Variable-thickness debris filter for the lower end of a nuclear fuel assembly

Abstract

Disclosed is a debris filter formed by a grid (32) having a first face (32A) and an opposite second face (32B), the grid (36) having passages (36) which extend between an inlet (36A) located on the first face (32A) and an outlet (36B) located on the second face (32B) and which allow a cooling fluid to flow through the grid (32), the grid (32) having a first zone (Z1) and at least one second zone (Z2) in which the grid (32) has a thickness greater than that of the grid (32) in the first zone (Z1), passages (36) being present in the first zone (Z1) and in each second zone (Z2).

Description

[0001] Debris filter for lower nozzle of nuclear fuel assembly with variable thickness

[0002] The present invention relates to the field of nuclear fuel assemblies, in particular for pressurized water nuclear reactors (or PWR for “Pressurized Water Reactor”).

[0003] A nuclear fuel assembly for a pressurized water nuclear reactor generally comprises a bundle of nuclear fuel rods extending along a longitudinal axis and a support skeleton configured to support the nuclear fuel rods. The support skeleton comprises a lower end cap and an upper end cap spaced apart from the longitudinal axis, a plurality of guide tubes extending along the longitudinal axis connecting the end caps to each other, and spacer grids distributed along the guide tubes and fixed to the guide tubes, each spacer grid being configured to support the nuclear fuel rods.

[0004] In operation, the nuclear fuel assembly is arranged vertically in a vessel of a nuclear reactor, resting on a lower core plate provided with openings through which a coolant enters and circulates vertically from bottom to top through the nuclear fuel assembly.

[0005] Debris present in the coolant could damage components of the nuclear fuel assembly.

[0006] It is possible to provide the lower nozzle of the nuclear fuel assembly with an anti-debris filter allowing the flow of the coolant while retaining any debris that may be present in the coolant. Such an anti-debris filter is disclosed in W02005 / 059923A2.

[0007] One of the aims of the invention is to provide an anti-debris filter which has limited hydraulic resistance while having a satisfactory debris retention capacity.

[0008] To this end, the invention provides an anti-debris filter for a lower nozzle of a nuclear fuel assembly, the anti-debris filter being formed of a grid having a first face and a second opposite face, the grid having passages extending between an inlet located on the first face and an outlet located on the second face for the flow of a coolant through the grid, the grid having a first zone and at least one second zone in which the grid has a thickness greater than that of the grid in the first zone, passages being present in the first zone and in each second zone. The zones of different thicknesses make it possible to adjust the debris retention capacity and the flow resistance of the grid.A thicker area has a higher retention capacity and higher flow resistance and a thinner area has a lower retention capacity and lower flow resistance.

[0009] In particular embodiments, the debris filter comprises one or more of the following optional features, taken individually or in any possible technical combination:

[0010] - each second zone has passages with an entrance and an exit offset transversely relative to each other;

[0011] - each second zone has passages with an entrance and an exit inclined relative to each other with a non-zero angle of inclination;

[0012] - each second zone has passages extending in a non-rectilinear manner;

[0013] - the grid has in each second zone an increasing thickness from the periphery of the second zone towards the center of the second zone;

[0014] - each second zone has a circular outline;

[0015] - the side walls of the passages located in each second zone are higher than the side walls of the passages located in the first zone;

[0016] - at least one passage located in a second zone is delimited between two opposite curved side walls;

[0017] - the grid is formed of intersecting grid elements between which the passages are delimited, including at least one variable height grid element extending in the first zone and at least one second zone, the height of each variable height grid element being greater in each second zone crossed by the variable height grid element and smaller in the first zone;

[0018] - the grid has a quadrangular outline, in particular a square outline;

[0019] - the grid has four second zones;

[0020] - the second zones are distributed on the grid in a matrix manner.

[0021] The invention also relates to a lower nozzle of a nuclear fuel assembly equipped with an anti-debris filter as defined above.

