Patent Number: 
Section: claims

1. A core of a light water reactor, comprising:a plurality of fuel assemblies having a nuclear fuel material zone including nuclear fuel material that includes a plurality of isotopes of transuranic nuclides disposed in said core,wherein said fuel assemblies have a lower fuel support member supporting each lower end portion of a plurality of fuel rods internally forming said nuclear fuel material zone, and an upper fuel support member supporting an upper end portion of each of said plurality of fuel rods,wherein a plenum is formed above said nuclear fuel material zone in said fuel rod, andwherein an outside diameter of a first portion of said fuel rod in a first position in which said plenum is formed is smaller than an outside diameter of a second portion of said fuel rod in a second position in which said nuclear fuel material zone is formed and is within a range of 3 mm or more, andwherein a length of said plenum in an axial direction of said core is within a range from 400 mm to 2500 mm. 2. A fuel assembly, comprising:a plurality of fuel rods; a lower fuel support member supporting a lower end portion of each of said plurality of fuel rods; an upper fuel support member supporting an upper end portion of each of said plurality of fuel rods; and a plurality of neutron absorbing members,wherein said plurality of fuel rods internally form a nuclear fuel material zone having a nuclear fuel material including a plurality of isotopes of transuranic nuclides,wherein a plenum is formed above said nuclear fuel material zone in each of said fuel rods,wherein an outside diameter of a first portion of said fuel rod where said plenum is formed is smaller than an outside diameter of a second portion of said fuel rod where said nuclear fuel material zone is formed and is within a range of 3 mm or more, andwherein a length of said plenum in an axial direction of said fuel assembly is within a range from 400 mm to 2500 mm. 3. A core of a light water reactor, comprising:a plurality of fuel assemblies having a nuclear fuel material zone including nuclear fuel material disposed in said core,wherein said fuel assemblies form an upper blanket zone, an upper fissile zone, an internal blanket zone, and a lower fissile zone in said nuclear fuel material zone in an axial direction in this order in said core; andwherein a plurality of isotopes of transuranic nuclides are included in said upper fissile zone and said lower fissile zone; andwherein said fuel assemblies disposed in said core include at least one fuel assembly having a burnup of 0, and a ratio of fissionable plutonium to a total of all said nuclear fuel materials in said lower fissile zone is larger than a ratio of fissionable plutonium to a total of all said nuclear fuel material in said upper fissile zone. 4. The core of a light water reactor according to claim 3,wherein when said fuel assembly of a burnup of 0 is included in said core, an average of enrichment of fissionable plutonium to a total of all nuclear fuel material in said lower fissile zone and an average of enrichment of fissionable plutonium to a total of all nuclear fuel material in said upper fissile zone is within a range from 16% to 20%; and said enrichment of fissionable plutonium to the total of all nuclear fuel material in said lower fissile zone is within a range from 1.05 to 1.6 times said enrichment of fissionable plutonium to the total of all nuclear fuel material in said upper fissile zone. 5. The core of a light water reactor according to claim 3, wherein said lower blanket zone is disposed under said lower fissile zone in said nuclear fuel material zone. 6. The core of a light water reactor according to claim 3, wherein a ratio of plutonium-239 to all said transuranic nuclides included in said nuclear fuel material zone is within either of a range from 40% to 60% and a range from 5% or more to less than 40%. 7. A core of a light water reactor, comprising:a plurality of fuel assemblies having a nuclear fuel material including nuclear fuel material disposed in said core,wherein said fuel assemblies form an upper blanket zone, an upper fissile zone, an internal blanket zone, and a lower fissile zone in said nuclear fuel material zone in an axial direction in this order in said core;wherein a plurality of isotopes of transuranic nuclides are included in said upper fissile zone and said lower fissile zone; andwherein said fuel assemblies disposed in said core include at least one fuel assembly having a burnup of 0, a total of a height of said lower fissile zone and a height of said upper fissile zone is within a range from 350 mm to 600 mm, and said height of said upper fissile zone is within a range from 1.1 to 2.1 times said height of said lower fissile zone. 8. A core of a light water reactor, comprising:a plurality of fuel assemblies having a nuclear fuel material zone including nuclear fuel material disposed in said core,wherein said fuel assemblies form an upper blanket zone, an upper fissile zone, an internal blanket zone, and a lower fissile zone in said nuclear fuel material zone in an axial direction in this order in said core;wherein a plurality of isotopes of transuranic nuclides are included in said upper fissile zone and said lower fissile zone;wherein said fuel assemblies disposed in said core include at least one fuel assembly having a burnup of 0, and an average of an enrichment of fissionable plutonium to a total of all nuclear fuel material in said lower fissile zone and an average of an enrichment of fissionable plutonium to a total