Debris filter with variable deflection channel for nuclear fuel assembly lower end

Abstract

There is disclosed a debris filter formed from a grid (32) having a first face (32A) and an opposite second face (32B), the grid (32) having channels (36) for a cooling fluid to flow through the grid (32), each channel (36) extending between an inlet (36A) located on the first face (32A) and having an inlet axis (A1) and an outlet (36B) located on the second face (32B) and having an outlet axis (A2), an angle of inclination is defined between the inlet axis (A1) and the outlet axis (A2), and the grille (32) comprises channels (36) having different angles of inclination between its inlet axis (A1) and its outlet axis (A2).

Description

Technical Field

[0001] The present invention relates to the field of nuclear fuel assemblies, more particularly for use in pressurized water reactors (PWR). Background Art

[0002] A nuclear fuel assembly of a pressurized water nuclear reactor generally includes a bundle of nuclear fuel rods extending along a longitudinal axis and a support frame configured to support the nuclear fuel rods. The support frame includes a lower end piece and an upper end piece spaced apart along the longitudinal axis, a plurality of guide tubes extending along the longitudinal axis to connect 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 placed vertically in the vessel of the nuclear reactor, on a lower core plate provided with openings through which a cooling fluid enters, the cooling fluid flowing vertically upwards through the nuclear fuel assembly.

[0004] Debris that may be present in the coolant may damage components of the nuclear fuel assemblies.

[0005] The lower end piece of a nuclear fuel assembly may be provided with a debris filter which allows the flow of cooling fluid whilst retaining any debris that may be present in the cooling fluid.Such a debris filter is disclosed in WO 2005 / 059923 A2. Summary of the invention

[0006] One of the objects of the present invention is to provide a debris filter which has limited hydraulic resistance and at the same time has a satisfactory debris retention capacity.

[0007] To this end, the present invention proposes a debris filter for a lower end piece of a nuclear fuel assembly, the debris filter being formed by a grid having a first face and a second face opposite to each other, the grid having channels for a cooling fluid to flow through the grid, each channel extending between an inlet located on the first face and having an inlet axis and an outlet located on the second face and having an outlet axis, defining an inclination angle between the inlet axis and the outlet axis, the grid including channels having different inclination angles between its inlet axis and its outlet axis.

[0008] Channels having different inclination angles between their inlet axis and their outlet axis (ie having different deflections between their inlet and outlet) can adjust the debris retention capacity and flow resistance of different areas of the grille.

[0009] Regions with more deflected channels have higher retention capacity and higher resistance to flow, whereas regions with less deflected channels have lower retention capacity and lower resistance to flow.

[0010] According to a particular embodiment, the debris filter comprises one or more of the following optional features, taken alone or in all technically possible combinations:

[0011] - the debris filter comprises a straight channel defining a zero inclination angle and a curved channel defining a non-zero inclination angle;

[0012] - the inclination angle defined by each channel is comprised between 0° and 60°;

[0013] - the channel has an inlet axis forming a non-zero angle with the direction of fluid flow through the grille, and / or the channel has an outlet axis parallel to the direction of fluid flow through the grille;

[0014] - the inlet and outlet of each channel defining a non-zero inclination angle are laterally offset relative to each other;

[0015] - the grid has a first area and at least one second area, the inclination angle of the channels located in each second area being non-zero and greater than or equal to the maximum inclination angle of the channels located in the first area;

[0016] - the channels extend in parallel and the thickness of the grid in each second area is strictly greater than the thickness of the grid in the first area, more specifically the thickness of the grid in each second area increases from the periphery of the second area towards the center of the second area;

[0017] - each second region has a circular contour;

[0018] - the side walls of the channels in each second region are higher than the side walls of the channels in the first region;

[0019] - each channel located in the second region is defined between two opposite curved side walls;

[0020] - the grid has four second areas;

[0021] - the second areas are distributed as a matrix on the grid;

[0022] The grille has a quadrilateral profile, more particularly a square profile.

[0023] The invention also relates to a lower end piece of a nuclear fuel assembly provided with a debris filter as defined above.

