GB1097745A - Improvements in or relating to nuclear reactors - Google Patents

Abstract

1,097,745. Reactors. GENERAL DYNAMICS CORPORATION. June 2, 1965 [June 15, 1964], No. 23491/65. Heading G6C. A fast fission reactor is gas cooled and has housed within its prestressed concrete pressure vessel coolant circulators, steam generators, and conduits for passing gas from the core to the steam generators. The pressure vessel is cylindrical, and the circumferential and axial prestressing bands are connected to jacks which continuously measure and adjust the strain in each band; thus, should an explosion occur in the vessel, the concrete will crack and open to vent the pressure, after which the band strains will be automatically adjusted to close the cracks before radioactive material escapes to a dangerous extent. General construction (Fig. 1)-The pressure vessel comprises an inner part containing axial prestressing members 42, and an outer part containing the radial prestressing members 40. The inner part contains cooling tubes 66 adjacent to a steel lining 62 covered by thermal insulation 64. A concrete shield 46 with access plug 74 divides the vessel interior into two compartments. The lower compartment contains the core 50 and associated all-surrounding breeder blanket, and fuel handling machinery 127, 128. The upper compartment contains blowers 56, driven by steam from their associated boilers, steam generating heat exchangers 106, 108, 110, control rod drives 82, and an emergency water coolant tank 121, this tank is connected to the gas coolant conduits leading to the core by conduits 125 containing diaphragms 126 which are ruptured when a predetermined pressure different arises between gas conduits 58 and space 37 through which the gas passes from the heat exchangers to the circulators (tank 121 is vented at 124). To ensure that a reduction in reactivity takes place when the core is flooded with water, the core includes a small amount of a resonance neutron absorber such as gadolinium, indium, samarium, gold, or mixtures of these materials. Wherever possible, e.g. thermal shielding 86, porous concrete is utilized within the pressure vessel, in order to assist in explosion and pressure surge damping; expansion tanks can also be associated with the pressure vessel interior. The boron control rods incorporate iron or stainless steel follow-up sections. The coolant is preferably helium, but could alternatively be carbon dioxide or nitrogen. The Fuel handling system comprises a machine 127, a catch pot 128, a fuel supply tube 129 leading to a top face gas lock 130, spent fuel shoot and storage corral 131, 134, and fuel handling machine room 138 in which the machine is normally stored. The catch pot includes a mechanism for lowered used fuel assemblies into itself from the core, and is also able to receive new fuel assemblies from the tube 129. Refuelling can be conducted either with reactor top dome 145 removed and main sealing plug 44 in position with air being circulated instead of the normal coolant, or with the core water flooded and plugs 44 and 74 removed. The fuel comprises Pu 230 and Pu 240 and the fertile material U.238, the fuel being present as an oxide; alternatively, thorium can be used as the fertile material. The fuel can alterntively be used in carbide, phosphide or silicide form. The fuel elements, which are made up into fuel assemblies, comprise elongate cylindrical cans with central fuel portions and end blanket portions. The fuel is in the form of cylindrical pellets which are axially based to facilitate the migration of fission product gases to gas reservoirs in the tops of the fuel elements. Fine texture roughing is carried out on the can exteriors to improve heat transfer. Fuel assemblies and support.-Referring also to Fig. 7 (Figs. 4 to 6, not shown, are relevent), the fuel elements are assembled by being supported on a grid structure 190 at their lower ends and located at their upper ends by a similar grid 176. Intermediate straps (200) are also used. The grids are attached to a square section tube (26) in the upper end of which is mounted a plate 172 and a clamping unit 162, 164, 166. The core top from which the fuel assemblies are hung comprises a plurality of deep webs 94 forming a number of square section pockets into each of which a substantial portion of the length of fuel assembly is pulled. Diagonal webs 152 carry bosses into which the fuel assembly clamping units are drawn.