Patent Number: 
Section: claims

1. A nuclear reactor in which a coolant is contained comprising:a core composed of nuclear fuel, the coolant moving upwardly from the core by an operation thereof;an annular steam generator annularly arranged around an axis of the core in an upper side thereof into which the upwardly moving coolant flows and adapted to transfer heat in the coolant into water therein to generate a steam;a passage structure that defines a coolant passage for the coolant to an outside of the core, the heat-transferred coolant in the annular steam generator flowing downwardly in the coolant passage so as to flow into the core, thereby moving upwardly;a reactor vessel arranged to surround the coolant passage so as to contain the core, the annular steam generator and the coolant passage therein;a core barrel surrounding an outer periphery of the core;an annular reflector surrounding an outer periphery of the core barrel;a neutron shield arranged in the coolant passage and surrounding the outer periphery of the core;an electromagnetic pump annularly arranged in the coolant passage at a portion between outer and inner partition walls and above the neutron shield; anda guard vessel surrounding an outer periphery of the reactor vessel,wherein the pump is annularly displaced inside of the annular steam generator and the annular steam generator is arranged to surround an outer periphery of an upper portion of the pump so that at least lower portion of the steam generator is overlapped to the upper portion of the pump in an axial direction thereof, andwherein the core barrel, the annular reflector, the neutron shield and the solenoid pump are contained in the reactor vessel. 2. The nuclear reactor according to claim 1, wherein the steam generator is arranged outside of the pump at a predetermined space, and after flowing downwardly in the coolant passage from the annular steam generator, a part of the coolant flows upwardly through the predetermined space between an inner periphery of the steam generator and an outer periphery of the pump to be sucked from an upper end portion of the pump thereby flowing down into the core. 3. The nuclear reactor according to claim 2, wherein the passage structure includes an inner partition wall surrounding an outer periphery of the core barrel and an outer partition wall arranged to surround an outer periphery of the inner partition wall at a predetermined space, the predetermined space being defined as the coolant passage, the steam generator and the pump are constructed integrally with an upper structure of the nuclear reactor. 4. The nuclear reactor according to claim 3, further comprising a seal structural member interposed between an upper end portion of the inner partition wall and a lower end portion of the pump so as to define the coolant passage. 5. The nuclear reactor according to claim 3, wherein the reactor vessel is arranged to surround an outer periphery of the outer partition wall at an annular space, an upper end portion of the outer partition wall is opened in an upper space of the reactor vessel. 6. The nuclear reactor according to claim 5, further comprising a base plate on which the core is mounted to be supported in a lower portion of the reactor vessel said base plate being formed at its support portion with a bypass passage, the annular space being communicated through the bypass passage with a lower portion of the core. 7. The nuclear reactor according to claim 5, further comprising a base plate on which the core is mounted to be supported in a lower portion of the reactor vessel, the annular space being shielded from a lower portion of the core by a support portion of the base plate, and wherein the outer partition wall is formed with a plurality of opening portions at a vicinity of an outlet bottom portion of the steam generator so that the annular space is communicated through the opening portions with the coolant passage. 8. A nuclear reactor in which a coolant is contained comprising:a core composed of nuclear fuel, the coolant moving upwardly from the core by an operation thereof;an annular steam generator arranged in an upper side of the core into which the upwardly moving coolant flows and adapted to transfer heat in the coolant into water therein to generate a steam;a passage structure that defines a coolant passage for the coolant to an outside of the core, the heat-transferred coolant in the annular steam generator flowing downwardly in the coolant passage so as to flow into the core, thereby moving upwardly;a reactor vessel arranged to surround the coolant passage so as to contain the core, the annular steam generator and the coolant passage therein;a core barrel surrounding an outer periphery of the core;an annular reflector surrounding an outer periphery of the core barrel;a neutron shield arranged in the coolant passage and surrounding the outer periphery of the core;an electromagnetic pump annularly arranged in the coolant passage at a portion between outer and inner partition walls and above the neutron shield; anda guard vessel surrounding an outer periphery of the reactor vessel, wherein:the pump is annularly displaced inside of the annular steam generator and the annular steam generator is arranged to surround an outer periphery of an upper portion of the pump so that at least lower portion of the steam generator is overlapped to the upper portion of the pump in an axial direction thereof;the core barrel, the annular reflector, the neutron shield and the pump are contained in the reactor vessel;the steam generator is arranged outside of the pump at a predetermined space, and after flowing downwardly in the coolant passage from the annular steam generator, a part of the coolant flows upwardly through the predetermined space between an inner periphery of the steam generator and an outer periphery of the pump to be sucked from an upper end portion of the pump thereby flowing down into the core; andthe passage structure includes an inner partition wall surrounding an outer periphery of the core barrel and an outer partition wall arranged to surround an outer periphery of the inner partition wall at a predetermined space, the predetermined space being defined as the coolant passage, the steam generator and the pump are constructed integrally with an upper structure of the nuclear reactor. 9. The nuclear reactor according to claim 8, further comprising a seal structural member interposed between an upper end portion of the inner partition wall and a lower end portion of the pump so as to define the coolant passage. 10. A nuclear reactor in which a coolant is contained comprising:a core composed of nuclear fuel, the coolant moving upwardly from the core by an operation thereof;an annular steam generator arranged in an upper side of the core into which the upwardly moving coolant flows and adapted to transfer heat in the coolant into water therein to generate a steam;a passage structure that defines a coolant passage for the coolant to an outside of the core, the heat-transferred coolant in the annular steam generator flowing downwardly in the coolant passage so as to flow into the core, thereby moving upwardly;a reactor vessel arranged to surround the coolant passage so as to contain the core, the annular steam generator and the coolant passage therein;a core barrel surrounding an outer periphery of the core;an annular reflector surrounding an outer periphery of the core barrel;a neutron shield arranged in the coolant passage and surrounding the outer periphery of the core;an electromagnetic pump annularly arranged in the coolant passage at a portion between outer and inner partition walls and above the neutron shield; anda guard vessel surrounding an outer periphery of the reactor vessel, wherein:the pump is annularly displaced inside of the annular steam generator and the annular steam generator is arranged to surround an outer periphery of an upper portion of the pump so that at least lower portion of the steam generator is overlapped to the upper portion of the pump in an axial direction thereof;the core barrel, the annular reflector, the neutron shield and the pump are contained in the reactor vessel;the steam generator is arranged outside of the pump at a predetermined space, and after flowing downwardly in the coolant passage from the annular steam generator, a part of the coolant flows upwardly through the predetermined space between an inner periphery of the steam generator and an outer periphery of the pump to be sucked from an upper end portion of the pump thereby flowing down into the core; andthe reactor vessel is arranged to surround an outer periphery of the outer partition wall at an annular space, an upper end portion of the outer partition wall is opened in an upper space of the reactor vessel. 11. The nuclear reactor according to claim 10, further comprising a base plate on which the core is mounted to be supported in a lower portion of the reactor vessel said base plate being formed at its support portion with a bypass passage, the annular space being communicated through the bypass passage with a lower portion of the core. 12. The nuclear reactor according to claim 10, further comprising a base plate on which the core is mounted to be supported in a lower portion of the reactor vessel, the annular space being shielded from a lower portion of the core by a support portion of the base plate, and wherein the outer partition wall is formed with a plurality of opening portions at a vicinity of an outlet bottom portion of the steam generator so that the annular space is communicated through the opening portions with the coolant passage.