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

Abstract

Anti-debris filter for lower nozzle of nuclear fuel assembly with variable thickness The anti-debris filter is formed of a grid (32) having a first face (32A) and a second face (32B) opposite each other, the grid (36) 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 coolant 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). Figure for abstract: Figure 7

Description

Title of the invention: Anti-debris filter for lower nozzle of nuclear fuel assembly with variable thickness

[0001] The present invention relates to the field of nuclear fuel assemblies, in particular for pressurized water nuclear reactors (or PWR for “Pressurized Water Reactor”).

[0002] 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 piece and an upper end piece spaced apart from the longitudinal axis, a plurality of guide tubes extending along the longitudinal axis connecting the end pieces 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.

[0003] In operation, the nuclear fuel assembly is arranged vertically in a vessel of a nuclear reactor, being placed on a lower core plate provided with openings through which a cooling fluid enters which circulates vertically from bottom to top through the nuclear fuel assembly.

[0004] Debris present in the coolant could damage components of the nuclear fuel assembly.

[0005] 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 WO2005 / 059923A2.

[0006] 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.

[0007] 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 cooling fluid 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.

[0008] The zones of different thicknesses allow the debris retention capacity and flow resistance of the grid to be adjusted. A zone of greater thickness has a higher retention capacity and flow resistance and a zone of lesser thickness has a lower retention capacity and flow resistance.

[0009] In particular embodiments, the anti-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 having an entrance and an exit offset transversely relative to each other;

[0011] - each second zone has passages with an entrance and an exit inclined 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 pe edge of the second zone towards the center of the second zone;

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

[0015] - side walls of the passages located in each second zone are higher that 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 walls curved opposite sides;

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

[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 fuel assembly nozzle. nuclear 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.

[0023] The invention and its advantages will be better understood on reading the description which follows, given solely as a non-limiting example, and made with reference to the appended drawings, in which:

[0024] - [Fig.l] [Fig.l] is a side view of a nuclear fuel assembly;

[0025] - [Fig.2] [Fig.2] is a sectional view of a lower nozzle of the assembly; nuclear fuel of [Fig.l], equipped with an anti-debris filter;

[0026] - [Fig.3] [Fig.3] is a bottom view of the debris filter;

[0027] - [Fig.4] [Fig.4] is a bottom view of a quadrant of the debris filter;

[0028] - [Fig.5] [Fig.5] is a perspective view of the debris filter quadrant illustrated in [Fig.4];

[0029] - [Fig.6] [Fig.6] is a cutaway perspective view of the debris filter quadrant illustrated in [Fig.4];

[0030] - [Fig.7] [Fig.7] is a sectional view of the debris filter quadrant shown in [Fig.4];

[0031] - [Fig.8] [Fig.8] is a sectional view similar to that of [Fig.7], illustrating a anti-debris filter according to another embodiment;

[0032] - [Fig.9] [Fig.9] is a partial sectional view of an anti-debris filter according to another example of realization, illustrating two adjacent passages of the grid.

[0033] The nuclear fuel assembly 2 of [Fig.l] comprises a bundle of nuclear fuel rods 4 and a support skeleton 6 configured to support the nuclear fuel rods 4.

[0034] The nuclear fuel rods 4 extend parallel to each other and to a longitudinal axis L.

[0035] 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 [Fig.l].

[0036] 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.

[0037] 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.

[0038] The lower end piece 8 and the upper end piece 10 are spaced along the longitudinal axis L.

[0039] 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, while 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.

[0040] Each guide tube 12 is open at its upper end to allow the insertion of a control bar (not shown) inside the guide tube 12, through the upper end piece 10. Such a control bar makes it possible to control the reactivity of the nuclear reactor core into which the nuclear fuel assembly 2 is inserted.

[0041] 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.

[0042] Each spacer grid 14 is configured to support the nuclear fuel rods 4 by holding them in a configuration in which they are transversely spaced from each other. The nuclear fuel rods 4 are preferably held at the nodes of a substantially regular imaginary network.

[0043] As illustrated in [Fig.l], 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.

[0044] 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.

[0045] As illustrated in [Fig.2], the lower end piece 8 comprises for example an end piece plate 20 and feet 22 extending downwards 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.

[0046] The guide tubes 12 (not shown in Figure 2) are for example fixed to the end plate 20 by means of fixing screws 24 passing through the end plate 20.

[0047] The lower nozzle 8 is provided with an anti-debris filter 30 configured to filter the cooling fluid.

[0048] The debris filter 30 comprises a grid 32. The grid 32 preferably has the shape of a plate.

[0049] The grid 32 has a first face 32A and a second face 32B opposite each other.

[0050] The grid 32 has a thickness taken between the first face 32A of the grid and the second face 32B of grid 32.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Preferably, the grid 32 extends over the entire extent of the end plate 20, plus particularly the entire extent of the lower face 20A of the end plate 20.

