Patent GB-1446154-A (GB)
Title: Gripper mechanism for control and shut-down rods in a nuclear reactor
IPC: G21C7/14
Filed: 1974-08-29
Abstract: 1446154 Reactors FRIED KRUPP GmbH 29 Aug 1974 [1 Sept 1973] 37829/74 Heading G6C [Also in Division B8] A gripper mechanism includes a gripper body 2, 3 suspended within a guide mast 1 from a hoisting mechanism (not shown) and adapted to grip rod heads 29 which each hold together a bundle of control or shut-down rods 28 to be removed from or introduced into vertical holes within a nuclear fuel assembly, by their upper ends, to form a pattern such as that shown in Fig. 12 with the rods 28 projecting from the head 29. When such a bundle of rods is subjected to unequal thermal loading the rods tend to bend differentially and for this reason, together with the fact that the rods tend to oscillate when they are raised and lowered, lateral support of their lower ends is required. This is obtained by means of a mask 33 having an opening 34 which conforms to the control rod bundle profile and is mounted on guide rods 32 which are movable with respect to the gripper body, 2, 3, parallel to its axis and can be connected to the gripper body at different levels by means of hook-ended, spreadable pawls 38 which engage grooves 48 in the lower surfaces of locking bars 35 connecting the guide rods 32 in pairs at opposite ends of a diagonal of a rodgripping tool 10. The gripper body comprises a short lower part 3 telescopically mounted within a relatively long upper part 2 and is guided within the mast 1 by guide rollers (8) (Fig. 4, not shown) in diagonally opposite corners of the mast. Fig. 1 shows the gripper body 2, 3 being lowered towards the rod-gripping tool 10 with the lower part 3 projecting from the upper part 2 to the maximum extent permitted by the coaction of rollers 4 within slots 5. Compressed air is admitted to a cylinder 40 (Fig. 3) to raise a piston-rod 39 against the action of a spring 42 and thereby draw the ends 45 of the pawls 38 within the upper part 2 of the gripper body. Compressed air is also admitted to a cylinder 23 (Fig. 11) to raise a pusher 21 and thus free a plurality of balls 20 in radial holes in a collar 16 on the lower part 3 of the gripper body. A flange 17 on the collar 16 finally seats on a collar 13 of the rod-gripping tool 10 and the pusher 21, after air pressure has been removed from the cylinder 23, is moved down by springs (not shown) to push the balls 21 into an annular groove 15 and prevent them from leaving it. Compressed air is then exhausted from the cylinder 40 so that the pawls 38 may assume their spread position. When the upper part 2 of the gripper body is then raised, the hooked ends 45 of the pawls 38 engage in the grooves 48 in the bars 35 to lift the rods 32 and therefore the mask 33. The gripper mechanism is now ready to withdraw the bundle of control rods 28 from the fuel assembly, the head of which is shown at 26 (Fig. 11). To this end, the gripper body 2, 3 is lowered over the rod head 29 which consists of a cylindrical sleeve and narrow arms 30 which project from the sleeve to obscure the upper ends of the control rods 28 (Fig. 12). The rod head 29 passes through the opening 34 and the mask 33 finally rests on abutments 50 on the fuel assembly head 26. The rod gripping tool 10 is now to be coupled to the rod head 29. A rod 57 having limited vertical movement within a central sleeve 51 carried by the rod head 29 is depressed by a punch 68 moved down by a spring (not shown) on exhaustion of air from a cylinder 69 so that balls 53 in radial holes in a collar 52 forming a continuation below the rod head 29 of the sleeve 51 enter a groove 58 in the rod 57, being no longer held in a groove 56 in a sleeve 54 extending upwardly from the fuel assembly head 26. The rod head 29 is therefore uncoupled from the fuel assembly head 26. At the same time a pin 63 moves into a position whereby it prevents balls 62 from leaving a groove in the sleeve 51 and the rod head 29 is therefore coupled to the rod-gripping tool 10. On deposition of the rodgripping tool 10 on the fuel assembly head 26 in the position shown in Fig. 11, the upper part 2 of the gripper body moves downwardly with respect to the lower part 3 by a distance h and the pawls 38 partake of this movement so that their hooked ends 45 leave the grooves 48 in the bars 35. After admitting compressed air to the cylinder 40 to retract the pawls 38, the upper part 2 of the gripper body is lifted by the hoisting mechanism and when it has moved the distance h in relation to the lower part 3, this partakes of the upward movement and the control rods 28 are lifted from the fuel assembly by the rod-gripping tool 10 coupled to the part 3. When the control rods 28 have moved up to an extent such that only their lower ends project below the mask 33, the pawls 38 are spread out so that their ends 45 engage beneath the bars 35 just above them. The guide rods 32 are therefore lifted by continued upward movement of the gripper body 2, 3 so that the mask 33 remains just above the lower ends of the control rods 28. The control rods are thus held at the correct spacing so that they can be introduced without difficulty into a holder or other fuel assembly.