Patent Number: 040509842
Section: summary

BACKGROUND OF THE INVENTION The present invention is directed to a closed cycle gas-cooled nuclear power plant including a high-temperature nuclear reactor, a gas turboset, heat exchange apparatus consisting of recuperators, pre-coolers and intermediate coolers, and a conduit system for conducting the gas coolant through the individual components of the plant and, more particularly, it is directed to the arrangement of the plant within a prestressed concrete pressure tank (cycle-tank construction). Closed cycle plants have an obvious advantage over nuclear power plants of the type where the energy is given off in a secondary cycle, since they combine the simplicity and good output of single circuit plants with the advantages of gas turbines. By arranging the nuclear reactor, the gas turboset and the other cycle components in a common pressure tank (integrated construction), special connecting elements are avoided between individual parts of the plant through which the gas coolant flows and, as a result, a very favorable effect is obtained in the construction and operation of high-temperature reactors. Therefore, an integrated construction is preferred in a number of special nuclear power plant types. In DAS 1, 156, 903 a power engine unit of the above type is disclosed which is used for vehicles and has a very compact design. In the turboset, the turbine and compressor are located on opposite sides of the reactor core and the common shaft is hollow and extends through the reactor core and the intermediate coolers are located in the annular space between the reactor core and the pressure tank wall. This compact design is based on the consideration that the turbine does not require attendance and, as a result, the turbine and the other cycle components cannot be disassembled. A similar design of the nuclear reactor is contained in DOS 2,005,208, however, in that arrangement a pressure blanket is provided inside the pressure tank which is open at its end faces and is spaced from the inner wall of the tank in such a way that the heat exchanger is accommodated in the space formed. In DOS 2,028,736 a closed cycle gas-cooled nuclear power plant is described. The power plant is of the two-tank type with the gas turbine and other components of the gas cycle positioned in a machine block formed of prestressed concrete and separated from the concrete pressure tank to afford a simpler construction of the charging and regulating unit. A similar design of the concrete pressure tank is illustrated in DAS 1,614,610 in which two closed pressure-proof chambers are provided, with one of the chambers containing the reactor and the other serving as a containment for the remaining power plant equipment. The working medium is carried in lines which penetrate through a partition between the two pressure-proof chambers passing from the reactor to the turbine to the compressor and then back into the annular space below the reactor core. This so-called igloo-construction is technically difficult to realize and the nuclear power plant is very uneconomical, because of the manner in which it is arranged. In DOS 2,062,934 another gas-cooled nuclear reactor is shown in an integrated construction with the gas turbine arranged in a cavity in the wall of the pressure tank surrounding the reactor core. By means of a bypass, a portion of the cold gas coolant for the reactor core can be bypassed about the core and mixed directly with the hot gas coolant issuing from the core. In still another nuclear power plant of the above-described type as set forth in DOS 1,764,248 the nuclear reactor and all of the coolant cycle components are arranged in closely spaced parallel vertical bores within the concrete pressure tank and the components are accessible from the exterior and passageways are provided for the cooling medium in the wall of the pressure tank and between the individual vertical bores. However, in this arrangement the cooling medium must traverse very long flow paths and the plant requires a relatively large pressure tank. SUMMARY OF THE INVENTION Therefore, based on the above state of the art, it is the primary object of the present invention to overcome the disadvantages of the known nuclear power plants by a special arrangement of all the plant components and the conduit system interconnecting the components which permits a compact construction of the nuclear power plant. In accordance with the present invention, a prestressed concrete pressure tank encloses the nuclear reactor and a number of vertical shafts (pods) are formed in the tank, the vertical shafts are disposed in an annular arrangement about the vertical axis of the tank and are located radially outwardly from the reactor and inwardly from the radially outer surface of the tank. The gas turboset is arranged within the pressure tank in a horizontal position spaced below the reactor and the various heat exchange components are located in the vertical shafts. The heat exchange components include recuperators, precoolers and intermediate coolers, with the recuperators positioned in the shaft either above or below the coolers. The conduit system for the entire coolant cycle downstream from the gas turboset is divided into partial flow paths which include lines connecting the turboset to separate ring segment conduits each of which conduits is connected to a group of the recuperators and another ring segment conduit collects the gas coolant from each group after it has passed through the coolant and returns the gas into a vertical collecting main. In accordance with the invention, the entire gas cycle is divided into several separate groups each of which has short tie lines interconnecting the gas turboset and the heat exchange components in each group. Further, ring segment conduits are associated with the inlet and outlet to each of the groups for providing a compact arrangement for supplying and collecting the gas flowing through the group. In this way an optimum distribution of the gas coolant conduit system is obtained within the pressure tank and it limits the number and the length of the individual conduits required. The hot low-pressure gas issuing from the turbine flows through the recuperators arranged in parallel within each of the groups which laterally enclose the reactor core in a blanket-like arrangement with the gas flowing upwardly and the same direction of flow is maintained in the pre-coolers