GB968137A - Improvements in and relating to grabs - Google Patents

Abstract

968,137. Fuelling reactors. NUCLEAR POWER PLANT CO. Ltd., and A.E.I.-JOHN THOMPSON NUCLEAR ENERGY CO. Ltd., [trading as NUCLEAR POWER GROUP ]. Aug. 20, 1963 [Nov. 9,1962], No. 42370/62. Heading G6C. In a grab having arms adapted to engage a body to be lifted or otherwise moved, the arms are arranged in at least two groups which operate independently of each other so that if the arms of any one group are impeded or prevented from engaging the body, the arms of another group are not so impeded or prevented and can engage the body. The grab is intended for handling fuel elements in the core channels of a reactor and particularly fuel elements having radial arms at their lifting ends so that if when the grab is lowered one set of its arms is impeded by the radial arms of the fuel element, another set of the grab arms may make lifting engagement with the fuel element. As shown, the grab comprises a casing 1 enclosing a sleeve 2 slidable over a distance determined by slots 2a in the sleeve and pins 3 secured to the casing and extending through the slots. A lifting cable 4 is attached to the sleeve 2. A cylinder 5 fixed to the casing 1 by the pins 3 houses a plunger 6 and between the cylinder and the sleeve 2 extended leg members 7a, 8a of two cages 7, 8. The leg members 7a, 8a comprise the upper ends of the cages 7, 8 and are arranged as shown in Fig. 2 which is a section on line A-A of Fig. 1, the cages being supported by arcuate plates 9 secured to the ends of the leg members and which rest in a recess in the sleeve 2, Fig. 3, which is a section on line B-B; The lower end of each cage supports the lifting arms 10 of the grab, arms 10a being pivotably supported by lugs 11 extending radially inwards from cage 7 and arms 10b by lugs 12 extending radially outwards from cage 8, Fig. 4, which is a section on line C-C. A probe 13 extending below the casing 1 has its upper cylindrical end between the leg members 7a, 8a and the cylinder 5, this upper end of the probe controlling locking balls 15, 16 so that in the position of the probe shown in Fig. 1 the cages 7, 8 and the plunger 6 are locked to the casing 1. A further ball locking arrangement is formed between balls 17 and recesses 18, 19 on cage 7 and between balls (not shown) and similar recesses on cage 8, these balls being controlled by the plunger 6 actuated by a solenoid 14 mounted in the sleeve 2. As shown in Fig. 1 the arms 10a, 10b are held in this retracted position by pins 21 fixed to the casing 1 and cooperating with arcuate slots 20 in the arms. On lowering the grab towards a fuel element 25 the probe 13 is raised unlocking balls 15, 16 and allowing the cages 7, 8 to drop'under gravity, this movement of the cages causing the pins 21 to move the arms 10a, 10b outwards and then to draw the arms inwardly under the head 27 of the fuel element. Also, the recesses 19 are brought opposite balls 17 so that when the solenoid 14 is energized the plunger 6 moves upwards and forces the balls into the recesses to lock the cages 7, 8. When the grab lifts the fuel element the probe 13 drops sufficiently to return the balls 15, 16 to their locking position whereby the arms 10a, 10b remain locked to the fuel element 25 should the electric supply to the solenoid fail. In order to release the fuel element it is lowered on to a supporting surface so that the probe 13 moves upwards and unlocks the balls 15, 16. The solenoid is de-energized so that plunger 6 moves down and unlocks balls 17 thereby releasing the cages 7, 8 and enabling the arms 10a, 10b to be lifted clear of the fuel element. If, as the grab is lowered on to the fuel element, one set of arms e.g. arms 10a, is impeded by radial members 28 of the fuel element the other arms 10b will pass between the members 28 and engage the element as before. The arms 10a will maintain cage 7 in the Fig. 1 position whilst the cage 8 drops as previously described. Since the balls 17 however, remain opposite recesses 18 in cage 7 the movement of the plunger 6 can still take place.