The internal structure comprises a bed (5) supporting the core (3) of the reactor and supplying liquid metal to the core, plating (6) resting on the bottom of the main vessel (1) of the reactor and an internal vessel (8) separating the hot collector (12) from the cold collector (13) of the liquid metal. The internal vessel (8) is directly fixed to the upper part of the bed (5) which rests on the plating (6) through the medium of slidable bearing means (21), (22). The bed (5) is connected to means (18) for supplying cooling liquid metal in a zone located at its periphery and outside the internal vessel (8) and the plating (6). Assemblies (31) providing a lateral neutronic protection are fixed to the bed (5) at the periphery of the fuel core (3).
