GB936870A - High flux beam nuclear reactor - Google Patents

Abstract

936,870. Nuclear reactors. UNITED STATES ATOMIC ENERGY COMMISSION. June 8, 1962, No. 22265/62. Class 39 (4). A heavy water moderated nuclear reactor for producing high flux thermal neutron beams comprises a vessel for containing the water, a removable portion containing highly enriched uranium fuel elements within the vessel and submerged in the water, inlet means above the removable portion and outlet means below the top of the removable portion for supplying and withdrawing the water, and means within and attached to the vessel for supporting the removable portion and for separating incoming and outgoing water, the reactor core being under-moderated but surrounded by a reflector so that the maximum thermal neutron flux is in the reflector. In Fig. 1 the reactor comprises a generally spherical vessel 12 closed at the top by a fuel handling cover 28 and supplied with heavy water flowing from an inlet 32 to an outlet 34. The removable portion is supported on a shoulder 36 and comprises an upper shroud 40 of cylindrical form and a lower shroud 44 which extends down to a grid plate 46 supported from the bottom of the vessel. As shown in Fig. 2 the lower shroud 44 comprises thirty rectangular cells of which twenty-eight contain fuel elements (not shown) and two contain irradiation tubes 84, 86. The core is under-moderated so that the maximum thermal neutron flux is in the surrounding reflector. Tubes 102, 104, 106, 108, 110 allow beams of thermal neutrons to be taken from the reactor and are arranged generally tangential to the core, to reduce fast neutron and gamma background, with their ends substantially in the region of maximum thermal flux. Tubes 112, 114 and 116 terminate closer to the core to obtain fluxes in the high energy levels. A cold beam tube 118 of extra large diameter permits a refrigerated moderator to be placed in the reflector region for the production of a low-energy neutron beam. An irradiation tube 88 may also be provided in the reflector region. Safety control rods 54 of L-shaped cross-section are slidable along the outside of the lower shroud 44 while auxiliary control rods 64 extend up through slots provided in grid plate 46. Rods 54 are used to shut down the reactor, and in normal operation rods 54 and 64 are operated together so that their ends are equidistant from the mid-plane of the reactor core. Fig. 8 shows a fuel element comprising a pair of extended flat plates 354, 356 with supporting eyes 358, 362 in the top. A plurality of spaced flat fuel aluminium clad plates 364 formed of an alloy of uranium and aluminium extend between slots in plates 354, 356. Below the plates 364 the side plates are provided with openings and are joined together by structural members 366, 368.