Patent GB-956769-A (GB)
Title: Improvements in or relating to grabs
Inventor: TINKLER ALMOND
IPC: G21C19/10
Filed: 1959-12-02
Abstract: 956,769. Fuelling reactors. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. Nov. 21, 1960 [Dec. 2, 1959], No. 40935/59. Heading G6C. A grab intended for retrieving a damaged fuel element from a reactor coolant channel comprises a tubular body having its lower end open so that the body can be passed between the fuel element and the channel wall, a lifting cable attached to the upper end of the body and latch means including one or more pawls at the lower end for engaging the underside of the element when it is located within the body. As shown, the grab comprises an outer sleeve 1 supported by a hollow cable 14 and an inner sleeve 3 rotatable and longitudinally slidable within the sleeve 1, this movement of the sleeve 3 being determined by pins 91 on that sleeve co-operating with slots 6 in the sleeve 1. The lower end of the sleeve 1 has longitudinal slots 8 and a splined inner band 2 and the lower end of the sleeve 3 has longitudinal slots 7 and a splined outer band 4. When the grab is in the fuel element gripping position as shown in the Figures the slots 7, 8 are out of alignment and the splines 2, 4 are in engagement. The grab is lowered over the fuel element 10 to be retrieved with the slots 7, 8.in alignment so that they may receive the three arms of a locating attachment 13 situated at the upper end of the element, the pins 91 then being at the lower ends 89 of the slots 6. Enlargements 92 at the upper ends of the slots 7, 8 receive the arms of the attachment 13 when the grab is in the gripping position. Tongues 76 formed by the slots 7 each carry a pawl 78 pivoted to the sleeve 3 by a pin 80 and loaded by a spring 81 acting through a plunger 83 and link 86. The pawl has a toe 79 whereby when the sleeve 3 is raised to its uppermost position within the sleeve 1 the toe is engaged by the lower end of the sleeve 1 and the pawl 78 moved inwardly to engage the lower end of the fuel element 10; also the splines 2, 4 engaged to produce a locking action between the sleeves 1, 3 so that the solid parts between the slots 7, 8 of the sleeves 3, 1 are keyed together to increase their combined hoop strength to resist forces acting in the radially outward direction. The movement of the sleeve 3 is produced by carbon dioxide under pressure and to this end the sleeve is provided at its upper end with a cylinder 23 having ends 24, 25, the cylinder receiving a piston 22 having a hollow stem 22a rigid at its upper end with a head 21 of the sleeve 1. The gas is supplied alternatively to the spaces 40,45 below or above the piston 22 to lower or raise the assembly 3, 23, 24, 25, the supply to the space 40 being controlled by a gas operated sliding valve member 34 having a port 41. A probe 54 slidable within the stem 22a and biased by a spring 55 is moved upwardly when it engages the attachment 13 during lowering of the grab to control valve ports (Figs. 7, 8 not shown) whereby the gas js supplied to space 45 and the pins 91 move out of parts 89 and along parts 90 of the slots 6. The space 40 is exhausted through ports 39, 38a, 38 and 37. An electric sensing device 11 then engages the attachment 13 of the fuel element immediately beneath the one being removed and upon receipt of a signal from this device gas is supplied to the space 45 through further ports 46,44 whereby the pins 91 are moved to their uppermost positions in the slot parts 88, the splines 2, 4 move into engagement and the pawls 78 engage the fuel element. A further signal is given by electric contact means (Figs. 5. 6, not shown). The cable 14 conducts pipe lines 15... 17 for the gas and leads 18, 19 for the two signalling devices.