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.