[0022] The invention also relates to a nuclear fuel assembly, in particular for a pressurized water nuclear reactor, comprising an anti-debris filter as defined above. The invention and its advantages will be better understood on reading the following description, given solely by way of non-limiting example, and with reference to the appended drawings, in which:

[0023] - Figure 1 is a side view of a nuclear fuel assembly;

[0024] - Figure 2 is a sectional view of a lower nozzle of the nuclear fuel assembly of Figure 1, provided with an anti-debris filter;

[0025] - Figure 3 is a bottom view of the debris filter;

[0026] - Figure 4 is a bottom view of one quadrant of the debris filter;

[0027] - Figure 5 is a perspective view of the debris filter quadrant shown in Figure 4;

[0028] - Figure 6 is a cutaway perspective view of the debris filter quadrant shown in Figure 4;

[0029] - Figure 7 is a sectional view of the debris filter quadrant shown in Figure 4;

[0030] - Figure 8 is a sectional view similar to that of Figure 7, illustrating an anti-debris filter according to another exemplary embodiment;

[0031] - Figure 9 is a partial sectional view of an anti-debris filter according to another exemplary embodiment, illustrating two adjacent passages of the grid;

[0032] - Figure 10 is a partial top view of an anti-debris filter according to another exemplary embodiment;

[0033] - Figure 11 is a sectional view of the debris filter of Figure 10, taken along line XI - XI in Figure 10;

[0034] - Figure 12 is a view similar to that of Figure 11, illustrating another example of embodiment.

[0035] The nuclear fuel assembly 2 of Figure 1 comprises a bundle of nuclear fuel rods 4 and a support skeleton 6 configured to support the nuclear fuel rods 4.

[0036] The nuclear fuel rods 4 extend parallel to each other and to a longitudinal axis L.

[0037] The longitudinal axis L extends vertically when the nuclear fuel assembly 2 is placed in a core of a nuclear reactor. In operation, a coolant circulates vertically from bottom to top through the nuclear fuel assembly 2 as shown by the arrows F in Figure 1.

[0038] In the remainder of the description, the terms “vertical”, “horizontal”, “top”, “bottom”, “longitudinal”, “transverse”, “upper” and “lower” are understood to refer to the position of the nuclear fuel assembly 2 in the core of the nuclear reactor, the longitudinal axis L being substantially vertical.

[0039] The support skeleton 6 comprises a lower end piece 8, an upper end piece 10, a plurality of guide tubes 12 and a plurality of spacer grids 14.

[0040] The lower end piece 8 and the upper end piece 10 are spaced along the longitudinal axis L.

[0041] The guide tubes 12 extend along the longitudinal axis L and connect the lower end piece 8 and the upper end piece 10 to each other, maintaining the spacing between the lower end piece 8 and the upper end piece 10. The nuclear fuel rods 4 are received between the lower end piece 8 and the upper end piece 10.

[0042] Each guide tube 12 is open at its upper end to allow the insertion of a control rod (not shown) inside the guide tube 12, through the upper end piece 10. Such a control rod makes it possible to control the reactivity of the nuclear reactor core in which the nuclear fuel assembly 2 is inserted.

[0043] The spacer grids 14 are distributed along the guide tubes 12, being spaced from each other along the longitudinal axis L. Each spacer grid 14 is rigidly fixed to the guide tubes 12, the guide tubes 12 extending through each spacer grid 14.

[0044] Each spacer grid 14 is configured to support the nuclear fuel rods 4 by maintaining them in a configuration in which they are transversely spaced from each other. The nuclear fuel rods 4 are preferably maintained at the nodes of a substantially regular imaginary network.

[0045] As illustrated in Figure 1, the nuclear fuel assembly 2 is placed on a lower core plate 16 via its lower end piece 8, opposite at least one opening 18 for the flow of a cooling fluid.

[0046] In operation, the coolant passes through each opening 18, enters the nuclear fuel assembly 2 via the lower nozzle 8, circulates along the nuclear fuel rods 4 and exits the nuclear fuel assembly 2 via the upper nozzle 10.

[0047] As illustrated in Figure 2, the lower end piece 8 comprises for example an end piece plate 20 and feet 22 extending downwardly from the end piece plate 20 to bear on the lower core plate 16. The end piece plate 20 has a lower face 20A and an upper face 20B. The guide tubes 12 (not shown in Figure 2) are for example fixed to the end piece plate 20 by means of fixing screws 24 passing through the end piece plate 20.

[0048] The lower nozzle 8 is provided with a debris filter 30 configured to filter the coolant.

[0049] The debris filter 30 comprises a grid 32. The grid 32 preferably has the shape of a plate.

[0050] The grid 32 has a first face 32A and a second face 32B opposite each other.

