Patent Number: 
Section: claims

1. A passive containment cooling and filtered venting system of a nuclear power plant, the plant including:a core,a reactor pressure vessel that accommodates the core,a containment vessel including:a dry well that contains the reactor pressure vessel,a wet well that contains in its lower portion a suppression pool connected to the dry well via a LOCA vent pipe and includes in its upper portion a wet well gas phase,a vacuum breaker that circulates gas in the wet well gas phase to the dry well, anda pedestal that supports the reactor pressure vessel in the containment vessel via an RPV skirt and an RPV support and forms a pedestal cavity inside,the passive containment cooling and filtered venting system comprising:an outer well that is provided outside the dry well and the wet well, surrounds at least a part of the dry wall and the wet wall, adjoins the dry well via a dry well common part wall, adjoins the wet well via a wet well common part wall, and has pressure resistance and gastightness equivalent to pressure resistance and gastightness of the dry well and the wet well;a scrubbing pool that is arranged in the outer well and stores water inside;a cooling water pool that is installed above the dry well and the outer well and reserves cooling water;a heat exchanger that includes an inlet plenum, an outlet plenum, and a heat exchanger tube, and is submerged at least in part in the cooling water;a gas supply pipe that is connected to the inlet plenum of the heat exchanger at a first end of the gas supply pipe and connected to a gas phase of the containment vessel at a second end of the gas supply pipe to lead gas in the containment vessel to the heat exchanger;a condensate return pipe that is connected to the outlet plenum of the heat exchanger at a first end of the condensate return pipe, passes through the outer well, and is connected to inside the containment vessel at a second end of the condensate return pipe to lead condensate in the heat exchanger into the containment vessel; anda gas vent pipe that is connected to the outlet plenum of the heat exchanger at a first end of the gas vent pipe, passes through the outer well, has a second end of the gas vent pipe installed as submerged in the scrubbing pool in the outer well, and releases noncondensable gas in the heat exchanger to the outer well. 2. The passive containment cooling and filtered venting system according to claim 1, further comprising:a lid that covers a top of the scrubbing pool to form a space above a surface of the water of the scrubbing pool; anda first outlet pipe that is connected to the lid at a first end of the first outlet pipe and that opens to a space of the outer well at a second end of the first outlet pipe. 3. The passive containment cooling and filtered venting system according to claim 2, further comprising:a filter that is connected to the first outlet pipe at the second end of the first outlet pipe; anda second outlet pipe that is connected to the filter at a first end of the second outlet pipe and opens to the outer well at a second end of the second outlet pipe. 4. The passive containment cooling and filtered venting system according to claim 1, further comprising:a flooder pipe that opens to the suppression pool at a first end of the flooder pipe and opens in the pedestal cavity at a second end of the flooder pipe;a flooder valve that is arranged on a portion of the flooder pipe inside the pedestal cavity; anda flooder check valve that is arranged on a portion of the flooder pipe inside the suppression pool. 5. The passive containment cooling and filtered venting system according to claim 1, whereinthe condensate return pipe includes a U-shaped water seal, and the second end of the condensate return pipe is connected to the dry well through the dry well common part wall, the U-shaped water seal being a U-bent portion storing sealing water inside. 6. The passive containment cooling and filtered venting system according to claim 5, further comprising a spray sparger at the second end of the condensate return pipe in the dry well. 7. The passive containment cooling and filtered venting system according to claim 1, further comprising:a PCCS drain tank that stores water inside, has a gas phase in its upper portion, and is arranged inside the outer well; andan overflow pipe that connects the gas phase of the PCCS drain tank at a first end of the overflow pipe with the dry well at a second end of the overflow pipe, whereinthe second end of the condensate return pipe is submerged in the water in the PCCS drain tank. 8. The passive containment cooling and filtered venting system according to claim 7, further comprising a spray sparger at the second end of the overflow pipe in the dry well. 9. The passive containment cooling and filtered venting system according to claim 7, further comprising:a water injection pipe that is connected to below a water surface of the water in the PCCS drain tank at a first end of the water injection pipe and led into the pedestal cavity at a second end of the water injection pipe;a water injection valve that is arranged on the water injection pipe; anda drain pit that is located in the PCCS drain tank and stores water inside the drain pit, whereinthe second end of the condensate return pipe is submerged in the drain pit. 10. The passive containment cooling and filtered venting system according to claim 1, further comprising a condensate check valve arranged on the condensate return pipe. 11. The passive containment cooling and filtered venting system according to claim 1, whereinthe gas supply pipe is connected to the inlet plenum of the heat exchanger at the first end of the gas supply pipe, passes through the outer well, and is connected to the dry well through the dry well common part wall at the second end of the gas supply pipe to lead the gas in the dry well to the heat exchanger. 12. The passive containment cooling and filtered venting system according to claim 11, further comprising:a cyclone separator that is arranged in the outer well; andan inlet pipe that connects the dry well with the cyclone separator and leads gas in the dry well to the cyclone separator, whereinthe gas supply pipe is connected to an outlet of the cyclone separator at the first end to lead gas discharged from the cyclone separator to the heat exchanger. 13. The passive containment cooling and filtered venting system according to claim 11, further comprising:a gas supply isolation valve that is installed on the gas supply pipe; anda wet well gas supply pipe that is connected at a first end of the wet well gas supply pipe to the inlet plenum of the heat exchanger or a portion of the gas supply pipe between the inlet plenum and the gas supply isolation valve, passes through the outer well, and is connected at a second end of the wet well gas supply pipe to inside the wet well gas phase through the wet well common part wall to lead the gas in the wet well to the heat exchanger. 14. The passive containment cooling and filtered venting system according to claim 13, wherein:the scrubbing pool is a filtered venting tank storing decontamination water inside;the second end of the gas vent pipe is connected to an inlet pipe of the filtered venting tank; andthe filtered venting tank opens to an interior of the outer well via an outlet pipe. 15. The passive containment cooling and filtered venting system according to claim 1, further comprising a screen located on a portion of the gas supply pipe that extends inside the dry well. 16. A nuclear power plant comprising:a containment vessel that contains a reactor pressure vessel, the containment vessel including a dry well and a wet well;an outer well that is provided outside the dry well and the wet well, surrounds at least a part of the dry well and the wet well, and has pressure resistance and gastightness;a scrubbing pool that is arranged in the outer well and stores water inside;a cooling water pool that is installed above the dry well and the outer well and reserves cooling water;a heat exchanger that includes an inlet plenum, an outlet plenum, and a heat exchanger tube, and is submerged at least in part in the cooling water;a gas supply pipe that is connected to the inlet plenum of the heat exchanger at a first end of the gas supply pipe and connected to a gas phase of the containment vessel at a second end of the gas supply pipe to lead gas in the containment vessel to the heat exchanger;a condensate return pipe that is connected to the outlet plenum of the heat exchanger at a first end of the condensate return pipe, passes through the outer wall, and is connected to inside the containment vessel at a second end of the condensate return pipe to lead condensate in the heat exchanger into the containment vessel; anda gas vent pipe that is connected to the outlet plenum of the heat exchanger at a first end of the gas vent pipe, passes through the outer well, has a second end of the gas vent pipe installed as submerged in the scrubbing pool in the outer well, and releases noncondensable gas in the heat exchanger to the outer well.