Abstract: A part of the cold liquid metal which is injected at the base of the reactor core is circulated along the bottom portion of the main reactor vessel and guided by a shell which is concentric with the vessel. A mass of inert gas is trapped within a leak-tight annular chamber above the liquid metal. During reactor operation, the gas pressure is adjusted in order to maintain the gas/liquid metal interface at a substantially constant level and to obtain along the vessel a temperature distribution which ensures limited amplitude of stress variation.

Abstract: A set of cylindrical shells is interposed between the main vessel wall of an integrated sodium-cooled fast reactor and the primary core containment vessel so as to form a siphon having two downwardly directed branches. One branch opens into the intervessel zone which is separated from the primary vessel by a shell. The other branch which is nearest the main vessel wall is supplied with part of the cold sodium which has been withdrawn from the intervessel zone by means of pumps and reinjected into the bottom of the reactor core.

Abstract: A heat-insulating structure is placed within an annular space located between the primary vessel suspension strake of a fast reactor and the cylindrical shell of a top concrete closure slab from which the primary vessel is suspended. The heat-insulating structure is tightly applied on one side against the primary vessel wall and on the other side against the cylindrical shell.