Patent GB-1014434-A (GB)
Title: Improved control rod drive for nuclear reactors
IPC: G21C7/14
Filed: 1964-02-05
Abstract: 1,014,434. Controlling reactors. GENERAL DYNAMICS CORPORATION. Feb. 5, 1964 [Feb. 11, 1963], No. 4920/64. Heading G6C. Apparatus for controlling the emergency fall of a vertically movable control rod of a nuclear reactor comprises a cable 11 for suspending the rod 10 wound around a grooved drum 12 which is coupled by means of a gear system and a solenoid clutch 27 to a motor 25, the drum 12 which acts as a flywheel and which may be filled with lead such as at 20 being caused to rotate as the rod 10 falls freely under gravity when the clutch 27 is released, a free-wheeling clutch enabling the drum 12 to continue its rotation after the rod 10 has reached its lowest position, and there being means for reducing the ratio between the linear speed of the rod 10 and the peripheral speed of the drum 12 towards the end of the descent of the rod 10 so that a greater percentage of the kinetic energy developed by the descent of the rod 10 will be absorbed by the drum 12 during the lower portion of the descent than during the upper portion. The solenoid clutch 27 includes a normally stationary collar 37 located by means of a pair of pins 39 between the arms of a bifurcated lever 40, the other end of which is mounted on a pivot pin carried by the solenoid frame, an intermediate part of the lever 40 being connected to the movable plunger of the solenoid. When the current to the solenoid is interrupted, a compression spring 35 surrounding a horizontal shaft 29 mounted so as to rotate in bearings 30, 31 in the side plates 23, 24 pushes a slide member 28, normally held in a fixed position, to the left causing a pinion G of the gear system to become disengaged from a spur gear H which forms an integral part of the drum 12. The drum 12 is then caused to spin freely together with a shaft 19 in bearings 21, 22 in the side plates 23, 24 as the rod 10 descends. On the right-hand end of the shaft 19 there is formed a spiral track member or cam 44 which forms a support for the terminal portion of the cable 11. The cam 44 is normally clutched to the drum 12 and rotates with it. During the scram operation, the cable end 45 runs off the last groove 14 of the drum 12 and transfers to a groove formed on the outer portion of the cam 44. An over-running clutch (Fig. 3) maintains the outer end of the cam 44 and the adjacent face of the drum 12 in driving engagement until the rod 10 reaches its lowest position. This clutch includes a pawl 46 pivoted at one end of a pin 47 on the drum 12 and forced inwardly by a compression spring 50 so that the point 54 of the pawl 46 is located inwardly of the outer edge 55 of a land 56 formed on the inside face of the cam 44. The cable end 45 is connected via a chain 63 to a pin 64 carried by the shaft 19 a short distance from the axis 58 around which the system rotates. At the end of the descent of the rod 10, the cam 44 makes one revolution to a position (Fig. 4, not shown) in which the chain 63 and cable end 45 are unwound from the cam 44 and hang vertically from the pin 64 to support the rod 10. During this revolution, the land 56 is forced against the pawl 46 so driving the drum 12 but when the cam 44 is stationary, the drum 12 is allowed to freewheel, the pawl 46 when it encounters the land 56 sliding along its sloping outer edge 55 and compressing the spring 50. When the drum 12 is rotated in the opposite direction to raise the rod 10, the pawl 46 moves into latching engagement with the land 56 and the drum 12 and the cam 44 rotate together again. The cam 44 is so shaped that the deceleration of the rod 10 during the final revolution of the cam 44 around the axis 58 is made substantially uniform so as to avoid placing any undue peak strain on the cable 11. The shaft 19 has at its right hand end an extension on which is mounted a pinion 65 meshing with a timing or programme gear 66 equipped with a cam element operating suitable relays or switches which indicate the position of the rod 10 at various times during the operation of the reactor. At the opposite end of shaft 19 is another shaft 70 which is geared to a conventional fine synchro device 71 and a rough synchro device 72 by means of which the position of the rod 10 may be adjusted or controlled. If a smaller or unweighted flywheel is needed, for example because of space limitations, the flywheel may be geared to run at a higher speed than the shaft 19. A wheel os relatively small size and weight can, for example, be arranged to rotate on an axis spaced outwardly from the periphery of the drum 12 and equipped with a small pinion meshing with the gear H on drum 12.