Patent Number: 047770120
Section: description

FIG. 1 shows a reactor pressure vessel 1, for example of prestressed concrete, with a cylindrical cavity 2, wherein a high temperature reactor 3 and a number of steam generators (not shown) are installed. The core of the high temperature reactor 3 is formed by a pile 4 of spherical fuel elements 5, which are removed by means of a pebble removal installation 6 from the pile 4. The charging installation for the fuel elements 5 is not shown. Helium as the cooling gas flows from top to bottom through the pile 4. The pile 4 is surrounded on all sides by a graphite reflector which comprises a roof reflector 7, a bottom reflector 8 serving as the supporting floor and a cylindrical side reflector 9. In the roof reflector 7, passages 10 are provided for the absorber rods (not shown). They may be isserted directly into the pile 4. The bottom reflector 8, assembled of adjacently arranged graphite columns (as seen in FIG. 2), rests on round columns 14 supported by the bottom layers 11 of the high temperature reactor 3. A thermal bottom shield 12 adjoins the bottom layers 11 as the bottom plate. The free space between the round columns 14 constitutes the hot gas collector compartment of the high temperature reactor 3; several hot gas conduits 15 are connected with the hot gas collector department. They communicate with the steam generators. After cooling and compression, the helium is returned through lines 16, installed coaxially with the hot gas lines 15 to the reactor core. The side reflector 9 is surrounded by a similarly cylindrical thermal side shield 17, whereby an annular space 18 is provided between the two structural parts in communication with the lines 16. In the annular space 18, elastic supporting elements are arranged whereby the side reflector 9 is supported on the thermal side shield 17 (not shown). The annular space 18 is connected in flow with a cold gas space 19 bounded in the downward direction by the roof reflector 7 and upwardly by the thermal roof shield 20. The pebble removal installation consists of six ceramic removal tubes 21, adjoined outside the bottom layers 11 by a metal pebble removal tube 22 each. Each ceramic pebble removal tube 21 is surrounded by a boron shield 23, as seen in more detail in FIGS. 2 and 3. FIGS. 2 and 3 show one of the ceramic pebble removal tubes 21 in their immediate surroundings. The bottom reflector 8 consists of graphite columns 8a and 8b, which in turn, are assembled of individual graphite blocks. The uppermost of these graphite blocks have a plurality of cooling gas bores 24 which are in communication with the collector compartments 25 of the adjacent graphite blocks. By means of larger bores 26, each collector compartment 25 is connected with the hot gas collector compartment 13. The ceramic pebble removal tube 21 is surrounded directly by a ring of graphite columns 8a, extending through the hot gas collector compartment 13 and resting directly on the bottom layers 11. The bottom layers 11 are assembled of graphite blocks 11a, maintained in position in the immediate vicinity of the ceramic pebble removal tube 21 by means of dowels 27. The aforementioned boron shield 23 consists of a plurality of boron rods 28 and a row of solid boron plates 29. The boron rods 28 are arranged in vertical bores adapted to the rods and extending through the entire length of the graphite columns 8a. In this embodiment, two rows a and b of bores are provided; each of them arranged on a circle with the center axis of the pebble removal tube 21 as its center. The bores of the two rows a and b are staggered with respect to each other, so that the boron rods 28 are facing gaps. The boron rods 28 fill the entire length of the bores. The solid boron plates 29 are located in the area of the bottom layers 11. They are arranged directly outside and around the ceramic pebble removal tube 21 and are shaped so that they surround the pebble removal tube 21 completely in the circumferential direction and nearly completely in the axial direction. The boron shield 23 comprising the bodies 28 and 29 prevents any output by the fuel elements 5 in the ceramic pebble removal tubes 21, whereby the temperature in the metal pebble removal tube 22 adjacent to the removal tube 21 may be kept at an acceptable level.