Patent GB-1034866-A (GB)
Title: Improvements in or relating to manipulating devices for use in nuclear reactors
Inventor: DODD JOHN ALAN
IPC: G21C1/00
Filed: 1963-03-25
Abstract: 1,034,866. Reactors; fuelling reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. March 17, 1964 [March 25, 1963]. No. 11796/63. Heading G6C. A manipulating device 66 for use in a reactor, especially one not having a fixed moderator, e.g. a high temperature gas-cooled reactor using fuel assemblies of moderator and fuel, and intended for removing the fuel assemblies or other items such as control drums, flux flattening assemblies and core structural members comprises, Fig. 6, a main member 67 supported at its lower end by a pad 70 in a socket 9 in a lower diagrid 5 of the reactor, a fuel assembly engaging member 68 being connected by a crosslinkage 69 to the member 67. The member 68 may be moved laterally with respect to the member 67 by rotating a screwed shaft 71 co-operating with a nut 94 so that a fork 81 engages and supports the lower end of the fuel assembly or other item to be removed. A solenoid-operated hook 80 at the upper end of member 68 is then de-energized so that the hook engages the upper end of the fuel assembly. Reactor.-This comprises a pressure vessel 1 within a biological shield 2 surrounded by a containment 36. The fuel assemblies 8 extend between the lower diagrid 5 and an upper diagrid 10, the diagrid 5 being supported by rods 6 slidably penetrating the top surface of the shield 2. The diagrid 10 comprises an annular member 10a and a plug member 10b. The core 7 includes one hundred and nine assemblies 8 surrounded by a beryllium oxide reflector 14, steel thermal shielding 15 and graphite shielding 16. The heated coolant gas from a header 13 passes through three ducts 27 to respective steam generators 25 and returns through ports 24, from which it reaches the lower end of the core 7 by passing through annular spaces in the shielding 15. The pressure vessel 1 and steam generators 25 are thermally insulated with magnesia 31. Control is effected by rods 19, shut-down rods 21, and emergency shut-down rods 23. An ion-chamber 35 is provided in the shield 2. Access to the core 7 is obtained through a stack 3, whereby after removal of the cover 4, the manipulating device 66 may be inserted. Fuel assembly.-Each assembly 8, Figs. 3, 4 (not shown), comprises a hexagonal beryllia sleeve 39 enclosing a hollow beryllia member 41, the annular space 42 providing a path for the coolant flow and also receiving eighteen fuel rods 43. Each rod 43 comprises a series of sleeves 44 consisting of a dispersion of plutonium dioxide and thoria in a dense beryllia matrix, the sleeves being threaded on to a beryllia spine 45. At each end of the spine 45 is a beryllia sleeve 46 collectively constituting top and bottom core reflectors. The rods 43 are linked by ceramic connectors 47 arranged to define a helical flow path for the coolant gas. The member 41 has an internal stainless steel tie tube 48 which houses beryllia discs 49, or, alternatively, a rod 19, 21 or 23. A stainless steel foot 50 on the lower end of the sleeve 39 and an extension 51 of the tube 48 slidably guide a nose 52 engaged by a compression spring 11 for compensating thermal and irradiation expansion. The nose 52 engages a socket 9 in the diagrid 5 having a spherical seating 58. The other end of the spring 11 acts on the rods 43 through a thrust ring 56, pads 55 and rods 54. The upper ends of the rods 43 are retained by a ring 60. A stainless steel fitting 12 attached to the upper end of the tie tube 48 has a seating 62 engaging a socket 9 in the upper diagrid 10 and a bore 65 for receiving the hook 80 of the device 66. Fuel removal.-The cover 4 is removed and a rotatable shield door 77 (Fig. 5, not shown), is placed on the stack 3 and the diagrid 5 is lowered to disengage the upper ends of the fuel assemblies 8 from the sockets 9 in the diagrid 10; also, a shield plug 18 and the plug 10b are withdrawn. Nineteen assemblies 8 at the centre of the core are withdrawn by simple vertical movement by a conventional grab (not shown) co-operating with the groove 64 in the fittings 12. The device 66 is lowered into the space vacated by the nineteen assemblies so that the pad 70 is located in a socket 9. A shield head 76 is placed on the door 77 and actuating shafts 74, 83, 90 on the head operated by hand wheels 75, 84, 91 are connected to the device 66. Shaft 74 drives the shaft 71 to laterally move the member 68. Shaft 83 rotates the member 67 about its vertical axis. Shaft 90 drives a shaft 88 connected through gears 89 to drive two vertical jacking shafts 85 threaded at their lower ends in brackets 86 (Fig. 8, not shown), connected to the member 67, the shafts 85 carrying pivotal pads 87. The device 66 may orbit about the axis of the core since the member 67 is eccentrically mounted in the head 76, and this movement together with the movements imparted by the hand wheels 75 and 84 enable the fork 81 to be aligned with the desired assembly 8. After this alignment the hook 80 is engaged with the upper end of the assembly 8 and the hand wheel 91 is operated to drive the jacking shafts 85 and lift the assembly from its socket 9 in the diagrid 5. The member 68 is then retracted, the hook 80 is raised, and the assembly 8 is removed by the conventional grab.