[0055] The grid 32 has fixing holes 34 for the passage of the fixing screws 24.

[0056] As illustrated in [Fig.3], the grid 32 has passages 36 extending through the grid 32 for the flow of coolant through the grid 32.

[0057] The grid 32 is for example formed by elongated grid elements 38, 40 which are intersected.

[0058] Each grid element 38, 40 has, for example, the shape of a bar or an elongated plate.

[0059] Each passage 36 is defined between adjacent intersecting grid elements 38, 40.

[0060] In particular, each passage 36 has, for example, side walls defined by two adjacent first grid elements 38 intersected with two adjacent second grid elements 40.

[0061] The grid 32 is for example formed of first grid elements 38 extending parallel along a first direction of extension T1 and second grid elements 40 extending parallel along a second direction of extension T2 perpendicular to the first direction of extension TL.

[0062] 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 contour of generally quadrangular shape, in particular a contour of generally square shape.

[0064] The grid 32 has for example four quadrants which are analogous, only one quadrant being illustrated in Figures 4 to 7 for reasons of clarity.

[0065] Furthermore, in Figures 4 to 7, the second face 32B of the grid 32 is facing upwards, this second face 32B 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 [Fig.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 inlet 36A to its outlet 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 angle of inclination 0. The angle of inclination 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 rectilinear 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 inlet axis A1 and the outlet axis A2.

[0075] Each passage 36 having a non-zero angle of inclination 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 [Fig.7], three different inclination angles 0 are shown, one of which is zero (on the right in [Fig.7]) and which corresponds to a rectilinear passage 36.

[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 angles of inclination 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 provision of passages 36 with different inclination angles 0 makes it possible to differentiate the retention capacity and the 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 retention 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 retention 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 entry axes Al of passages 36 of each second zone Z2 are for example inclined at a non-zero angle relative to the entry axes Al of the passages 36 of the first zone Z1. The entry axes Al of these passages 36 of each second zone Z2 make a non-zero angle with the entry axes Al of the passages 36 of the first zone ZL.

[0085] 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.

[0086] 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.

[0087] The grid 32 has for example four second zones Z2 distributed on 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.

[0088] The grid 32 here has four second zones Z2, each second zone Z2 being located in a respective quadrant of the grid 32.

[0089] 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 ZL.

[0090] As illustrated in Figures 4 to 7, and in particular in [Fig.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 ZL

[0091] Preferably, in the first zone Z1, the grid 32 has a substantially constant thickness, called the first thickness EL

[0092] The height of each grid element 38, 40 is taken according to the thickness of the grid 32.

[0093] In the first zone Zl, each grid element 38, 40 has a substantially constant height or first height HL. The first height H1 corresponds to the first thickness EL.

[0094] In each second zone Z2, the grid 32 has a second thickness E2 strictly greater than the first thickness El of the grid 32.

[0095] 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.

[0096] In each second zone Z2, at least a portion of the grid elements 38, 40 has a height strictly greater than the first height H1.

[0097] 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.

[0098] The first height Hl corresponds to the first thickness El and the second height H2 corresponds to the second thickness E2.

[0099] 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 HL

[0100] 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 HL.

[0101] 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 HL

[0102] The side walls of each passage 36 are defined by the portions of the grid elements 38, 40 delimiting the passage 36.

[0103] Thus, 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.

[0104] As illustrated in particular in [Fig.7], each passage 36 is delimited between two opposite side walls which extend substantially in parallel while being curved.

[0105] Thus each of these passages 36 extends in a curvilinear manner, its inlet 36A and its outlet 36B being offset transversely relative to each other and inclined relative to each other.

[0106] 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.

[0107] The upper portion 42 of each first grid element 38 is for example curved to define the curved passages 36.

[0108] Each of the second grid elements 40 extends for example substantially along a plane.

[0109] 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.

[0110] 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).

[0111] 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.

[0112] 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.

[0113] 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.

[0114] Due to the variation in thickness of the machined grid 32, certain passages 36 are reduced in height, and passages 36 finally have entry axes Al inclined relative to each other.

[0115] In particular, the passages 36 located in the thinnest regions of the machined grid 32 have the least inclined entry axes Al 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 Al and the largest inclination angles 0.

[0116] 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.

[0117] The thickness of the grid 32 is for example reduced in the first zone Zl 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 Zl before machining, each passage 36 of the first zone Zl therefore being rectilinear in the machined grid 32.

[0118] In a variant illustrated in [Fig.8], which is analogous to [Fig.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.

[0119] Such a grid 32 is for example obtained by additive manufacturing.

