Patent Number: 043303714
Section: summary

The present invention relates generally to nuclear reactors such as pool type liquid metal fast breeder reactor and more particularly to a specifically designed structural arrangement for supporting the core assembly of such a reactor. The nuclear reactor to be described in more detail hereinafter is one which includes a reactor vessel containing, among other internal components, a core assembly and a structural arrangement located below the core assembly for supporting the latter in a fixed position. In the past, a typical structural arrangement serving this purpose received most if not all of its structural integrity from welded joints interconnecting its various structural components. One major drawback in an arrangement of this general type is the inability in many cases to detect failures in individual welded joints until the joint failures progress to a point of collapse, that is, to a point where the overall structural arrangement is incapable of supporting the core assembly. This is to be contrasted with the present invention which, as will be seen hereinafter, utilizes a support structure including components which are not only connected by welded joints but are also mechanically interlocked to prevent the core assembly from totally collapsing into its support structure, even if all of the welded joints in the latter should fail. In view of the foregoing, one object of the present invention is to provide an uncomplicated and yet reliable arrangement for supporting a core assembly in a nuclear reactor, specifically in a pool type liquid metal fast breeder reactor. A more specific object of the present invention is to provide a structural support arrangement which, in part, receives its structural integrity from a number of individual components which are interconnected by means of welded joints but which does not rely in its entirety on these joints for structural integrity so that, even if the welded joints should completely fail, the overall support structure will nevertheless be capable of maintaining the core assembly in a supported position. Another specific object of the present invention is to provide a structural support arrangement which will support its core assembly in a limited but readily detectable downwardly deflected position in the event of a total failure in the structure's welded joints, thereby indicating such a failure before reaching the point where the entire core assembly collapses. As stated above, the nuclear reactor disclosed herein includes a reactor vessel, a core assembly to be maintained in a fixed position within the vessel and a structural arrangement, also located within the vessel, for supporting the core assembly in its fixed position. In accordance with the present invention, the structural support arrangement is comprised of a plurality of components interconnected to one another by welded joints and are also mechanically interlocked so as to define a unitary structure which supports the core assembly in its fixed position and which has sufficient structural integrity to support the assembly in a limited downwardly deflected position, even if all of the welded joints should fail. In a preferred embodiment, this downwardly deflected position is one which is readily detectable during normal operation of the reactor without special detection equipment. In an actual working embodiment, as will be seen hereinafter, the support arrangement disclosed includes a grillage of welded I-beams which are also mechanically interlocked to one another, a circumferential box girder welded to and around the outer periphery of the I-beams and also mechanically interlocked therewith. These I-beams and the box girder form a welded and mechanically interlocked unitary structure such that the welded joints interconnecting the various components are in states of compression and such that the structure will retain sufficient structural integrity to support its core assembly in the desired manner even if all of these welded joints should fail. The entire unitary structure is welded to and supported on the top edge of a circumferential support skirt, again in a state of compression, such that the circumferential skirt will nevertheless maintain the structural unit in a supported position should the welded joint between the two also fail.