[0051] The grid 32 has a thickness taken between the first face 32A of the grid and the second face 32B of the grid 32.

[0052] The first face 32A is intended to be turned downwards, i.e. upstream considering the direction of flow of the cooling fluid through the grid 32.

[0053] The second face 32B is intended to be turned upwards, i.e. downstream considering the direction of flow of the cooling fluid through the grid 32.

[0054] The grid 32 is arranged under the end plate 20 in such a way that the cooling fluid passes through the grid 32 before passing through the end plate 20.

[0055] Preferably, the grid 32 extends over the entire extent of the end plate 20, more particularly the entire extent of the lower face 20A of the end plate 20.

[0056] The grid 32 has fixing holes 34 for the passage of the fixing screws 24.

[0057] As illustrated in Figure 3, the grid 32 has passages 36 extending through the grid 32 for the flow of coolant through the grid 32.

[0058] The grid 32 is for example formed by elongated grid elements 38, 40 which are intersected.

[0059] Each grid element 38, 40 has, for example, the shape of a bar or an elongated plate.

[0060] Each passage 36 is defined between adjacent intersecting grid elements 38, 40.

[0061] In particular, each passage 36 has, for example, side walls defined by two adjacent first grid elements 38 intersecting with two adjacent second grid elements 40.

[0062] The grid 32 is for example formed of first grid elements 38 extending parallel in a first direction of extension T1 and second grid elements 40 extending parallel in a second direction of extension T2 perpendicular to the first direction of extension T1. Each passage 36 is delimited between two adjacent first grid elements 38 and two adjacent second grid elements 40.

[0063] The grid 32 has, for example, a generally quadrangular outline, in particular a generally square outline.

[0064] Grid 32, for example, has four quadrants that are analogous, with only one quadrant being shown in Figures 4 to 7 for clarity.

[0065] Furthermore, in Figures 4 to 7, the first face 32A of the grid 32 is facing upwards, this first face 32A being in practice facing downwards when the grid 32 is mounted on the lower end piece 8 and the nuclear fuel assembly 2 is installed in the core of the nuclear reactor.

[0066] As illustrated in particular in Figure 7, each passage 36 extends between an inlet 36A, located on the first face 32A, and an outlet 36B, located on the second face 32B.

[0067] The inlet 36A of each passage 36 has an inlet axis A1 and the outlet 36B of each passage 36 has an outlet axis A2.

[0068] Each passage 36 extends from its entrance 36A to its exit 36B along a central line C of this passage 36.

[0069] The center line C of each passage 36 is tangent to the inlet axis A1 at the inlet 36A of the passage 36 and tangent to the outlet axis A2 at the outlet of the passage 36.

[0070] The input axis A1 and the output axis A2 of each passage 36 define between them an inclination angle 0. The inclination angle 0 is also called the deflection angle.

[0071] The angle of inclination 0 between the input axis A1 and the output axis A2 of each passage 36 of the grid 32 is for example between 0° and 60°.

[0072] Each passage 36 having a zero inclination angle 0 (i.e. 0°) corresponds to a straight passage 36. The inlet axis A1 and the outlet axis A2 coincide. The passage 36 has zero deflection between its inlet 36A and its outlet 36B. The inlet 36A and the outlet 36B are aligned

[0073] Each passage 36 having a non-zero inclination angle 0 between its inlet axis A1 and its outlet axis A2 has a non-zero deflection between its inlet 36A and its outlet 36B.

[0074] A non-zero inclination angle 0 corresponds to a curved passage 36, i.e. extending along a curved central line C. The central line C of each curved passage 36 preferably has an inclination varying monotonically between the input axis A1 and the output axis A2.

[0075] Each passage 36 having a non-zero inclination angle 0 between its inlet axis A1 and its outlet axis A2 preferably has its inlet 36A and its outlet 36B offset transversely relative to each other considering the direction of flow of the fluid through the grid 32.

[0076] Advantageously, the grid 32 has passages 36 having different angles of inclination 0 between their input axis A1 and their output axis A2. In other words, the grid 32 has passages 36 having different respective deflections.

[0077] In Figure 7, three different inclination angles 0 are shown, one of which is zero (on the right in Figure 7) and which corresponds to a straight 36 passage.

[0078] In an exemplary embodiment, the output axes A2 of all the passages 36 are parallel to each other, the input axes A1 of passages 36 having different inclination angles 0 being inclined relative to each other.

