Patent Number: 047073276
Section: summary

The invention relates to a container system for a high-temperature nuclear reactor, including an outer metallic pressure vessel, and an inner metallic core barrel, feeding and discharge of cooling fluid taking place at the lower end of the core barrel. A reactor of this type has been described in German Published, Non-Prosecuted Application DE-AS No. 30 16 402, corresponding to U. S. Pat. No. 4,476,089. Among other things, that patent proposes the placement of a core barrel containing the nuclear reactor proper in a steel pressure vessel such as has been used heretofore in the construction of water-cooled reactors. It was assumed in that disclosure that the spaces between the pressure vessel and its internal parts would be in communication with each other everywhere and would be filled with the helium used as the cooling fluid. Furthermore, no statements were made in the above-mentioned publication regarding the manner in which the core barrel should be fastened in the pressure vessel. Additionally, there were no provisions for preventing contamination of spaces between the pressure vessel and core barrel during servicing. It is accordingly an object of the invention to provide a container system for a high-temperature nuclear reactor, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, and in which the part of the space between the core barrel and the pressure vessel, in which devices are disposed which need frequent testing or servicing (for instance, the absorber rod drives normally placed in the ceiling of the core barrel, or the feed device such as for spherical fuel elements) can be made accessible without the danger of a break-in of the ambient atmosphere (i.e., of oxygen-containing air) into the interior of the core barrel, which would lead to considerable corrosion of the internal parts thereof, formed of carbon blocks and/or graphite, or of the fuel elements. With the foregoing and other objections in view there is provided, in accordance with the invention, a container system for a high-temperature nuclear reactor, comprising an outer metallic pressure vessel having an inwardly-protruding flange, an inner metallic core barrel resting tightly on the flange, and means disposed below the flange at a lower end of the core barrel for feeding and discharging cooling fluid, the core barrel being gas-tight above the flange. A pad which is already required for holding the core barrel in the pressure vessel is constructed in such a way that it simultaneously serves as a partition between the upper part of the above-mentioned space and the lower part thereof. Only the feed and discharge devices for the cooling fluid are located in the space. If the weight of the core barrel is known, one of ordinary skill in the art can construct the required size of the sealing surface without difficulty so that with a suitable construction of the sealing surface, the required sealing effect is achieved due to the weight of the core barrel itself. (Due to the high operating temperatures, elastomer seals are out of the question, and preferably, metal O-rings are used). Since the core barrel should be removable for repair purposes, a form-locking connection of the core barrel and the mounting flange is dispensed with. A form-locking connection is one in which parts are locked together by virtue of their own shape. The weight of the core barrel is also sufficient to reliably prevent the core barrel from being lifted off if a slightly higher pressure prevails in the lower part of the space than in the upper part. (Such a pressure difference is 2 bar for an operating pressure of the reactor of, for instance, 40 bar). The upper space is advantageously also filled with helium which, however, is not contaminated because it does not circulate through the nuclear reactor and other parts of the plant (such as heat exchanger); therefore, no radioactive deposits can occur in the upper space, which would limit the desired accessibility of the core barrel. Since no piping carrying the cooling medium is present in the upper space, the core barrel can be made tight at that location, and the feedthroughs required for the absorber rod drives etc. can be made gas-tight by conventional means (such as sliding valves). In order to prevent possible contamination of the gas filling the upper space by microscopic leaks at the sealing surface between the core barrel and the pressure vessel, the upper space is advantageously kept at a slight overpressure. In accordance with another feature of the invention, the core barrel is disposed at a distance from the pressure vessel defining a space therebetween, the flange dividing the space into upper and lower spaces, and including an equalization line connected between the upper and lower spaces, and means for shutting off the line. In this way, larger pressure differences between the upper and the lower space are controlled. By limiting the pressure difference, the passage of larger leakage amounts in one direction or the other is prevented. This device is sufficient to equalize the pressure differences expected during normal operation. In accordance with a concomitant feature of the invention, there is provided another equalization line leading from the lower end to the upper end of the core barrel interconnecting the upper and lower spaces, and a rupture disc protector closing off the other line. These features are provided to take care of a sudden occurrence of a major leak in the pressure vessel. Rupture disc protectors are well or known components which are completely tight in normal operation but completely release a pipe line which is provided for this purpose and is constructed for obtaining a sufficiently fast pressure equalization if a given response pressure is exceeded. However, a line connecting the lower space to the upper space over the shortest path would favor the occurrence of natural convection, wherein the air penetrating into the upper space through the leak could also reach into the interior of the core barrel, which is to be avoided, as explained above. The second equalization line provides a direct path to the lower end of the lower space for the cold air which has penetrated through the leak into the upper space after the rupture disc has opened, and thus, the lower space is therefore also flooded. The temperature difference present in the gas which circulates in the core barrel by natural circulation after the cooling blowers have failed or have been shut down and which removes the decay heat, causes a stratification which prevents the penetration of the corroding air therein. 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 container system for a high-temperature nuclear reactor, 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.