Patent Number: 
Section: claims

1. A fuel assembly for a light-water nuclear reactor with a square shape in the plan view and comprising:a seed region, including a bundle of seed fuel elements that are arranged in the rows and columns of a square coordinate grid in a cross-section; wherein each seed fuel element has a four-lobed profile forming spiral ribs, and comprises a kernel that includes enriched uranium or plutonium; anda blanket region, surrounding the seed region and including a bundle of breeding fuel elements;wherein, when viewed in a plan-view cross-section, the breeding fuel elements are arranged in the rows and columns of a square coordinate grid, and the breeding fuel elements define a plurality of square-shaped rings surrounding the seed region;further wherein each of the seed fuel elements defines a first circumscribed diameter defined by a circle circumscribing the seed fuel element, and each of the breeding fuel elements defines a second circumscribed diameter defined by a circle circumscribing the breeding fuel element that is different than the first circumscribed diameter. 2. The fuel assembly of claim 1, wherein the blanket region comprises a lower nozzle of blanket region, as well as lengthwise-arranged angle elements and several lengthwise-arranged poles; herewith, the lower nozzle of blanket region is rigidly connected to the aforementioned angle elements and poles, thereby forming a frame structure of blanket region. 3. The fuel assembly of claim 1, the dimensions and shape, as well as the neutronic and thermo hydraulic properties of which, match the dimensions and shape, as well as the neutronic and thermohydraulic properties, of a traditional fuel assembly for a PWR-type reactor, thereby ensuring their interchangeability. 4. The fuel assembly of claim 1, comprising guiding channels, some of which are situated within the seed region, while the remaining channels are situated within the blanket region; herewith, all the guide tubes are positioned in such a manner, as to match the position of the guide tubes for the fuel assembly control rods of a PWR-type nuclear reactor. 5. A light-water nuclear reactor comprising a set of fuel assemblies, wherein the set of fuel assemblies comprises at least one fuel assembly according to claim 1. 6. The fuel assembly of claim 1, wherein the seed region does not include breeding fuel elements, and the blanket region does not include seed fuel elements. 7. The fuel assembly of claim 1, wherein each of the breeding fuel elements comprises ceramic thorium. 8. The fuel assembly of claim 1, wherein the first circumscribed diameter is defined by a width across corners, and is 12.6 millimeters, and the second circumscribed diameter is 8.6 millimeters. 9. The fuel assembly of claim 1, wherein the second circumscribed diameter is smaller than the first circumscribed diameter. 10. The fuel assembly of claim 1, wherein the plurality of square-shaped rings consists of two square-shaped rings. 11. The fuel assembly of claim 10, further comprising guiding channels, positioned within the seed region in such a manner, as to match the position of the guide tubes for the fuel assembly control rods of a PWR-type nuclear reactor. 12. The fuel assembly of claim 11, wherein the fuel assembly comprises 24 guiding channels, positioned within the seed region in such a manner, as to match the position of the 24 guide tubes of the 17×17 fuel assembly control rods of a PWR-type reactor. 13. The fuel assembly of claim 1, wherein the plurality of square-shaped rings consists of three square-shaped rings. 14. The fuel assembly of claim 13, wherein the fuel elements of seed and blanket region within the fuel assembly's cross-section are arranged in the 17 rows and 17 columns of a square coordinate grid; wherein the seed fuel elements are positioned in 11 rows and 11 columns within this grid's midsection. 15. The fuel element of claim 14, wherein the plurality of seed fuel elements includes a plurality of primary seed fuel elements that are located in the fuel assembly's cross-section and that are arranged in 9 rows and 9 columns in the midsection of a square coordinate grid, as well as a plurality of secondary seed fuel elements that are positioned in the outermost rows and columns of the midsection of a square coordinate grid; wherein each of the plurality of primary seed fuel elements has a larger width across corners than that of each secondary seed fuel element. 16. The fuel assembly of claim 1, wherein the fuel elements of blanket region in the fuel assembly's cross-section are positioned in the two outermost rows and columns of a square coordinate grid made up of 19 rows and 19 columns, while the seed fuel elements are positioned in the rows and columns of a square coordinate grid, made up of 13 rows and 13 columns. 17. The fuel assembly of claim 16, comprising a shroud that has a square cross-sectional shape and separates the fuel elements of seed region from the fuel elements of the blanket region. 18. The fuel assembly of claim 17, comprising a lower nozzle of the seed region, connected to the shroud, wherein the fuel assembly further comprises a supporting frame structure that is fastened to the lower nozzle of the seed region, wherein the supporting frame structure is adapted to secure the seed fuel elements to the lower nozzle. 19. The fuel assembly of claim 17, comprising a guiding grid that is secured to the upper section of the shroud, wherein the guiding grid is adapted to receive the seed fuel elements in a manner that permits free axial movement of the seed fuel elements. 20. A fuel assembly for a light water nuclear reactor with a square shape in the plan view, the fuel assembly comprising:a frame defining a square coordinate grid of positions;a first plurality of fuel elements that are arranged in the rows and columns of the square coordinate grid in cross-section, each of the first plurality of fuel elements has a four-lobed profile forming spiral ribs, and comprises an alloy of fissile material; anda second plurality of fuel elements that are arranged in the rows and columns of the square coordinate grid in cross-section and encircle the first plurality of fuel elements;wherein the first plurality of fuel elements includes a plurality of primary first fuel elements that are arranged in the rows and columns in a midsection of the square coordinate grid, as well as a plurality of secondary first fuel elements that are arranged in rows and columns of the square coordinate grid that surround the plurality of primary first fuel elements; wherein each of the plurality of primary first fuel elements has a larger width across corners than that of each secondary first fuel element. 21. The fuel assembly of claim 20, wherein:the second plurality of fuel elements define two peripheral square-shaped rings of positions surrounding the first plurality of fuel elements. 22. The fuel assembly of claim 20, wherein:the first plurality of fuel elements comprises seed fuel elements, and the second plurality of fuel elements comprises breeding fuel elements.