[0079] Preferably, the outlet axes A2 of the passages 36 are parallel to the direction of flow of the fluid. This makes it possible to limit disturbances to the flow of the fluid at the outlet of the grid 32.

[0080] The prediction of passages 36 with different inclination angles 0 makes it possible to differentiate the retention capacity and flow resistance of different areas of the grid 32.

[0081] An area of ​​the grid with passages 36 having larger inclination angles 0 (i.e. larger deflections) has a larger debris holding capacity and a larger flow resistance, whereas an area of ​​the grid with passages 36 having smaller inclination angles 0 (i.e. smaller deflections) has a smaller debris holding capacity and a smaller flow resistance.

[0082] Preferably, the grid 32 has a first zone Z1, the first zone Z1 having a plurality of passages 36, and at least one second zone Z2, each second zone Z2 having a plurality of passages 36, the inclination angles 0 of the passages 36 located in each second zone Z2 being unaffected and greater than or equal to the maximum inclination angle 0 of the passages 36 located in the first zone Z1.

[0083] In particular, the output axes A2 of the passages 36 of the first zone Z1 and of each second zone Z2 are for example parallel to each other.

[0084] The input axes A1 of passages 36 of each second zone Z2 are for example inclined at a non-zero angle relative to the input axes A1 of the passages 36 of the first zone Z1. The input axes A1 of these passages 36 of each second zone Z2 make a non-zero angle with the input axes A1 of the passages 36 of the first zone Z1. The angle of inclination 0 between the input axis A1 and the output axis A2 of each passage 36 of the first zone Z1 is for example substantially zero. The passages 36 of the first zone Z1 are for example rectilinear.

[0085] Preferably, the grid 32 has a second respective zone Z2 associated with each opening 18 of the lower core plate 16 located under the lower nozzle 8 when the nuclear fuel assembly 2 is arranged on the lower core plate 16.

[0086] The grid 32 has, for example, four second zones Z2 distributed over the grid 32 in a quadrangular and in particular square shape, the second zones Z2 being, for example, distributed according to a 2X2 matrix distribution.

[0087] Grid 32 here has four second zones Z2, each second zone Z2 being located in a respective quadrant of grid 32.

[0088] The grid 32 has for example a variable thickness, the thickness of the grid 32 in each second zone Z2 being strictly greater than the thickness of the grid in the first zone Z1.

[0089] As illustrated in Figures 4 to 7, and in particular in Figure 7, in each second zone Z2, the grid 32 has a thickness strictly greater than the thickness of the grid 32 in the first zone Z1.

[0090] Preferably, in the first zone Z1, the grid 32 has a substantially constant thickness, called the first thickness E1.

[0091] The height of each grid element 38, 40 is taken according to the thickness of the grid 32.

[0092] In the first zone Z1, each grid element 38, 40 has a substantially constant height or first height H1. The first height H1 corresponds to the first thickness E1.

[0093] In each second zone Z2, the grid 32 has a second thickness E2 strictly greater than the first thickness E1 of the grid 32.

[0094] The grid 32 has for example a variable thickness, varying between the first thickness E1 at the periphery of each second zone Z2 up to a second thickness E2, for example at the center of the second zone Z2.

[0095] In each second zone Z2, at least part of the grid elements 38, 40 has a height strictly greater than the first height H1.

[0096] At least a portion of the grid elements 38, 40 has, for example, a variable height, varying for example between the first height H1 and a second height H2.

[0097] The first height H1 corresponds to the first thickness E1 and the second height H2 corresponds to the second thickness E2. For example, in each second zone Z2, each grid element 38, 40 has a height greater than the first height H1 or only a portion of the grid elements 38, 40 has a height greater than the first height H1.

[0098] In particular, in each second zone Z2, each first grid element 38 or only a portion of the grid elements 38 has a height greater than the first height H1 and / or each second grid element 40 or only a portion of the second grid elements 40 has a height greater than the first height H1.

[0099] In Figures 4 to 7, in each second zone Z2, each first grid element 38 has a height greater than the first height H1 and a second grid element 40 out of three has a height greater than the first height H1.

[0100] The side walls of each passage 36 are defined by the portions of the grid elements 38, 40 delimiting the passage 36.

