Patent Number: 039980570
Section: summary

BACKGROUND OF THE INVENTION The invention covers a nuclear power plant with a closed system of circulating cooling gas. The equipment consists of a high-temperature reactor, a gas turbine assembly and heat exchangers. The latter are made up of recuperators, pre- and intermediate coolers as well as pipes carrying the gas between the several components. The entire assembly is encased in a housing made of pre-stressed concrete (single-unit construction). Plants of the type described offer obvious advantages over nuclear power installations of a different, existing type in which the energy is transferred to a secondary circuit, because they combine the advantages of gas turbines with the high efficiency and simplicity in operation which is typical of single-circuit construction. By integrating the reactor, the turbines, the required coolers, and all other circuit components in a single pressure tight vessel, separate connecting elements connecting the components that contain "live" fuel are rendered unnecessary, a fact which offers distinct advantages in the construction and operation of high-temperature reactors. The integrated design is therefore preferred for a large number of specialized nuclear power plants. For example, German Auslegeschrift No. 1,156,903 describes a compact power plant of the above-mentioned type intended for vehicles. In this design the turbine and the compressor are located on opposite faces of the reactor core, a hollow shaft passing through the core, with intermediate coolers being located in the annular space between the reactor and the wall of the pressure chamber. In this compact design it is assumed that the turbine used will not require any maintenance, and therefore no provision has been made for the removal of the turbine or any other components of the circuit. A similar construction is shown in a nuclear reactor disclosed in German Offenlegungschrift No. 2,005,208 where a pressure jacket, open at its frontal surfaces, is located inside the pressure chamber and is spaced relative to the inside wall of the pressure vessel so as to accommodate the heat exchangers. Also, the German Offenlegungsschrift No. 2,028,736 a nuclear power plant is described having a system of closed circulation of gas. This power plant is built on the principle of dual chambers. The gas turbine together with the components belonging to the gas circulation system are contained in a block of prestressed concrete separate from the concrete pressure vessel, with the object of simplifying the fueling- and controlling processes. A similar construction is used in the high-pressure concrete vessel described in German Auslegeschrift No. 1,614,610, consisting of two separate pressure-tight chambers, one containing the reactor, the other the secondary equipment. The working medium is carried by pipes protruding through the pressure-tight walls, first from the reactor to the turbine and from the compressor then back into an annular-shaped space below the reactor core. This so-called "igloo-method" however offers technical difficulties in construction, and the nuclear power plant, because of the principles applied in the arrangement of components, is highly uneconomical. German Offenlegungsschrift No. 2,062,934 likewise discloses a gas-cooled nuclear reactor of integrated construction in which the gas turbine is located inside the hollow wall of the pressure chamber enclosing the reactor core. Through a by-pass mechanism a part of the cooling gas carried past the core of the reactor can be diverted and directly combined with the hot exhaust gas emitted from the core. Another nuclear power plant of the type originally defined is described in German Offenlegungsschrift No. 1,764,249. Here the nuclear reactor together and all circulatory components are located in closely spaced, parallel, vertical shafts inside the concrete pressure vessel, with all components being fully accessible from the outside. Passages for the cooling media are provided within the wall of the pressure vessel as well as between the several vertical shafts. In this design the cooling media has to flow over an extensive area, resulting in the need for a relatively bulky pressure vessel in this type plant. SUMMARY OF THE INVENTION The present invention proceeds from the foregoing state of the art and has as an object to correct the shortcomings inherent in the known nuclear power plants through a particular arrangement of all components. It is a particular object of the invention to provide a compact nuclear power plant, while at the same time rendering all components easily accessible. In accomplishing these and other objects, there has been provided in accordance with the present invention a nuclear power plant comprising an inner, generally cylindrical vessel; a high-temperature reactor contained within the inner vessel; a gas turbine assembly located in a horizontally oriented chamber positioned in the inner vessel beneath the reactor; a plurality of heat exchanger means positioned in a plurality of vertically oriented pods spaced radially, preferably in a circle about the reactor in the inner vessel; and conduit means interconnecting the reactor, the turbine assembly and the heat exchanger means for carrying a gas between these components. The conduit means are arranged