Patent Number: 047568720
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention: The invention relates to a nuclear reactor housed in a prestressed concrete pressure vessel secure against bursting. The station includes a gas cooled high temperature reactor having primary loop components comprising steam generators and blowers in a large cavity clad with a liner of the prestressed concrete pressure vessel. A liner cooling system and at least one shut-down system are also included. A reactor core, the spherical fuel elements whereof comprise coated particles of a fissionable material embedded in a graphite matrix, is cooled by helium flowing from top to bottom through the reactor core as the cooling gas. 2. Background of the Art: The THTR-300 MW.sub.el prototype nuclear power station is a nuclear power installation of the aforementioned high temperature, gas-cooled type. It comprises a high temperature reactor with spehrical fuel elements utilizing helium as the cooling gas. Such reactor is often referred to as a pebble bed reactor which provides the environment of the present invention. A high temperature reactor of this configuration possesses a series of specific safety characteristics, whereby the risk of an accident in the course of the operation of such a power plant is reduced to a minimum. Even in the case of hypothetical incidents (accidents) the system's inherent safety characteristics of such high temperature reactors act to restrict environmental effects to relatively low values. The characteristics of a high temperature reactor include the negative temperature and power coefficient under all operating conditions. The use of a gaseous and, thus phase stable coolant, specifically a neutron physically neutral inert gas is also characteristic whereby, even in the case of a pressure relief accident, the coolant cannot be lost entirely. A low ratio of power density/heat capacity is another characteristic. In the case of interference with the production or removal of heat, only slow changes occur in the temperature of the core. A further characteristic of high temperature reactors is the high temperature strength of the core material comprising ceramic material (graphite) and the fuel elements, wherein the fuel is embedded in the form of particles coated with pyrocarbon in a gas tight manner, so that fission products are retained in the graphite shell. SUMMARY OF THE INVENTION It is an object of the present invention to provide a nuclear power station of the aforedescribed structural type, which may be operated economically in a capacity range of 300-600 MW.sub.el and wherein simultaneously high safety standards may be maintained by utilizing the favorable accident behavior of the high temperature reactor. This and other objects are attained by a nuclear power station for a gas-cooled high temperature pebble bed reactor having a pebble bed reactor core housed in a prestressed concrete pressure vessel 2, an operating cooling circuit comprising at least one steam generator 7 and blower 8, a secondary cooling circuit 9 and primary loop for flow of cooling medium through the reactor core from top to bottom and at least one reactor shutdown system 13. The nuclear power station according to the present invention comprises: a reactor protection building surrounding the prestressed concrete pressure vessel and cooling circuits, means for relieving the pressure in the reactor protection building, means for filtering radioactive contaminants in the reactor protection building in combination with the pressure relief means, a plurality of auxiliary cooling circuits separate and independent from the operating and secondary cooling circuits and means for removal of decay heat of the reactor core in the event of failure of the auxiliary cooling circuits the means including a liner cooling circuit for the prestressed concrete pressure vessel. The assurance of the retention of activities in case of incidents up to hypothetical accidents is to be considered the primary measure to reduce or eliminate risks in the operation of a nuclear power station. The retention of activities is determined essentially by the operating and accident temperatures and operating and accident pressures. The safety of a nuclear power station, therefore, depends primarily on the control of temperature and pressure problems; i.e. exceeding the failure temperature of the fuel elements and of the prestressed concrete pressure vessel must be sufficiently unlikely or excluded and the pressure integrity of the installation must be assured. In a nuclear power station according to the invention, the aforementioned temperature and power problems are safely under control.