[0101] Thus, the side walls of the passages located in each second zone Z2 are higher than the side walls of the passages located in the first zone Z1.

[0102] As illustrated in particular in Figure 7, each passage 36 is delimited between two opposite side walls which extend substantially parallel while being curved.

[0103] Thus each of these passages 36 extends in a curvilinear manner, its inlet 36A and its outlet 36B being offset transversely with respect to each other and inclined with respect to each other.

[0104] In particular, in each second zone Z2, each first grid element 38 of variable height, and in particular each first grid element 38, has an upper portion 42 which extends higher than the rest of the first face 32A of the grid 32 in the first zone Z1.

[0105] The upper portion 42 of each first grid element 38 is for example curved to define the curved passages 36.

[0106] Each of the second grid elements 40 extends, for example, substantially along a plane.

[0107] In each second zone Z2, second grid elements 40 of variable height have upper portions 44 which intersect the upper portions 42 of the first grid elements 38 of variable height.

[0108] The grid 30 is for example produced by a manufacturing process by adding material (additive manufacturing) and / or by a manufacturing process with material removal (machining). To obtain the grid 32 with passages 36 having inlet axes A1 inclined relative to each other and outlet axes A2 parallel to each other, a grid blank 32 is for example initially manufactured with a constant thickness, each passage 36 extending along a curved central line C with a non-zero angle of inclination between its inlet axis A1 and its outlet axis A2, the passages 36 extending parallel to each other.

[0109] Initially, the input axes A1 of the passages 36 are parallel to each other and the output axes A2 of the passages 36 are parallel to each other.

[0110] Then, the grid blank 32 is machined on its first face 32A so as to form the first zone Z1 and each second zone Z2.

[0111] Due to the variation in thickness of the machined grid 32, certain passages 36 are reduced in height, and passages 36 ultimately have inlet axes A1 inclined relative to each other.

[0112] In particular, the passages 36 located in the thinnest regions of the machined grid 32 have the least inclined entry axes A1 and the smallest inclination angles 0, and the passages 36 located in the thickest regions of the grid 32 have the most inclined entry axes A1 and the largest inclination angles 0.

[0113] Thus, passages 36 located in each second zone Z2 have a greater inclination angle 0 than the passages 36 located in the first zone Z1.

[0114] The thickness of the grid 32 is for example reduced in the first zone Z1 in such a way that only a rectilinear exit section of passage 36 of the grid 32 remains in each passage 36 of the first zone Z1 before machining, each passage 36 of the first zone Z1 therefore being rectilinear in the machined grid 32.

[0115] In a variant illustrated in Figure 8, which is analogous to Figure 7 and in which the numerical references to the analogous elements are repeated, a grid 32 has for example a constant thickness, the differences in inclination between the passages 36 resulting from differences in curvature between the central lines C of the passages 36, for example from differences in curvature between the side walls of the passages 36.

[0116] Such a grid 32 is for example obtained by additive manufacturing.

[0117] As illustrated in Figure 9, it is possible to provide passages 36 of variable cross-section along the passage 36, each passage 36 of variable cross-section having a converging inlet section 46 (considering the direction of flow of the fluid in the passage 36 from the inlet 36A to the outlet 36B) and / or a diverging outlet section 48. A converging inlet section 46 or a diverging outlet section 48 is obtained for example by providing a chamfer on side walls respectively of the inlet section 46 and of the outlet section.

[0118] Each passage 36 of variable cross-section is provided with a converging inlet section 46 and a diverging outlet section 48, with or without an intermediate section of constant cross-section, a converging inlet section 46, the remainder of the passage having a constant cross-section or a diverging outlet section 46, the remainder of the passage having a constant cross-section.

[0119] A passage 36 of variable cross-section provided with a converging inlet section 46 and a diverging outlet section 48 without an intermediate section of constant cross-section, has for example curved and convex side walls.

[0120] The variation in cross-section of a passage 36 makes it possible to generate a venturi effect in the fluid circulating in the passage 36.

[0121] As also illustrated in Figure 9, preferably the lower edge and / or the upper edge of each side wall of each passage 36 is preferably rounded. This helps promote fluid flow by limiting the flow resistance of the grid 32.

[0122] The passage prediction 36 with different inclination angles 0 between the inlet 36A and the outlet 36B makes it possible to differentiate the retention capacity and the flow resistance of different areas of the grid 32.

