Patent Number: 
Section: claims

1. A fuel assembly comprising:a plurality of fuel rods supported vertically; anda channel box having a structure configured for advancement into a boiling-water reactor (BWR), the channel box surrounding the outer circumference of the plurality of fuel rods;the fuel assembly having a plurality of regular dodecagon fuel rod arrangements, wherein a single fuel rod of the plurality of fuel rods is provided at each apex of each regular dodecagon, wherein each side of the regular dodecagon has length A;the plurality of regular dodecagon fuel rod arrangements being arranged in regular intervals respectively in a transverse direction and a longitudinal direction, the transverse direction perpendicular to the longitudinal direction;a first two regular dodecagon fuel rod arrangements of the plurality of regular dodecagon fuel rod arrangements adjacent in the transverse direction and arranged with two opposing sides of the first two regular dodecagons in parallel and apart by a first distance mA, wherein m is a non-negative integer; anda second two regular dodecagon fuel rod arrangements of the plurality of regular dodecagon fuel rod arrangements adjacent in the longitudinal direction and arranged with two opposing sides of the second two regular dodecagons in parallel and apart by a second distance nA, wherein n is a non-negative integer. 2. The fuel assembly according to claim 1,wherein a diagonal line is formed from a first corner of the channel box to a second corner of the channel box, the second corner being a corner of the channel box furthest from the first corner, the first corner being a corner of the channel box closest to a control rod;wherein either the transverse direction or the longitudinal direction is parallel to the diagonal line; andwherein the plurality of regular dodecagon fuel rod arrangements are arranged symmetrically against the diagonal line. 3. The fuel assembly according to claim 2,wherein a row of the plurality of regular dodecagon fuel rod arrangements is aligned in either the transverse direction or the longitudinal direction on the diagonal line. 4. The fuel assembly according to claim 2,wherein rows of the plurality of regular dodecagon fuel rod arrangements are aligned in either the transverse direction or the longitudinal direction and arranged symmetrically sandwiching the diagonal line. 5. The fuel assembly according to claim 1,wherein either the transverse direction or the longitudinal direction is substantially parallel to a side of the channel box; andwherein the plurality of regular dodecagon fuel rod arrangements are arranged symmetrically against a diagonal line, the diagonal line connecting a corner of the channel box closest to a control rod and a diagonal corner of the channel box furthest from the corner of the channel box closest to a control rod. 6. The fuel assembly according to claim 5,wherein the plurality of regular dodecagon fuel rod arrangements are further arranged symmetrically against a line connecting midpoints of opposing sides of the channel box. 7. The fuel assembly according to claim 1,wherein at least one of the plurality of regular dodecagon fuel rod arrangements includes, at the inside thereof, a regular hexagon fuel rod arrangement in which a single fuel rod of the plurality of fuel rods is provided at each apex of the regular hexagon; andwherein each side of the regular hexagon has length A, and each side of the regular hexagon is parallel to a corresponding side of the regular dodecagon. 8. The fuel assembly according to claim 7,wherein the regular hexagon fuel rod arrangement includes a fuel rod of the plurality of fuel rods at the center of the regular hexagon. 9. The fuel assembly according to claim 1,wherein at least one of the plurality of regular dodecagon fuel rod arrangements includes, at the inside thereof, a regular tetragon fuel rod arrangement in which a single fuel rod of the plurality of fuel rods is provided at each apex of the regular tetragon; andwherein each apex of the regular tetragon is located at a vertex of a regular triangle, the regular triangle having as the base one of every three sides of the regular dodecagon. 10. The fuel assembly according to claim 9,wherein the regular tetragon fuel rod arrangement includes a fuel rod of the plurality of fuel rods at the center of the regular tetragon.