Patent Number: 056595913
Section: summary

CROSS-REFERENCE TO RELATED APPLICATION This application is a Continuation of International Application Ser. No. PCT/DE94/01473, filed Dec. 12, 1994. BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a containment spray system for a light-water reactor, having a water trough in a safety tank and having a spray branch, a pump and an outlet-side spray nozzle array, connected to the water trough, for injecting water into the containment in finely dispersed form in the event of an operational incident. One such containment spray system is known from German Patent DE 22 07 870 C3, corresponding to U.S. Pat. No. 3,966,548. In that system, the water trough communicates with a sump cooler disposed in the containment through supply and drainage lines. Accordingly, not only trough water but water from the sump cooler as well is used for the spraying. Such containment spray systems have the task of spraying water being aspirated through a pump, in finely dispersed form in the safety tank, in order to allow both the temperature and the pressure in the safety tank to be reduced and also to allow radioactive aerosols, which form inside the safety tank to be bound, in an incident that cannot reach the outside. Containment spray systems like that referred to above, which aspirate the spray water from the sump of the safety tank, cannot spray with the desired fineness because if the return cooling water and emergency core cooling water fed into the primary loop during the incident is returned to it, the sump can contain contaminants or impurities that can stop up the nozzles. Published Japanese Patent Application 60-31092 describes a spray apparatus for a nuclear reactor with a pressure vessel. The pressure vessel is surrounded by a safety tank in which two water-filled chambers are present below the pressure vessel. The spray apparatus is disposed both on the walls of the safety tank and on a ceiling of the water-filled chamber. The spray apparatus on the safety tank wall is supplied with water from the chamber or from an additional tank located outside the safety tank through a pump, which is disposed in a separate chamber outside the safety tank. German Published, Non-Prosecuted Patent Application DE 33 02 773 A1, corresponding to U.S. Pat. No. 4,587,080, describes an emergency core cooling system for a pressurized water nuclear reactor plant. The emergency core cooling system has a building spray pump that communicates with a fuel exchange and water storage tank. Through the emergency core cooling system, if an elevated pressure occurs in the reactor building, water is sprayed in through a spray apparatus on the ceiling of the reactor building. The water is pumped to the spray apparatus from an emergency water storage tank located inside the reactor building or a water storage tank located outside the reactor building through a pump, in particular a low-pressure pump. The pump is located in a directly attached structure outside the reactor building. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a containment spray system for a light-water reactor, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, which assures highly effective trapping of fission products, suppression of pressure and heat dissipation over long-term operation in the context of overcoming severe incidents and which excels in having substantially smaller spray droplet sizes than with previously known spray systems. The novel spray system is not intended to share a supply of boron water with the nuclear emergency core cooling and aftercooling systems, in order to make it possible to avoid any competing or rival circuits. Another aspect of the stated object is that the containment spray system according to the invention should be disposed entirely inside the containment, except for energy supply devices. With the foregoing and other objects in view there is provided, in accordance with the invention, in a light-water reactor having a safety tank defining a containment, a containment spray system, comprising a water trough being disposed in the safety tank and having a bottom; and an immersion pump disposed in the vicinity of the bottom of the water trough, a spray branch and an outlet-side spray nozzle array, connected to the water trough for injecting water into the containment in finely dispersed form in the event of an operational incident. It is characteristic for the invention that except for the electrical energy supply for the spray pump, the novel containment spray system is disposed inside the containment. It includes an immersion pump which is disposed inside a water trough near the bottom, a riser line and the distribution system having the spray nozzles. In accordance with another feature of the invention, the water trough is a fuel assembly storage trough that during normal operation is not used and is decoupled from a reactor sump circuit and in particular is filled with borated water. The spray medium is the boron water of the fuel assembly trough which contains fuel assemblies only in the fuel assembly changing phase. The boron water surrounds the spray pump. In accordance with a further feature of the invention, the fuel assembly trough is an inner trough toward the reactor pressure vessel. In accordance with an added feature of the invention, protection against the effects of severe accidents is provided by suitable devices or coverings of the fuel assembly trough, particularly in the region of the surface of the water. Rubble and other contaminants are thus unable to reach the interior of the fuel assembly trough, so that on one hand the spray pump is protected and on the other hand nothing but clear spray medium is available. Accordingly, small bore diameters for the spray nozzles are possible which in turn brings about the desired high effectiveness of the spraying. In accordance with an additional feature of the invention, the spray system of the invention has a bore diameter of the spray nozzles and a feed pressure of the immersion pump ensuring that the maximum droplet diameter of a spray mist being produced is 100 .mu.m. Preferably, droplet diameters in the range below 100 .mu.m are employed. The feed pressure in the lower range must be raised in accordance with the nozzle bore diameters. In accordance with a concomitant feature of the invention, for a bore diameter in the range between 0.5 mm and 1 mm, the feed pressure of the immersion pump is between approximately 3 bar and 80 bar and for a bore diameter in the range between 1 mm and 1.5 mm, the feed pressure of the immersion pump is between approximately 6 bar and 80 bar. The advantages attainable with the invention and/or its features are considered to be above all that: the novel spray system does not or need not have any water supply shared with the nuclear emergency core cooling and aftercooling systems; the spray pump is located in the containment; the spray pump is constructed as an immersion pump; the spray pump is or may be disposed in the inner fuel assembly trough which is filled with boron water, in such a way that it is secure against the effects of a severe accident; the spray pump has optimal inflow conditions; clean boron water is used for the spraying; minimal-sized spray droplets with a diameter of less than 100 .mu.m are possible; and the supply of boron water of the inner fuel assembly trough is pumped for long periods into the sump of the containment. 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 containment spray system for a light-water reactor, 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.