[0024] The invention also relates to a nuclear fuel assembly, more particularly for a pressurized water nuclear reactor, comprising a debris filter as defined above. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention and its advantages will be better understood on reading the following description given purely as a non-limiting example and with reference to the accompanying drawings, in which:

[0026] - Figure 1 is a side view of a nuclear fuel assembly;

[0027] - Figure 2 Is equipped with a debris filter Figure 1 A cross-sectional view of the lower end piece of the nuclear fuel assembly shown;

[0028] - Figure 3 is a top view of a debris filter;

[0029] - Figure 4 is a top view of one quarter of a debris filter;

[0030] - Figure 5 yes Figure 4 a perspective view of one quarter of a debris filter as shown;

[0031] - Figure 6 yes Figure 4 a cutaway perspective view of one quarter of a debris filter as shown;

[0032] - Figure 7 yes Figure 4 a cross-sectional view of one quarter of a debris filter shown;

[0033] - Figure 8 is similar to Figure 7 a cross-sectional view of the illustrated view showing a debris filter according to another embodiment example;

[0034] - Fig. 9 is a partial cross-sectional view of a debris filter according to another embodiment showing two adjacent channels of a grille;

[0035] - Fig.10 is a partial top view of a debris filter according to another example embodiment;

[0036] - Fig.11 yes Fig.10 The debris filter is shown along Fig.10 A cross-sectional view taken along line XI-XI in FIG. DETAILED DESCRIPTION

[0037] Figure 1 The nuclear fuel assembly 2 includes a bundle of nuclear fuel rods 4 and a support skeleton 6 configured to support the nuclear fuel rods 4 .

[0038] The nuclear fuel rods 4 extend parallel to each other and parallel to the longitudinal axis L.

[0039] When the nuclear fuel assembly 2 is placed in the core of a nuclear reactor, the longitudinal axis L extends vertically. In operation, a cooling fluid circulates vertically through the nuclear fuel assembly 2 from the bottom upwards, such as Figure 1 As shown by arrow F in FIG.

[0040] Hereinafter, in the description, the terms "vertical", "horizontal", "top", "bottom", "longitudinal", "lateral", "upper" and "lower" are understood by reference to the position of the nuclear fuel assembly 2 in the core of the nuclear reactor, and the longitudinal axis L is basically vertical.

[0041] The supporting frame 6 includes a lower end member 8 , an upper end member 10 , a plurality of guide tubes 12 and a plurality of spacer grids 14 .

[0042] The lower end piece 8 and the upper end piece 10 are spaced apart along the longitudinal axis L.

[0043] The guide tube 12 extends along the longitudinal axis L and connects the lower end piece 8 and the upper end piece 10 together, thereby maintaining the spacing between the lower end piece 8 and the upper end piece 10. The nuclear fuel rod 4 is received between the lower end piece 8 and the upper end piece 10.

[0044] Each guide tube 12 is open at its upper end to allow a control rod (not shown) to be inserted through the upper end piece 10 into the interior of the guide tube 12. Such a control rod can control the reactivity of the nuclear reactor core into which the nuclear fuel assembly 2 is inserted.

[0045] The spacing grids 14 are distributed along the guide tube 12 and are spaced apart from one another along the longitudinal axis L. Each spacing grid 14 is rigidly attached to the guide tube 12 , the guide tube 12 extending through each spacing grid 14 .

[0046] Each spacing grid 14 is configured to support the nuclear fuel rods 4 by holding them in a configuration in which they are laterally spaced apart from each other. The nuclear fuel rods 4 are preferably held at the nodes of a substantially regular imaginary network.

[0047] like Figure 1 As shown, the nuclear fuel assembly 2 is placed via its lower end piece 8 on the lower core plate 16 , opposite at least one opening 18 for the flow of a cooling fluid.

[0048] In operation, cooling fluid passes through each opening 18 , enters the nuclear fuel assembly 2 via the lower end piece 8 , circulates along the nuclear fuel rods 4 , and leaves the nuclear fuel assembly 2 via the upper end piece 10 .

[0049] like Figure 2 As shown, the lower end piece 8 includes, for example, an end piece plate 20 and legs 22 extending downward from the end piece plate 20 so as to press on the lower core plate 16. The end piece plate 20 has a lower face 20A and an upper face 20B.

[0050] Guide tube 12 (not in Figure 2 ) is attached to the end piece plate 20 , for example by means of fastening screws 24 which pass through the end piece plate 20 .

[0051] The lower end piece 8 is provided with a debris filter 30 configured to filter the cooling fluid.