[0123] An area of ​​the grid with passages 36 having larger 0 inclination angles has a larger debris holding capacity and a larger flow resistance, while an area of ​​the grid with passages 36 having smaller 0 inclination angles has a smaller debris holding capacity and a smaller flow resistance.

[0124] The provision of a first zone Z1 with a first thickness E1 and one or more second zones Z2 with a thickness strictly greater than the first thickness E1 makes it possible to easily form passages 36 with smaller inclination angles 0 between the inlet 36A and the outlet 36B in the first zone Z1 and passages 36 with larger inclination angles 0 between the inlet 36A and the outlet 36B in each second zone Z2, from a grid blank of constant thickness whose passages 36 are parallel with identical and uninterrupted inclination angles 0 between the inlet 36A and the outlet 36B.

[0125] The second zone(s) Z2 may be placed on the grid 30 at the location(s) where the probability of debris passing is greatest, which is most often opposite the openings 18 of the lower core plate 16 through which the coolant arrives under the nuclear fuel assemblies 2.

[0126] Thus, it is possible to obtain a grid 30 having limited hydraulic resistance while presenting a satisfactory debris retention capacity.

[0127] The grid 30 can be manufactured easily, for example by additive manufacturing and / or by machining.

[0128] The invention is not limited to the example and the variants described, other examples and other variants being conceivable.

[0129] The passages 36 of the grid of Figures 4 and 7 are delimited between curved first grid elements 38 and flat second grid elements 40, so that the entry axes A1 of the passages 36 are all inclined in the same direction. The entry axes A1 of the passages 36 are all parallel to the same reference plane. The entry axes A1 can be parallel if the angles of inclination of the passages 36 are the same or not if passages have different angles of inclination.

[0130] Of course, in a variant, input axes A1 of the passages 36 can be inclined in different directions. To do this, it is possible to provide that the second grid elements 40 are also curved.

[0131] Furthermore, it is possible to provide output axes A2 which are not parallel to each other, with in particular output axes A2 which have a non-zero inclination with the longitudinal axis L of the nuclear fuel assembly 2 when the grid 30 is mounted on the lower end piece 8.

[0132] In particular, it is possible to provide that the input axes A1 are parallel to each other and that the output axes A2 are inclined relative to each other to obtain different angles of inclination, the output axes A2 being for example all parallel to the same reference plane or inclined in different directions.

[0133] The provision of a first zone Z1 having a first thickness E1 and at least one second zone Z2 having a second thickness E2 is advantageous regardless of the fact that the passages 36 have non-zero inclination angles between an inlet axis A1 and an outlet axis A2, in particular differentiated inclination angles between different passages 36.

[0134] Thus, according to another aspect, the invention provides an anti-debris filter for a lower nozzle of a nuclear fuel assembly, the anti-debris filter being formed of a grid 32 having a first face 32A and a second face 32B opposite each other, the grid 32 having passages 36 extending between an inlet 36A located on the first face 32A and an outlet 36B located on the second face 32B for the flow of a cooling fluid through the grid 32, the grid 32 having a first zone Z1 and at least one second zone Z2 in which the grid 32 has a thickness greater than that of the plate in the first zone Z1, passages 36 being present in the first zone Z1 and in each second zone Z2.

[0135] Each second zone Z2 thicker than the first zone Z1 has a higher retention capacity than the first zone Z1 and a higher flow resistance than the first zone Z1.

[0136] The passages 36 located in each second zone Z2 are a priori longer than the passages 36 located in the second zone Z2, and allow for example longer debris to be filtered.

[0137] The provision of a first zone Z1 and at least a second zone Z2 thicker than the first zone Z1 makes it possible to locally adapt the retention capacity, depending on the probability of the presence of debris, while limiting the flow resistance of the grid 32 as a whole.

[0138] Such a grid with a first zone Z1 and at least one second zone Z2 with different thicknesses can be provided with rectilinear passages 36 and / or curved passages 36, and in particular with passages 36 all rectilinear or all curved, the curved passages 36 having identical or differentiated angles of inclination.

[0139] The features discussed in connection with the embodiment of Figures 4 to 7 may be provided as options on the grid 32.

