Patent Number: 042253896
Section: claims

1. A nuclear reactor construction comprising a wall and thermal insulation cladding a surface of said wall, the thermal insulation comprising a plurality of spaced layers of material lying substantially parallel to the wall surface,  each layer of material comprising a plurality of rectilinear panels secured to the wall surface in spaced array in vertical and horizontal rows, and  closure members for the spaces between the panels, said closure members being cruciform in shape, the edges of adjacent panels being received in elongate channels formed by the longitudinal edges of the arms of the cruciform-shaped closure members whereby peripheral face regions of both sides of each panel in an array are overlapped by the sides of the channels, the cruciform members and panels being stacked and arranged so that successive superposed arms of a stack of cruciform members overlap peripheral regions of both faces of successive panels in an adjacent stack, the panels being spaced from the walls and bases of the channels thereby to create labyrinth barriers to fluid flow through the spaced layers. 2. A nuclear reactor construction according to claim 1 wherein each closure member comprises a pair of superposed cruciform sealing strips and a cruciform spacer disposed intermediate the sealing strips, the sealing strips of each closure member being disposed such that they form the sides of the channels to overlap the peripheral face regions of both sides of complementary panels, and each arm of the cruciform member co-operating with an arm of a neighbouring cruciform member to extend along and overlap adjacent sides of adjacent panels. 3. A nuclear reactor construction according to claim 1 wherein the vertical rows of panels in one layer are displaced relative to the vertical rows of panels in an adjacent layer, the displacement being one half of the pitch of the rows in both horizontal and vertical directions. 4. A nuclear reactor construction according to claim 3 wherein the thermal insulation comprises stainless steel. 5. A nuclear reactor construction according to claim 4 wherein the panels each comprise two opposed membranes sealed together along their edges to define a sachet, and an inert gas enclosed within the sachet. 6. A nuclear reactor construction according to claim 4 wherein the nuclear reactor is of the liquid metal cooled fast breeder kind comprising a fast breeder fuel assembly submerged in a pool of liquid metal coolant within a primary vessel, a barrier surrounding the fuel assembly thereby defining inner and outer regions of the pool and a coolant pump in the outer region for circulating coolant through the sub-assembly and through a heat exchanger disposed in the inner region and wherein the inner wall surface of the barrier is clad with said thermal insulation. 7. A nuclear reactor construction according to claim 5 wherein the nuclear reactor is of the liquid metal cooled fast breeder kind comprising a fast breeder fuel assembly submerged in a pool of liquid metal coolant within a primary vessel, a barrier surrounding the fuel assembly thereby defining inner and outer regions of the pool and a coolant pump in the outer region for circulating coolant through the sub-assembly and through a heat exchanger disposed in the inner region and wherein the inner wall surface of the barrier is clad with said thermal insulation.