Patent GB-872091-A (GB)
Title: Improvements in or relating to gas cooled nuclear reactors
Inventor: HACKNEY STANLEY
IPC: G21C5/06
Filed: 1958-09-01
Abstract: 872,091. Nuclear reactors; handling nuclear fuel elements. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Aug. 6, 1959 [Sept. 1, 1958], No. 28070/58. Class 39(4). A reactor for marine use in which a fuel element charge/discharge machine is only available for positioning at the charge face 19 when the ship is in port has means enabling a fuel element (in particular a damaged element) to be withdrawn from the core at any time during which the reactor is in operation, the withdrawn fuel element being retained within the pressure vessel. As shown, a gas-cooled graphite-moderated reactor has a pressure vessel 1 having a cylindrical side wall 2, a base 3 and spaced upper ends 4, 5. The core 6 has vertical channels 7 receiving trains of interconnected fuel elements 8 and is surrounded by a reflector 9 having upper and lower neutron shields 10, 11. An annular passage surrounding a thermal shield 12 is connected to an annular duct 16 receiving coolant from a heat exchanger, the coolant being caused to flow as indicated by the arrows past the fuel elements into a header 13 connected by a duct 14 to the heat exchanger. The upper fuel element of each train is connected to a shielding plug 18 extending through an aligned channel 17 in the shield 10 and through an access tube 20 extending between the shield 10 and charge face 19, the plug being provided with a tortuous path for the coolant flow. The upper end of each tube 20 is normally closed by a cap 22 and a sealing plunger 31 is connected by a lip 30 with a lip 29 at the upper end of the plug 18 is normally maintained in the position shown by the coolant pressure and by the pressure of spring 44 so that a locking piece 35 on a locking member 33 is held in a notch 36 at the upper end of the tube 20. If it is desired to withdraw a fuel element train due to the presence of a damaged fuel element, the cap 22 is replaced by an extended cap 23, Fig. 2, which is secured to the tube 20 by a screwed sleeve 43 and a shackle 25 on a piston 24 within the cap 23 is connected by remote operation to a shackle 38 on the member 33 by means of a shackle pin 39. Ports 41, 42 permit the supply of coolant at controlled pressures through valves (Fig. 8, not shown). Initially, coolant at reactor pressure is applied to both ports 41, 42 whereby a locking plunger 28 is raised against its spring pressure. The pressure at port 41 is then increased whereby the gas pressure acting through passage 40 causes the plunger 31 to move downwards (Fig. 5, not shown) and shoulder 37 releases the locking piece 35 whereupon the gas pressure is able to raise the piston 24. The pressure at port 41 is progressively reduced to reactor pressure and that at port 42 to atmospheric pressure such that when the piston 24 has arrived at the top of the cap 23 and the fuel element train 8 lifted out of the core the plunger 28 is moved downwards by its spring to lock a locking piece 26 on the piston against a notch 27 in the cap, Fig. 7. The coolant continues to flow over the raised fuel element chain and to remove radio-active particles in the coolant due to the damaged element the port 41 is connected to a filter (Fig. 8, not shown).