located within the shafts above the recuperators, the pre-coolers cool the gas to the inlet temperature of the compressor. The arrangement of the individual components is selected so that the plant can be arranged for any desired power increase, that is, the extrapolation to a larger or smaller power unit is readily possible, and such a feature is of great importance in the development of new nulear reactors. Preferably, the gas turboset is located in a horizontally extending tunnel spaced a sufficient distance below the nuclear reactor so that adequate shielding of the turboset from radiation is ensured. For its assembly and disassembly, the turboset is arranged in a so-called plug-in design. The turboset has one shaft, since a single-shaft plant has decisive advantages over a multiple-shaft plant, that is, its operating and regulating behavior are easy to control, only one shaft packing is required in the prestressed concrete tank, and the costs of a single-shaft plant are lower. In this arrangement, the turbine is rigidly coupled with the generator. High temperature gas issuing from the nuclear reactor flows first to a collecting chamber and then over vertically arranged lines directly into the turbine inlet. To increase the efficiency of the nuclear power plant, an intermediate cooling system is provided in the main cycle and preferably is arranged in the vertical shafts of the pressure tank. In a preferred arrangement, the intermediate coolers of the intermediate cooling system are positioned in the spaces below the recuperators in the shafts. Like the recuperators and pre-coolers, the intermediate coolers are combined in groups and each group is connected by a ring segment conduit, which, in turn, is connected to the compressor by a short tie line. Gas flowing from the intermediate coolers in each group is received in a separate ring segment conduit and a tie line carries the gas from the ring segment conduit to the high-pressure stage of the compressor. Downstream from the compressor, the gas flow is again divided over tie lines and directed to separate ring segment conduits. Each of these ring segment conduits is connected to the nests of tubes in one group of the recuperators for proportioning the flow of high-pressure gas and such gas is preheated by the low-pressure gas flowing through the recuperators about the nest of tubes. From the recuperators, radially arranged lines conduct the gas coolant back into the cold gas collecting chamber of the reactor. In this arrangement, the same number of recuperators and pre-coolers are always combined in a group. In a plant rated at about 1,000 MW, two separate groups of recuperators and pre-coolers are provided with each group containing three recuperators and three pre-coolers interconnected by ring segment conduits. This particular arrangement represents the optimum solution, as far as the required conduit system for the plant is concerned. The two groups are symmetrically disclosed in an annular arrangement. If a nuclear power plant of this rating is equipped with intermediate coolers, four such coolers are sufficient with two being arranged in each group and they are connected to the gas flow conduit system by a gas inlet and a gas outlet ring segment conduit. As indicated above, the intermediate coolers improve the efficiency of the plant. However, it is possible to provide a nuclear power plant in which a reduction in efficiency is intentionally accepted by omitting the intermediate coolers for obtaining a number of other advantages. Briefly, the more important of these advantages are as follows: a considerable reduction in the size of the prestressed concrete plant, the elimination of expensive parts (that is, in addition to the intermediate coolers, armored pipes, gas coolant supply means and means for facilitating disassembly), a reduction in the cooling system, and a reduction in cycle pressure losses. In such a nuclear power plant, the gas flow from the compressor is directed into the recuperators. Preferably, a shut-down heat elimination system is provided within the prestressed concrete pressure tank which includes, in a known manner, a blower with or without a recuperator and a cooler. This emergency cooling system, which is independent of the main coolant cycle, ensures the elimination of reactor heat if the turboset fails in a single-shaft gas turbine plant either during down time or in the event of a problem within the reactor plant. The shut-down heat elimination system can be arranged in one of the vertical shafts. For the regulation of the single-shaft gas turboset, in addition to regulation of a bypass and the filling capacity, a frequency regulating system is provided which serves to control the frequency of the gas turboset due to the fluctuation of flow within the mains. The frequency regulating system consists of several gas storage tanks which are preferably housed in the vertical shafts. This arrangement affords particularly short flow paths for the gas as it flows back and forth between the storage tanks and the main cycle as required. Other advantages of this arrangement are the ready availability of the gas and its great safety and compactness. Further, it is preferable if all of the main cycle fittings are arranged within the prestressed concrete pressure tank so that the safety and compactness of the plant is enhanced. The fittings within the tank are arranged so that they are accessible from the exterior of the tank. All of the parts of the nuclear power plant carrying the gas coolant are preferably arranged within a safety tank (containment) into which access can be gained during the operation of the power plant. Further, the safety tank contains the necessary openings for the disassembly of the plant components which require maintenance and repair. The prestressed concrete tank is centered within and spaced inwardly from the safety tank and a revolving crane is located in the upper part of the safety tank for use in the disassembly of the plant components. In a nuclear power plant rated at about 1,000 MW, it is preferably if the safety tank is provided with a cylindrical recess which can be closed in a pressure-and gas-tight manner as an enclosure for the generator rigidly coupled within the gas turboset. If necessary, the generator can be inserted into the cylindrical recess along with its foundation so that it can be disassembled. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.