[0140] In particular, in embodiments, the grid 32 comprises one or more of the following optional features, taken individually or in any technically possible combination:

[0141] - each second zone Z2 has passages 36 having an inlet 36A and an outlet 36B offset transversely relative to each other;

[0142] - each second zone Z2 has passages 36 having an inlet 36A and an outlet 36B inclined relative to each other with a non-zero angle of inclination.

[0143] - each second zone Z2 has passages 36 extending in a non-rectilinear manner;

[0144] - the grid 32 has in each second zone Z2 a thickness increasing from the periphery of the second zone Z2 towards the center of the second zone Z2;

[0145] - each second zone Z2 has a circular outline.

[0146] - at least one passage 36 located in a second zone Z2 is delimited between two opposite curved side walls;

[0147] - the grid 32 is formed of intersecting grid elements 38, 40 between which the passages 36 are delimited, including at least one grid element 38, 40 of variable height extending in the first zone Z1 and at least one second zone Z2, the height of each grid element 38, 40 of variable height being greater in each second zone Z2 crossed by the grid element 38, 40 of variable height and smaller in the first zone Z1;

[0148] - grid 32 has a quadrangular outline, in particular a square outline;

[0149] - grid 32 has four second zones Z2;

[0150] - the second zones Z2 are distributed on the grid 32 in a matrix manner;

[0151] According to said other aspect, the invention also proposes a lower nozzle for a nuclear fuel assembly equipped with an anti-debris filter as defined above and / or a nuclear fuel assembly, in particular for a pressurized water nuclear reactor, comprising an anti-debris filter as defined above.

[0152] The grid 32 of the debris filter 30 illustrated in Figures 10 and 11 comprises a plurality of cells 50 separated by partitions 52. Each cell 50 passes through the grid 32. Each cell 50 extends between the first face 32A of the grid 32 and the second face 32B of the grid 32. Each cell 50 allows the flow of fluid through the grid 32, as illustrated by the arrow F in Figure 11.

[0153] The grid 32 has, in each cell 50, a plurality of separate passages 36. The passages 36 of each cell 50 are separated from each other by side walls or dividing walls 54, which are for example intersecting grid elements.

[0154] The grid 32 has a plurality of cells 50, the number of cells 50 preferably being equal to or greater than five. The cells 50 are for example distributed on the grid 32 according to a matrix distribution.

[0155] The partitions 52 are for example higher than the passages 36 and / or than the separation walls 54.

[0156] Each cell 50 has a first empty section 50A (Figure 11) and a second empty section 50B (Figure 11) in which the passages 36 are delimited, i.e. across which the separation walls 54 extend.

[0157] The first section 50A is for example adjacent to the first face 32A of the grid 32, the second section 50B being adjacent to the second face 32B of the grid 32. The first section 50A is preferably located upstream of the second section 50B considering the direction of circulation of the fluid through the grid 32.

[0158] In one or more cells 50, and in particular in each cell 50, the grid 32 has a variable thickness, with in particular a first zone Z1 which is less thick and a second zone Z2 in which the grid 32 has a thicker thickness. In each cell 50, in which the grid 32 has a variable thickness, the first zone Z1 has a thickness strictly less than that of the second zone Z2.

[0159] Each cell 50, in which the grid 32 has a variable thickness, comprises passages 36 of different heights. The cell 50 comprises in particular lower passages 36, located in the first zone Z1, and higher passages 36, located in the second zone Z2.

[0160] In each cell 50, in which the grid 32 has a variable thickness, the first zone Z1 is for example a peripheral zone of the cell 50, the second zone Z2 being a central zone of the cell 50.

[0161] In each cell 50, in which the grid 32 has a variable thickness, the grid 32 is, for example, non-planar on the side of the first face 32A and planar on the side of the second face 32B.

[0162] When it is non-planar, the first face 32A is for example of a generally convex shape. The first face 32A is for example in the general shape of a spherical cap projecting from the side of the first face 32A.

[0163] The grid 32 having cells 50 separated by partitions 52 with a plurality of separate passages 36 delimited in each cell 50, in particular passages 36 of different heights, for example due to a variable height of the grid 32, allows effective filtering of debris.

[0164] As illustrated in Figure 11, in one or more cells 50, and in particular in each cell 50, each passage 36 is for example rectilinear. The inlet 36A and the outlet 36B of each rectilinear passage are aligned and coaxial.

