Patent GB-953650-A (GB)
Title: Improvements in and relating to nuclear reactors
IPC: G21C5/08
Filed: 1959-09-29
Abstract: 953,650. Moderator structures. NUCLEAR POWER PLANT CO. Ltd., and R. TAYLOR. Sept. 15, 1960 [Sept. 29, 1959], No. 33080/59. Heading G6C. In a moderator core structure comprising blocks of neutron moderating material, e.g. graphite or beryllium, assembled to mutually support each other within a constraining framework which restricts movement of the blocks in directions parallel to a chosen plane, at least some of the blocks have at each end mutually inclined plane surfaces through which all forces acting on the blocks affecting their transverse geometry are transmitted to adjacent blocks and thence to the constraining framework, these blocks being free to move relative to one another and to the framework in a direction perpendicular to the chosen plane so as to maintain predetermined spacing between the centre lines of adjacent blocks in directions parallel to said plane. This is achieved in one embodiment of the invention (Fig. 3) by arranging the blocks 6 in vertical columns, dynamic columns alternating with static columns, the blocks in a dynamic column having at each end mutually inclined plane surfaces which are in sliding contact with corresponding surfaces on wedge-shaped members 7 located between the blocks, these wedges 7 having vertical plane surfaces in sliding contact with vertical faces of spacing blocks 8 separating adjacent blocks in the static columns. The wedges 7 may fit into recesses in the blocks 8. Gas seals 9 are provided between adjacent blocks of the dynamic columns so as to permit axial displacement of these blocks relative to one another without leakage of coolant gas from the channels 10 occurring. The core is radially confined by restraints 3 (Fig. 5), each of which has grooves on its inner surface into which fit projections 12 on graphite members 13 which transmit the wedging forces exerted on the outermost dynamic colums (marked with a cross in Fig. 5) to the restraints 3. With the above core construction there is freedom of vertical motion between adjacent blocks of a dynamic column, and also between adjacent columns, resulting from differential irradiation growth, differential thermal expansion or other dimensional changes. The blocks 6 in adjacent columns are twisted so that the paths for neutrons between adjacent columns are discontinuous, the twisting of adjacent blocks of a column being of opposite hand. In an alternative embodiment (Fig. 11), all the columns are dynamic columns and adjacent blocks 6 of a column are separated by two wedges 7a instead of four as previously, the wedges also sliding in slots 17 cut in the blocks of adjacent columns. A third embodiment is shown in Figs. 14a and b each block 6 having four sloping faces 6b at each end and being stacked as shown in staggered relationship in successive horizontal layers. The use of sliding wedges is thus eliminated as the blocks exert wedging forces directly on one another. This embodiment is suitable for a reactor in which the nuclear fuel is totally enclosed in the moderator blocks and cooling fluid is circulated between adjacent blocks. All three embodiments described permit the lower block of each column to be keyed to the supporting base plate of the core and this prevents displacement between the holes 10 of the columns and the corresponding holes in the base plate through which the coolant enters. Differential thermal expansion is eliminated by making the restraints 3 and the base plate of the same material, thus eliminating the need for any frictionless bearings between the core and the base plate.