Abstract: A nuclear reactor having integral heat exchangers comprises intermediate heat exchangers (35) which are entirely contained within the reactor vessel (1) and bear on the support (4) for the reactor core (5) at the periphery of the latter. Each one of the intermediate heat exchangers (35) is connected to the secondary liquid sodium circuit by a conduit (50) which passes through a slab (8) closing off the top of the reactor. An upper rotating stopper (15) includes an opening (53) of a size which is comparable to that of the cross-section of an intermediate heat exchanger (35), the opening being located at such a distance from the axis of rotation (12) of the stopper that the opening (53) can be brought into vertical alignment with each one of the intermediate heat exchangers (35) in succession. The invention particularly relates to fast neutron reactors which are cooled with liquid sodium.