Core for nuclear reactors

A description is given of a core for a nuclear reactor which includes a moderator tank and fuel assemblies within the moderator tank. The tank has a lid. The fuel assemblies are fixed by an assembly grid shaped as a lattice, each fuel assembly including a polygonal shroud and a plurality of control rod guide tubes surrounded by the shroud. The walls of the shrouds extend upwardly above the control rod guide tubes. The grid is secured in place by the lid of the moderator tank. The grid has mechanical contact with the upper edges of the shrouds, the vertical planes along the surface of the grids crossing the planes along the surfaces of the shrouds. The mechanical contact is made by downwardly open slots in the sheet metal parts constituting the grid which engage the upwardly extending edges of the shroud