Control rod drive system for a high temperature gas-cooled reactor

Abstract

The first commercial application of a high temperature gas-cooled reactor presented some rather unique functional and material requirements for the control rod system mechanical components. Reactor core geometry and coolant temperature distribution required the control rod drives to be located below the reactor vessel and to operate against gravity for shutting down the reactor. High temperature, high radiation, and the characteristic inertness of the helium coolant imposed operating conditions on materials and lubricants for which little or no previous operating and test experience existed. This paper covers the philosophy behind the design, a description of the equipment and its operation, and a description of the research and development program. Since this equipment has been exposed to both low- and fullpower reactor operation, a portion of this paper deals with the experience encountered in these areas. Significantly useful information was derived in the area of material combinations and component lubrication under unusual environmental conditions. The application of a hydraulic motor as the motive power source for the control rods resulted in the development of a unique and releable mechanism for automatically decelerating a high velocity shaft rotation at a fixed limit of revolutions.