of all nuclear fuel material in said upper fissile zone is within a range from 16% to 20%; andwherein said enrichment of fissionable plutonium to the total of all nuclear fuel material in said lower fissile zone is within a range from 1.05 to 1.6 times said enrichment of fissionable plutonium to the total of all nuclear fuel material in said upper fissile zone. 9. A fuel assembly, comprising:a plurality of fuel rods;a lower fuel support member supporting a lower end portion of each of said plurality of fuel rods;an upper fuel support member supporting an upper end portion of each of said plurality of fuel rods; anda plurality of neutron absorbing members,wherein said plurality of fuel rods internally form a nuclear fuel material zone having a nuclear fuel material including a plurality of isotopes of transuranic nuclides;wherein said nuclear fuel material zone includes an upper blanket zone, an upper fissile zone, an internal blanket zone, and a lower fissile zone; said upper blanket zone, said upper fissile zone, said internal blanket zone, and said lower fissile zone are disposed in an axial direction in this order; and said upper fissile zone and said lower fissile zone include said plurality of isotopes; andwherein said fuel assembly has a burnup of 0, a ratio of fissionable plutonium to a total of all of the nuclear fuel materials in said lower fissile zone is larger than a ratio of fissionable plutonium to a total of all of the nuclear fuel materials in said upper fissile zone. 10. A core of a light water reactor, comprising:a plurality of fuel assemblies having a nuclear fuel material zone including nuclear fuel material that includes a plurality of isotopes of transuranic nuclides disposed in said core;wherein a plurality of neutron absorbing members are disposed above said nuclear fuel material zone;wherein said fuel assembly has a plurality of fuel rods internally forming said nuclear fuel material zone and a plenum formed above said nuclear fuel material zone, a lower fuel support member supporting a lower end portion of each of said plurality of fuel rods, and an upper fuel support member supporting an upper end portion of each of said plurality of fuel rods;wherein each of said neutron absorbing members is disposed below said upper fuel support member and between said plenum of neighboring fuel rods, and is attached to said upper fuel support member; andwherein a total of cross sectional areas of all said neutron absorbing members in said fuel assembly is within a range from 10% to 50% of a cross sectional area of a fuel assembly lattice. 11. The core of a light water reactor according to claim 10,wherein a height of said nuclear fuel material zone is within a range from 20 cm to 250 cm. 12. The core of a light water reactor according to claim 11, wherein an outside diameter of a first portion of said plenum of said fuel rod is smaller than an outside diameter of a second portion of said fuel rod in said nuclear fuel material zone and is within a range of 3 mm or more and a length of said plenums in said axial direction of said core is within a range from 400 mm to 2500 mm. 13. The core of a light water reactor according to claim 11, wherein said plenum include a first zone and a second zone disposed above said first zone, and an outside diameter of a first portion of said fuel rod in said first zone is smaller than an outside diameter of a third portion of said fuel rod in said nuclear fuel material zone, and an outside diameter of a second portion of said fuel rod in said second zone is smaller than said outside diameter of said third portion of said fuel rod in said nuclear fuel material zone and is larger than said outside diameter of said first portion in said first zone, and said neutron absorbing members are disposed between a lower end of said second zone and said upper end of said nuclear fuel material zone. 14. The core of a light water reactor according to claim 11, wherein a ratio of plutonium-239 occupying in all said transuranic nuclides included in said nuclear fuel material zone is within a range from 5% or more to less than 40%. 15. The core of a light water reactor according to claim 10, wherein a length of said plurality of neutron absorbing members in an axial direction of said core are within a range from 20 mm to 700 mm and a distance between an upper end of said nuclear fuel material zone and a lower end of said neutron absorbing member is within a range from 230 mm to 500 mm. 16. The core of a light water reactor according to claim 10, wherein another neutron absorbing member is disposed below said nuclear fuel material zone. 17. The core of a light water reactor according to claim 10, wherein a neutron absorbing material filling zone is formed below said nuclear fuel material zone in said fuel rod. 18. The core of a light water reactor according to claim 17, wherein a length of said neutron absorbing material filling zone in said axial direction of said core is within a range from 10 mm to 150 mm. 19. The core of a light water reactor according to claim 17, wherein an outside diameter of a first portion of said fuel rod in said neutron absorbing material filling zone is larger than an outside diameter of a second portion of said fuel rods in said nuclear fuel material zone and an interval between mutual outside surfaces of said first portions of said neighboring fuel rods in said neutron absorbing material filling zone is within a range of 1.3 mm or more. 20. The core of a light water reactor according to claim 10,wherein said nuclear fuel material zone