CORE FORMING STRUCTURE CONTROLLER

In an installation for handling assemblies between the main vessel of a fast neutron nuclear reactor and an adjoining vessel, use is made of a transfer hood formed by a thick tube whose inclined axis can be moved alternatively into the prolongation of the axes of two inclined ramps opening into the main vessel and adjoining vessel respectively, by the rotation of a platform of vertical axis bearing the hood and also two flaps which close the ramps when the reactor is operating, so that an assembly-transferring pot can be guided isostatically inside the ramps and the hood, the platform also possibly comprising a spare flap. Application to all assemblies forming a reactor core, such as fuel assemblies, lateral neutron screening assemblies and absorbing assemblies.