[0120] As illustrated in [Fig.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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] As also illustrated in [Fig.9], preferably the lower edge and / or the upper edge of each side wall of each passage 36 is preferably rounded. This makes it possible to promote the flow of the fluid by limiting the flow resistance of the grid 32.

[0126] The provision of passage 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 zones of the grid 32.

[0127] An area of ​​the grid with passages 36 having larger θ inclination angles has a larger debris holding capacity and a larger flow resistance, while an area of ​​the grid with passages 36 having smaller θ inclination angles has a smaller debris holding capacity and a smaller flow resistance.

[0128] The provision of a first zone ZI with a first thickness El and one or more second zones Z2 with a thickness strictly greater than the first thickness El 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 ZI 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 angles of inclination 0 between input 36A and output 36B identical and not damaged.

[0129] The second zone(s) Z2 may be placed on the grid 30 at the location(s) where the probability of the debris passing is greatest, which is most of the time opposite the openings 18 of the lower core plate 16 through which the cooling fluid arrives under the nuclear fuel assemblies 2.

[0130] Thus, it is possible to obtain a grid 30 having limited hydraulic resistance while presenting a satisfactory debris retention capacity.

[0131] The grid 30 can be manufactured easily, for example by additive manufacturing and / or by machining.

[0132] The invention is not limited to the example and the variants described, other examples and other variants being conceivable.

[0133] 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 Al of the passages 36 are all inclined in the same direction. The entry axes Al of the passages 36 are all parallel to the same reference plane. The entry axes Al can be parallel if the angles of inclination of the passages 36 are the same or not if passages have different angles of inclination.

[0134] Of course, in a variant, input axes A1 of the passages 36 may be inclined in different directions. To do this, it is possible to provide that the second grid elements 40 are also curved.

[0135] 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.

[0136] 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.

[0137] The provision of a first zone ZI 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.

[0138] 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.

[0139] Each second zone Z2 thicker than the first zone Zl has a higher retention capacity than the first zone Zl and a higher flow resistance than the first zone Zl.

[0140] 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.

[0141] The provision of a first zone Z1 and at least one 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 resistance to flow of the grid 32 as a whole.

[0142] 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.

[0143] The features discussed in connection with the embodiment of Figures 4 to 7 may be provided as an option on the grid 32.

[0144] In particular, in embodiments, the grid 32 comprises one or more of the following optional features, taken individually or in any technically possible combination:

[0145] - each second zone Z2 has passages 36 having an entrance 36A and a 36B exit offset transversely relative to each other;

[0146] - each second zone Z2 has passages 36 having an entrance 36A and a 36B outlet inclined relative to each other with a non-zero inclination angle.

[0147] - each second zone Z2 has passages 36 extending in a non- straight;

[0148] - the grid 32 has in each second zone Z2 an increasing thickness from the periphery of the second zone Z2 towards the center of the second zone Z2;

[0149] - each second zone Z2 has a circular outline.

[0150] - at least one passage 36 located in a second zone Z2 is delimited between two curved opposite side walls;

[0151] - the grid 32 is formed of intersecting grid elements 38, 40 between which are delimited the passages 36, 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;

[0152] - the grid 32 has a quadrangular outline, in particular a square outline;

[0153] - grid 32 has four second zones Z2;

[0154] - the second zones Z2 are distributed on the grid 32 in a matrix manner;

[0155] According to said other aspect, the invention also proposes a lower nozzle of 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.

Claims

Claims

1. A debris filter for a lower nozzle of a nuclear fuel assembly, the debris filter being formed of a grid (32) having a first face (32A) and a second face (32B) opposite each other, the grid (36) 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), characterized in that each second zone (Z2) has passages (36) having an inlet (36A) and an outlet (36B) offset transversely relative to each other.

2. The debris filter of claim 1, 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.

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

4. 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).

5. A debris filter according to any preceding claim, wherein each second zone (Z2) has a circular outline.

6. 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).

7. A debris filter according to any preceding claim, wherein at least one passage (36) located in a second zone (Z2) is delimited between two opposite curved side walls.

8. A debris filter according to any preceding claim, wherein the grid (32) is formed of intersecting grid elements (38, 40) between which the passages (36) are defined, including at least at least one grid element (38, 40) of variable height extending in the first zone (Zl) 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 (Zl).

9. A debris filter according to any preceding claim, wherein the grid (32) has a quadrangular outline, in particular a square outline.

10. A debris filter according to any preceding claim, wherein the grid (32) has a square outline.

11. A debris filter according to any preceding claim, wherein the grid (32) has four second zones (Z2).

12. A debris filter according to any preceding claim, wherein the second zones (Z2) are distributed on the grid (32) in a matrix manner.

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

14. Nuclear fuel assembly, in particular for a pressurized water nuclear reactor, comprising an anti-debris filter according to any one of claims 1 to 12.

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