Patent Number: 
Section: claims

1. A nuclear reactor, comprising a nuclear fuel reactor core inside a pressure vessel; the pressure vessel having a shroud surrounding said reactor core and a downcomer of an outer region of said shroud; and a containment vessel surrounding said pressure vessel and having a pressure suppression pool, said nuclear reactor being one of a light water reactor and a heavy water reactor, wherein said pressure vessel contains the reactor core and a first heat exchanger for generating secondary steam, an inside of said containment vessel except a region installing said pressure vessel being vertically partitioned into three compartments, the pressure suppression pool having cooling water being formed in the upper compartment, a drywell for placing a feed water pipe of secondary cooling water, a main steam pipe of secondary steam being formed in the middle compartment, a wetwell of pressure suppression space being formed in the lower compartment, said drywell communicating with said pressure suppression pool through a plurality of vent pipes, an upper space of said pressure suppression pool communicating with said wetwell through a plurality of communicating pipes, a heat pipe containment vessel cooling system having a condensing heat exchanger arranged in a space above said pressure suppression pool and a first heat dissipater arranged outside said containment vessel in a position at a level higher than a level of said condensing heat exchanger, an interior of said condensing heat exchanger being filled with a heat medium, a gravitational water injection system being constructed as a plurality of gravitationally flow-down water injection pipes having an isolation valve between said pressure suppression pool and said pressure vessel, a pressure vessel bottom water flooding system being constructed as a plurality of pressure vessel bottom water flooding pipes between said pressure suppression pool and a lower portion of said drywell, an upper end of said gravitationally flow-down water injection pipe being arranged at a level higher than an upper end of said bottom, an upper end of said pressure vessel bottom water flooding pipe being arranged at a level higher than an upper end of said bottom, a lower portion of said pressure vessel bottom water flooding pipe being branched to a plurality of systems, at least one of said plurality of systems being connected to a fuse valve arranged in contact with an outer surface of a bottom portion of said pressure vessel, at least one other of said plurality of systems being opened to a lower space of said drywell through an isolation valve, a reactor core isolation cooling system being constructed as a cooling vessel and a second heat dissipater, said cooling vessel being filled with a coolant and containing a second heat exchanger in said coolant, said cooling vessel being arranged at a level higher than said reactor core inside said containment vessel, said second heat exchanger being connected to said pressure vessel using an inflow pipe and a water injection pipe, a lower end of said inflow pipe and a lower end of said water injection pipe being opened to said pressure vessel at a level lower than a water surface level in said pressure vessel during operation of said nuclear reactor, said second heat dissipater being arranged outside said containment vessel at a level higher than said cooling vessel, an upper end of said cooling vessel communicating with a cooler through a gas inflow pipe, said cooler communicating with said cooling vessel through a liquid returning pipe. 2. A nuclear reactor according to  claim 1 , wherein claim 1 at least one heat exchanger system arranged inside said pressure vessel, said at least one heat exchanger system being heated by primary cooling water recirculating through said reactor core to generate steam to be supplied to a turbine or a heat supply system, a secondary steam passage of said at least one heat exchanger system being branched to communicate with a portion under water of a pressure suppression pool arranged inside said containment vessel through an isolation valve, a secondary cooling water passage of said at least one heat exchanger system being branched to communicate with a portion under the water of said pressure suppression pool inside said containment vessel through an isolation valve, decay heat generated by said reactor core during reactor core isolation being heat exchanged by said at least one heat exchanger system to condense steam generated by the decay heat under the water of said pressure suppression pool and at the same time to supply the water of said pressure suppression pool to said at least one heat exchanger system. 3. A nuclear reactor according to  claim 1 , wherein claim 1 at least one heat exchanger system arranged inside said pressure vessel, said at least one heat exchanger system being heated by primary cooling water recirculating through said reactor core to generate steam to be supplied to a turbine or a heat supply system, a third heat exchanger being arranged under water of a pressure suppression pool inside said containment vessel, a secondary steam passage of said at least one heat exchanger system in said pressure vessel being branched to communicate with said third heat exchanger under the water of a pressure suppression pool through an isolation valve, a secondary cooling water passage of said at least one heat exchanger system in said pressure vessel being branched to communicate with said third heat exchanger under the water of the pressure suppression pool through an isolation valve, decay heat generated by said reactor core during reactor core isolation being heat exchanged by said at least one heat exchanger system in said pressure vessel to condense steam generated by the decay heat using said third heat exchanger under the water of said pressure suppression pool and at the same time to supply the condensed water to said at least one heat exchanger system in said pressure vessel. 4. A nuclear reactor, comprising: a pressure vessel having a shroud surrounding a nuclear fuel reactor core inside the pressure vessel and a downcomer of an outer region of said shroud; and  a containment vessel surrounding said pressure vessel and having a pressure suppression pool, said nuclear reactor being a light water reactor or a heavy water reactor;  a heat pipe containment vessel cooling system having a condensing heat exchanger arranged in a space above said pressure suppression pool, wherein an inside of said condensing heat exchanger is filled with a heat medium; and  a heat dissipater arranged outside said containment vessel in a position at a level higher than a level of said condensing heat exchanger, said heat dissipater communicating with said condensing heat exchanger through a gas inflow pipe and a liquid returning pipe to form a closed loop for the heat medium. 5. A nuclear reactor, comprising: a nuclear fuel reactor core inside a pressure vessel, the pressure vessel having a shroud surrounding said reactor core and a downcomer of an outer region of said shroud;  a containment vessel surrounding said pressure vessel and having a pressure suppression pool, said nuclear reactor being a light water reactor or a heavy water reactor,  wherein an inside of said containment vessel except a region installing said pressure vessel is vertically partitioned into three compartments,  a pressure suppression pool having cooling water being formed in the upper compartment,  a drywell for placing a feed water pipe of secondary cooling water and a main steam pipe of secondary steam being formed in the middle compartment,  a wetwell of a pressure suppression space being formed in the lower compartment,  said drywell communicating with said pressure suppression pool through a plurality of vent pipes, an upper space of said pressure suppression pool communicating with said wetwell through a plurality of communicating pipes. 6. A nuclear reactor, comprising: a nuclear fuel reactor core inside a pressure vessel, the pressure vessel having a shroud surrounding said reactor core and a downcomer of an outer region of said shroud;  a containment vessel surrounding said pressure vessel and having a pressure suppression pool, said nuclear reactor being one of a light water reactor and a heavy water reactor,  wherein a pressure vessel bottom water flooding system is comprised of a pressure vessel bottom water flood pipe, a lower portion of the pressure vessel bottom water flooding pipe is branched to a plurality of systems, and at least one of said plurality of systems is connected to a fuse valve arranged in contact with an outer surface of a bottom portion of said pressure vessel, and at least the other one of said plurality of systems is opened to a lower space of said drywell through an isolation valve.