Diagrid for supporting a nuclear reactor core

A nuclear reactor diagrid combination for supporting the core of a nuclear reactor in which a liquid sodium coolant is circulated within a vessel containing the core and diagrid, said diagrid being constituted by a box structure having end-walls formed by two metallic plates braced by hollow cylindrical support columns which are suitably disposed at intervals within the box structure on a uniform pitch, the upper end plate being flat and horizontal and the axis of the reactor core being vertical, said diagrid being provided with means for applying the box structure against a support which forms part of the reactor vessel, wherein the lower end plate of said box structure has the shape of an upwardly convex spherical segment which terminates at its periphery in a flat rim and wherein the upper flat end plate has a circular flange which is parallel to the peripheral rim of the lower plate, said rim and said flange being braced with respect to each other, the flange of the upper end plate resting on a ring-girder supported by the vessel which provides the box structure with a peripheral side restraint and the flat rim of the lower end plate being supported by a flat circular flange formed on a shell element rigidly fixed to the reactor vessel, wherein the shell element has a conical shape and is in the line of extension of the spherical segment of the lower end plate of the box structure, and wherein the ring-girder is a hollow metallic torus opening laterally toward the box structure, said torus being a manifold for supplying the diagrid with the coolant sodium.