GB1007207A - Nuclear reactor - Google Patents

Abstract

1,007,207. Reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Sept. 22, 1964 [Oct. 11, 1963], No. 40170/63. Heading G6C. In a reactor of the type in which the fuel is contained in a cluster of tubes, also containing a heat transfer fluid, and cooled by external contact of a reactor coolant, the tubes in a central zone and in an outer surrounding zone of the cluster are each divided into two groups; the flow direction of heat transfer fluid is in opposite directions in the two groups of each zone, and a group from each zone is interconnected with a group from the other zone of opposite flow direction; a pump for circulating the heat transfer fluid has its inlet and outlet connected to the two remaining groups to form a closed circuit. The heat transfer fluid is also the moderator, and may be light or heavy water or an organic liquid, and the arrangement of the four. passes this fluid makes through the core is intended to reduce the temperature range across the cluster and so reduce the pressurization required to prevent boiling. The secondary coolant is normal water, and also functions as a moderator. The tube cluster (Fig. 1), has the fuel bearing sections located in the volume bounded by a doubled-walled pot ] 4. Each tube extends above the level defined by the pot 14 to provide adequate heat transfer surface. The secondary coolant enters at ports 25, passes downwards through the space defined by the double walls of the pot 14, upwards through the base of the inner wall, upwards through the exteriors of the tubes 32, to a steam separator. Steam leaves through an outlet 19 and water through two outlets 24, from which it is recirculated. Concentric gas bottles 62, containing helium, hydrogen, or nitrogen, arranged around a baffle 13 are used to maintain the primary coolant pressure at a level to prevent boiling, regardless of reactor performance. Primary coolant pumps 54 and motors 59 are arranged in extensions 57 of the reactor pressure vessel. Each tube 32 is preferably of zirconium with 2¢% niobium, and contains in its lower half a ring of five parallel fuel rods, about a central burnable poison rod. Tube assembly.-The tubes 32 are arranged in modules of twelve. Six U-bends at the top of the module interconnect pairs of tubes. Inlets and outlets are connected to each pair of tubes in the module at the bottom end. Tube cluster connections.-The tube cluster is divided into a central zone containing nineteen, and an outer zone containing eighteen modules. Header rings 43, 44, 45 provide respectively inlet, outlet, and transfer from inner to outer zone, connections. The flow circuit is thus: pumps 54, downcomer feed tubes 51C, inlet ring 43, up-comer 32 in inner zone, downcomer 32 in inner zone, intermediate ring 45, upcomer 32 in outer zone, downcomer 32 in outer zone, outlet ring 44, up-comer feed tubes 56a, pumps 54. Control rods (Figs. 3a, 3b).-A hollow neutron absorbing tube 67 is associated with each tube module, and is arranged concentrically inside the hexagonal ring of twelve fuel rods. The cylindrical space within the neutron absorbing tube contains a cylindrical zirconium sheathed graphite filler rod. A fixed piston 68 is mounted on top of the filler rod, and a hollow piston rod 69 contains parts to allow secondary coolant to enter the space bounded by the fixed piston 68, the neutron absorbing tube 67, and the top closure to the tube 67. The neutron absorbing tube is urged downwards by springs 70, this being resisted by the coolant pressure within the space mentioned previously.