in essentially horizontal and vertical straight lines, and the conduit means connecting the reactor and the turbine for carrying high pressure gas are provided with horizontal connections to the reactor and the turbine. The conduit means for carrying low pressure gas comprises a horizontal conduit system positioned beneath the turbine assembly and is comprised of a plurality of coaxial connecting tubes, collectors and distributors and a plurality of normal conduits. The remainder of the heat exchange means comprise intermediate coolers, preferably arranged in vertically stacked pairs in each pod, and coaxial conduits are provided for transporting gas from the low-pressure compressor to the intermediate coolers, through the outer passage of the conduit, and back from the coolers to the high-pressure compressor through the inner passage of the conduit. A plurality of secondary heat absorption devices are preferably also located in additional vertical pods arranged around the reactor. The structural features of the present invention may thus be summarized as follows: The gas-turbine system is installed in a horizontal pod located underneath the reactor which is located centrally inside a vessel; several vertical pods, placed symmetrically around the reactor, contain the recuperators and the pre-coolers; the pre-coolers serving the recuperators are placed above or below the recuperators; the tubes carrying the gas between components run in a straight path, either vertically or horizontally, with vertical tubes being in pods; the high-pressure circuit runs through several vertical pods equipped with horizontally placed connections; a horizontally positioned system of tubes carrying low-pressure gases is placed underneath the turbine compartment. The principles realized in the nuclear power plant according to the invention may be briefly summarized as follows: a largely symmetrical structure of the vessel made of pre-stressed concrete; development of pods as vertical gas lines; gas lines connecting the various components in the primary circuit are direct and in straight lines; gas lines are arranged coaxially and maintain in normal operation only minor differences in pressure between the gas streams flowing coaxially; streams of hot gases flow coaxially inside an isolated system of tubes that are freely distributed inside the pre-stressed concrete vessel and shielded by high-pressure jackets which are surrounded by a circuit of cold gas; easy accessibility from the outside of secondary equipment built into the structure, such as gas lines, heat exchangers, values, heat insulators, etc. for the purpose of inspection, maintenance, repair, and removal after shutting off certain sections of the plant. All pods, gas lines and components of the primary circuit are geometrically accessible upon the removal of the lid of the concrete container, allowing for inspection, maintenance and repair by remote control. The convenient accessibility is the result of the coaxial arrangement of gas lines in relatively large concrete channels, the direct gas leads being arranged in straight lines, and the use of pods serving as vertical gas ducts. By locating two separate gas circuits in one single concrete unit, compactness of the primary circuit is achieved, and the dimensions of the concrete container can be held down to a relatively small size. The arrangement of the various components is such that it can be retained at any desired level of varying output without difficulty, a fact which is of great importance in the development of new types of nuclear reactors. The turbine assembly is built in a horizontal chamber placed at a distance from the nuclear reactor which offers adequate shielding to the turbine assembly against neutron radiation. For the installation and removal of the turbine assembly a sliding device has been provided. The turbine assembly is constructed with a single shaft, offering distinct advantages over a multiple-shaft design: its operation and normal functioning are easy to supervise and of proven reliability; it requires only a single seal where the shaft penetrates through the concrete jacket; and its cost is lower. The turbine is rigidly coupled to the generator. The hot gas coming from the reactor is first taken up by four radially located connecting pipes and then carried over vertical ducts containing hot gas, designed as pods. Then, it is carried by four horizontal connecting tubes to the symmetrically designed intake tubes of the turbine. The four radial connecting pipes together with their graphite packings extend all the way to the vertical gas pipes formed as pods. The exhaust gas from the turbine (approx. 