Patent GB-989167-A (GB)
Title: Improvements in nuclear reactors
Inventor: WORDSWORTH ALFRED DERRICK
IPC: G21C17/112
Filed: 1960-08-19
Abstract: 989,167. Reactors. BABCOCK & WILCOX Ltd. Aug. 18, 1961 [Aug. 19,1960], No. 28885/60. Heading G6C. In a nuclear reactor, thermocouples and their associated leads are mounted on the fuel elements. During refuelling the thermocouple leads are severed and withdrawn prior to the removal of the fuel elements. The fresh fuel elements carry new thermocouples and leads. Under normal running conditions (as on Fig. 4D) the main standpipe 10 contains the control drive unit 14 and plug 13, and the auxiliary standpipe 11 contains the shield plug 61 and a magazine 16 sealed within the socket 29. The cable 35,which contains thermo-couple leads, extends from the magazine to the fuel elements 18. Also leads extend upwards from the magazine through the standpipe 11 to temperature monitoring instruments. When the reactor 13 being refuelled the magazine 16 is placed on top of the string of elements 18, and the magazine consists of (Fig. 3) a graphite sleeve 22, fuel pins 23 which are cooled by a flow of gas through the sleeve 22, and an inwardly turned lifting flange 26. A spigot 27 provides a pedestal on which the lower end of the magazine, comprising a casing 28, is a sliding fit. The thermocouple leads 19 extend through to grid 24 and plate 31 to the frusto-conical members 33 which gather them together to form a cable 35. Alongside the rupture link 32 each lead is provided with a loop 34 made weaker to tensile stresses than the remaining portions of the lead. The cable 35 is of sufficient length to extend when the string of fuel elements is on the fuel element channel from the spigot 27 to a magazine socket 29. The upper end of the bottom casing 28 is closed by a pressure seal disc 36 through which pass the leads 19. Above pivot 45 a lever arm 43 is formed with a sloping camming surface 46 which terminates at its upper end in a catch 48. The surface 46 engages a flange 51 formed at the lower end of an actuating sleeve 52 slidably mounted in the casing 38. The actuating sleeve 52 surrounds a cable holder 55 which is locked to the magazine by the catch 48 until counter-clockwise rotation of the lever arm 43 causes the catch 48 to disengage from the rim 54. The knob 56 may be gripped by a grab so that the magazine may be drawn upwardly by the holder 55 from the spigot 27. A sufficient length of cable 57 is coiled within the holder 55 to connect the socket 29 to temperature monitoring instruments. To replace the fuel elements the refuelling machine 230 draws the shield plug 61 into the storage compartment of the machine (Fig. 4E), and in so doing causes the rupture link 32 to break and also the loops 34 to break in turn, thus enabling the frusto-conical members 33 to be drawn up into the refuelling machine. A new shield plug and an empty magazine socket 29 is inserted on the standpipe 11. The refuelling machine is then connected to the standpipe 10 (as on Fig. 4A), the plug 13, drive unit 14 and control rod 15 withdrawn, and a fuel element charge shoot 71 lowered into the standpipe. A grab engages the lifting flange 26 and the fuel element string is withdrawn. A fresh string topped by a magazine 16 is lowered into the channel 3,and the control rod 15, plug 13 and drive unit 14 replaced. The machine 230 (Fig. 4B) then lowers a grab 9 through the standpipe 11 to grip the knob 56, the grab 9 is raised and the bottom casing 28 (Fig. 3) slides off the spigot 27 and is drawn upwardly to the socket 29 (as on Fig. 4C). When the upper end 53 of the actuating sleeve 52 abuts the annular shoulder at the top of the socket 29, further movement of the grab 9 slides the sleeve 52 downwards so rotating the lever 43 counter-clockwise causing the bolts 42 to engage on the annular groove 30 on the socket 29 and locking the magazine firmly. Further counterclockwise rotation of the arm 43 causes the catch 48 to release the rim 54 so that the holder is free to be drawn upwards by the grab 9, and the cable 57 to be uncoiled. In another arrangement (Fig. 5) (not shown) the magazine is formed in part by a reflector plug to minimize neutron streaming. The hollow reflector plug 81 comprises a lower axial bore forming a cable storage chamber 83, a displaceable member 96 connected to the upper end of the cable 87 and adapted to be raised by grabbing means to the standpipe 11, coolant passages 82 provided between the plug and side wall of the channel 3, a sleeve open at its upper end to provide entry to the member 96 for the grabbing means, an intermediate larger bore for accomodating the sleeve while the fuel element is being fed into the reactor,and an upper outwardly flared opening 84 to guide the grabbing means. In Fig. 7 (not shown) the member 96 drawn into the socket 29 in the shield plug 101 by grabbing means 97. The plug 101 has three spring-loaded latches 126 which prevent the members from dropping. At the top of the socket is an electric plug 127 having pin inserts 128 which slide into the socket inserts 125. The pin inserts are connected to electric leads 133 which pass through conduits 132. The member 96 is rotated on entering the plug socket in order to align the pin and socket inserts. The grabbing means 97 has adjacent its lower end retractable outwardlybiased lifting arms movable to retracted positions by the release mechanism against a spring bias. The lifting arms comprise the longer arms 153 of bell-crank levers 151 having shorter arms 148 pressed by a spring 147 against a push-rod 159 which is axially movable against the spring to retract the lifting arms by an actuator forming part of the release mechanism at the other end of the rod. The actuator comprises a hinged plate 162 having one arm acting on the push-rod, and a curved edge 165 which projects through the wall of the grabbing means for engagement with an annular bearing surface on the shield plug. To enable the member 96 to be lifted to the socket 29, the grab 97 is lowered through the flared end 84 (Fig. 5) to the sleeve 105. The triangular outwardly projecting portions of the arms 153 engage the annular flange 121 and are pressed into their retracted positions in the grab. When the arms 153 descend below the level of flange 121 the spring 147 forces the arms apart. If the spring 147 is ineffective in forcing them apart further lowering of the grab causes the prod 111 to enter the throat 144 and force the piston 146 upwards to force the arms apart. The grab 97 is then raised so that the upper edges of the arms 153 catch beneath the flange 121 and lift the member 96. Specification 936,454 is referred to.