Patent Number: 047132132
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention concerns a nuclear reactor plant housed in a steel pressure vessel. More particularly, a plant with a gas cooled, small high temperature reactor, the core of which contains a pile of spherical fuel elements through which a cooling gas flows from bottom to top. A heat utilization system placed in the flow of cooling gas is installed above the small high temperature reactor in a reactor pressure vessel, followed in line preferably by two circulating blowers with at least one decay heat exchanger installed in the steel pressure vessel. 2. Description of the Prior Art A nuclear reactor installation is described in DE P No. 34 35 255.4. In this plant the decay heat exchangers on the primary side are installed immediately following in the direction of flow the main heat exchangers forming the heat utilization system and are traversed constantly by the entire flow of cooling gas. They are arranged under the main heat exchanger. On the secondary side the decay heat exchangers are connected by means of a decay heat removal water circulation loop with a geodesically higher located recooling heat exchanger, which in turn is connected with a further heat sink, such as for example a cooling tower. A plant for the nuclear generation of heat is shown in DE-OS No. 32 12 264, which also uses a small high temperature reactor as the source of energy. This small high temperature reactor is designed so that different heat utilization systems, such as steam generators, split tubular furnaces or He/He heat exchangers may be connected with it. There are no special installations in this plant for the removal of decay heat. SUMMARY OF THE INVENTION It is an object of the present invention to design a nuclear reactor plant housed in a steel pressure vessel, with a gas cooled small high temperature reactor, the core of which contains a pile of spherical fuel elements traversed from bottom to top by a cooling gas, with a heat utilization system arranged in the flow of cooling gas and installed above the small high temperature reactor in the reactor pressure vessel and which is followed in line preferably by two circulating blowers, and with at least one decay heat exchanger installed in the steel pressure vessel so that heat generated may be removed in an intermediate circulation loop and the safe removal of the decay heat from the reactor core is assured. This object is attained by the following characteristics: a. The heat utilization system comprises He/He heat exchanger, in which the primary helium transfers its heat to a secondary helium flow circulating in an intermediate loop; PA0 b. The He/He heat exchanger comprises at least one annular helix coil bundle extending to a hot gas collector chamber located above the reactor core and exposed from below to hot gas; PA0 c. The decay heat exchanger is arranged in the direction of flow immediately following the He/He heat exchanger and is constantly traversed by the entire flow of the cooling gas; PA0 d. The circulating blowers located in the flow of cold gas are connected parallel with respect to each other. The hot gas coming from the small high temperature reactor flows through a roof reflector into the hot gas collector chamber and enters the He/He heat exchanger from below, where it flows around the bundle of tubes while transferring its heat to the secondary helium flowing in the tubes. The cooled primary helium is conducted to the circulating blowers. After passing through the circulating blowers the cold primary helium is returned to the reactor core, which it enters from below. Decay heat is removed by means of the decay heat exchangers located in the primary circulation loop, which in normal operation is exposed on the primary side to the temperature of the cold gas. No special butterfly valves or blowers are required for the decay heat exchangers and none are therefore provided. In case of a failure of the two circulating blowers for the He/He heat exchangers, the decay heat is removed by natural convection. As the He/He heat exchanger is under the same pressure on the primary and the secondary side, it is not endangered by the decay heat removal operation. An alternative solution may be seen in removing the decay heat of a small high temperature reactor combined with a He/He heat exchanger by means of the heat exchangers arranged in the secondary heat circulation loop. Advantageous further developments of the invention are set forth in the dependent claims and the description below of a preferred embodiment.