Fast nuclear reactor

A fast neutron nuclear reactor comprising a vesel having a vertical axis and containing a reactor core, a volume of liquid metal for cooling the core, at least one main heat exchanger and at least one auxiliary heat exchanger, said reactor vessel being closed at the top by a reactor vault roof, said auxiliary heat exchanger being constituted by a plurality of vertical heat-exchanger modules, each of said modules comprising a circuit for the flow of coolant fluid, said reactor vault roof being pierced by a single orifice in vertical alignment with the vertical axis of said auxiliary heat exchanger, the dimension of said orifice in horizontal cross-section being larger than that of each one of said heat-exchanger modules but smaller than the overall dimension of the auxiliary heat exchanger in horizontal cross-section, and a removable shield plug closing said orifice, said shield plug having a depending axial extension penetrating into said reactor vessel with said modules disposed around said extension, the fluid circuit of each module communicating with an inlet tube and with an outlet tube for admission and discharge of the coolant fluid, said inlet and oulet tubes of each module extending in a direction parallel to the shield plug and the axial extension thereof within a respective recess formed in the inner surface of one of said orifice and said shield plug, whereby any of said modules of said auxiliary heat exchanger can be individually introduced into and taken out of said reactor in any order through said orifice after removal of said shield plug.