ES331698A1 - Control rod actuating mechanism - Google Patents

Abstract

A control rod actuating mechanism for use with a liquid metal cooled fast reactor comprises elements 2 for gripping the top of the control rod 1, a rod 3 for actuating the gripping elements by displacement in a coaxial tube 4, means outside the reactor vessel for displacing the tube 4 through the reactor vessel wall, a metal bellows 10 as sealing means between the tube 4 and the actuating rod 3 and a gasket (not shown) as sealing means between the tube 4 and the reactor vessel wall, apertures 13 in the lower part 4a of the tube 4 which enable the liquid metal to flow freely through the tube 4, and guiding elements 14 rigidly connected to the tube 4 which make point contact with the actuating rod 3. The tube 4 is guided in its displacement by keys 15 which slide in longitudinal apertures 16 in a stationary outer guide tube. The liquid metal can enter the tube 17 freely through the apertures 16. The liquid metal provides continuous lubrication of the mechanism. The stationary outer guide tube is secured to a stationary tube which extends through the reactor vessel wall and supports a biological protection plug encircling the upper part 4b of the displaceable tube 4. The gasket which is located in the stationary tube cooperates with the displaceable tube 4 to bound a number of consecutive annular chambers and a sealing block. A small flow of gas derived continuously from a gas blanket above the liquid metal in the reactor vessel experiences a series of expansion steps in the annular chambers, the pressure differences being produced in a direction such that there is no leakage of active gas outside the reactor vessel. The gas circuit includes a reservoir, the dwell time of the gas in the reservoir being long enough for satisfactory deactivation. With such a gasket, high-speed rod movements of several metres become a possibility while on the other hand the movements of the bellows are short and slow with no maintenance problems arising.