Patent Number: 042343844
Section: description

DETAILED DESCRIPTION OF THE INVENTION As disclosed, generally FIG. 1 and, in greater detail, in FIG. 3, the core 1 of a high temperature gas cooled nuclear reactor is formed by a bed of spherical fuel elements 2 and is generally surrounded by an annular side reflector 3. The reflector 3 is constructed of a plurality of graphite bricks 4. Removal tubes 5 are illustrated at the bottom of the bed of spherical fuel elements hereinafter referred to as the pebble bed. Six of these removal tubes lead from the pebble bed to a charging installation (not illustrated). In FIG. 2 the regular arrangement of the pebble bed removal tubes 5 is illustrated on a pit circle around the axis of the reactor core. For each pebble removal tube 5, a conical pebble inlet 6 is provided. The inlet itselt is formed by part of the support structure. The support structure consists of three layers of prismatic graphite blocks constructed as a closed unit without expansion gaps, as illustrated in FIG. 2. The top layer 7 and the intermediate layer 8 are composed of a plurality of hexagonal graphite blocks 9 connected through a keying arrangement 10 with each other. The graphite blocks 9 of the top layer 7 and intermediate layer 8 are designed with respect to their height so that the conical pebble inlets 6 are necessarily formed, as illustrated in FIG. 3. The bottom layer 11 of the support structure is formed by a number of support units 12. These units are also interkeyed with the intermediate layer 8 which is located above them. Beneath bottom layer 11, a hot gas collector space 13 is provided for collecting cooling gas. The cooling gas flowing through the fuel element pebble bed from top to bottom collects in this space. In the area of the pebble removal tubes 5, support units 12 are designed so that no gaps remain between the pebble removal tubes and the various support units. The support units 12 and the graphite blocks 9 again exhibit different cross sections toward the side reflector 3. Beneath the side reflector 3, the hot gas collector space 13 is in direct communication with an expanding area 14 making possible the connection of the radial cooling gas conduits with the collector space. As illustrated in FIG. 5, each support unit 12 consists of several support segments 15 fitted together into a hexagonal cross section. At the location of lower layer 11 representing the juncture of three support units 12, cooling gas channels 16 are provided. These terminate in the hot gas collector space 13. All of the support units 12 rest on a round column 17, directly through a column head 18. The column head 18 is set into a recess located in the center of the support unit and interkeyed with it. The round columns 17 traverse the hot gas collector space 13 and adjoin to the bottom of the nuclear reactor. As illustrated in FIG. 2, the support units 12 are of a hexagonal cross section and are significantly larger than the hexagonal graphite blocks 9 of the uppermost and intermediate layer of the support structure. Each support unit must, according to the invention, carrying of several graphite blocks 9 and of the fuel element pebbles 2 resting on the graphite blocks. In the top layer 7 and intermediate layer 8, a plurality of "central" graphite blocks 19 is present. The central blocks 19 are always surrounded by six "peripheral" graphite blocks 20 as illustrated in FIG. 4. Each of the peripheral graphite blocks 20 forms a part of the boundary of three different central graphite blocks 19. In this manner, the group comprising seven graphite blocks are each boxed in with each other over the layer 11. Each of the central graphite blocks 19 is aligned with one of the round columns 17. In all of the hexagonal graphite blocks 9 of the uppermost layer 7, a plurality of small vertical borings 21 are provided for the cooling gas. These are connected with the collector spaces 22 present in the graphite blocks 9 of the intermediate layer 8, while the collector space is located in the central graphite block 19 are designed as sack-like borings 22A. The collector spaces in the peripheral blocks 2 present continuous borings 22B. These borings are aligned with a cooling gas channel 16 in the support units 12. The sack-like borings 22A in the central graphite blocks 19 are connected with the continuous borings 22B connected with several connecting borings 23 as illustrated in FIGS. 3 and 4. In FIG. 3 one of the connecting borings 23 is rotated in the illustration. Furthermore, FIG. 3 illustrates the way by which differential expansion of the side reflector 3 in the three layers, 7, 8 and 11, of the support structure is permitted in the continuous vertical separating gap 24. The drawings are illustrative of the preferred embodiment of the present invention and are not intended to limit the disclosure of the present invention in any unduly restrictive manner. Obvious equivalents will be recognized as suitable to the skilled artisan and are considered to be included in the concept of the invention.