GB1264473A - - Google Patents

Abstract

1,264,473. Reactors. BRITISH NUCLEAR DESIGN & CONSTRUCTION Ltd. 21 Feb., 1969 [22 Feb., 1968], No. 8688/68. Heading G6C. In a guide tube arrangement for a re-entrant type gas-cooled nuclear reactor, the guide tube 4 extends between a pressure vessel standpipe 1 and a corresponding fuel or control rod channel 6, and passes through an aperture 11 in a pressure membrane 8 and through a tube 13 which is shorter than the guide tube 4, one end of the tube 13 being attached and sealed to the membrane 8 and the other end being attached and sealed to the guide tube 4 at a point intermediate along its length. Relative movement between the membrane 8 and the standpipe 1 is accommodated in the plane of the membrane 8 by the flexibility of the guide tube 4 and the tube 13, and in a perpendicular direction by relative axial movement permitted the ends of the guide tube 4. The guide tube 4 is in two parts 4A, 4B, the upper part 4A being provided with an enlarged head portion 16 which is a sliding fit within an enlarged bore portion 3 of the standpipe 1, and with a flange 17 at its lower end, while the lower part 4B is provided with a flange 18 at its upper end and with circumferentially spaced ribs 19 at its lower end which are a sliding fit in an enlarged bore portion 5 of the channel 6. The end wall 14 of the tube 13 and the flanges 17, 18 of the guide tube parts 4A, 4B are rigidly connected and sealed together. The diameters of the channel 6, the guide tube 4 and the smaller diameter portion of the standpipe 1 are substantially the same and are just sufficient to accommodate fuel element strings (not shown), so as to reduce the possibility of the strings rattling whilst being transferred from a suitable charge/servicing machine into the reactor core 7. During operation of the reactor, cool gas flows down through the annular passage defined between the fuel channel 6 and the fuel sleeve assembly 20 and is joined at the bottom of the reactor core 7 by further coolant fed to below the core. The coolant is returned through the fuel sleeve bore 21, and thence to the hot-box 9 by way of the guide tube 4 and ports 4C.