Patent Number: 048083704
Section: summary

The invention relates to a gas-cooled, high-temperature nuclear reactor with a metallic core barrel having a lining formed of graphite or carbon blocks, and a hot gas line having an outer metallic pipe for confining pressure and a ceramic flow guidance pipe separated therefrom by insulation. Such a nuclear reactor is known from European Patent No. 0 039 016 and a further development is described in German Published, Non-Prosecuted Application DE-OS No. 33 45 457, corresponding to U.S. application Ser. No. 681,544, filed Dec. 14, 1984. Such hot gas lines have exhibited disadvantages stemming from the large temperature gradients, which will be described below. It is accordingly an object of the invention to provide a connection of the hot gas line to the core barrel of a gas-cooled, high-temperature nuclear reactor, which overcomes the hereinaforementioned disadvantages of the heretofore-known devices of this general type. This connection presents particular difficulties since it must withstand cooling gas which has been heated in the nuclear reactor to temperatures up to 950.degree. C.; hot gas leaks that might occur at the connection could therefore endanger metallic components located in the vicinity thereof (for instance at the corc barrel) In addition, leakage streams could lead to an erosion of the heat insulation material which is provided for the necessary temperature breakdown between the flow guidance pipe exposed to the hot gas temperature and a metallic pipe which surrounds the flow guidance pipe and provides a pressure seal. Due to the large temperature differences to which the components are subjected by the transition from the shut down to the operating phase, changes of position relative to each other which can be traced to different thermal expansion, must be expected; an angular offset between the core barrel and the hot gas line also occurs in this case, which would lead to excessive stresses if the two parts were rigidly connected to each other. In addition, it should be possible to replace components that have become defective, even under conditions of difficult access and if only remotely-controlled tools are used. With the foregoing and other objects in view there is provided, in accordance with the invention, a gas-cooled, high-temperature nuclear reactor, comprising a metallic core barrel, a graphite or carbon block lining disposed in the core barrel, a hot gas line including an outer pressure-confining metallic pipe and a ceramic flow guidance pipe, insulation separating the metallic pipe from the ceramic pipe, a stub concentric with the hot gas line, means for detachably connecting the stub to the core barrel, the metallic pipe being tightly disposed in the stub, means for detachably fastening the metallic pipe to the stub, a sleeve, means for detachably fastening the sleeve to the lining, a bellows compensator being disposed in the stub and having one end tightly fastened to the stub and another end, and means for connecting the other end to the sleeve It is known to use bellows-type compensators for equalizing position changes of components. The structure according to the invention utilizes these properties while at the same time protecting the parts which are necessarily metallic from the temperature of the hot gas. The joint produced in this manner is additionally completely gastight, and the gas-tightness thereof can be checked after installation without difficulty, since the hot gas line is only assembled later by a simple insertion into the stub Since the stub is detachably fastened to the core barrel it can be replaced, if necessary, tigether with the hot gas line, so that fit problems between these two parts after reassembly are avoided. In accordance with another feature of the invention, the ceramic pipe and the sleeve are formed of carbon fiber-reinforced carbon. Thus, not only the flow guidance pipe but also the sleeve which serves for breaking down the temperature between the hot lining of the core barrel and the bellows is made of carbon reinforced with carbon fibers (also known under the designation CFC). This material has sufficient strength even at the high temperatures prevailing at that location and is protected against oxidation, i.e., burn-up, by the provision that it is used only in an inert gas atmosphere (for instance helium). In accordance with a further feature of the invention, the stub and the bellows compensator define a space therebetween and the stub has openings formed therein and including a cold gas line coaxially surrounding the hot gas line. In nuclear reactors which are equipped like those described in the abovementioned publications, in other words with a cold gas line concentrically outside the hot gas line, the openings in the stub enclosing the bellows conduct a small shunt flow (in the order of 1/1000) of the cold gas to the outside of the bellows. This contributes to cooling the bellows, especially for compensating the temperatures which may vary over the periphery thereof. In accordance with an added feature of the invention, the means for detachably fastening the sleeve to the lining are in the form of carbon screws reinforced with carbon fibers In accordance with an additional feature of the invention, the metallic pipe has an outer surface and the outer surface of the metallic pipe and the stub have regions of mutual contact, and including a coating disposed on the regions for preventing friction welding of the metallic pipe to the stub in the cooling gas atmosphere. This is done to ensure the later disassembly of the pressure pipe from the stub. Welding of the two parts together cannot be precluded in a helium atmosphere. In accordance with again another feature of the invention, the stub has a flange to which the means for detachably fastening the stub to the core barrel are connected, the flange being offset or stepped back from the wall of the core barrel defining a gap therebetween for accomodating tools for cutting the fastening means. This is done in order to assure that the stub can be detached from the core barrel even if the basically detachable screws used for fastening can no longer be removed because they are welded fast or due to other reasons The cutoff stumps of the screws then remain in the core barrel and during reassembly, new tapped holes are cut in the core barrel which are offset by a given angle relative to the old ones. In accordance with a concomitant feature of the invention, the means for detachably fastening the metallic pipe to the stub include means for making the fastening means accessible to removal by milling tools, preferably including the screws This is done since hot gas pipes and stubs may in some cases be replaced together. This raises no special problem, even when working from the inside of the flow guidance pipe. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a connection of a hot gas line to the core barrel of a gas-cooled high-temperature nuclear rector, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.