GB817754A - Nuclear reactor - Google Patents

Abstract

817,754. Nuclear reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Feb. 21, 1946 [Feb. 16, 1945], No. 5513/46. Class 39(4). A nuclear reactor comprises bodies of fissile material geometrically arranged in a low neutron absorbing moderator material, means for passing a fluid in heat exchange relationship with the fissile material, and means for extracting heat from the fluid. Fig 2 shows a cross-section of a graphite moderated helium cooled reactor. The lower chamber 35 serves as a gas inlet and fuel element discharge chamber ; above this in the chamber 37 is the reactor core (not shown) comprising graphite bricks secured together by dowel pins and provided with vertical fuel channels, the lattice being surrounded on all sides and at the top and bottom by less pure graphite which acts as a reflector. Guide tubes 58 fit into the tops of the fuel channels and are provided with slots to allow the coolant gas to pass to the discharge nozzles 57. Above the outlet gas chamber is a neutron and gamma ray shield comprising a layer of steel plates 64 and a layer of graphite 62 supported on a steel floor 60 ; the guide tubes extend through the shield and are normally closed by removable shield plugs of steel and graphite, similar to the neutron and gamma ray shield. The dome 39 is provided with a manhole 73 to allow access for loading fuel elements into the reactor. Each row of fuel element columns is supported on two cans 59 provided with small apertures through which the helium coolant can pass and with large apertures through which the fuel elements can pass ; thus if the cans are moved to place their large apertures underneath the fuel channels, the row of fuel elements is discharged into the chamber 35 from which the fuel elements may be removed through a gate valve 89. The reactor is surrounded by a concrete shield 96, and the space between the reactor and the shield is filled with water. Figs. 10 and 11 show a cross-section and plan of fuel elements in a fuel channel in the moderator bricks 41. The uranium plates 49 are spaced apart by lugs 50 and rest on a ledge 48 in a cylindrical graphite cartridge 40. The cartridge is provided with a throat 46 to restrict the flow of coolant gas, and the areas of these constrictions are varied at different parts of the lattice to secure the most efficient heat removal from the system. The thickness of the uranium plates 49 is also varied; those which are used in the centre of the lattice are thinner, to provide a greater cooling surface, than those near the outside. The reactor includes five safety rods and four control rods, of which one is shown in Fig. 23 ; this comprises two concentric tubes arranged so that cooling water can circulate through them. The positions of the control rods may be controlled automatically to maintain a constant neutron flux. The helium leaving the reactor may pass through a heat exchanger to a filter which removes any solid fission products entrained by the helium, and thence through a compressor back to the reactor. Specifications 817,751 and 817,752 are referred to.