Patent Number: 046559965
Section: summary

BACKGROUND OF THE INVENTION The invention relates to a fast neutron nuclear reactor having a storage structure independent of the core structure. It more particularly applies to a fast neutron reactor cooled by means of a liquid metal, e.g. sodium. Such a reactor has a vertically axed main vessel containing the liquid cooling metal in which is immersed the reactor core. The core is constituted by a group of elongated boxes, each containing a bundle of sheathed needles or rods containing the fissile and/or fertile material. At the upper end of said boxes, there is a gripping head, which makes it possible to raise and transfer them. At the bottom thereof, there is a base or foot making it possible to position them in a horizontal support structure, which rests on a flooring fixed to the bottom of the vessel. During the life of the reactor, it is necessary to periodically replace the spent assemblies by new assemblies. This handling operation is generally carried out by means of an arm or a grapnel, which transfers the assemblies into a loading and unloading container, which makes it possible to remove the assemblies from the reactor vessel. In the known solutions, the extraction from the core of irradiated assemblies with a view to their replacement by new assemblies, is followed by storage within the vessel and outside the core in an area where the assembly in question can be partly cooled and lose part of its residual activity before being removed from the main vessel for storing outside, where its activity continues to decrease. However, in the present state of the art, the storage area forms an integral part of the core structure. This leads to an increase in the dimensions of said structure and particularly an increase in its diameter. Among the other disadvantages caused by it, it makes it necessary to provide in the slab sealing the vessel, an opening which is sufficiently large to permit the passage of the structure. SUMMARY OF THE INVENTION The present invention relates to a fast neutron nuclear reactor, which solves these problems due to the presence of a storage structure independent of the core structure. More specifically, the present invention relates to a fast neutron nuclear reactor, which comprises a vessel containing a liquid cooling metal, a core immersed in this metal, the vessel having a flooring on which rests a structure for the core, said core being constituted by a juxtapositioning of assemblies fixed into the structure, the liquid cooling metal circulating in an upwards manner in the core, the liquid metal being called "cold liquid metal" before its circulation in the core and "hot liquid metal" after it has passed into the latter, wherein it comprises a fuel element storage structure, which is independent of the core structure and is arranged concentrically with respect to the latter and rests on the flooring, a circulation of cold liquid metal being ensured in the assembly by recovering leaks of the core structure. Numerous advantages result from this arrangement. The core structure and the storage structure are two separate parts, which can be installed separately in the reactor. The dimensions of the core structure and in particular its diameter are reduced. As the core structure is preferably introduced by the opening of the rotary plug, this permits the reduction to the same extent of the thrust or abutment on the minimum diameter of the rotary plug. Moreover, the storage structure does not require such a precise machining as the core structure. The storage structure which is hydraulically connected to the flooring can be constituted by a one-piece ring, or can be formed from two or more modules. This storage structure can be placed and fixed on the flooring, or constitutes a monolithic structure with the flooring in the variant of a one-piece ring. Preferably, the storage structure has a free space in which is placed a reactor loading and unloading station. This arrangement makes it possible to move this station closer to the core and consequently reduce the diameter of the main vessel, which is a very important advantage in view of the economies resulting therefrom.