GB965209A - Improvements in and relating to core structures for nuclear reactors - Google Patents

Abstract

965,209. Moderator structures. NUCLEAR POWER PLANT CO. Ltd., L. PAGGI. and J. OLIVER. Oct 13, 1960 [Nov. 12, 1959], No.38455/59. Heading G6C. A moderator core structure comprises an assembly of blocks of solid material, e.g. graphite, with keys 4 located in keyways 5 formed in the sides of the blocks and so disposed that the keys between any one block and the adjacent blocks lie in at least three different planes containing the central axes of the blocks. In the embodiment described, the blocks are of two different sizes,the smaller blocks 2 being of square cross-section and the larger blocks 1 of octagonal cross-section. The blocks are formed with keyways 5 in each side and are stacked in adjacent columns with keys 4 located in the keyways as shown in the plan view of Fig. 3. The keys 4 thus lie in four perpendicular planes spaced 45 degrees apart and containing the central axes of the blocks. The length of the keys 4 is substantially less than that of the blocks. The bottom layer of blocks is formed of alternate long and short blocks thus providing axial overlapping of adjacent blocks through a layer of the core. Leakage of cooling fluid from the fuel channels 3 of each block is prevented by the provision of spigots or sleeves extending from one block into the next in each column. The above-described structure is such that should shrinkage of the blocks occur due to Wigner changes, the spacing and alignment of the fuel channels 3 will not be affected. If necessary, the columns of blocks may initially have a small space separating them to allow for irradiation growth. Omission of a limited number of keys 4 is permissible and this permits the insertion of interstitial channels 6 (Fig. 3,) by suitably shaping the opposed sides of adjacent pairs of larger blocks 1. In an alternative embodiment, one or more keys in any one block form an integral part of the block. The sides of the core are surrounded and constrained by a metallic structure, the thermal expansion properties of which conform closely to those of the block material, each individual column of blocks being movably supported at its base on a steel plate by means of ball races interposed between the steel plate and a base support plate for the core. Where, however, the metallic structure containing the core has thermal expansion properties which conform closely to those of the base support plate, the individual columns can be fixed directly to the base support plate and the ball races dispensed with.