DEVELOPMENT OF THE SRE THIMBLE-TYPE CONTROL RODS MARK I AND II

摘要

Two thimble control rods were developed for the Sodium Reactor Experiment. In the Mark I design, all components, except the easily-removed drive motor assembly, are located below the reactor shield. The Mark I is presently- limited by life expectancy to the slow and infrequent motion required of a shim rod. The Mark II, designed with the traversing mechanism located above the shield, is used for the fast and frequent regulating motion.nAll components of the control rods are protected from the sodium coolant by 23-ft-long stainless-steel "thimbles" that extend from the reactor loading face downward through the active core. The nuclear poison elements of the control rods, formed by a series of short, hollow boron-nickel cylinders stacked on stainless-steel pull tubes, are moved vertically in a helium atmosphere by a recirculating ball-screw and nut.