Patent Number: 042279682
Section: summary

FIELD OF THE INVENTION The present invention relates to a nuclear-reactor assembly and, more particularly, to an assembly which consists of a pressure vessel containing the nuclear reactor and additional vessels arrayed around the reactor vessel for components of the system, for example heat exchangers, which communicate with the central or reactor vessel by horizontal passages which can lie in a common horizontal plane. BACKGROUND OF THE INVENTION It is known to provide prestressed pressure vessels of cast material, e.g. cast iron or steel, as pressure vessels for nuclear-reactor installations and particularly for housing the high-temperature reactor core. In such systems it is also a common practice to provide a number of heat-exchange components and horizontal gas passages which communicate between the heat exchangers and the reactor vessel for connecting the high-temperature reactor with the primary coolant flow. In such systems, the pressure vessel for the high-temperature reactor can be centrally located and the centrally disposed reactor vessel can be surround by a plurality of pressure vessels each containing heat-exchanger or other components. These auxiliary vessels may also be provided as separate prestressed pressure vessels of cast material. The component vessels can be disposed in a partial circle around the central or reactor vessel, i.e. can be annularly spaced therearound. Prior to the development of such systems, efforts in this field concentrated upon the provision of a completely integrated reactor assembly in which the high-temperature reactor and the primary coolant components, such as tube furnaces or steam generators (more generally referred to as heat exchangers) were provided in a common prestressed concrete pressure vessel. When, however, attempts are made to construct similar vessels from cast materials such as cast iron or cast steel (more generally cast metals) problems were encountered not only because of the large quantities of materials which were required and their expense, but also because the fabrication time was realtively great and it was difficult, even with existing casting technology, to fabricate such vessels. This is especially the case because nuclear-reactor installations with their primary coolant components are extremely large and the tendency toward the fabrication of still larger units is increasing. The fabrication of a single pressure vessel for such systems has thus become not only difficult but also uneconomical. As a result, it has been proposed to substitute for this single housing for the integrated system, an arrangement in which the high-temperature reactor and the primary coolant components are contained in separate pressure vessels in a satellite construction wherein the component vessels are disposed around a central reactor vessel. In this case, the pressure vessels for the primary coolant components are disposed in a partial circle around the reactor pressure vessel. Two horizontal gas conduits generally connect each of the component vessels with the high-temeprature reactor vessel for the delivery of the gas to the component vessel and return of the primary coolant to the reactor, respectively. These gas conduits required a correspondingly large number of passages in the cylinder walls of the prestressed pressure vessels which detrimentally effected the strength of both the reactor vessel and the component vessel. Naturally, attempts were made to overcome this weakening of the reactor vessel by reinforcement, although this increases the cost and amount of material which must be used. In the German patent publication (open application or Offenlegungsschrift) No. 23 26 917, there is described a nuclear-reactor installation in which the nuclear reactor is contained in a high-pressure vessel which is, in turn, surrounded by a cylindrical concrete containment or structure. Two heat exchangers are, in this system, connected with the reactor pressure vessel by coaxial ducts and are received, in turn, with respective burst-resisting containments reinforced by steel reinforcing cables or the like and composed of concrete. The containments are each applied to a concrete cylinder and the two concrete cylinders form part of the cylindrical concrete housing and are adapted to receive the drive motors for the primary coolant circulating pumps. It is also known in this art to provide a reinforced concrete pressure vessel for nuclear reactors in which the desired or required volume is subdivided between two or more vessels each of which can be prestressed and all of which can be collectively surrounded by further prestressing cables into a unit. In this construction, represented by the German Patent document (open application or Offenlegungsschrift) 16 84 594, the central vessel is larger than the peripheral vessels and serves to receive the nuclear reactor while four smaller vessels grouped around the central vessel receive the primary coolant components such as heat exchangers and coolant circulation components. The central vessel and the outer vessels are provided with horizontal passages so that the central vessel is connected with each of the outer vessels by two gas conduits. In still another prior-art proposal, the pressure vessel for the high-temperature reactor is connected with the pressure vessels for the steam-generating components by burst-resisting connecting passages disposed beneath these pressure vessels. In this fashion the weakening of the cylindrical wall portions of the pressure vessels is avoided but the cost is increased since the passages must be sufficiently prestressed and strengthened in a redundant manner. OBJECTS OF THE INVENTION It is an object of the present invention to provide a nuclear reactor installation or assembly whereby the disadvantages of the aforedescribed systems are avoided. Another object of the invention is to provide a pressure-vessel assembly, especially for a high-temperature nuclear reactor, in which weakening of the vessel walls is avoided but more direct gas passages can be provided that have been used at least in the last-mentioned prior-art solution. It is also an object of the invention to provide a pressure-vessel assembly which affords a compact construction at relatively low cost and which does not require special prestressing or reinforcing of the gas passages. SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are attained, in accordance with the present invention in which the pressure vessel assembly for the nuclear reactor installation comprises a cylindrical central vessel of cast metal and intrinsically prestressed, in addition to a plurality of peripheral, satellite or outer auxiliary pressure vessels which also may be axially and peripherally prestressed individually and likewise composed of cast material being generally of cylindrical configuration and annularly spaced about the central vessel over at least a partial circle. According to the invention, each of the peripheral vessels is connected to the central vessel by a