GB1146152A - Improvements in moderator core structures for nuclear reactors - Google Patents

Abstract

1,146,152. Moderator structures. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. 21 July, 1966 [28 July, 1965; 21 March, 1966], Nos. 32380/65 and 12419/66. Heading G6C. A nuclear reactor core structure comprises an assembly of prismatic blocks of neutron moderating material, e.g. graphite, arranged end to end in columns, having fuel element channels passing through the structure and keying members fitted in keyways orientated so as to be radial relative to the axes of the blocks to key the blocks together, the outer blocks being secured to a rigid restraint structure surrounding the core structure by pivoted links permitting, on the one hand, movement of the links and outer blocks in a direction parallel to the longitudinal axes of the columns and causing, on the other hand, the outer blocks to follow the expansion and contraction of the restraint structure by tensile and compressive stresses respectively in the links. In one embodiment, each of the pivoted links 31 is in two parts 32, 33 coupled by a shackle 34. Coupling bars 35 are fitted in longitudinal holes 36 in the outer reflector blocks 2 which have cut-away portions 37 to allow for connection of the links 31 with the bars 35. The ends of the parts 32 are pivotally connected with the bars 35 by horizontal pivot pins 38. The ends of the parts 33 are pivoted on brackets 39 welded to the surrounding restraint cylinder 30. Blocks 40 are pivoted on vertical pivot pins 41 mounted in the brackets 39 and the ends of the parts 33 are pivoted on the blocks 40 by horizontal pivot pins 43. The links 31 are adjustable in length by means of the shackles 34 and this, together with the fact that the links 31 are pivoted about the vertical pins 41, allows some latitude in placing of the reflector blocks 2 during the building up of the core structure. In another form, suitable for use in earthquake zones, the pivoted links are made in flat plate form and are secured against movement in the planes of the plates. A circumferential channel 24 is formed around the lower end of each of the core blocks 4 in the bottom layer and these channels 24 are connected with the bores 5 of the blocks by radial ports 25. The channels 24, in combination, form a common gas voidage space 26 extending across the lower end of the inner core region 3 of the structure. Tubes 27 forming part of a structure for support of fuel elements in each channel 8 extend downwards from the apertures in the bottom support plate 6 and have coolant gas inlet ports 29. The gaseous coolant is passed through the core structure in two fractions, the first being passed directly into the bottom end of the fuel element channels 8 through the ports 29 and the second being passed down moderator coolant channels 9 defined between the columns of core blocks 4. The second fraction enters the common gas voidage space and then passes through the radial ports 25 to join the first fraction.