Patent GB-967203-A (GB)
Title: Improvements in or relating to grabs,primarily grabs for nuclear reactor fuel elements
Inventor: CHALLENDER RONALD SCOTT
IPC: G21C19/105
Filed: 1962-06-07
Abstract: 967, 203. Fuelling reactors. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. May 21, 1963 [June 7, 1962], No. 22045/62. Heading G6C. A graphite sheathed fuel element having a longitudinal cavity therethrough is manipulated by a grab head which is lowered into the cavity and operated to engage the base of the element. The grab comprises a grappling member 1 attached at 2 to a tubular lifting cable and defining at its lower end an annular series of resiliently deflectable fingers 3. A draw bar 4 is axially slidable within the fingers 3 to deflect them radially outwards to engage the rim R of a cavity C situated at the base of the fuel element, the cavity C comprising the lower end of a longitudinal cavity extending through the fuel element (not shown). The member 1 comprises a rod 5 having a counterbore 6 formed in a tubular extension 13, the lower end of the extension being slit to define the fingers 3. The fingers define a lip 16, an internal tapered surface 31 and a recess 33. The upper end of the rod 5 has a cap 8 and is enclosed by a jacket 7. The draw bar 4 has upper, intermediate and lower sections 17, 18, 19, the upper section 17 having seating rings 21 the intermediate section being surrounded by a spring 36 acting between a shoulder 14 on the extension 13 and a shoulder provided by the section 17, and the lower section 19 being profiled to define a tapered surface 25, a convexity 33a and an axial bore 26. A locking member 27 comprises a sleeve 28 slidable on the member 1 and having a flange 29 carrying internal and external sealing rings 30. A tubular extension 34 of the sleeve 28 slides on a land 15 of the extension 13 and has a rim 35 at its lower end. A spring 37 acts between the land 15 and a shoulder 38 on the extension 34. A probe 41 slidable in the bore 26 is connected to a waisted plunger 39 biased by a spring 40 within a bore 23 of the intermediate draw bar section 18. The plunger 39 controls locking balls 44 located in apertures 42 in the wall 43 of the draw bar and co-operating, alternatively, with annular grooves 45, 46 in the land 15. Further balls 48 in apertures 47 in the extension 13 co-operate with an annular groove 50 in the draw bar section 17. In operation pressurized gas is fed to the tubular lifting cable, the gas flowing through ducts 10, 11 to the counterbore 6 and the cavity 24 between the rod 5 and the jacket 7 so that the locking member 27 and draw bar 4 are held down against the springs 37, 36. The draw bar 4 is locked to the grappling member 1 by the balls 44, 48 co-operating with grooves 45, 50. As the grab is lowered through the fuel element, the fingers 3 pass through the rim R and the probe 41 contacts the bottom of the cavity C to displace the plunger 39 upwardly, Fig. 2. The gas pressure is released whereupon the spring 37 moves the locking member 27 upwards to align a groove 51 in the locking member with the balls 48 and the spring 36 moves the draw bar 4 upwards displacing the balls 48 into the groove 51 and the balls 44 into the waist of the plunger 39, Fig. 3b. The upward movement of the draw bar urges its surface 25 against the surface 31 of the fingers 3 so that the latter are deflected outwards; also, the convexity 33a is latched in the recess 33. On lifting the grab the lip 16 engages the rim R to raise the fuel element and the spring 40 moves the probe 41 and the plunger 39 downwards so that the balls 44 are urged into the groove 46 and the draw bar 4 is locked to the grappling member 1 to prevent inadvertent release of the fuel element. In order to release the fuel element the grab is lowered to free the lip 16 from rim R and displace the probe 41 whereby the balls 44 cease to have their locking action and the gas pressure is re-applied to move the draw bar 4 down relatively to the grappling member 1.