[0052] The debris filter 30 includes a grille 32. The grille 32 preferably has the shape of a plate.

[0053] The grille 32 has at least a first surface 32A and a second surface 32B.

[0054] The grid 32 has a thickness obtained between a first face 32A of the grid and a second face 32B of the grid 32 .

[0055] The first face 32A is intended to face downwards, ie upstream when considering the direction of flow of the cooling fluid through the grid 32 .

[0056] The second face 32B is intended to be oriented upwards, ie towards downstream when considering the direction of flow of the cooling fluid through the grid 32 .

[0057] The grid 32 is arranged below the end piece plate 20 so that the cooling fluid passes through the grid 32 before passing through the end piece plate 20 .

[0058] Preferably, the grid 32 extends over the entire extent of the end piece plate 20 , more specifically over the entire extent of the lower face 20A of the end piece plate 20 .

[0059] The grille 32 has fastening holes 34 for the fastening screws 24 to pass through.

[0060] like Figure 3 As shown, the grille 32 has passages 36 extending therethrough for the flow of cooling fluid through the grille 32 .

[0061] The grid 32 is formed, for example, from staggered elongated grid elements 38 , 40 .

[0062] Each grid element 38 , 40 has a shape of, for example, a rod or an elongated flat plate.

[0063] Each channel 36 is defined between adjacent staggered grid elements 38 , 40 .

[0064] More specifically, each channel 36 has side walls defined, for example, by two adjacent first grid elements 38 interleaved with two adjacent second grid elements 40 .

[0065] The grid 32 is formed, for example, by first grid elements 38 extending in parallel along a first extension direction T1 and second grid elements 40 extending in parallel along a second extension direction T2 perpendicular to the first extension direction T1 .

[0066] Each channel 36 is defined between two adjacent first grid elements 38 and two adjacent second grid elements 40 .

[0067] The grille 32 has, for example, a substantially quadrilateral-shaped outline, more specifically, a substantially square-shaped outline.

[0068] The grid 32 has, for example, four similar quarters, which are shown in FIG. Figures 4 to 7 Only one quarter is shown.

[0069] In addition, Figures 4 to 7 In the embodiment, the first face 32A of the grid 32 is oriented upward, and when the grid 32 is mounted on the lower end piece 8 and the nuclear fuel assembly 2 is mounted in the core of the nuclear reactor, the first face 32A actually faces downward.

[0070] Especially if Figure 7 As shown, each channel 36 extends between an inlet 36A located on the first face 32A and an outlet 36B located on the second face 32B.

[0071] The inlet 36A of each channel 36 has an inlet axis A1 , and the outlet 36B of each channel 36 has an outlet axis A2 .

[0072] Each channel 36 extends from its inlet 36A to its outlet 36B along a centerline C of the channel 36 .

[0073] The centerline C of each channel 36 is tangent to the inlet axis A1 at the inlet 36A of the channel 36 , and is tangent to the outlet axis A2 at the outlet of the channel 36 .

[0074] The inlet axis A1 and the outlet axis A2 of each channel 36 define an inclination angle θ therebetween. The inclination angle θ is also referred to as a deflection angle.

[0075] The inclination angle θ between the inlet axis A1 and the outlet axis A2 of each channel 36 of the grille 32 is comprised between, for example, 0° and 60°.

[0076] Each channel 36 having a zero inclination angle θ (ie 0°) corresponds to a straight channel 36. The inlet axis A1 and the outlet axis A2 coincide. The channel 36 has zero deflection between its inlet 36A and its outlet 36B. The inlet 36A and the outlet 36B are aligned.

[0077] Each channel 36 having a non-zero inclination angle θ between its inlet axis A1 and its outlet axis A2 has a non-zero deflection between its inlet 36A and its outlet 36B.

[0078] A non-zero inclination angle θ corresponds to a curved channel 36 , ie, extending along a curved centerline C. The centerline C of each curved channel 36 preferably has an inclination that varies monotonically between the inlet axis A1 and the outlet axis A2 .

[0079] Each channel 36 having a non-zero inclination angle θ between its inlet axis A1 and its outlet axis A2 preferably has an inlet 36A and an outlet 36B that are laterally offset relative to each other when considering the direction of fluid flow through the grid 32 .

[0080] Advantageously, the grille 32 has channels 36 with different inclination angles θ between its inlet axis A1 and its outlet axis A2. In other words, the grille 32 has channels 36 with different respective deflections.

