Patent Number: 047028793
Section: claims

1. A nuclear reactor comprising: a substantially cylindrical flow liner having an open top, a cylindrical wall section, and a bottom wall, said cylindrical wall section forming a lower reactor internals chamber;  an upright cylindrical barrel within said cylindrical wall section having a bottom support plate spaced from said bottom wall, forming a downcomer annular passage between the cylindrical wall section and said barrel, and an upright riser chamber within said barrel;  a lower internals portion in the cylindrical flow liner containing a nuclear core having at least one fuel assembly, comprising a plurality of elongated fuel rods containing nuclear fuel to provide a fission-type chain reaction, and a plurality of elongated control rod assemblies contained within elongated thimbles disposed between said fuel rods, located in the riser chamber of said barrel;  at least one hot primary coolant discharge means in said flow liner intermediate said lower internals portion and said open top;  at least one cooled primary coolant return means in said flow liner intermediate said lower internals portion and said open top;  means for circulating primary coolant, at an elevated pressure upwardly through said nuclear core and riser chamber for heating thereof and discharge therefrom, and cooled primary coolant downwardly through said downcomer;  a pressure vessel having an upper removable top, an intermediate cylindrical wall section and a lower wall section, enclosing said flow liner and lower internals portion, the lower wall thereof spaced from said flow liner to form a second annular chamber therebetween, and the intermediate cylindrical wall section thereof having at least one outlet nozzle communicating with said at least one discharge means in the flow liner, and at least one inlet nozzle communicating with said at least one return means in the flow liner;  a supply of supplementary liquid coolant contained in said second annular chamber;  means communicating between said second annular chamber and said riser chamber for supplying supplementary liquid coolant directly to the nuclear core within said riser chamber;  means for cooling the major portion of said supplementary liquid coolant within said second annular chamber to a first elevated temperature; and  means for maintaining a localized minor portion of said supplementary liquid coolant at a second elevated temperature in excess of said first elevated temperature, and approximate that of coolant in said cooled primary coolant return means; whereby upon a decrease in the pressure of the primary coolant in said riser below a predetermined pressure, volatilization of said localized minor portion of supplemental liquid coolant is effected and the pressure increase resulting therefrom in said second annular chamber will feed remaining supplemental coolant through said means communicating between said second annular chamber to said nuclear core in said riser chamber.  (a) a nuclear reactor having;  a substantially cylindrical flow liner having an open top, a cylindrical wall section, and a bottom wall, said cylindrical wall section forming a lower reactor internals chamber;  an upright cylindrical barrel within said cylindrical wall section having a bottom support plate spaced from said bottom wall, forming a downcomer annular passage between the cylindrical wall section and said barrel and an upright riser chamber within said barrel;  a lower internals portion in the cylindrical flow liner containing a nuclear core having at least one fuel assembly, comprising a plurality of elongated fuel rods containing nuclear fuel to provide a fission-type chain reaction, and a plurality of elongated control rod assemblies contained within elongated thimbles disposed between said fuel rods, located in the riser chamber of said barrel;  at least one hot primary coolant discharge means in said flow liner intermediate said lower internals portion and said open top;  at least one cooled primary coolant return means in said flow liner intermediate said lower internals portion and said open top;  means for circulating primary coolant, at an elevated pressure upwardly through said nuclear core and riser chamber for heating thereof and discharge therefrom, and cooled primary coolant downwardly through said downcomer;  a pressure vessel having an upper removable top, an intermediate cylindrical wall section and a lower wall section, enclosing said flow liner and lower internals portion, the lower wall thereof spaced from said flow liner to form a second annular chamber therebetween, and the intermediate cylindrical wall section thereof having at least one outlet nozzle communicating with said at least one discharge means in the flow liner, and at least one inlet nozzle communicating with said at least one return means in the flow liner;  a supply of supplementary liquid coolant contained in said second annular chamber;  means communicating between said second annular chamber and said riser chamber for supplying supplementary liquid coolant directly to the nuclear