Patent Number: 
Section: claims

1. A nuclear reactor system including a nuclear reactor vessel,wherein the nuclear reactor vessel includes a first vessel serving as a region using fast neutrons, and a second vessel serving as a region using thermal neutrons in a nuclear reactor, energy of each thermal neutron being approximately 0.5 MeV or less, and the second vessel for the thermal neutrons is placed inside the first vessel for the fast neutrons or the first vessel for the fast neutrons is placed inside the second vessel for the thermal neutrons,the region using the fast neutrons includesa plurality of fuel assemblies, each fuel assembly being a bundle of 50 or more metal fuel rods, each metal fuel rod being obtained by inserting a metal fuel pin into a sheath made of stainless steel, the metal fuel pin having an alloy composition of zirconium (Zr) with uranium (U) and/or plutonium (Pu), anda liquid metal selected from metallic sodium (Na), Pb—Bi or Pb working as a primary coolant,a non-metallic material and radioactivity reducing assemblies are loaded in the region using the thermal neutrons, the non-metallic material being usable as a neutron moderator and as a secondary coolant, each radioactivity reducing assembly being obtained by putting a radioactive material into a sheath made of stainless steel or a Zr material, the radioactive material being obtained by processing minor actinide nuclides separated from spent fuel rods through reprocessing or radioactive nuclear fission products (FPs) separated and refined from the spent nuclear fuel, at least one selected from the group consisting of Se79, Sr90, Zr93, Tc99, Sn126, Cs135 and Cs137, being mixed and formed into a shape of a pellet or a pin, andthe nuclear reactor system is configuredto generate electricity by transferring thermal energy generated by the fast neutrons to a heat exchanger by use of the primary coolant, exchanging heat between the primary coolant and the secondary coolant in the heat exchanger, and thereafter supplying the thermal energy to a turbine system by use of the secondary coolant, andto simultaneously decrease a concentration of radionuclides by accelerating a rate of transmutation of radionuclides into stable nuclides by use of thermal neutrons generated by decelerating the fast neutrons. 2. The nuclear reactor system according to claim 1,wherein the nuclear reactor system uses metallic sodium (Na) as the primary coolant for the fuel assemblies, and carbon dioxide gas (CO2) as the secondary coolant for the radioactivity reducing assemblies, the carbon dioxide gas working as the coolant and as the moderator,the nuclear reactor system further includes a CO2 gas driven turbine, andwherein the nuclear reactor system enhances heat exchange efficiency by once supplying the CO2 gas, returning from the turbine system, to the radioactivity reducing second vessel, and thereafter supplying the CO2 gas to the heat exchanger for transferring heat between the primary coolant and the secondary coolant. 3. The nuclear reactor system according to claim 1,wherein the nuclear reactor system uses lead-bismuth (Pb—Bi) or Pb alone as the primary coolant for the fuel assemblies, and water (H2O) as the secondary coolant concurrently working as a moderator for the radioactivity reducing assemblies,the nuclear reactor system further includes a steam turbine, andwherein the nuclear reactor system enhances heat exchange efficiency by supplying H2O, returning from the turbine system, to the second vessel in which the radioactivity reducing assemblies are loaded, and thereafter supplying the H2O to the heat exchanger for transferring heat between the primary coolant and the secondary coolant. 4. The nuclear reactor system according to claim 1, wherein the nuclear reactor system uses supercritical carbon dioxide (CO2) gas as the secondary coolant. 5. The nuclear reactor system according to claim 1, wherein the reflector is arranged surrounding the plurality of fuel assemblies loaded in the first vessel, the reflector being deformable due to thermal expansion, the reflector having a structure which makes temperature and reflector efficiency inversely correlated to each other, the reflector being capable of automatically controlling nuclear fission reaction induced by fast neutrons. 6. The nuclear reactor system according to claim 5, whereina structure of the reflector uses carbon (C) or beryllium (Be) as a constituent material,the reflector is divided into four or more segments in a circumferential direction,a spring made of stainless steel with a large thermal expansion coefficient is attached to each reflector segment, andthe structure of the reflector is configured to decrease reflection efficiency depending on thermal expansion of the spring with a rise in temperature. 