[0081] exist Figure 7 In FIG. 1 , three different tilt angles θ are shown, one of which is zero (at Figure 7 on the right side) and corresponds to the straight channel 36.

[0082] In one embodiment, the outlet axes A2 of all channels 36 are parallel to each other, and the inlet axes A1 of channels 36 having different inclination angles θ are inclined relative to each other.

[0083] Preferably, the outlet axis A2 of the channel 36 is parallel to the flow direction of the fluid, which can limit the disturbance of the fluid flow at the outlet of the grille 32 .

[0084] Providing channels 36 with different inclination angles θ can differentiate the retention capacity and flow resistance of different areas of the grid 32 .

[0085] Areas of the grille containing channels 36 having a larger inclination angle θ (i.e., larger deflections) have a larger debris retention capacity and a larger flow resistance, while areas of the grille containing channels 36 having a smaller inclination angle θ (i.e., smaller deflections) have a smaller debris retention capacity and a smaller flow resistance.

[0086] Preferably, the grille 32 has a first area Z1 and at least one second area Z2, the first area Z1 has a plurality of channels 36, each second area Z2 has a plurality of channels 36, and the inclination angle θ of the channels 36 located in each second area Z2 is non-zero and greater than or equal to the maximum inclination angle θ of the channels 36 located in the first area Z1.

[0087] More specifically, the outlet axes A2 of the channels 36 of the first zone Z1 and of each second zone Z2 are, for example, parallel to one another.

[0088] The inlet axis A1 of each channel 36 of the second zone Z2 is for example inclined at a non-zero angle relative to the inlet axis A1 of the channel 36 of the first zone Z1. The inlet axis A1 of each channel 36 of the second zone Z2 forms a non-zero angle with the inlet axis A1 of the channel 36 of the first zone Z1.

[0089] The inclination angle θ between the inlet axis A1 and the outlet axis A2 of each channel 36 of the first zone Z1 is, for example, substantially zero. The channels 36 of the first zone Z1 are, for example, rectilinear.

[0090] Preferably, when the nuclear fuel assembly 2 is arranged on the lower core plate 16 , the grid 32 has a respective second zone Z2 associated with each opening 18 of the lower core plate 16 situated below the lower end piece 8 .

[0091] The grid 32 has, for example, four second areas Z2 distributed on the grid 32 of a quadrilateral shape, more specifically a square shape, and the second areas Z2 are distributed according to, for example, a 2×2 matrix distribution.

[0092] In this case, the grid 32 has four second zones Z2 , each second zone Z2 being located in a respective quarter of the grid 32 .

[0093] 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 .

[0094] like Figures 4 to 7 As shown, more specifically in Figure 7 In each second zone Z2 , the thickness of the grid 32 is strictly greater than the thickness of the grid 32 in the first zone Z1 .

[0095] Preferably, in the first zone Z1 , the grid 32 has a substantially constant thickness, called first thickness E1 .

[0096] The height of each grid element 38 , 40 is obtained as a function of the thickness of the grid 32 .

[0097] 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 .

[0098] In each second zone Z2 , the grid 32 has a second thickness E2 that is strictly greater than the first thickness E1 of the grid 32 .

[0099] The grid 32 has, for example, a variable thickness that varies between a first thickness E1 at the periphery of each second zone Z2 to a second thickness E2, for example at the center of the second zone Z2.

[0100] In each second zone Z2 , at least a portion of the grid elements 38 , 40 has a height that is strictly greater than the first height H1 .

[0101] At least a portion of the grid elements 38 , 40 has, for example, a variable height that varies, for example, between a first height H1 and a second height H2 .

[0102] The first height H1 corresponds to the first thickness E1 , and the second height H2 corresponds to the second thickness E2 .

[0103] 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 .

[0104] More specifically, in each second zone Z2, each first grid element 38 or only a portion of grid elements 38 has a height greater than first height H1, and / or each second grid element 40 or only a portion of second grid elements 40 has a height greater than first height H1.

[0105] exist Figures 4 to 7 In each second zone Z2 , each first grid element 38 has a height greater than the first height H1 , and each third second grid element 40 has a height greater than the first height H1 .

[0106] The side walls of each channel 36 are defined by portions of the grid elements 38 , 40 that bound the channel 36 .

