Patent GB-1182239-A (GB)
Title: Drive and Coupling Mechanisms for Nuclear Reactor Control Elements.
IPC: G21C19/105
Filed: 1968-10-08
Abstract: 1,182,239. Grippers for nuclear fuel elements. COMBUSTION ENG. Inc. 8 Oct., 1968 [10 Oct., 1967], No. 47682/68. Heading B8H. [Also in Division G6] A control element is coupled to a drive mechanism by means of a gripper comprising fingers 64 movable between their locking and unlocking positions by the action of the head 68 of a rod 66. Attached to the rod 66 by means of a pin 70 is a cylindrical member 72 at the lower end of which are camming members 74. The entire gripper operating mechanism reciprocates vertically relative to the fingers 64 and when lowered, the camming members 74 (as shown in Fig. 4) release the fingers 64 and the head 68 forces the fingers apart to release the lifting attachment 75 on the control element. The entire gripper operating mechanism is attached by means of a rotatable joint (not shown) to a rod 76 which extends vertically through a tube 60 screw-threaded at its lower portion 63 to the upper end of the fingers 64 and screwthreaded at its upper portion 61 to a threaded portion 78 on the rod 76. The tube 60 in turn extends vertically through a hollow rack 26 forming part of a rack and pinion drive. An elongated nut-like member 62 is screwthreaded on to the upper portion 61 and the tube 60 is suspended by means of this nut 62 from the head 42 of the rack 26. Since vibration or operation of the drive mechanism could cause the nut 62 to rotate relative to the tube 60, locking means are provided comprising a sleeve 80 extending upwardly from the nut 62 and surrounding the upper portion 61. A lock operator 82 is mounted around the sleeve 80 with pins 84 extending inwardly into slots 86 in the sleeve. A spring 87 between the nut 62 and the operator 82 forces the latter upwardly into a position in which a ball detent mechanism locks the sleeve 80 and thus the nut 62 to the tube 60. In order to unlock and rotate the nut 62 a tool is employed first to depress the operator 82 against the force of the spring 87 and release the detent mechanism and then to rotate the operator 82. The pins 84 cause the nut 62 to rotate, thereby lowering the tube 60 within the rack 26. The control element is uncoupled by lowering the rack 26 as far as possible in which position the control element is located just above the reactor core base and then a first tool is inserted to operate the nut locking mechanism as described above. The tube 60 is then lowered within the rack 26 and the control element thus lowered on to the core base. The tool is then removed and a second tool inserted to operate the grippers. This tool fits over pin 97 at the upper end of the rod 76 and rotates the rod so as to screw it down within the tube 60, causing the gripper operating mechanism to be lowered with respect to the fingers 64 whereby the fingers are opened and the control element released. The rack 26 is then driven to its upper limit of travel. After this procedure has been followed for each of the control element drive assemblies, the head may be removed from the reactor vessel together with the drive assemblies. In an alternative arrangement for raising and lowering the rod 76 within the tube 60 (Figs. 8 and 9, not shown), the tube has a bayonet slot with the hooked end uppermost into which a pin extends. The pin is received in the shorter leg of the bayonet slot when the rod is held within the tube. The pin is attached to the rod by means comprising a sleeve to which the pin is attached extending over the end of the rod, the sleeve being provided with a U-slot with upwardly extending arms, a second pin attached to the rod and extending outwardly so as to be received in one of the legs of the U-slot, a spring biasing the sleeve down on to the end of the rod, and means for lifting the sleeve against the force of the spring and for rotating the sleeve so that the pins take positions in the other legs of the bayonet slot and the U-slot respectively.