horizontal passage, the horizontal passages of all of the vessels lying in a common horizontal plane. In accordance with an essential feature of the invention, the central vessel is provided with generally tangential and vertical planar surfaces in this horizontal plane while the pripheral of auxiliary vessels likewise have generally tangential and vertical surfaces. More particularly, at least one of the vertical surfaces of the central vessel lies perpendicular to the axis of each of the horizontal passages while at least one of the surfaces of each of the auxiliary vessels lies perpendicular to its horizontal passage and is flat against or flush with the corresponding horizontal surface of the passage of the central vessel communicating with its passage. More particularly, the substantially cylindrical pressure vessels have in the region of the horizontal gas passages, which lie in a horizontal plane and run generally radially, an array of vertical planar surfaces. At least a portion of the planar surfaces of the reactor vessel are thus at right angles to the horizontal (radial) gas passages and each component vessel has a planar surface which lies directly against a corresponding planar surface of the central or reactor vessel. The component vessels are angularly spaced and the spaces between the individual component vessels, at least in the region of these vertical planar surfaces and the horizontal plane of the passages, is filled with support blocks until the assembly of component vessels and support blocks form a circle which completely surrounds the reactor vessel. The support blocks, in turn, have planar surfaces which directly abut, on the one hand, the planar surfaces of the reactor vessel between those planar surfaces against which the component vessels lie, and the lateral planar surfaces of the component vessels themselves. The support blocks and the component vessels thus form a composite disk which, in accordance with another essential feature of the invention, is prestressed inwardly by at least one peripheral prestressing strand surrounding this composite or compound disk. The inward prestress, therefore, applies the component vessels against the reactor vessel and, in addition, wedges the support blocks against the component vessels. The prestress is thus in the horizontal direction. Each of the pressure vessels can, in accordance with a feature of the present invention, be prestressed in vertical and horizontal directions as well, i.e. by vertical prestressing cables extending along generatrices of the pressure vessel and received in the walls thereof. These vertical prestressing cables or bars can be used also to hold cover and base plates onto the cylindrical wall structures of the pressure vessels. The peripheral prestressing can be afforded by external cables or bands which are stressed inwardly while extending around the individual pressure vessels. The vertical and horizontal prestressing systems can be dimensioned to maintain the pressure forces on the walls of the vessel in equilibrium when the reactor system is in operation. In addition, when the pressure vessels are composed of cast iron or cast steel blocks, they can hold the joints between the blocks closed against any inward pressure which can normally develop in the reactor or auxiliary vessels. In the region of the disk-shaped composite body, moreover, the horizontal prestressing arrangements of the individual vessels can be omitted since the horizontal prestress is provided by the common prestressing member or members which encircle the compound disk. In this case, the inner prestress afforded by this peripheral prestressing member or such prestressing members is such that the prestress balances the internal forces and sheer-resisting keys or the like need not be employed to prevent separation at the junctions of the various members. The resulting structure has been found to be extremely compact and of exceptionally low cost since only in the region of the horizontal gas passages is it necessary to provide an inward prestressing member that surrounds all of the pressure vessels, i.e. the entire assembly. The use of the vertical prestressing members for the individual pressure vessels is uninhibited by this outer prestressing member or such outer prestressing members. The system of the present invention has, by comparison with the integrated structures mentioned previously, a much shorter reaction time, thereby reducing the cost of setting up the assembly. The individual vessels are more readily accessible so that maintenance and repair of the components is possible with less difficulty. Naturally, individual satellite vessels can be replaced if necessary when relining or reinsulation is necessary, e.g. upon the failure of a liner or layer of insulation. The heat-exchanger components which can be introduced into the component vessels can be steam generators which can be connected to electric-current generating systems and it has been found to be advantageous to provide the blowers, pumps and motors for circulating the cooling gases above the heat exchangers in the component vessels. One or more of the component vessels can be used for other purposes as may be required. For example, the waste-heat recovery system of the nuclear reactor can be installed in one or more component vessels. Such a system can include, in the conventional manner, a plurality of blowers with or without recuperative heat exchangers and a number of coolers. The component vessel or vessels for the waste-heat removal system can be interposed between other heat exchanger vessels, i.e. those for steam generation and either the steam-generating vessels or the waste-heat recovery vessels can be provided with blowers with or without recuperators and coolers. It has been found to be advantageous to provide at least one disk-shaped composite body. However, the construction can also be made in such a manner that two disk-shaped composite bodies are provided on above the other with the upper body lying just above the horizontal gas passages with the lower body lying just below them. Advantageously the pressure vessels are composed of grey cast iron or cast steel while the support blocks are composed of grey cast iron and are made of hollow construction. This utilizes substantially less material. In the plane of the passages, moreover, the reactor vessel can have the configuration of a polygon, i.e. all of the vertical surfaces may angularly adjoin other vertical surfaces all around the periphery of the vessel. The component pressure vessels, however, may be prismatic only in part, in the region in which they contact the support blocks or the central vessel, and may have a cylindrical curvature elsewhere, e.g. in the region in which they are contacted by the stressing element which passes around the composite disk. The support blocks may be composed of hollow members with converging flanks which are wedged between converging flanks of successive component vessels. Two such blocks may be provided in each gap between a pair of component vessels.