[0107] Therefore, the side walls of the channels located in each second zone Z2 are higher than the side walls of the channels located in the first zone Z1.

[0108] Especially if Figure 7 As shown, each channel 36 is defined between two opposing side walls that extend substantially parallel while being curved.

[0109] Thus, each channel 36 extends curvilinearly, with its inlet 36A and outlet 36B being laterally offset and inclined relative to each other.

[0110] More specifically, in each second zone Z2 , each first grid element 38 of variable height, in particular each first grid element 38 , has an upper portion 42 extending higher than the rest of the first face 32A of the grid 32 in the first zone Z1 .

[0111] The upper portion 42 of each first grid element 38 is, for example, curved to define the curved channel 36 .

[0112] Each second grid element 40 extends, for example, substantially along a plane.

[0113] In each second zone Z2 , second variable height grid element 40 has an upper portion 44 that intersects upper portion 42 of first variable height grid element 38 .

[0114] The grid 30 is produced, for example, by a manufacturing method that adds material (additive manufacturing) and / or by a manufacturing method that removes material (machining).

[0115] In order to obtain a grid 32 having channels 36 with inlet axes A1 inclined relative to each other and outlet axes A2 parallel to each other, the grid blank 32 is, for example, initially manufactured to have a constant thickness, each channel 36 extending along a curved center line C with a non-zero inclination angle between its inlet axis A1 and outlet axis A2, and the channels 36 extending parallel to each other.

[0116] Initially, the inlet axes A1 of the channels 36 are parallel to each other, and the outlet axes A2 of the channels 36 are parallel to each other.

[0117] The grid blank 32 is then machined on the first face 32A to form the first zone Z1 and the respective second zones Z2.

[0118] Due to the thickness variation of the machined grid 32 , the height of some of the channels 36 is reduced, and the channels 36 eventually have inlet axes A1 that are inclined relative to each other.

[0119] More specifically, the channels 36 located in the thinnest region of the machined grid 32 have the least inclined inlet axis A1 and the smallest inclination angle θ, while the channels 36 located in the thickest region of the grid 32 have the most inclined inlet axis A1 and the largest inclination angle θ.

[0120] Therefore, the channels 36 located in each second zone Z2 have a larger inclination angle θ than the channels 36 located in the first zone Z1 .

[0121] The thickness of the grid 32 is reduced, for example, in the first zone Z1 so that only a straight outlet portion 36 of the grid 32 remains in each channel 36 of the first zone Z1 before machining, so that each channel 36 of the first zone Z1 is straight in the machined grid 32 .

[0122] In a similar Figure 7 and wherein reference numerals of similar elements are repeated Figure 8 In the variant shown, the grid 32 has, for example, a constant thickness, the differences in inclination between the channels 36 being caused by differences in curvature between the centre lines C of the channels 36 , for example between the side walls of the channels 36 .

[0123] Such a grid 32 is obtained, for example, by additive manufacturing.

[0124] like Fig. 9 As shown, channels 36 having variable cross-sections may be provided along the channels 36 , each channel 36 having a converging inlet section 46 (when considering the flow direction of the fluid in the channel 36 from the inlet 36A to the outlet 36B) and / or a diverging outlet section 48 .

[0125] A converging inlet section 46 or a diverging outlet section 48 is obtained, for example, by providing chamfers on the side walls of the inlet section 46 and the outlet section, respectively.

[0126] Each channel 36 with 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, with a converging inlet section 46 and the rest of the channel having a constant cross-section, or with a diverging outlet section 46 and the rest of the channel having a constant cross-section.

[0127] A channel 36 with a variable cross section provided with a converging inlet section 46 and a diverging outlet section 48 without a middle section of constant cross section has, for example, curved and convex side walls.

[0128] The variation in the cross-section of the channel 36 can generate a Venturi effect in the fluid circulating in the channel 36 .

[0129] Likewise Fig. 9 As shown, preferably, the lower edge and / or upper edge of each side wall of each channel 36 is preferably rounded. It can enhance the flow of the fluid by limiting the flow resistance of the grid 32.

[0130] The provision of channels 36 having different inclination angles θ between inlet 36A and outlet 36B can differentiate the retention capacity and flow resistance of different areas of grid 32 .

