Patent Number: 045267430
Section: claims

1. A containment vessel for a nuclear reactor comprising a dry well mounting therein a pressure vessel containing the nuclear reactor and having a vertically extending center line, non-condensable gases normally being present in an internal space of said dry well, a pressure suppression chamber annularly arranged to surround the center line of said pressure vessel and containing a pool of coolant, a partition separating said dry well from said pressure suppressing chamber, a pedestal extending from said pressure suppressing chamber through said partition into said dry well for supporting within said dry well said pressure vessel containing said nuclear reactor, and vent pipe means for releasing therethrough into said pool of coolant within said pressure suppression chamber steam which will be discharged from said pressure vessel into the internal space of said dry well as a result of an accident, said vent pipe means comprising a plurality of separated and individually mounted vent pipe members each inserted into said pool of coolant and having at least one exhaust port opening in said pool of coolant, said vent pipe members each continuously communicating the internal space of said dry well with said pool of coolant, said vent pipe members each being constructed and arranged such that said at least one exhaust port is immersed in said pool of coolant at all times even if the internal pressure of said dry well becomes lower than the pressure prevailing in a space formed within said pressure suppression chamber and disposed above a liquid level of said pool of coolant, the improvement comprising said vent pipe means being arranged for inhibiting sudden initial increases of pressure in said pressure suppression chamber resulting from transient release of said non-condensable gases into said coolant through said vent pipe means occurring as a result of an accident and enabling the pressures applied to walls of said pressure suppression chamber due to the transient release of said non-condensable gases to become balanced about the center line of said pressure vessel, said vent pipe members of said vent pipe means being divided into a plurality of groups in such a manner that said vent pipe members of different groups differ from one another in the length of submerged portions of said vent pipe members interposed between the liquid level of said pool of coolant within said pressure suppression chamber and said at least one exhaust port of said vent pipe members for inhibiting sudden initial increases of pressure in said pressure suppression chamber resulting from the transient release of said non-condensable gases into said coolant through said vent pipe members occurring as a result of an accident, said vent pipe members of said vent pipe means being arranged in said pressure suppression chamber in such a manner that the pressures applied to the walls of said pressure suppression chamber due to the transient release of said non-condensable gases become balanced about the center line of said pressure vessel, and communicating means for permitting an internal spaced formed in said pedestal to communicate only with said space formed in said pressure suppressing chamber and disposed above the liquid level of said pool of coolant. 2. A containment vessel for a nuclear reactor as claimed in claim 1, wherein the length h.sub.n of the submerged portions of said vent pipe members between the liquid level of said pool of coolant and the exhaust ports of said vent pipe members, which length is in the nth order by starting from the pipes of the shortest submerged length h.sub.1 is determined by using the following equation: EQU h.sub.n =h.sub.1 +(n-1).DELTA.h 3. A containment vessel for a nuclear reactor comprising a dry well mounting therein a pressure vessel containing the nuclear reactor and having a vertically extending center line, non-condensable gases normally being present in an internal space of said dry well, a pressure suppression chamber annularly arranged to surround the center line of said pressure vessel and containing a pool of coolant, a partition separating said dry well from said pressure suppressing chamber, a pedestal extending from said pressure suppressing chamber through said partition into said dry well for supporting within said dry well said pressure vessel containing said nuclear reactor, and vent pipe means for releasing therethrough into said pool of coolant within said pressure suppression chamber steam which will be discharged from said pressure vessel into the internal space of said dry well as a result of an accident, said vent pipe means comprising a plurality of separated and individually mounted vent pipe members each inserted into said pool of coolant and having at least one exhaust port opening in said pool of coolant, said vent pipe members each continuously communicating the internal space of said dry well with said pool of coolant, said vent pipe members each being constructed and arranged such that said at least one exhaust port is immersed in said pool of coolant at all times even if the internal pressure of said dry well becomes lower than