GB977020A - Improvements in or relating to moderator structures for nuclear reactors - Google Patents

Abstract

977,020. Moderator structures. COMMISSARIAT A L'ENERGIE ATOMIQUE. March 8, 1961 [March 11, 1960], No. 8047/63. Divided out of 977, 019. Heading G6C. A moderator structure for a nuclear reactor comprises a plurality of parallel adjacent prismatic columns 12 of moderator material, e.g. graphite, around the periphery of which a plurality of rigid pillars 9 form a supporting squirrel cage, the pillars 9 being fixed at one extremity to a seat 2 supporting the columns 12 and at the other extremity to connecting means, and being coupled to the adjacent columns 12 by keys engaging in grooves in the pillars 9 and columns 12. These keys are similar to the keys 14 which connect adjacent columns 12, the grooves being situated in both the side faces and in one pair of opposite corners of the pillars 9 and columns 12. In the embodiment described, each pillar 9 comprises a cylindrical hollow steel post 17 located within stacked graphite bars 18. The posts 17 (Fig. 4) have crowns 19 provided with centering lugs 20 engaging in radial grooves 21 of the bars 18, and are mounted on the seat 2 by means of ball and socket joints 22. At their upper extremities, the posts 17 are secured by links, such as 23a and 23b, one link joining two adjacent pillars with the next link joining one of these pillars to a further adjacent pillar, whereby the links form a chainlike connection between the pillars. The columns 12 and the bars 18 are surmounted by pieces of ballast 29, 29a of steel, for example, and those surmounting the bars 18 are provided with lugs 24 engaging in corresponding holes in the links 23a, 23b. The links 23a, 23b are formed in a steel of low coefficient of thermal expansion while the seat 2 is formed in a steel having a normal coefficient of thermal expansion thus allowing for the difference between the input and output temperatures of the coolant and maintaining the columns 12 substantially vertical in spite of this difference. The links 23a, 23b have fingers 25 projecting to engage with play in recesses 26 in the outer metallic vessel 27 of the reactor in order to limit deformations of the moderator structure arising from radial loads. According to a variation of the above embodiment,the posts 17 are replaced by prestressed tie rods while in another embodiment, each pillar 9 is formed of hollow prismatic bars of metallic material. Specification 913,818 also is referred to.