[0131] Regions of the grid containing channels 36 having a larger inclination angle θ have a larger debris retention capacity and a larger flow resistance, whereas regions of the grid containing channels 36 having a smaller inclination angle θ have a smaller debris retention capacity and a smaller flow resistance.

[0132] Providing a first region Z1 having a first thickness E1 and one or more second regions Z2 having a thickness strictly greater than the first thickness E1 can easily form a channel 36 having a smaller inclination angle θ between the inlet 36A and the outlet 36B in the first region Z1 and a channel 36 having a larger inclination angle θ between the inlet 36A and the outlet 36B in each second region Z2 from a grid workpiece blank having a constant thickness, the channels 36 being parallel and the inclination angle θ between the inlet 36A and the outlet 36B being the same and non-zero.

[0133] One or more second zones Z2 may be located at one or more positions on the grid 30 where debris passage is most likely, such positions being opposed to the openings 18 of the lower core plate 16 most of the time, through which cooling fluid reaches below the nuclear fuel assembly 2 .

[0134] Thus, a grid 30 having limited hydraulic resistance while having satisfactory debris retention capacity can be obtained.

[0135] The grid 30 may be easily manufactured, for example by additive manufacturing and / or by machining.

[0136] The present invention is not limited to the examples and modifications described above, and other examples and modifications are conceivable.

[0137] Figure 4 and Figure 7 The channels 36 of the grid are defined between the curved first grid element 38 and the flat second grid element 40 so that the inlet axes A1 of the channels 36 are all inclined in the same direction. The inlet axes A1 of the channels 36 are all parallel to the same reference plane. The inlet axes A1 can be parallel if the inclination angles of the channels 36 are the same or different (if the channels have different inclination angles).

[0138] Of course, in a variant, the inlet axis A1 of the channel 36 may be inclined in a different direction. To this end, provision may be made for the second grid element 40 to be curved as well.

[0139] Furthermore, it is possible to provide outlet axes A2 which are non-parallel to one another and which, moreover, have a non-zero inclination relative to the longitudinal axis L of the nuclear fuel assembly 2 when the grid 30 is mounted on the lower end piece 8 .

[0140] More specifically, provision may be made for the inlet axes A1 to be parallel to each other and for the outlet axes A2 to be inclined relative to each other so as to obtain different inclination angles, the outlet axes A2 for example all parallel to the same reference plane or inclined in different directions.

[0141] Providing a first zone Z1 with a first thickness E1 and at least one second zone Z2 with a second thickness E2 is advantageous regardless of the channels 36 having a non-zero inclination angle between the inlet axis A1 and the outlet axis A2 (more specifically, different inclination angles between different channels 36 ).

[0142] Therefore, according to another aspect, the present invention proposes a debris filter for a lower end piece of a nuclear fuel assembly, the debris filter being formed by a grid 32 having a first face 32A and an opposite second face 32B, the grid 32 having a channel 36 extending between an inlet 36A located on the first face 32A and an outlet 36B located on the second face 32B, for a cooling fluid to flow through the grid 32, the grid 32 having a first region Z1 and at least one second region Z2, the thickness of the grid 32 in the second region Z2 being greater than the thickness of the plate in the first region Z1, the channel 36 being present in the first region Z1 and each second region Z2.

[0143] Each second region Z2 that is thicker than the first region Z1 has a higher retention capacity than the first region Z1 and a higher flow resistance than the first region Z1.

[0144] The channels 36 situated in each second zone Z2 are a priori longer than the channels 36 situated in the second zone Z2 and make it possible, for example, to filter longer debris.

[0145] Providing the first zone Z1 and at least one second zone Z2 thicker than the first zone Z1 can locally adjust the retention capacity according to the possibility of debris presence while limiting the flow resistance of the entire grid 32 .

[0146] Such a grid having a first region Z1 and at least one second region Z2 of different thicknesses may be provided with straight channels 36 and / or curved channels 36, more specifically, may be provided with all straight channels 36 or all curved channels 36, wherein the curved channels 36 have the same or different inclination angles.

[0147] about Figures 4 to 7 The features discussed with respect to the embodiment shown in FIG. 3 may be provided on the grille 32 as options.

[0148] More specifically, in an embodiment, the grille 32 comprises one or more of the following optional features, taken alone or in all technically possible combinations:

[0149] - each second zone Z2 has a channel 36 with an inlet 36A and an outlet 36B laterally offset relative to each other;

[0150] Each second zone Z2 has a channel 36 having an inlet 36A and an outlet 36B inclined at a non-zero inclination angle relative to each other.