the pressure prevailing in a space formed within said pressure suppression chamber and disposed above a liquid level of said pool of coolant, the improvement comprising said vent pipe means being arranged for inhibiting sudden initial increases of pressure in said pressure suppression chamber resulting from transient release of said non-condensable gases into said coolant through said vent pipe means occurring as a result of an accident and enabling the pressures applied to walls of said pressure suppression chamber due to the transient release of said non-condensable gases to become balanced about the center line of said pressure vessel, said vent pipe members of said vent pipe means being divided into a plurality of groups in such a manner that said vent pipe members of different groups differ from one another in the length of submerged portions of said vent pipe members interposed between the liquid level of said pool of coolant within said pressure suppression chamber and said at least one exhaust port of said vent pipe members for inhibiting sudden initial increases of pressure in said pressure suppression chamber resulting from the transient release of said non-condensable gases into said coolant through said vent pipe members occurring as a result of an accident, said vent pipe members of said vent pipe means being arranged in said pressure suppression chamber in such a manner that the pressures applied to the walls of said pressure suppression chamber due to the transient release of said non-condensable gases become balanced about the center line of said pressure vessel, the length h.sub.n of the submerged portions of said vent pipe members between the liquid level of said pool of coolant and the exhaust ports of said vent pipe members, which length is in the nth order by starting from the pipes of the shortest submerged length h.sub.1 is determined by using the following equation: EQU h.sub.n =h.sub.1 +(n-1).DELTA.h 4. A containment vessel for a nuclear reactor as claimed in claim 1, wherein each of said vent pipe members is formed with an exhaust port at a lower end thereof. 5. A containment vessel for a nuclear reactor as claimed in claim 1, wherein each of said vent pipe members is formed with a pair of exhaust ports disposed in diametrically opposed positions in a side wall near a lower end thereof. 6. A containment vessel for a nuclear reactor as claimed in claim 1, wherein said vent pipe members of a plurality of groups having submerged portions of different lengths interposed between the liquid level of said pool of coolant in the pressure suppressing chamber and the lower ends of the vent pipe members are disposed symmetrically with respect to the center line of said pedestal. 7. A containment vessel for a nuclear reactor comprising a dry well for mounting therein a pressure vessel containing the nuclear reactor, a pressure suppressing chamber having a pool of coolant therein, a partition separating said dry well from said pressure suppressing chamber, a pedestal extending from said pressure suppressing chamber through said partition into said dry well for supporting within the dry well the pressure vessel containing the nuclear reactor, and a plurality of separated and individually mounted vent pipe members for releasing therethrough into said pool of coolant in said pressure suppressing chamber steam which will be generated in said dry well when an accident occurs and, said vent pipe members being inserted in said pool of coolant in said pressure suppressing chamber and each having at least one exhaust port opening in said pool of coolant, said vent pipe members each being constructed and arranged such that said exhaust port is immersed in said pool of coolant at all times even if the internal pressure of said dry well becomes lower than the pressure prevailing in a space formed in said pressure suppressing chamber and disposed above a liquid level of said pool of coolant, wherein the improvement comprises the arrangement whereby said separated and individually mounted vent pipe members are divided into a plurality of groups in such a manner that the separated and individually mounted vent pipe members of different groups differ from one another in the length of submerged portions of the vent pipe members interposed between the liquid level of the pool of coolant within the pressure suppressing chamber and the exhaust ports of the vent pipe members, wherein the length h.sub.n of the submerged portions of the vent pipe members between the liquid level of said pool of coolant and the exhaust ports of the vent pipe members, which length is in the nth order by starting from the pipes of the shortest submerged length h.sub.1 is determined by using the following equation: EQU h.sub.n =h.sub.1 +(n-1).DELTA.h 8. A containment vessel for a nuclear reactor as claimed in claim 7, wherein each of said vent pipe members is formed with an exhaust port at a lower end thereof. 9. A containment vessel for a nuclear reactor as claimed in claim 7, wherein each of said vent pipe members is formed with a pair of exhaust ports disposed in diametrically opposed positions in a side wall near a lower end thereof.