Patent Number: 048896829
Section: summary

FIELD OF THE INVENTION This invention relates to liquid cooled, nuclear fission reactor plant complexes. The invention is particularly concerned with a passive or self-acting cooling system for the containment structure housing a fissionable fuel containing nuclear reactor. BACKGROUND OF THE INVENTION Typically nuclear fission reactors for power generation are housed within a containment structure as a safety measure. Nuclear reactor containments are designed and employed to enclose the nuclear reactor pressure vessel containing the core of heat generating fissionable fuel and ancillary components of the system, such as portions of the coolant/heat transfer means which constitute a source and/or means of conveyance of radiation and/or radioactive fission products. As such, the containment structure housing a nuclear reactor must effectively isolate the reactor system and components enclosed within its confines by sealing in all contents including any water, steam, gases or vapor and entrained fission products or other sources of radiation that may have escaped from the reactor vessel and in particular its associated cooling system. The provision of a construction fulfilling such requirements with an effective fluid impermeable confinement structure securely isolating its enclosed contents from the external atmosphere does not generally present either a significant engineering or construction obstacle or achievement. However, in the event of certain malfunctions in a nuclear reactor system, such as a loss of coolant, large volumes of very hot pressurized water may be released from the system into the interior of the containment structure. This very hot pressurized water flashes into steam which may carry along radioactive fission products, and substantially increase the pressure and temperature within the containment structure. Such accidents can produce very high pressures and temperatures within the confines of the "leak proof" containment structure thereby imposing heavy demands upon its integrity and ability to perform its designed role of retaining all potentially hazardous matter derived from the nuclear reactor system. Potentially deleterious high pressure due to the inherent high thermal energy and flashing steam cannot simply be released by venting from the containment or otherwise permitted to escape to the outside atmosphere since the steam vapor may entrain and carry radioactive fission products which would also be released into the environment. A variety of suppression schemes have been proposed and devised to cope with the problem of excessive pressure. They include a variety of measures or arrangements for condensing evolving or flashing steam and reducing the resultant over-pressure caused by accidents, for example, the designs disclosed in U.S. Letters Pat. Nos. 3,713,968; 4,362,693; 4,473,528; and 4,526,743. In the absence of an effective suppression means to mitigate steam generated high pressures, the enveloping containment structure must be designed and constructed at excessively high costs and maintained to resist and retain substantial internal fluid pressures. Nevertheless, even a significantly reinforced containment structure cannot be assured to be resistant to breaching considering the temperature/pressure potential of a typical power generating nuclear reactor plant. SUMMARY OF THE INVENTION This invention comprises a passive cooling system for the containment structure of a nuclear fission reactor plant. The cooling system provides means for lowering the temperature of the interior environment of a reactor containment to relieve or preclude over-pressure therein by reducing ambient temperatures and thus condensing steam. The passive cooling system entails a heat transfer sequence that permits the safe dissipation of thermal energy out into the environment free of contaminating radioactive fission products. OBJECTS OF THE INVENTION It is a primary object of this invention to provide a new and improved containment system for nuclear fission reactor plants. It is also an object of this invention to provide a passive cooling system for nuclear fission reactor containment structures. It is a further object of this invention to provide functional improvements in a nuclear reactor containment comprising a passive or self-acting cooling arrangement. It is a still further object of this invention to provide passive pressure suppression system for containment structures of nuclear reactor plants. It is another object of this invention to provide a cooling system for nuclear fission reactor containment structures which is based upon natural convection heat transfer.