In a pressure vessel of a nuclear reactor containing a core assembly enclosed within a core shroud, the core shroud spaced radially inwardly of a side wall of the pressure vessel with an annular pump deck located in an annular radial space between the core shroud and the side wall of the pressure vessel, the improvement wherein the shroud is removably secured to an annular support leg extending upwardly from the bottom of the pressure vessel; and further wherein the annular pump deck is provided in the form of a plurality of removable segments.