GB1384701A - Nuclear reactors - Google Patents

Abstract

1384701 Moderator structures BRITISH NUCLEAR DESIGN & CONSTRUCTION Ltd 28 Jan 1972 [25 Feb 1971] 5494/71 Heading G6C The horizontal movement of a rigid nuclear reactor core composed of vertically-disposed columns supported from below is restrained by a system including a plurality of essentially cylindrical rollers disposed over the periphery of the core and located against movement in the peripheral direction of the core, the rotational axis of each roller extending horizontally in the peripheral direction and being urged downwardly against a respective upwardly-facing surface associated with peripherally disposed ones of the columns, whereby each roller can accommodate movement of the upwardly-facing surface in the radial direction of the core and upwardly by rolling and by bodily upward movement of the roller, but by frictional contact with said surface resists movement of the surface in the peripheral direction of the core. The core comprises an assembly of parallel hexagonal graphite columns 10 and is enclosed within a concrete pressure vessel 12. The inner surface of the vessel 12 is provided with a steel liner 14 protected by a layer of thermal insulation 16. Adjacent columns 10 are in contact via projecting surfaces 18, 36 at their upper and lower ends respectively. To restrain horizontal movement of the top of the core as a whole, rollers 20 are disposed around the core periphery adjacent the level of the projecting surfaces 18, the rollers in cross-section having two redundant segments 21 removed (cf. Fig. 3). Each roller 20 rests on a bedplate 22 supported on the outermost of the columns 10 and is urged downwardly by a hinged frame 24 carrying weights 26. When, in operation of the reactor, thermal expansion of the core occurs rotation of the rollers enables horizontal expansion of the core at the level of the projecting surfaces 18 to be accommodated, whilst preventing movement of the core as a whole. Each roller 20 has a horizontal component of force transmitted to the columns 10 via the projecting surfaces 18 and serves to assist in holding the core together. The outermost columns 10 are divided into sections pivotally connected at points 30, 32, 34 and the downward component applied to these columns thus creates a horizontal force which is transferred to adjacent ones of the columns 10 via the projecting surfaces 36. The weights 26 are constructed to act as a neutron shield to reduce upward streaming of neutrons between the pressure vessel wall and the core periphery, the gap between the weights and the wall being covered by a shelf 38 supported by the pressure vessel.