7. The nuclear reactor system according to claim 5, whereina structure of the reflector is divided into segments in a radial direction and in a height direction,each reflector segment is formed by filling graphite or carbon into a case made of stainless steel,each two reflector segments are connected by stainless steel, andthe structure of the reflector is configured to be capable of decreasing neutron reflection efficiency of the reflector depending on thermal expansion of the stainless steel. 8. The nuclear reactor system according to claim 1, whereina solenoid coil is arranged surrounding the radioactivity reducing assemblies which are loaded in the second vessel, the nuclear fission products (FPs) being mixed into each radioactivity reducing assembly, andthe nuclear reactor system is configured to accelerate a rate of β-decay of the radioactive nuclear fission products bygenerating a low-frequency electromagnetic field at a frequency of 50 kHz to 50 MHz, andconcurrently applying the thermal neutrons to the radioactivity reducing assemblies, the thermal neutrons being obtained by decelerating the fast neutrons which are generated in the first vessel outside the second vessel. 9. The nuclear reactor system according to claim 1, whereinsolenoid-shaped winding is arranged along a radial circumference of the second vessel,the radioactivity reducing assemblies into which the radioactive nuclear fission waste is mixed are loaded in the second vessel, andthe nuclear reactor system is configured to accelerate a rate of transmutation of FP elements into stable elements byapplying a low-frequency electromagnetic field at a frequency of 100 kHz to 10 MHz to the radioactivity reducing assemblies, andfurther bombarding an inside of the first vessel placed in the second vessel with thermal neutrons which are generated from a reactor core including the reflector. 10. The nuclear reactor system according to claim 1, whereinthe first vessel is formed in a shape of a cylinder with a diameter of 2 m or less,each fuel assembly to be contained in the nuclear reactor vessel includes 50 or more fuel rods, each of which is formed with a diameter of 5 to 15 mm and with a length of 2 m or less,six or more of the fuel assemblies are loaded in the first vessel, andthe reflector deformable due to thermal expansion is arranged surrounding the fuel assemblies in order to realize a load following control scheme. 11. The nuclear reactor system according to claim 1, whereinin the fuel assemblies, a fuel pin into which minor actinide elements are mixed is inserted into each fuel rod sheath, andthe nuclear reactor system is thereby configured to accelerate transmutation of radioactive minor actinide elements into stable elements by use of the fast neutrons. 12. The nuclear reactor system according to claim 1, whereina diameter of the nuclear reactor vessel is 2 m or greater,two or more of the first vessels serving as the fast neutron region and two or more of the second vessels serving as the thermal neutron region are set in the vessel,the metal fuel assemblies are loaded in each first vessel, and each first vessel is filled with the primary coolant of liquid metal,the radioactivity reducing assemblies containing minor actinides and/or radioactive nuclear fission products (FPs) separated and refined from the spent nuclear fuel, at least one selected from the group consisting of Se79, Sr90, Zr93, Tc99, Sn126, Cs135 and Cs137, being mixed and formed into a shape of a pellet or a pin, are loaded in each second vessel, andthe nuclear reactor system removes heat from the vessel and the radioactivity reducing assemblies containing the radioactive waste by making the secondary coolant flow in the vessel and the radioactivity reducing assemblies, and further uses the heat to generate electricity. 