Patent Number: 
Section: claims

1. A core of a light water reactor having a plurality of fuel assemblies, which are loaded in said core, having nuclear fuel material containing a plurality of isotopes of transuranium nuclides, an upper blanket zone, a lower blanket zone, and a fissile zone, in which said transuranium nuclides are contained, disposed between said upper blanket zone and said lower blanket zone;wherein a ratio of Pu-239 in all said transuranium nuclides contained in said loaded fuel assembly is in a range of 40 to 60% when burnup of said fuel assembly is 0;a sum of an axial length of said lower blanket zone and an axial length of said upper blanket zone is in a range of 250 to 600 mm; andthe axial length of said lower blanket zone is in a range of 1.6 to 12 times the axial length of said upper blanket zone. 2. The core of the light water reactor according to claim 1, wherein the axial length of said upper blanket zone is in a range of 30 to 105 mm. 3. The core of the light water reactor according to claim 1,wherein said core has an inner blanket zone between said upper blanket zone and said lower blanket zone;said fissile zone includes a upper fissile zone containing said transuranium nuclides and disposed between said upper blanket zone and said inner blanket zone, and a lower fissile zone containing said transuranium nuclides and disposed between said inner blanket zone and said lower blanket zone; andan axial length of said upper fissile zone is larger than an axial length of said lower fissile zone within a range of 10 to 25 mm. 4. The reactor core of the light water reactor according to claim 1,wherein an upper end of a neutron absorber zone of a safety rod provided in said light water reactor is positioned in a region between a lower end of said core and 5 mm below said lower end of said core. 5. A fuel assembly having nuclear fuel material containing a plurality of isotopes of transuranium nuclides, an upper blanket zone, a lower blanket zone, and a fissile zone containing said transuranium nuclides and disposed between said upper blanket zone and said lower blanket zone;wherein a ratio of Pu-239 in all said transuranium nuclides contained in said nuclear fuel material is in a range of 40 to 60% when burnup of said fuel assembly is 0;a sum of an axial length of said lower blanket zone and an axial length of said upper blanket zone is in a range of 250 to 600 mm, andthe axial length of said lower blanket zone is in a range of 1.6 to 12 times the axial length of said upper blanket zone. 6. The fuel assembly according to claim 5,wherein the axial length of said upper blanket zone is in a range of 30 to 105 mm. 7. The fuel assembly according to claim 5,wherein said fuel assembly has an inner blanket zone between said lower blanket zone and said upper blanket zone;said fissile zone includes an upper fissile zone containing said transuranium nuclides and disposed between said upper blanket zone and said inner blanket zone, and a lower fissile zone containing said transuranium nuclides and disposed between said inner blanket zone and said lower blanket zone; andan axial length of said upper fissile zone is larger than an axial length of said lower fissile zone within a range of 10 to 25 mm. 8. The fuel assembly according to claim 5,wherein nuclear fuel material containing a neutron absorber is disposed below said lower blanket zone.