GB944699A - Improvements in or relating to nuclear reactors - Google Patents

Abstract

944,699. Nuclear fuel elements. BABCOCK & WILCOX Ltd. Aug. 26, 1960 [Aug. 27, 1959 (2)], Nos. 29310/59 and 29311/59. Heading G6C. The fuel elements of a nuclear reactor comprise rods arranged in units contained within sleeves of graphite moderating material in relation to which they are withdrawable or insertable. As shown in Fig. 1, graphite sleeves 2 are joined end-to-end by means of beryllium coupling rings 10, each of which has external bayonet projections 14 of rectangular crosssection at the upper end and an internal annular flange 20 and external bayonet projections 22 of semi-circular cross-section at the lower end. The bayonet projections 14 co-operate with L- shaped slots 8 (Fig. 5) in the lower end of a sleeve 2 to position the ring within the end of the sleeve and a beryllium grid 28 is placed upon the annular flange 20 to support an assembly of fuel rods 30 which extend as far as a lower intermediate grid 32. Further fuel rods 30 extend between the grid 32 and an upper intermediate grid 34, and between the grid 34 and an upper grid 36. A further coupling ring 10 (shown in a raised position in Fig. 1) fits within the upper end of the sleeve 2, its bayonet projections 22 co-operating with further L-shaped slots 8 (Fig. 5) and rotation of the sleeve 2 relative to the ring 10 is prevented by means of a set screw 48. Each end surface 50 of the sleeves 2 is formed as a frustum of a wide angled cone and the ends of the sleeves 2 between the L-shaped slots 8 flare outwardly, which construction, together with suitable spacing of the bayonet projections 14, 22 at each end of the sleeves 2, permits a degree of articulation between the sleeves 2 when these are coupled together. When in position within the core of a nuclear reactor, the lower coupling ring 10 of the lowermost sleeve 2 rests upon a supporting stool while the uppermost sleeve 2 is connected by a coupling ring 10 to a neutron shield plug, the raising of which serves to lift the sleeves and their contained fuel rods. The fuel rods 30 comprise both thin-walled fuel rods 54 and structural fuel rods 56, the former consisting of thin-walled berryllium tubes 58 filled with pellets 60 of uranium oxide and closed with compressed alumina plugs 62 and axial beryllium pins 64 which engage within apertures 66 in the corresponding grids, while the latter consist of thick-walled beryllium tubes 67 similarly filled and plugged. The tubes 67 are provided at their ends with threaded beryllium pins 78, 84 and threaded bores 80, 86 which are connected together through corresponding holes in grids 32, 34, while pins 74 on the lower set of tubes 67 are screwed into threaded holes in grid 28 and screws 90 connected to the upper grid 36 are threaded into the upper set of tubes 67.