500.degree. C.) first flows downward in a vertical pipe where it enters into the horizontal system of tubes carrying low-pressure gas. By distributors and coaxial cross-connections or feeder lines the gas is distributed to the pods which contain the recuperators and pre-coolers. Upon entering the recuperators it flows through them along the jacket side. The gas subsequently passes through the pre-coolers and is finally returned to the horizontal pipe system. In the return flow, the gas is directed through the outer passages if the coaxial ducts, while on its way to the recuperators it is directed through the interior passages of the coaxial feeder line system. The coaxial network of cross-connections or feeder lines is designed in such a manner that the exhaust gases leaving the turbine at about 500.degree. C. are encircled on all sides by cold gas, whereby thermal stresses in the gas lines are minimized. The cold gas (30.degree. C.) from the horizontal pipe system enters a vertical cylindrical duct through several simple horizontal ducts and is then brought into the low-pressure compartment of the compressor. Here it is compressed to 36 bar. In an advantageous embodiment of the invention six recuperators are provided, which are connected in pairs via a coaxial feeder line to a collector and a distributor. Accompanying pre-coolers are located respectively vertically underneath the recuperators. The compressed gas is carried back to the recuperators by six pipes. A major portion of four of these six pipes runs coaxially to the vertical gas pipes leading from the reactor to the turbine. Thereby the relatively cold high-pressure gas (125.degree. C.) encircles the four hot-gas pipes between the reactor and the turbine. In order to increase the efficiency of the nuclear power plant, an intermediate cooling system is provided in the primary circuit, also located in the vertical shafts or pods. These pods are arranged in the same circle about the reactor as the pods holding the recuperators and pre-coolers and are symmetrically placed with respect thereto. The intermediate coolers are connected in two groups, each containing a pair of intermediate coolers, installed on top of each other in a single pod. Two coaxial pipes lead from the low-pressure compartment of the compressor to the two pods holding the pair of intermediate coolers. The gas flows in the outer pipes toward the pods where it is divided into two partial streams, one flowing upward, the other downward. After passing through the intermediate coolers the gas is carried back to the high-pressure compartment of the compressor through the interior tube of the coaxial system. The hollow pods in the concrete housing, designed to house the components, such as the reactor, the horizontal turbine compartment, vertical pods for heat exchangers, gas ducts and regulators, are preferably lined with gas-tight steel liners. Excess pressures are taken up by the concrete jacket and to reduce the build-up of excessively high temperatures in the concrete, the liners are watercooled and further protected by insulation. As mentioned before, the intermediate coolers serve to increase the efficiency of the plant. It is, however, conceivable to design nuclear power plants in which intermediate coolers are omitted, whereby a reduction in efficiency may be accepted in exchange for various other advantages. The most important of these advantages may be summarized briefly as follows: smaller dimensions of the pre-stressed concrete vessel; elimination of expensive components (besides the intermediate cooling units also steel liners, gas ducts, and other devices connected with the construction of the installation); a reduction in the size of the cooling system; and a reduction of pressure-losses connected with circulating systems. In a power plant of this type the stream of gas leaving the compressor is conveyed directly into the recuperators. It is of advantage to additionally provide a final stage for the elimination of heat inside the stressed-concrete casing, conventionally consisting of a blower, equipped either with or without a recuperator, and a cooler. Such a cooling system operates independently of the main circulation system for the described single-shafted gas turbine assembly; it provides for the disposal of the reactor's heat in the event of a turbine failure, in times of shut-downs, and in the event of break-downs. The secondary heat disposal system (4 .times. 50%) is located in four vertical shafts or pods distributed symmetrically around the reactor. It is designed to afford a possible by-pass of the main circuit in the event of a break-down, without requiring additional safety valves for a shut off. All valves needed for shutting down the nuclear reactor are advantageously located inside the concrete housing, also placed in vertical pods or shafts, further adding to the safety and compactness of the plant, with these valves being readily accessible from the outside. All components carrying active gas are advantageously integrated inside a safety housing and are accessible while the plant is in operation. The housing has openings required for the installation and removal of components in need of maintenance or repair. The housing, made of pre-stressed concrete, is located in the central area of the safety tank. On the top of this tank is placed a revolving crane used for moving major components in or out of the tank. In the case of a power plant having an output of 1,000 MW, the safety tank is equipped with a cylindrical compartment, which can be sealed off, gas- and pressure-tight, by a simple lid, for holding the generator which is rigidly coupled with the gas turbine assembly. The generator, together with its mounting, can be slid into the compartment, and if necessary, removed again. Further objects, features and advantages of the invention will become apparent from the following detailed description of a preferred embodiment when considered with the attached figures of drawing.