Patent GB-915773-A (GB)
Title: A graphite moderated heterogeneous nuclear reactor
IPC: G21C15/10
Filed: 1959-11-20
Abstract: 915,773. Nuclear reactors. RNB CORPORATION. Nov. 20, 1959 [Nov. 26, 1958], No. 39392/59. Class 39 (4). A graphite moderated nuclear reactor has fuel passages containing fuel elements and coolant tubes separated from the fuel passages in order that the moderator may transfer heat from the fuel to the coolant. The reactor core 20, Fig. 1, is constructed of a plurality of cubeshaped graphite blocks, and each block has a coolant tube passage 24 and fuel passages 26 parallel or perpendicular to the coolant tube. The fuel element is placed in an atmosphere of carbon monoxide, helium or nitrogen and is contained in containers of graphite. Uranium carbide or thorium carbide may be contained in thorium oxide containers themselves within graphite containers. Uranium carbide may be contained in depleted uranium carbide containers. The reactor is supported on three of its faces with the common apex directed downwardly so that the blocks may slide into close packed formation. In this position the reactor may be tilted, e.g. by earthquakes, as much as 40 degrees from the vertical without dislocating the blocks. Also this method of support allows even thermal expansion of all faces of the blocks. Fuel elements 28, Fig. 3, are loaded in the magazine 59 and are automatically fed into tube 67. Valves 55 and 53 may be manipulated to discharge an element into the ready position between valves 51 and 53, and when a new element is desired in the core the valve 51 is opened. To dispose of used elements the vibrator 47 shakes an element into the discharge tube 54. The fuel is cooled by radiant heat transfer to the graphite which then radiates heat to the coolant tubes. The coolant tube shown in Fig. 8 has a shut-down rod 70 of boron steel positioned within the inner tube 62, and a gas cushioning arrangement is provided at the bottom of the tube 62 to prevent damaging the tube when it is dropped. The coolant is water which is injected by nozzles 64, 65, 66 into the helical baffle 68 which causes the water to be thrown against the side walls of the tube 58 where it is vaporized, the amount of water utilized being sufficiently small so that instant loss will not cause such a change in the multiplication factor as to cause the reactor to go into the prompt critical region. The nozzles 64 and 66 inject coolant faster as the load demand increases, and the nozzle 65 is utilized for controlling the neutron flux density. Fission products are removed by passing helium over the fuel elements which conveys the fission products to heat exchangers where condensation takes place. The helium containing the condensed fumes is further cooled and passed through a series of tubular electric precipitators where a high-voltage field is applied to fix the particles against the walls of the tubes. The gas still containing some radioactive particles is further cooled and passed through more electric precipitators, and is again cooled before passing through packed absorber towers of unglazed ceramic shapes impregnated with silver nitrate which ensure the removal of radioactive iodine. In the power generating system the feedwater is maintained under a hydrogen gas cap at 80% of the system pressure. Also steam is vaporized in the centre part of the core and superheated in the periphery. The feed water is withdrawn through outlets by pumps 114, 116 and 118 and then pumped through regulating valves to the flash evaporator tubes and a direct contact de-superheater. Each pump 114, 116 and 118 has a by-pass line 120, 122 and 124 having check valves 126, 128 and 130, respectively. These check valves and the 80% of system pressure maintained in reservoir 112 assure that in the event of a drop in steam pressure to less than 80% of its normal value, the water pressure on the inlet side of the valves will exceed the steam pressure. The valves will then open and automatic water injection to the coolant tubes and desuperheaters will take place by by-passing the pumps. This will cause a reactor shut-down by water absorption of neutrons. The reactor core is surrounded by a primary and secondary thermal shield, both of which are cooled by coolant from the main circuit passing through passages in the shields.