GB849277A - Improvements in nuclear reactors - Google Patents

Abstract

849,277. Nuclear reactors; handling materials in radioactive environment. BABCOCK & WILCOX Ltd. Jan. 30, 1958 [Jan. 31, 1957], No. 3481/57. Class 39(4). A pressurised water reactor in which fuel elements and control rods may be removed and inserted without reducing the pressure in the pressure vessel comprises, Fig. 1, a vessel 1 surrounded by a biological shield 17, the water entering at 7 and leaving at 11 and passing through a heat exchanger. The reactor core 21 is mounted on a turntable 31 and comprises a number of fuel element rods 23 of rectangular cross-section, the rods forming a group roughly circular in plan, this group being divided into four sectors by a cruciform-shaped gap, Fig. 2 (not shown), each of the four arms of the gap receiving a group of control plates, one such group 27A being shown in the raised position. Each fuel element 23 is formed of a number of longitudinal plates arranged parallel to one another with a slight space therebetween so that the water is heated by flowing through these spaces. The water space around the core forms a neutron reflector. The turntable 31 has teeth 45 engaged by a worm driven by a motor exterior to the vessel 1, Fig. 3 (not shown) whereby it may be rotated upon a carriage 33, this carriage being mounted on rollers 39 for rectilinear movement upon a support 41. The carriage movement is performed by a motor 61 and thus by energisation of this motor together with the motor driving the turntable any selected one of the fuel elements may be stationed beneath a charge/discharge aperture 71. The aperture 71 is connected with an auxiliary pressure chamber 79 through a valve 77, the chamber being water-filled, and when a fuel element is to be transferred between the vessel 1 and the chamber the pressure in the latter is made equal to that in the vessel prior to the opening of the valve. A guide tube 89 for the fuel element extends through the aperture 71 and to remove a fuel element 23 an electromagnetic grab 97 on a cable 95 is lowered from a pipe 83 through a guide tube 101 and the tube 89 to engage the element, the grab then being returned to the chamber and the valve 77 closed. The pressure in the chamber 79 is reduced and the tube 101 tilted to position 101C whereby the fuel element may be lowered by the grab through an aperture 125 and a valve 129, which is now opened, into a chamber 133 of a magazine 131. The magazine is rotatable in a water-filled chamber 132 by a motor 139 and is moved so that the chamber 133 occupies position 133B beneath a water-filled pipe 135. A grab (not shown) similar to grab 97 is now lowered down the pipe 135 to remove the spent fuel element for disposal. The tube 101 is tilted to position 101B and the grab 97 lowered through aperture 105 and the opened valve 109 to retrieve a new fuel element from a chamber 113 in a magazine 111 similar to the magazine 131, the magazine 111 being loaded by a grab in the water-filled pipe 115. The grab 97 is withdrawn into the chamber 79, the chamber is re-pressurised, the valves 109, 129 being closed, the valve 77 is opened and the new fuel element is lowered to take the place of the element previously removed. This process may be repeated for all the elements by further movements of the turntable 31. The control plates 27A may be made smaller than as shown so that they may be similarly removed by the grab 97. Prior to the removal of the fuel elements the reactor is made non-critical by lowering the control plates by rams 141 attached thereto by electromagnetic grabs 143, each group of plates having, its own ram moved by a ram cylinder 147. The rams may be attached to the plates when the turntable is in its normal position and are detached there-from before the turntable is moved to the various fuel element handling positions. In another embodiment, Figs. 4, 5, the turntable 231 supporting the core 221 is itself supported on a lower turntable 233 having an eccentric axis 238. The turntables 231, 233 are respectively driven by motors 247, 261 through gears 253, 264 whereby any selected fuel element 223 may be positioned beneath a charge/discharge aperture 271 in the pressure vessel 201. An auxiliary water-filled pressure chamber 279 is connected to the aperture 271 through a valve 277 and contains a magazine 301 having a fuel element chamber 309, the magazine being rotatable by a motor 307 so that the chamber 309 may be in line with the valve 277 or with a valve 313 connecting the chamber 279 with a horizontal water-filled conduit 314 in the biological shield 217. Hydraulically-operated rams 288, 338 operated by pistons in cylinders 283, 333 may be lowered, respectively, through the valves 277, 313 and have at their lower ends the male part of a bayonet coupling for engagement with the female part of the coupling provided at the upper end of each fuel element 223, the engagement being effected by rotation of the rams by electric motors, Fig. 6 (not shown), provided at the ram upper ends . To remove a fuel element the chamber 279 is pressurised, the valve 277 is opened and the ram 288 lowered and rotated to engage the fuel element previously stationed therebeneath. The ram 288 is raised to bring the fuel element into the magazine chamber 309 where it is retained by movement of a shutter 310, whereupon the ram is rotated to unlock the bayonet coupling. Valve 277 is closed, the pressure in chamber 279 is reduced and valve 313 is opened so that upon rotation of the chamber 309 to position 309B the ram 338 may be lowered and rotated to engage the fuel element and after retraction of the shutter 310 the fuel element may be lowered into one of four compartments provided in a carriage 319 movable along the conduit 314. This operation is performed four times to fill the carriage 319 which is then traversed to a position above a pipe 323 where shutters provided at the lower ends of the carriage compartments are opened and the fuel elements are lowered into a magazine 321 by a ram (similar to rams 288, 338). Four new fuel elements are loaded into the carriage by this ram through a water tower 317 and the elements are fed one-by-one into the core by the rams 288, 338 by a process similar to the unloading operation. Interlocks ensure correct operating sequence and indicators show the position of the magazines and rams. Specification 849,278 is referred to.