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A single piece fuel element and fast spectrum boiling water reactor using such a single piece fuel element. The single piece fuel element is formed from coated fissile particles embedded in a matrix made from a material such as SiC that is inert to all fissile and fertile heavy nuclei and to the coo

A single piece fuel element and fast spectrum boiling water reactor using such a single piece fuel element. The single piece fuel element is formed from coated fissile particles embedded in a matrix made from a material such as SiC that is inert to all fissile and fertile heavy nuclei and to the coolant fluid circulating in and around this element. Furthermore, the fuel element includes parallel plates delimiting spaces between them. A ratio between the thickness of the plates and the width of the spaces is set so that the fuel element can be put in fast spectrum or thermal spectrum at will. An application of the single piece fuel element to a fast spectrum boiling water nuclear reactor operating with natural circulation in which the above mentioned ratio is approximately equal to 1 enables a high consumption of plutonium.

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1. A fuel element for a nuclear reactor, formed from coated fissile particles embedded in a matrix, comprising: a monolithic member formed of a single piece including: plural parallel plates separated by spaces; and junction parts configured to connect said parallel plates, wherein the matri

1. A fuel element for a nuclear reactor, formed from coated fissile particles embedded in a matrix, comprising: a monolithic member formed of a single piece including: plural parallel plates separated by spaces; and junction parts configured to connect said parallel plates, wherein the matrix is inert to heavy nuclei, fissile and fertile, and neutral to a coolant fluid that circulates in the spaces. 2. The fuel element according to claim 1, wherein the fuel element has a parallelepiped-like shape. 3. The fuel element according to claim 1, wherein the plates are approximately plane. 4. The fuel element according to claim 1, wherein the plates are approximately vertical and one of the spaces is configured to contain a control device. 5. The fuel element according to claim 4, wherein the junction parts and the parallel plates are perforated at predetermined levels to form windows through which the coolant fluid can circulate. 6. The fuel element according to claim 4, wherein the space in which the control device is configured to be contained has a horizontal cross-section in a shape of a cross, and the space divides the fuel element in four sub-assemblies each comprising plural plates connected to each other by some of the junction parts, others of the junction parts connecting the sub-assemblies to each other. 7. The fuel element according to claim 6, wherein the plates of contiguous sub-assemblies are perpendicular to each other. 8. The fuel element according to claim 6, wherein the plates of the four sub-assemblies are parallel to each other. 9. The fuel element according to claim 1, wherein the plates and spaces have thicknesses and widths with a ratio suitable for defining a fast spectrum for the coolant fluid. 10. The fuel element according to claim 9, wherein the ratio is approximately equal to 1 when water is used as the coolant fluid. 11. The fuel element according to claim 1, wherein the fuel element is protected by a metal duct. 12. The fuel element according to claim 1, wherein the fuel material particles comprise fissile particles chosen from the group comprising uranium and plutonium. 13. The fuel element according to claim 1, wherein the inert matrix is made from a material chosen from the group comprising silicon carbide SiC, a metal, and a combination of the two.