Patent Number: 059303190
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a nuclear reactor with a propagation space for core melt, the propagation space being provided with a coolant conduit which leads to a coolant reservoir and which has a valve opening in a temperature-dependent manner. In a nuclear reactor of the above-mentioned type, which is known from German Published, Non-Prosecuted Patent Application DE 40 41 295 A1, a steel crucible disposed in a reactor pit receiving a reactor pressure vessel has a plurality of inner protective layers, in order to withstand the high temperature of the core melt. A coolant pipe leads in an upper half through a wall of the crucible and a melting plug is located at an end of the coolant pipe which is inside the crucible. Another end of the coolant pipe leads to a coolant reservoir. If core melt escapes from the reactor pressure vessel, it is intercepted directly below the reactor pressure vessel within the reactor pit. If the core melt rises level with an outlet orifice of the cooling conduit, the melting plug is melted open as a result of direct contact or as a consequence of heat radiation. Cooling water is thereby guided in a large quantity onto the surface of the core melt for the direct cooling of the latter. Indirect cooling of the core melt takes place through a cooling system disposed outside the crucible. Direct cooling does not commence until clearly after indirect cooling and leads to a rapid flooding of the crucible, in which case large quantities of cooling water can come into contact with the core melt. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a nuclear reactor with a core melt propagation space provided with a coolant conduit leading to a coolant reservoir, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which allows early direct cooling of a core melt, flowing into a propagation space, over a region of large area. With the foregoing and other objects in view there is provided, in accordance with the invention, a nuclear reactor, comprising a coolant reservoir; a propagation space for core melt, the propagation space having a given cross-section; a spray conduit disposed in the propagation space, fed by the coolant reservoir and having a spraying area covering a large area of the given cross-section; and a device associated with the spray conduit and controlled for temperature-dependent opening when the core melt enters the propagation space. The cross-section of the propagation space can be spheroidal or polygonal (rectangular, hexagonal). The rapid, large-area spraying which takes effect from the outset gives rise to a crust on the core melt that appreciably reduces heat radiation. At the same time, an intercepting space above the crust fills with a steam atmosphere which drastically lowers the thermal load on the building structures, so that special protective layers (for example on the ceiling) can be avoided. As a result of the spraying of the core-melt surface, the water is distributed uniformly on the latter, thereby preventing water from infiltrating into the core melt and causing steam explosions. The crust, which becomes constantly thicker as a result of the spraying, acts in the same way, because it limits interactions between the core melt and water, that is to say, above all, it prevents steam explosions. In accordance with another feature of the invention, the spray conduit is disposed on the walls of the propagation or intercepting space, in such a way that it encloses the cross-section of the propagation or intercepting space. It can be fastened there in a simple way and, without further action, produces a large-area spray mist. In accordance with a further feature of the invention, the spray conduit is alternatively or additionally run at a distance from the bottom, over the cross-section of the propagation space. Such a configuration is provided, for example, in sprinkler systems in agriculture with pipelines running parallel to one another in order to cover a large area. For this purpose, it is possible to provide a multiplicity of spray conduits, which run parallel to one another or which intersect. In accordance with an added feature of the invention, in order to increase operating reliability, the spray conduit is a ring conduit having a plurality of feeds. It is advantageous for spraying to commence rapidly. In accordance with an additional feature of the invention, the device is a passively opening fitting which causes an opening of the coolant conduit, particularly in a temperature-dependent manner. In accordance with a concomitant feature of the invention, the device opening in a temperature-dependent manner is consequently disposed below the spray conduit, in such a way that a melting body keeping a sealing disc closed counter to the pressure of the coolant is located at the bottom of the propagation space. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a nuclear reactor with a core melt propagation space provided with a coolant conduit leading to a coolant reservoir, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.