includes an upper blanket zone, an upper fissile zone, an internal blanket zone, and a lower fissile zone, and said upper blanket zone, said upper fissile zone, said internal blanket zone; said lower fissile zone are disposed in said axial direction of said core in this order; and said upper fissile zone and said lower fissile zone include said plurality of isotopes, andwherein when said fuel assemblies of a burnup of 0 are included, a rate of fissionable plutonium to a total of all nuclear fuel material in said lower fissile zone is larger than a rate of fissionable plutonium to a total of all nuclear fuel material in said upper fissile zone. 21. The core of a light water reactor according to any one of claims 11, 15, 16, 17, 18, 12, 20 and 10, wherein a ratio of plutonium-239 to all said transuranic nuclides included in said nuclear fuel material zone is within a range from 40% to 60%. 22. A fuel assembly, comprising:a plurality of fuel rods;a lower fuel support member supporting a lower end portion of each of said plurality of fuel rods;an upper fuel support member supporting an upper end portion of each of said plurality of fuel rods; anda plurality of neutron absorbing members;wherein said plurality of fuel rods internally form a nuclear fuel material zone having nuclear fuel material including a plurality of isotopes of transuranic nuclides,wherein a plenums is formed above said nuclear fuel material zone;wherein said plurality of neutron absorbing members are disposed above said nuclear fuel material zone and below said upper fuel support member, and are attached to said upper fuel support member; andwherein each of said neutron absorbing members is disposed between said plenum of neighboring fuel rods. 23. The fuel assembly according to claim 22, wherein said plurality of fuel rods internally form a nuclear fuel material zone having a height within a range from 20 cm to 250 cm. 24. The fuel assembly according to claim 23, wherein said neutron absorbing members are disposed below said upper fuel support member. 25. The fuel assembly according to claim 24, wherein each of said neutron absorbing members is disposed between said mutual plenums of said neighboring fuel rods. 26. The fuel assembly according to claim 23,wherein said plenum includes a first zone and a second zone disposed above said first zone; an outside diameter of a first portion of said fuel rod in said first zone is smaller than an outside diameter of a third portion of said fuel rod in said nuclear fuel material zone; and an outside diameter of a second portion of said fuel rod in said second zone is smaller than said outside diameter of said third portion of said fuel rod in said nuclear fuel material zone and is larger than said outside diameter of said first portion in said first zone; andwherein said neutron absorbing member is disposed between a lower end of said second zone and said upper end of said nuclear fuel material zone. 27. The fuel assembly according to claim 23 or 22, wherein a length of said neutron absorbing member in an axial direction of said fuel assemblies is within a range from 20 mm to 700 mm and a distance between an upper end of said nuclear fuel material zone and a lower end of said neutron absorbing member is within a range from 230 mm to 500 mm. 28. The fuel assembly according to claim 23 or 22, wherein a neutron absorbing material filling zone is formed below said nuclear fuel material zone in said fuel rod. 29. The fuel assembly according to claim 28, wherein a length of said neutron absorbing material filling zone in an axial direction of said fuel assembly is within a range from 10 mm to 150 mm. 30. The fuel assembly according to claim 28, wherein an outside diameter of a first portion of said fuel rod in said neutron absorbing material filling zone is larger than an outside diameter of a second portion of said fuel rod in said nuclear fuel material zone and an interval between mutual outside surfaces of said first portions of said neighboring fuel rods in said neutron absorbing material filling zone is within a range of 1.3 mm or more. 31. The core of a light water reactor according to claim 3, wherein when said fuel assembly of a burnup of 0 is included in said core, a total of a height of said lower fissile zone and a height of said upper fissile zone is within a range from 350 mm to 600 mm; and said height of said upper fissile zone is within a range from 1.1 to 2.1 times said height of said lower fissile zone. 32. The fuel assembly according to claim 23, 24 or 22, wherein an outside diameter of a first portion of said plenum of said fuel rod is smaller than an outside diameter of a second portion of said fuel rod in said nuclear fuel material zone and is within a range of 3 mm or more and a length of said plenum in an axial direction of said fuel assembly is within a range from 400 mm to 2500 mm. 33. The fuel assembly according to claim 22,wherein said nuclear fuel material zone includes an upper blanket zone, an upper fissile zone, an internal blanket zone, and a lower fissile zone; said upper blanket zone, said upper fissile zone, said internal blanket zone, and said lower fissile zone are disposed in an axial direction in this order; and said upper fissile zone and said lower fissile zone include said plurality of isotopes; andwherein said fuel assembly has a burnup of 0, and a ratio of fissionable plutonium to a total of all nuclear fuel material in said lower fissile zone is larger than a ratio of fissionable plutonium to a total of all nuclear fuel material in said upper fissile zone.