperation of these fine-setting control rods, the range of movement in and out of the case of the reactor of the main rods may be limited and more precise and effective control achieved. In addition, the fine-setting control rods displace the coolant and limit the moderating effect of the coolant on the neutron flux. The zirconium-oxide pellets being refractory ceramics, resist crumbling during CRDM stepping of the control rods.