Nuclear fuel pellet incorporating a thermally conductive insert in the form of branching arms distributed from an inner hollow cylinder to the outside of the pellet.

Abstract

A nuclear fuel pellet incorporating a thermally conductive insert in the form of branching limbs extending from a hollow inner cylinder to the outside of the pellet. The invention essentially consists of a nuclear fuel pellet that incorporates, within a straight cylindrical ring of fissile material, a thermal conductor, particularly metallic, in the form of main branching limbs extending from the inside of the ring outwards, advantageously distributed homogeneously within the ring. The insert formed by its limbs and branches at the macrostructural scale reduces the maximum fuel temperature by several hundred degrees Celsius, depending on its dimensions, its constituent material, and the distribution of its limbs within the straight cylindrical fuel ring. Figure for the abstract: Fig. 4

Claims

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7. Claims Nuclear fuel pellet (6), comprising: - a straight cylindrical ring (60) of fissile material with a central axis (X) delimited by an inner straight cylinder (61) and an outer straight cylinder (62) whose length defines the length (H) of the pellet, the inner straight cylinder being hollowed out and defining the inner diameter (0int), the outer straight cylinder defining the outer diameter (0ext) of the pellet; - an insert (7) made of thermally conductive material, in the form of at least three branched main branches (7.1 to 7.6) which extend over all or part of the length of the pellet and radially from the periphery of the hollowed-out inner straight cylinder towards the outside of the pellet, each of the main branches being branched symmetrically or not at least p times, p being greater than or equal to 1; the number n of symmetrical or not branches (70, 71, 72, 73) per main branch and per branch being equal to n, n being greater than or equal to 2; the main branches with their branches being regularly distributed in the volume of the ring and distant from each other. Pastille (6) according to claim 1, the number p being between 1 and 7, the number n being equal to 2. Pellet (6) according to one of claims 1 or 2, the main branches with their ramifications being rectilinear or curved. Pellet (6) according to one of the preceding claims, the main branches with their ramifications being of square, rectangular, circular or elliptical cross-section. Pellet (6) according to one of the preceding claims, each of the main branches and its ramifications extending radially to the outer diameter of the pellet. Pastille (6) according to one of the preceding claims, the ratio between the section of each branch and that of each main branch being less than 1. Pellet (6) according to claim 6, the section of each branch main being less than 0.5 mm2, preferably less than 0.1 mm2

8. Pastille (6) according to one of the preceding claims, the ratio between section and length of each of the main branches and its ramifications being less than 0.5 mm, preferably less than 0.1 mm.

9. Pellet (6) according to one of the preceding claims, the material of the main branches and its ramifications being chosen from Molybdenum (Mo), niobium (Nb) or their alloys, preferably an NbZr alloy or an NbZrC alloy.

10. Pellet (6) according to one of the preceding claims, the fissile material of the right cylinder being chosen from uranium (IV) oxide (UO2), mixed oxide (U, Pu)O2 or a mixed mixture based on uranium oxide and reprocessed plutonium oxides (MOx).

11. Pastille (6) according to one of the preceding claims, the volume percentage of the main branches with their ramifications being between 1 and 20%.

12. Nuclear fuel needle (1) extending in a longitudinal direction (XX1) comprising: a plurality of nuclear pellets (6) according to one of the preceding claims, stacked on top of each other; a sheath (2) made of material transparent to neutrons surrounding the stack of pellets.

13. Needle (1) according to claim 12, the sheath being made of zirconium alloy, in particular Zircaloy-4 (Zr4), or M5® alloy (ZrNbO).

14. Use of a nuclear fuel pellet (6) according to one of claims 1 to 11 or a nuclear fuel needle (1) according to claim 12 or 13 in a fast neutron reactor (RNR), in particular cooled by liquid metal, such as liquid sodium (RNR-Na), a pressurized water reactor (PWR), a boiling water reactor (BWR).

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