Patent GB-1211445-A (GB)
Title: Improvements in or relating to nuclear reactor fuelling systems
IPC: G21C19/16
Filed: 1968-04-04
Abstract: 1,211,445. Fuelling reactors. GULF GENERAL ATOMIC Inc. 4 April, 1968 [14 April, 1967], No. 16176/68. Heading G6C. A gas-cooled reactor, Figs. 1, 2, comprises a core 19 in a chamber 18 in a concrete pressure vessel 11, further chambers 16, 17 housing steam generators 21, 22 and coolant circulators 23, 24 being mounted in the vessel walls. The fuel assemblies 54, Figs. 4, 8, constituting the core are of square cross-section and each is suspended by a rod 77 penetrating a hole 31 extending through the roof of the vessel 11. The weight of each assembly 54 is taken by a grid 69 secured to the side walls of the chamber 18 and before an assembly may be removed from the core 19 the top end of the rod 77 must be released at a position situated above the vessel roof. This arrangement facilitates removal of the fuel assemblies whilst the vessel roof containing the holes 31 does not carry the weight of the core. A central penetration 36 beneath the core is normally closed by a plug 37 but this plug may be lowered, after reduction of the coolant pressure, into a flask 41 and a fuel handling machine 42, Figs. 9, 9a, 10, 11, 12, may be raised by a ram 43 into the penetration. Two further penetrations 32, 33 beneath the core serve, respectively, for introducing new fuel assemblies into the chamber 18 and for removing spent fuel assemblies from the chamber. The spent fuel passes through a waterfilled passage 49 into a storage pond 46. Two further penetrations in the vessel roof situated directly above the penetrations 32, 33 each house a fuel assembly handling tool 174 (Fig. 13, not shown). Each handling tool 174 includes a rod, corresponding to the rods 77, all these rods being rotatable and axially movable whereby the lower ends of the rods may be coupled to or uncoupled from the top ends of assemblies 54 by means of a bayonet connection (Fig. 14, not shown) and the assemblies may be raised or lowered within the chamber 18. This raising and lowering action is performed by a hoist (not shown) situated above the pressure vessel roof and which may be coupled to the top ends of the rods. Each tool 174 includes a squaresection casing corresponding in size to the casing of the assemblies 54, the ends of these casings abutting to provide a coolant duct whereby the assemblies are cooled whilst handling. Fuel handling machine 42.-This machine comprises an elongated housing 104 supported for rotation by bearings 105, 106 and a ring 110, the housing being rotated by a motor 118 through gearing 116, 117. The upper portion of the housing 104, which extends into the chamber 18, has an elongated opening 125 through which an arm 122, pivoted at 128, can swing to the horizontal position. This swinging action is determined by an arcuate gearing 129 secured to a side wall 126 of the arm 122 and engaged by a worm gear 131 driven by a shaft 132. A fuel assembly receiving tube 137 mounted on a hollow base 138 having rollers 141 may be moved along tracks 136 on the arm 122 by rotating threaded rods 151, 152 cooperating with nuts 148, 149, these nuts being connected by arms 146, 147 to collars 144, 143 on the tube. Thus by rotating the housing 104 and by moving the tube 137 along the arm 122, the tube may take up any desired position beneath the core 19. A frusto-conical section 173 mounted on the top of the tube 137 by a rotatable plate 167 has a square opening normally closed by spring-biased flaps 171, the section being orientated to be aligned with the orientation of the fuel assembly being handled. The section 173 is supported on the plate 167 by posts 168 and the plate has a square opening 170 aligned with the opening formed by the flaps 171 whereby coolant is caused to flow through the fuel assembly 54 within the tube 137 and cannot flow in the space between the assembly and the tube. At the lower end of the tube 137 the coolant flow path is continued by a passage 161 in the arm 122 formed by a hood 159 having a longitudinal slot 163. The end of the passage 161 adjacent the pivot 128 is continued by a conduit 157 extending through the housing 104. The slot 163 is closed, except for that portion beneath the base 138, by two leaf springs 164, 165 which wind on and off rollers 166 on the base 138 as the tube 137 moves along the tracks 136. Fuel assembly 54.-Each assembly comprises a casing 57 housing fuel pins 58 of fissile or fertile material. The upper end of each pin has a plug 59 welded to a cross member 61. Similar cross members 61 at the lower end of the casing 57 serve to locate the pins 58 but allow for axial expansion (Fig. 5, not shown). Bowing of the pins 58 is prevented by grids formed by wires 64, 66, 67 of stream-line cross-section, Fig. 6, situated at intervals along the casing. The top end of the casing 57 has webs 71 supporting a hollow plug 73 having a shoulder 72. When the assembly 54 is supported in its box-shaped compartment of the grid 69, the shoulder 72 abuts the lower end surface of a collar 76 carried by webs 74 situated at the top end of the box-shaped compartment. The rod 77 is releasably connected to the assembly 54 by a bayonet connection within the plug 73. The weight of the assembly is transferred to the grid 69 by a nut 83 threaded on the end of the rod 77, the lower surface of the nut abutting a sleeve 81, the lower surface of the sleeve abutting the top of the collar 76. The rod 77 is keyed at 87 to the sleeve 81 for sliding movement relatively thereto. A plate 88 having orifices 91 is attached to a sleeve 89 axially movable on the sleeve 81 whereby the coolant flow through the assembly 54 may be varied by operating rack and pinion gearing 93, 94. In a core arrangement described with reference to Fig. 3 (not shown), the core operates with fast neutrons and has a central fissile region surrounded by a fertile blanket. Fuelling procedure.-A new fuel assembly 54 is pushed up through the penetration 32 by means (not shown) and the tool 174 situated above the penetration is lowered to engage the fuel assembly by means of the bayonet connection. The tool 174 lifts the assembly 54 so that its lower end clears the top of the tube 137. The tube 137 is aligned with the tool 174 and the latter lowers the assembly into the tube 137 until it is supported on the base 138. The tool 174 is disconnected from the assembly and raised out of the way. The tube 137 is aligned with the appropriate part of the core 19, the nut 83 of the corresponding rod 77 is removed, and the rod is lowered and coupled to the assembly. The assembly 54 is now raised and secured in the core by replacement of the nut 83. Removal of a spent fuel assembly is similar except that it is lowered through the penetration 33 into the pond 46.