[0151] - Each second zone Z2 has a channel 36 extending in a non-linear manner;

[0152] - the grid 32 has, in each second zone Z2, a thickness that increases from the periphery of the second zone Z2 towards the centre of the second zone Z2;

[0153] - Each second zone Z2 has a circular outline.

[0154] - at least one channel 36 situated in the second zone Z2 is defined between two opposite curved side walls;

[0155] - the grid 32 is formed by staggered grid elements 38, 40 defining channels 36 therebetween, including at least one grid element 38, 40 of variable height extending in a first zone Z1 and in 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;

[0156] - the grille 32 has a quadrilateral profile, more particularly a square profile;

[0157] - the grid 32 has four second zones Z2;

[0158] - the second zones Z2 are distributed as a matrix on the grid 32;

[0159] According to said further aspect, the invention also proposes a lower end piece of a nuclear fuel assembly equipped with a debris filter as defined above and / or more particularly a nuclear fuel assembly for a pressurized water nuclear reactor comprising a debris filter as defined above.

[0160] Fig.10 and Fig.11 The grille 32 of the debris filter 30 shown in FIG. 1 includes a plurality of cells 50 separated by partitions 52. Each cell 50 passes through the grille 32. Each cell 50 extends between a first face 32A of the grille 32 and a second face 32B of the grille 32. Each cell 50 allows fluid to flow through the grille 32, such as Fig.11 As shown by arrow F in FIG.

[0161] The grid 32 has a plurality of individual channels 36 in each cell 50. The channels 36 of each cell 50 are separated from one another by side walls or dividers 54, such as staggered grid elements.

[0162] The grid 32 has a plurality of cells 50 , the number of which is preferably greater than or equal to 5. The cells 50 are distributed on the grid 32 , for example, in a matrix distribution.

[0163] The partition 52 is, for example, higher than the channel 36 and / or higher than the partition wall 54 .

[0164] Each cell 50 has a first section 50A which is empty and a second section 50B in which the channel 36 is defined, ie through which the partition wall 54 extends.

[0165] The first section 50A is adjacent to the first face 32A of the grille 32, for example, and the second section 50B is adjacent to the second face 32B of the grille 32. Considering the circulation direction of the fluid through the grille 32, the first section 50A is preferably located upstream of the second section 50B.

[0166] In one or more cells 50 , and more specifically in each cell 50 , the grid 32 has a variable thickness, more specifically a first zone Z1 which is thinner and a second zone Z2 in which the grid has a thicker thickness.

[0167] In each cell 50 of the grid 32 having a variable thickness, the thickness of the first zone Z1 is strictly smaller than the thickness of the second zone Z2.

[0168] Each cell 50 in which the grid 32 has a variable thickness comprises channels 36 of different heights. The cell 50 more particularly comprises channels 36 of lower height in the first zone Z1 and higher channels 36 in the second zone Z.

[0169] In each cell 50 in which the grid 32 has a variable thickness, the first area Z1 is, for example, a peripheral area of ​​the cell 50 , and the second area Z2 is a central area of ​​the cell 50 .

[0170] In each unit 50 in which the grid 32 has a variable thickness, the grid 32 is not flat on the first face 32A side and is flat on the second face 32B side, for example.

[0171] When the first surface 32A is not flat, the first surface 32A has, for example, a substantially convex shape. The first surface 32A has, for example, a substantially spherical cap shape protruding from the first surface 32A side.

[0172] The grille 32 has cells 50 separated by partitions 52, has a plurality of individual channels 36 defined in each cell 50, and more specifically, has channels 36 of different heights, such as due to the variable height of the grille 32, resulting in effective filtering of debris.

[0173] like Fig.11 As shown, in one or more of the cells 50 , and more particularly in each cell 50 , one or more of the channels 36 have a non-zero deflection between the inlet 36A and the outlet 36B of the channel 36 .

[0174] The grid 32 comprises channels 36 having different deflections.

[0175] Preferably, channels 36 of one and the same unit 50 have different deflections.

[0176] In an example of implementation, in each of the one or more cells 50 , the channels of the cells 50 have a different deflection.

