Patent Number: 046817263
Section: summary

BACKGROUND OF THE INVENTION (Field of the Invention) The present invention relates to a fast breeder reactor and, more particularly, to a technique most suitable for use in a tank-type fast breeder reactor in which a reactor core is supported at an inner lower portion of the reactor container of a nuclear reactor. A typical conventional tank-type fast breeder reactor (referred to simply as a "tank-type FBR", hereinafter) is arranged such that a reactor core, intermediate heat exchangers and circulation pumps are installed inside a nuclear reactor container known as a main container which contains sodium as a liquid metal. A roof slab having a rotational plug is attached to the upper end portion of the nuclear reactor container such as to cover the upper side thereof. The intermediate heat exchangers and the circulation pumps are mounted on the roof slab. The reactor core in which a multiplicity of fuel assemblies are disposed is supported by a core-supporting structural member which is mounted on the bottom portion of the nuclear reactor container. Examples of such core-supporting structure are respectively shown in FIG. 1 of the specification of Japanese Patent Laid-Open No. 15,895/1974, FIG. 1 of the specification of Japanese Patent Laid-Open No. 126,887/1979 and FIG. 1 of the specification of Japanese Patent Laid-Open No. 133,379/1982. The core-supporting structural member in these examples is adapted to support the reactor core and to apply the load of the reactor core to the pressure vessel of a nuclear reactor. The core-supporting structural member has a tapered shape, such as a truncated cone shape, in cross-section in order to support the reactor core stably. Even if the core-supporting structural member is formed into a specific cross-sectional configuration as described above, it is still preferable to take a measure to suppress the generation of vibration due to an exciting force produced by, for example, an earthquake, since the reactor core has a large weight and a center of gravity which is located higher than the core-supporting structural member. SUMMARY OF THE INVENTION (Object of the Invention) Accordingly, a primary object of the invention is to suppress the vibration of the reactor core of a fast breeder reactor. (Feature of the Invention) According to a first aspect of the invention, there is provided a fast breeder reactor having a nuclear reactor container filled with a liquid metal, a reactor core disposed within the nuclear reactor container, and a first supporting structural member mounted to the nuclear reactor container such as to support the reactor core, characterized by comprising: a cylindrical structural member which surrounds the periphery of the reactor core such as to define an annular gap between the cylindrical structural member and the reactor core for allowing the liquid metal to exist therein, the cylindrical structural member being mounted to the nuclear reactor container by means of a second supporting structural member. Further, according to a second aspect of the invention, there is provided in a tank-type fast breeder reactor having a nuclear reactor container filled with a liquid metal, a reactor core disposed within the reactor core container, a roof slab mounted on the upper portion of the nuclear reactor container, a core upper mechanism which is mounted on the roof slab and inserted into the nuclear reactor container, heat exchangers and circulation pumps, a fast breeder reactor characterized by comprising: a first supporting structural member for supporting the reactor core, the first supporting structural member being mounted on the bottom portion of the nuclear reactor container; a cylindrical structural member which surrounds the periphery of the reactor core such as to define an annular gap between the cylindrical structural member and the reactor core for allowing the liquid metal to exist therein, the cylindrical structural member being mounted to the nuclear reactor container by means of a second supporting structural member; and a partition wall which separates the inside of the nuclear reactor container into a low-temperature plenum and a high-temperature plenum, the partition wall being disposed above the cylindrical structural member and between an outer shroud of the reactor core and the nuclear reactor container.