GB933982A - Improvements in or relating to solid moderator arrangements for nuclear reactors - Google Patents

Abstract

933,982. Moderator structures. COMMISSARIAT A L'ENERGIE ATOMIQUE. May 11, 1961 [May 25, 1960], No. 17246/61. Class 39 (4). A solid moderator structure, e.g. of graphite, comprising adjacent parallel vertical columns of square cross-section with vertical axial channels has two coaxial groups of columns, the columns of one group being of different crosssectional area to those of the other group, each column being formed by a number of rods separated by briquettes of the same cross-section and having channels coaxial with those of the rods, the briquettes forming horizontal layers, and connection means being provided between the columns of the groups, and between the two groups, at the level of each layer of briquettes. In the embodiment described, there is a central group 1 of 256 (16 x 16) columns surrounded by a peripheral group 2 of 60 columns, 16 columns of group 1 being equal in length to 14 columns of group 2. The number of vertical channels per unit volume is thus greater at the centre of the reactor core than at the periphery in order that the neutron flux may be more uniformly distributed. The columns in both groups are spaced from each other to allow for Wigner growth. Connection between the columns of group 1 is made in a similar way to that between the columns of group 2, as shown in Fig. 2, rods 5 forming the columns being separated by briquettes 8 to which they are connected by mortice-and-tenon joints. The briquettes 8 are provided with grooves, one in each lateral face and one in each of a pair of opposed comers, so that they may be connected to adjacent briquettes by keys of length slightly less than that of the grooves in which they fit with clearances between their lateral faces and the grooves. As shown in Fig. 1, briquette 8 is connected to briquettes 10, 11 by keys 12, to briquettes 13, 14 by keys 15, and to briquettes 16, 17 by keys 18. Clearances are provided between the ends of the keys and the bottoms of the grooves to allow for Wigner growth. The connection between the two groups is effected by 24 keys, briquette 23 being connected to briquettes 3, 24 and 25 by keys 26. 28 at each corner of group 1 and briquettes 19, 20 to briquettes 21, 22 by keys 26, 27 mid-way between each corner. In this embodiment, the rods and briquettes are of graphite but any other suitable material, e.g. beryllium or beryllia may be used. Specification 897,534 is referred to.