core within said riser chamber;  means for cooling the major portion of said supplementary liquid coolant within said second annular chamber to a first elevated temperature; and  means for maintaining a localized minor portion of said supplementary liquid coolant at a second elevated temperature in excess of said first elevated temperature, and approximate that of coolant in said cooled primary coolant return means; whereby upon a decrease in the pressure of the primary coolant in said riser below a predetermined pressure, volatilization of said localized minor portion of supplemental liquid coolant is effected and the pressure increase resulting therefrom in said second annular chamber will feed remaining supplemental coolant through said means communicating between said second annular chamber to said nuclear core in said riser chamber;  (b) means for circulating water solely by natural convection from said hot leg to said cold leg with circumvention of said steam generator including:  means for heat exchange, for cooling water flowing from said hot leg to said cold leg; and  valve means for allowing flow of water from said hot leg to said cold leg; and  (c) further means for introducing stored coolant, under a superatmospheric pressure of gas, into the cylindrical vessel of said nuclear reactor. 2. A nuclear reactor as defined in claim 1 wherein said means communicating between said second annular chamber and said riser chamber comprises at least one opening through said flow liner bottom wall and an axially aligned opening through said bottom support plate of the upright cylindrical barrel; hollow tubular members providing flow communication between the axially aligned openings in said bottom wall and said bottom support plate; and elongated thimble connected to said bottom support plate extending upwardly into said riser chamber in the region of each said fuel assembly, and closed at the top thereof, said elongated thimble having a plurality of spaced apertures therealong. 3. A nuclear reactor as defined in claim 2 wherein said means for cooling the major portion of said supplementary coolant within said second annular chamber comprises insulating means on said cylindrical wall section and bottom of said flow liner enclosed within said pressure vessel lower wall section. 4. A nuclear reactor as defined in claim 3 wherein said insulating means comprises spaced planar sheets which form said cylindrical wall section, and a supply of liquid enclosed within said spaced wall sections. 5. A nuclear reactor as defined in claim 4 wherein said supply of liquid comprises water and said spaced wall sections are formed from stainless steel. 6. A nuclear reactor as defined in claim 3 wherein said insulating means comprises a coating of insulation material on said cylindrical wall section and said bottom. 7. A nuclear reactor as defined in claim 3 wherein further said means for cooling the major portion of said supplementary coolant within said second annular chamber is provided comprising means for containing a pool of liquid coolant about the exterior surface of said pressure vessel lower wall section and bottom, to a level spaced from the top end of said second annular chamber to expose an upper region of said pressure vessel lower wall. 8. A nuclear reactor as defined in claim 7 wherein said means for maintaining a localized minor portion of said supplementary coolant at the second elevated temperature comprises a heat retentive coating on said exposed upper region of the pressure vessel lower wall. 9. A nuclear reactor as defined in claim 1 wherein said pressure vessel lower wall is spherical in shape. 10. A nuclear reactor as defined in claim 1 wherein said pressure vessel lower wall is cylindrical in shape. 11. A passive safety system for a pressurized water nuclear reactor wherein the reactor-vessel is contained in a shield building, with a heat-conducting containment shell situated in the shield building containing said reactor, at least one steam generator, a primary coolant circuit for the reactor having a hot leg and a cold leg, and with a pressurizer connected to said circuit for maintaining primary coolant therein at a predetermined pressure, comprising: 12. A passive safety system as defined in claim 11 wherein said means for heat exchange includes a water storage tank within said containment shell adapted to contain a supply of water sufficient to flood the containment shell to a level above the hot leg, cold leg and reactor core, and a heat exchanger contained in said storage tank. 13. A passive safety system as defined in claim 12 wherein said heat exchanger has a horizontal intake manifold, an outlet manifold, and an interconnecting plurality of heat exchange tubes, first means connecting the inlet manifold with said hot leg and second means connecting the outlet manifold with said cold leg, and valve means are provided in said second means to control the flow of liquid therethrough. 14. A passive safety system as defined in claim 13 wherein a depressurizer line is provided between said pressurizer and said storage tank.