GB969471A - Improvements in core structures of nuclear reactors - Google Patents

Abstract

969,471. Moderator strictures. HEAD WRIGHTSON & CO. Ltd. Jan. 2, 1961 [Oct. 16, 1959], No.35159/59. Heading G6C. A nuclear reactor core structure comprising a moderator part and a reflector, each composed of bricks of moderator material,e.g. graphite, arranged end to end in vertical volumns with vertical holes extending through the. centres of those bricks in the moderator part so as to form vertical channels for fuel elements or control rods, the whole being held together by external circum ferential tension bands spaced so as to overlap the horizontal joints: between the reflector bricks, is characterised in that alternate or. certain of the moderator-columns are so. constructed that they or at least, some of their component bricks are capable of vertical displacement relatively, to mutually adjacent columns and that support elements are provided between such vertically displaceable bricks and the adjacent vertically located bricks of one or more adjacent columns, such support elements being so shaped and disposed as to bear against complementary surfaces of the mutually adjacent bricks and on the occurrence (or increase) of lateral separation between the mutually adjacent bricks to exert opposed lateral forces thereon tending to stabilize the columns laterally ,thereby to compensate the unstabilizing effects tending to vary lattice pitch(of vertical channels in the columns enclosing fuel ele ments or control rods), of Wigner. shrinkage, and to compensate for thermal expansion. In one embodiment (Fig 1) the support elements com prise pegs 3 with rounded ends which fit into recesses 2, 6 formed in the bricks 1,8 of "compensating" columns (i.e. those comprising bricks capable of mutual vertical displacement) and "static" or "rigid" columns (i.e.those in which the bricks are not capable of mutual vertical displacement) respectively. Any shrinkage of the bricks or increase in their lattice pitch results in an increase in the tilt of the pegs 3 and a corresponding vertical displacement of the bricks 1 of the "compensating" columns, lateral stability being maintained by the couples tending to move the lower end of each peg 3 outwards and provided by the vertical components of the weights of the bricks 1. In an alternative embodiment (Fig. 2(b)), the support means comprise keys 15 of square crosssection housed in recesses 6,formed in the end faces of the bricks. The bricks 7 of the "compensating" columns 11 are slightly shorter than the bricks 8 of the "rigid" columns 10, clearances thus being provided in the columns 11. One pair of opposite corners 17 of the recesses 6 are chamfered while clearances are provided at the other corners, thus enabling the keys 15 to tilt when an increase in the lattice pitch and/or a shrinkage of the bricks 7, 8 occurs and so providing the required stabilising force. In a further embodiment (Fig. 5), the keys 22 are of square or rectangular cross-section with chamfered corners 26, 26<SP>1</SP> and are housed in recesses provided in the blocks 23 of the "compensating" columns, their outer surfaces abutting the faces of the bricks in the "rigid" columns which are not provided with recesses. The arrow in Fig. 5 indicates the direction in which the keys 22 tilt.