Abstract: A hexagonal ring structure whose internal contour conforms to the external contour of the reactor core rests on the periphery of the reactor diagrid and is constituted by a plurality of layers of metallic plates. The layers are maintained in relative positional relation by means of clamping members, the plates of one layer being angularly displaced with respect to the plates of adjacent layers. The bottom end-connectors of the elements constituting the lateral shield system are fitted in vertical through-holes formed in the ring structure.

Abstract: The system comprises an assembly of uniformly spaced horizontal plates extending parallel to a horizontal closure surface, an outer shell and a thick bottom plate suspended from the horizontal surface by means of spaced suspension members attached to the horizontal surface and to the thick plate respectively. The thick plate supports stacked metallic plates held in spaced relation and protected by a lateral shell which is capable of free expansion at the upper extremity and joined to said thick plate in leak-tight manner.

Abstract: The upper portion of a hollow cylindrical spacer column is rigidly fixed to the reactor diagrid and supports a fuel assembly end-fitting by means of a removable sleeve having a conical bearing surface for sealing and centering the fuel assembly. The sleeve is engaged in interfitting relation with the column head and secured thereto by means of a removable annular weld connection.

Abstract: In a sodium-cooled fast reactor comprising a reactor tank and diagrid, a core support grid carried by the reactor diagrid and a number of pipes each supplying the support grid with liquid sodium coolant through a bellows seal, the reactor diagrid is constituted by a rigid annular structure having a flat annular bearing face resting on an annular bearing face of the core support grid. High flexural rigidity of the support grid is provided by strengthening ribs, by welded through-passage columns for the fuel elements and by a raised peripheral framework mounted on the support grid for carrying the shield system.