Patent Number: 048083704
Section: description

Referring now to the figures in detail and first, particularly, to FIG. 1 thereof, there is seen a concrete structure serving as a radiation shield 1, inside of which a steel pressure vessel 2 is disposed. The pressure vessel is equipped with a removable cover 3 at the upper end thereof Disposed inside the pressure vessel 2 is a metallic core barrel 4, which has a circular projection 5 that rests on a circular flange 6 formed on the inside of the pressure vessel 2. The core barrel 4 contains a lining of built-in ceramic parts or internals 9 formed of carbon blocks and/or graphite which surround a space for receiving a fission zone 10 formed of a multiplicity of spherical fuel assemblies Among other things, canals 11 extend through the built-in parts 9. Absorber rods can be moved in the canals 11 by means of conventional drives 12 which are disposed at the ceiling of the core barrel 4, for controlling the fission zone The built-in parts 9 include other canals 13, through which cooling gas coming from non-illustrated heat sink is conducted into an upper plenum and is sent from the plenum through the fission zone 10 from the top down The heated cooling gas converging in a lower plenum 15 is fed to a non-illustrated heat sink through a hot gas line 16 disposed in a stub or connecting piece 17 of the pressure vessel 2. As seen in FIG. 2, the hot gas line 16 includes an outer tight metallic pipe 22 The flow of the hot gas itself is guided by an inner pipe 23 which is concentric with the pipe 22 and is formed of carbon fiber-reinforced carbon The hot gas line 16 is inserted into a wider stub or connecting piece 24 which is fastened to the core barrel 4 and is fastened to the line 16 by a number of screws 25 distributed over the periphery, as seen in FIG. 3. The breakdown of the hot gas temperature which is as high as 950.degree. C., to a level of about 300.degree. C. which is peraissible for the pressure-carrying pipe 22, is accomplished by heat insulation which can be partially formed of a filamentary ceramic material 26 and partially (at particularl highly mechanically stressed points) of a highly porous solid ceramic 27. A bellows compensator 28 is disposed in the interior of the wider stub 24 and is tightly connected thereto The bellows compensator may be optionally formed of two parts that are joined together by a rigid intermediate part. The bellow:s compensator is connected by means of screws 29 to a sleeve 30, which is also formed of carbon fiberreinforced carbon The sleeve 30 is in turn fastened by means of further screws 31 formed of the same material, to the builtin graphite or carbon block parts of the core barrel 4. The temperature breakdown at the built-in parts 9 from the hot gas temperature to the temperature permissible for the bellows compensator 28, takes place by way of the sleeve 30 A displacement which may occur during operation due to temperature changes between the core barrel 4 and the hot gas line 16 (even in the vertical direction) is compensated by the bellows compensator 28, while at the same time tightness is maintained, so that hot gas leaks from the line 16 which could endanger the core barrel 4 do not take place The outside of the bellows compensator 28 is then cooled by part of the stream of the cooled gas which returns from the heat sink and flows in a space 32 between the hot gas line 16 and a cold gas line 33 which surrounds the line 16 coaxially and is connected to the stub 17. To this end, holes 34 are provided in the wider stub 24 The wider stub 24 is detachably fastened to the core barrel 4 by means of additional screws 35 distributed over the periphery. It can become necessary to detach the stub 24 if the hot gas line 16 is to be replaced because of damage. Due to the necesary close fit between the line 16 and the wider stub 24, it appears more advantageous to replace both parts together If the screws 35 cannot be loosened(such as because of mechanical bending or due to a weld in the thread) they can be cut off between the wall of the core barrel 4 and the flange of the wider stub 24, by means of non-illustrated cutting tools During the reassembly, new tapped holes are cut in the core barrel 4, offset at an angle thereto. During the disassembly of the gas line 16, insulating plugs 36 as well as the screws 25 covered by the plugs can be removed from the inside of the flow guiding inner pipe 23 by chip-producing or milling machinery. This can be done more easily with remotely controlled tools Undesirable friction welding of the pressure pipe 22 to the wider stub 24 in the hot helium atmosphere, is prevented by a suitable coating of these parts, such as with chromium carbide The advantage of the illustrated construction is that during installation the wider flange 24, the bellows compensator 28 and the sleeve 30 can be tested for leaks in a completely assembled condition, before the hot gas line 16 is placed in the wider stub 24. The foregoing is a description corresponding in substance to German Application No. P 35 18 609.7, filed May 23, 1985, the International priority of which is being claimed for the instant application, and which is hereby made part of this application. Any material discrepancies between the foregoing specification and the aforementioned corresponding German application are to be resolved in favor of the latter.