[0165] In a variant, as illustrated in Figure 12, in at least one cell 50, and in particular in each cell 50, passages 36 of the cell 50 have a non-zero deflection between the inlet 36A and the outlet 36B of this or these passages 36.

[0166] The grid 32 preferably comprises passages 36 which have different deflections. In exemplary embodiments, in at least one cell, passages of the cell 50 have different deflections.

Claims

CLAIMS 1. Anti-debris filter for a lower nozzle of a nuclear fuel assembly, the anti-debris filter being formed of a grid (32) having a first face (32A) and a second face (32B) opposite each other, the grid (32) having passages (36) extending between an inlet (36A) located on the first face (32A) and an outlet (36B) located on the second face (32B) for the flow of a cooling fluid through the grid (32), the grid (32) having a first zone (Z1) and at least one second zone (Z2) in which the grid (32) has a thickness greater than that of the grid (32) in the first zone (Z1), passages (36) being present in the first zone (Z1) and in each second zone (Z2).

2. Anti-debris filter according to claim 1, in which each second zone (Z2) has passages (36) having an inlet (36A) and an outlet (36B) offset transversely relative to each other.

3. A debris filter according to claim 1 or claim 2, wherein each second zone (Z2) has passages (36) having an inlet (36A) and an outlet (36B) inclined relative to each other with a non-zero angle of inclination.

4. A debris filter according to any preceding claim, wherein each second zone (Z2) has passages (36) extending in a non-rectilinear manner.

5. Anti-debris filter according to any one of the preceding claims, in which the grid (32) has in each second zone (Z2) a thickness increasing from the periphery of the second zone (Z2) towards the center of the second zone (Z2).

6. Anti-debris filter according to any one of the preceding claims, in which each second zone (Z2) has a circular outline.

7. A debris filter according to any preceding claim, wherein side walls of the passages (36) in each second zone (Z2) are higher than the side walls of the passages (36) in the first zone (Z1).

8. Anti-debris filter according to any one of the preceding claims, in which at least one passage (36) located in a second zone (Z2) is delimited between two opposite curved side walls.

9. Anti-debris filter according to any one of the preceding claims, in which the grid (32) is formed of intersecting grid elements (38, 40) between which the passages (36) are delimited, including at least one grid element (38, 40) of variable height extending in the first zone (Z1) and at least one second zone (Z2), the height of each grid element (38, 40) of variable height being greater in each second zone (Z2) crossed by the grid element (38, 40) of variable height and smaller in the first zone (Z1).

10. Anti-debris filter according to any one of the preceding claims, wherein the grid (32) has a quadrangular outline, in particular a square outline.

11. Anti-debris filter according to any one of the preceding claims, wherein the grid (32) has four second zones (Z2) or at least five second zones (Z2).

12. Anti-debris filter according to any one of the preceding claims, in which the second zones (Z2) are distributed on the grid (32) in a matrix manner.

13. A debris filter according to any preceding claim, wherein the grid comprises a plurality of cells (50) separated by partitions (52), each cell (50) containing a plurality of separate passages (36) defined by side walls.

14. Anti-debris filter according to claim 13, wherein each cell (50) contains a first zone (Z1), preferably the periphery of the cell (50), and / a second zone (Z2), preferably in the center of the cell (50).

15. Anti-debris filter according to claim 13 or 14, in which the partitions (52) of each cell (50) are strictly higher than the passages (36) provided in this cell (50).

16. Anti-debris filter according to any one of claims 13 to 15, in which each cell (50) comprises a first section (50A), preferably empty, and a second section (50B) in which the passages (36) are located, the first section (50A) being preferably located upstream of the second section (50B) in the direction of flow of the fluid through the anti-debris filter.

17. Anti-debris filter according to any one of claims 13 to 16, wherein in each cell (50), the first face (32A) of the grid (32) is of generally non-planar shape, preferably convex, and / or the second face 32(B) of the grid (32) is planar.

18. A debris filter according to any one of claims 13 to 17, wherein the grid (32) comprises at least five cells (50) and / or the cells (50) are distributed in a matrix manner on the grid (32).

19. Lower nozzle of a nuclear fuel assembly equipped with an anti-debris filter according to any one of the preceding claims.

20. Nuclear fuel assembly, in particular for a pressurized water nuclear reactor, comprising an anti-debris filter according to any one of claims 1 to 18 or a lower nozzle according to claim 19.

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