Claims

1. A debris filter for a lower end piece of a nuclear fuel assembly, the debris filter being formed by a grid (32) having a first face (32A) and a second face (32B) opposite to each other, the grid (32) having channels (36) for allowing a cooling fluid to flow through the grid (32), each channel (36) extending between an inlet (36A) located on the first face (32A) and having an inlet axis (A1) and an outlet (36B) located on the second face (32B) and having an outlet axis (A2), an inclination angle being defined between the inlet axis (A1) and the outlet axis (A2), the grid (32) including channels (36) having different inclination angles between its inlet axis (A1) and its outlet axis (A2).

2. The debris filter of claim 1, comprising straight channels (36) defining a zero inclination angle and curved channels (36) defining a non-zero inclination angle.

3. Debris filter according to claim 1 or 2, wherein the angle of inclination defined by each channel (36) is comprised between 0° and 60°.

4. A debris filter according to any one of the preceding claims, wherein the channel (36) has an inlet axis (A1) that forms a non-zero angle with the direction of fluid flow through the grille (32), and / or the channel has an outlet axis (A2) that is parallel to the direction of fluid flow through the grille (32).

5. A debris filter according to any one of the preceding claims, wherein the inlet (36A) and outlet (36B) of each channel (36) defining a non-zero angle of inclination are laterally offset from one another.

6. A debris filter according to any one of the preceding claims, wherein the grille (32) has a first area (Z1) and at least one second area (Z2), the inclination angle of the channels (36) in each second area (Z2) being non-zero and greater than or equal to the maximum inclination angle of the channels (36) in the first area (Z1).

7. A debris filter according to claim 6, wherein the channels (36) extend in parallel and the thickness of the grille (32) in each second zone (Z2) is strictly greater than the thickness of the grille (32) in the first zone (Z1), more specifically, the thickness of the grille in each second zone increases from the periphery of the second zone (Z2) toward the center of the second zone (Z2).

8. The debris filter according to claim 6 or 7, wherein each second zone (Z2) has a circular contour.

9. The debris filter according to any one of claims 6 to 8, wherein the side walls of the channels (36) located in each second zone (Z2) are higher than the side walls of the channels (36) located in the first zone (Z1).

10. A debris filter according to any one of claims 6 to 9, wherein each channel (36) in the second zone (Z2) is defined between two opposing curved side walls.

11. The debris filter according to any one of claims 6 to 10, wherein the grid (32) has four second zones (Z2).

12. The debris filter according to any one of claims 6 to 11, wherein the second regions (Z2) are distributed as a matrix on the grid (32).

13. Debris filter according to any of the preceding claims, wherein the grille (32) has a quadrilateral profile, more particularly a square profile.

14. 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 individual channels (36) defined by side walls.

15. The debris filter according to claim 14, wherein each cell (50) comprises a first zone (Z1) and / or a second zone (Z2), the first zone being preferably the periphery of the cell (50) and the second zone being preferably at the center of the cell (50).

16. A debris filter according to claim 14 or 15, wherein the partition (52) of each cell (50) is strictly higher than the channel (36) provided in the cell (50).

17. A debris filter according to any one of claims 14 to 16, wherein each unit (50) comprises a first section (50A) and a second section (50B), the first section (50A) being preferably empty, the channel (36) being located in the second section (50B), the first section (50A) being preferably located upstream of the second section (50B) along the direction of fluid flow through the debris filter.

18. A debris filter according to any one of claims 14 to 17, wherein in each unit (50) the first face (32A) of the grille (32) is generally non-planar, preferably convex, and / or the second face (32B) of the grille (32) is planar.

19. The debris filter according to any one of claims 14 to 18, wherein the grid (32) comprises at least five cells (50) and / or the cells (50) are distributed as a matrix on the grid (32).

20. A debris filter according to any one of claims 14 to 19, wherein in each of the one or more units (50), the channels (36) of the units (50) have different inclination angles between their inlet axis (A1) and outlet axis (A2).

21. The debris filter according to any one of claims 14 to 20, wherein the grid (32) comprises at least five cells (50) and / or the cells (50) are distributed as a matrix on the grid (32).

22. A lower end piece of a nuclear fuel assembly provided with a debris filter according to any one of the preceding claims.

23. A nuclear fuel assembly, more particularly for a pressurized water nuclear reactor, comprising a debris filter according to any one of claims 1 to 21 or a lower end piece according to claim 22.

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