13. A method comprising: in a nuclear reactor system,forming a nuclear reactor vessel with a first vessel serving as a region using fast neutrons, and a second vessel serving as a region using thermal neutrons, energy of each thermal neutron being approximately 0.5 MeV or less;arranging a plurality of fuel assemblies and a liquid metal in the region using the fast neutrons, each fuel assembly being a bundle of 50 or more metal fuel rods, each metal fuel rod being obtained by inserting a metal fuel pin into a sheath made of stainless steel, the metal fuel pin having an alloy composition of zirconium (Zr) with uranium (U) and/or plutonium (Pu), the liquid metal working as a primary coolant;accelerating transmutation of radioactive minor actinide elements into stable elements by use of fast neutrons by inserting the metal fuel pin, into which minor actinide elements are mixed, into each fuel rod sheath in the fuel assemblies; andloading a non-metallic material and radioactivity reducing assemblies in the region using the thermal neutrons, the non-metallic material being usable as a neutron moderator and a secondary coolant, each radioactivity reducing assembly being obtained by putting a radioactive material into a sheath made of stainless steel or a Zr material, the radioactive material being obtained by processing minor actinide nuclides separated from spent fuel rods through reprocessing, or radionuclides as nuclear fission products, into a shape of a pellet or a pin, whereinthe methodgenerates electricity by transferring thermal energy generated by the fast neutrons to a heat exchanger by use of the primary coolant, exchanging heat between the primary coolant and the secondary coolant in the heat exchanger, and thereafter supplying the thermal energy to a turbine system by use of the secondary coolant, andsimultaneously decreases a concentration of radionuclides by accelerating a rate of transmutation of radionuclides into stable nuclides by use of thermal neutrons generated by decelerating the fast neutrons. 14. The method according to claim 13,wherein the method uses metallic sodium (Na) as the primary coolant for the fuel assemblies, and carbon dioxide (CO2) gas as the secondary coolant for the radioactivity reducing assemblies, the carbon dioxide gas working as the coolant and as the moderator,the method further uses a CO2 gas driven turbine, andwherein the method enhances heat exchange efficiency by once supplying the CO2 gas, returning from the turbine system, to the radioactivity reducing second vessel, and thereafter supplying the CO2 gas to the heat exchanger for transferring heat between the primary coolant and the secondary coolant. 15. The method according to claim 13,wherein the method uses lead-bismuth (Pb—Bi) or Pb alone as the primary coolant for the fuel assemblies, and water (H2O) as the secondary coolant concurrently working as a moderator for the reducing assemblies,the method further uses a steam turbine, andwherein the method enhances heat exchange efficiency by supplying H2O, returning from the turbine system, to the second vessel in which the radioactivity reducing assemblies are loaded, and thereafter supplying the H2O to the heat exchanger for transferring heat between the primary coolant and the secondary coolant. 16. The method according to claim 13, whereina solenoid coil is arranged surrounding the radioactivity reducing assemblies which are loaded in the second vessel, the nuclear fission products (FPs) being mixed into each radioactivity reducing assembly, andthe method accelerates a rate of β-decay of the radioactive nuclear fission products bygenerating a low-frequency electromagnetic field at a frequency of 50 kHz to 50 MHz, andconcurrently applying the thermal neutrons to the radioactivity reducing assemblies, the thermal neutrons being obtained by decelerating the fast neutrons which are generated in the first vessel outside the second vessel. 17. The method according to claim 13, whereinsolenoid-shaped winding is arranged along a radial circumference of the second vessel,the radioactivity reducing assemblies into which the radioactive nuclear fission waste is mixed are loaded in the second vessel, andthe method accelerates a rate of transmutation of FP elements into stable elements byapplying a low-frequency electromagnetic field at a frequency of 100 kHz to 10 MHz to the radioactivity reducing assemblies, andfurther bombarding an inside of the first vessel placed in the second vessel with thermal neutrons which are generated from a reactor core including the reflector. 18. The method according to claim 13, wherein the method performs load following control byforming the first vessel in a shape of a cylinder with a diameter of 2 m or less,using 50 or more fuel rods, each formed with a diameter of 5 to 15 mm and with a length of 2 m or less, in each fuel assembly to be contained in the nuclear reactor vessel,loading six or more of the fuel assemblies in the first vessel, andarranging the reflector, deformable due to thermal expansion, to surround the fuel assemblies.