Loading and unloading of a nuclear reactor core

A nuclear reactor of the water-cooled type, comprising an outer containment vessel, a pressure vessel in the lower portion of said outer vessel, a top flange and a top closure cap for said pressure vessel and containing a reactor core, a plurality of vertical fuel assemblies for said core, upper internal structures above said core and said pressure vessel, a structure having a horizontal bottom wall serving as a pool, a first orifice in said bottom wall located above said pressure vessel and having a diameter slightly larger than that of said closure cap, a second orifice in said bottom wall in communication between said structure and a leak-tight storage compartment partially within said outer containment vessel and partially exterior to said outer containment vessel and at a lower level than said structure, closure means for said second orifice, said compartment receiving containers for the storage of fuel assemblies, means for moving said containers from a position beneath said second orifice to a position beneath a third orifice in said storage compartment opening to the exterior of said outer containment vessel, said third orifice providing for discharge of containers through it, a storage zone for said pressure vessel closure cap, first means for lifting said pressure vessel closure cap and for transferring said cap to said storage zone, second means for lifting the fuel assemblies and transferring said assemblies directly from said reactor core to said storage compartment and a removable shell providing a leak-tight connection between said bottom wall of said structure at the level of said first orifice and said top flange of said pressure vessel said first means for lifting including means for storing said removable shell.