Patent Number: 044420668
Section: description

DETAILED DESCRIPTION OF EMBODIMENTS FIG. 1 shows the core 1 of a gas cooled high temperature reactor formed by a pile of spherical fuel elements, surrounded by an annular side reflector 2. The side reflector is surrounded in turn by a thermal side shield 3, wherein an annular space 4 is provided between the two structural parts. Several pebble removal tubes (one such tube 16 is shown in FIG. 3) exit through the bottom of the pebble bed. Depending on the size of the nuclear reactor installation, the number of pebble removal tubes may vary between 1 and 7. A conical pebble inlet 17 shown in FIG. 3 is provided for each pebble removal tube, which is formed by a part of the support floor. The portion of the support floor arrangement of the invention shown in FIG. 2 consists of a plurality of graphite blocks 6a, arranged in vertical columns 6. The vertical columns 6 have hexagonal cross sections shown in FIG. 4 and are equipped with numerous bores 7 extending in the longitudinal direction through which the cooling gas heated in the core 1 may exit from the core. The structure shown in FIG. 2 illustrates a single column 6 with cooling gas bores 7. The cooling gas bores 7 are established with respect to number, diameter and distance so that no or only slight non-stationary thermal stresses may be generated in the individual vertical columns. The graphite blocks 6a located at different heights or in different layers may have different configurations with respect to the cooling gas bores 7. In the embodiments shown herein, the uppermost layer of the graphite blocks 6a has a greater number of cooling gas bores 7 than the other layers and a small gas collector space 8 is located at the upper end of the second layer from the top. This space is interconnected with the cooling gas bores in the uppermost and the second layer from the top. The vertical columns 6 of the support floor 5 may be constructed of hexagonal graphite blocks having different widths across the flats in the individual layers. As shown in FIGS. 1 and 2, each vertical column 6 resting on a circular column 9 is in turn supported on the bottom layers 10 of the high temperature reactor. The bottom layers 10 are supported by a floor plate 11. The diameter of the circular columns 9 is smaller than the flat width or end surface of the vertical columns 6. The free space between the circular columns 9 forms the hot gas collector space 12 of the high temperature reactor and is, therefore, interconnected with the cooling gas bores 7 in the graphite blocks 6a in such a manner that the gas freely flows therebetween. Because the vertical columns 6 are placed adjacent to each other as independent single columns without expansion gaps, the support floor arrangement 5 as a whole is not sensitive to thermal stresses and is capable of adjusting without strain to deformations of the bottom layers 10 and the floor plate 11. In order to keep the size of the gaps between the columns within the design parameters under all manufacturing, operational and thermal conditions, retaining means 13 acting inwardly in the radial direction are arranged in the annular space 4 as indicated in FIG. 1 by arrows. The type and layout of the retaining means 13 is determined by the reactor capacity and the core dimensions of the high temperature reactor. In FIG. 3, a support floor 5 for a high temperature reactor of small or intermediate capacity is shown. Identical structural elements are designated by the same reference symbols as in FIGS. 1 and 2. FIG. 3 shows that the side reflector consists of a plurality of stacked graphite blocks 2a and rests by means of roller bearings on the bottom of the reinforced concrete pressure vessel 15 surrounding the high temperature reactor. The restoring elements arranged between the thermal side shield 3 and the side reflector 2 consist of supporting struts 13a, provided with a clearance corresponding to the maximum possible differential radial thermal expansion of the support floor 5 and the thermal side shield 3. In the event that the reactor is designed to utilize absorber balls for the shutdown of the high temperature reactor, the restoring elements consist of spring supports in order to suppress or limit the gaps with respect to size. The reactor core 1 has several pebble outlet tubes 16 passing through the support floor 5, each of them being provided with a conical pebble inlet 17. The surface of the support floor 5 is designed so as to form the said conical pebble inlets. FIG. 4 exhibits another embodiment of the support floor 5 according to the invention, intended for a high capacity, high temperature reactor. A total of seven pebble outlet tubes 16 are provided under the reactor core 1, four of which are shown in the drawing. Toward the side reflector 2, the graphite blocks 6a of the vertical columns 6 have a different configuration in cross section. The shape of the cross sections are varied so that each individual graphite block 6a is radially restrained. FIG. 4 demonstrates the arrangement of the vertical columns 6 directly adjacent to each other. As the restoring elements for this support floor, spring supports 13b are provided; they are arranged in the annular space 4 and hold the vertical columns 6 together in the radial direction. In order to prevent the development of a pressure ring support effect in the side reflector 2, the latter is provided with a series of gaps 18 between the individual graphite blocks 2a. The spring supports 13b are laid out that the gaps developing after an extended period of operation of the high temperature reactor between the vertical column 6, remain under a predetermined maximum size. If in the high temperature reactor absorber balls having diameters substantially smaller than those of the fuel elements are used to affect the reactivity of the reactor, the predetermined maximum size of the gaps is also given by the diameter of the absorber balls.