Debris filter for nuclear fuel assembly bottom end part and method of manufacturing such debris filter

Abstract

To provide, in a nuclear fuel assembly for use in nuclear reactors, a debris filter which has a low or adaptable pressure loss and is easy to manufacture.SOLUTION: A debris filter is designed for a nuclear fuel assembly bottom end part which includes a lower nozzle (8) and the debris filter (18) supported by the lower nozzle (8). The debris filter (18) has an inlet face (18A) and an outlet face (18B) opposed to the inlet face (18A), and comprises at least one filtering section that has a retention capacity that increases gradually or stepwise from the inlet face (18A) toward the outlet face (18B).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to nuclear fuel assemblies for use in nuclear reactors, and in particular to nuclear fuel assemblies for use in light water reactors. [Background technology]

[0002] Nuclear fuel assemblies for light water reactors generally include a bundle of fuel rods extending along a longitudinal axis while being supported longitudinally and laterally in spaced apart relationship by a support structure.

[0003] In use, a number of nuclear fuel assemblies are positioned vertically side-by-side within a reactor vessel, thus forming a nuclear core, and a coolant fluid, e.g., water, is flowed vertically through the nuclear fuel assemblies to moderate the nuclear reaction and to recover heat from the fuel rods of the nuclear fuel assemblies.

[0004] Debris present in the coolant fluid can potentially damage the fuel rods of the nuclear fuel assembly, and to prevent this risk, the nuclear fuel assembly may be provided with a bottom end portion including a bottom nozzle for receiving the coolant fluid flow and a debris filter, as disclosed, for example, in EP 2 204 819 A1 and EP 2 164 076 A1. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent Application Publication No. 2204819 [Patent Document 2] European Patent Application Publication No. 2164076 Summary of the Invention [Problem to be solved by the invention]

[0006] One of the objects of the present invention is to be able to provide a nuclear fuel assembly bottom end debris filter that efficiently captures debris with low or adaptable pressure loss, which debris filter is preferably easy to manufacture. [Means for solving the problem]

[0007] For this reason, the present invention proposes a debris filter for a bottom end part of a nuclear fuel assembly, comprising a bottom nozzle and a debris filter supported by the bottom nozzle, the debris filter having an inlet face and an outlet face opposite the inlet face, the debris filter including at least one filtering section having a retention capacity that increases gradually or in steps from the inlet face towards the outlet face (18B).

[0008] With an increasing retention capacity from the inlet face to the outlet face, larger debris is retained closer to the inlet face of the debris filter and smaller debris enters the debris filter but is retained closer to the outlet face of the debris filter.

[0009] It is possible for layers or portions of the debris filter with lower retention capacity and / or larger sized flow openings to have higher mechanical strength than layers or portions of the debris filter with higher retention capacity and / or smaller sized flow openings.

[0010] Layers with higher retention capacities may have thinner walls than layers with lower retention capacities to maximize the number of flow openings and limit pressure drop through the debris filter.

[0011] In specific embodiments, the debris filter comprises one or more of any of the following features, taken alone or in any technically feasible combination: - the debris filter includes a plurality of superposed filtration layers positioned one above the other between an inlet face and an outlet face, the filtration layers having different retention capacities; - when considering the filtration layers from the inlet face to the outlet face, each preceding filtration layer has a retention capacity strictly lower than that of the next filtration layer; - the debris filter further includes a plurality of filtering structures projecting above the inlet face of the debris filter, each filtering structure having a structural base and a structural top spaced apart along a structural axis, each filtering structure including blades circumferentially distributed about the structural axis, each blade having one end connected to the structural base and one end connected to the structural top, each blade defining a slot with each adjacent blade of the same filtering structure; - Each blade overlaps circumferentially with each adjacent blade of the same filtering structure; - each blade of each filtering structure extends helically around a structural axis of said filtering structure; Each filtering structure is configured to generate a cyclone effect or vortex about a structural axis on a fluid flowing through the filtering structure.

[0012] The invention also relates to a nuclear fuel assembly comprising a bottom end portion including a debris filter as defined above.

[0013] The invention also relates to a method of manufacturing a debris filter, comprising manufacturing the debris filter at least in part by additive manufacturing.

[0014] In specific embodiments, the method comprises one or more of any of the following features, taken alone or in any technically feasible combination: - the debris filter is constructed on the lower nozzle at least partially by additive manufacturing; - at least two of the filtration layers are manufactured separately and assembled together to obtain the debris filter; - at least two filtration layers are made integrally in a single piece of material by additive manufacturing;

[0015] The invention and its advantages will be better understood on reading the following description, given purely by way of example and made with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a side elevation view of a BWR nuclear fuel assembly. [Diagram 2] FIG. 2 is a cross-sectional view of the bottom end portion of a nuclear fuel assembly. [Diagram 3] FIG. 11 is a cross-sectional view of a bottom end portion according to another embodiment. [Figure 4] FIG. 2 is a partial side view of the debris filter. [Diagram 5] 5 is a cross-sectional view of the filtering structure of the debris filter of FIG. 4 taken along VV in FIG. 4. [Figure 6] FIG. 5 is a partial top view of the debris filter of FIG. [Figure 7] FIG. 2 is a side elevational view of a debris filter. [Figure 8] FIG. 2 is a side elevation view of a PWR nuclear fuel assembly. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The nuclear fuel assembly 2 illustrated in Figure 1 is elongated along a longitudinal axis L. In use, the nuclear fuel assembly is positioned within a nuclear reactor core with the longitudinal axis L extending substantially vertically and the nuclear fuel assembly resting on a lower core plate.

[0018] Hereinafter, unless otherwise specified, the terms "longitudinal", "transverse", "vertical", "horizontal", "top", "bottom", "upper" and "lower" are used with reference to the position of use of the nuclear fuel assembly 2.

[0019] The nuclear fuel assembly 2 comprises a bundle of fuel rods 4 which are elongated and extend parallel to one another along a longitudinal axis L.

[0020] Each fuel rod 4 includes a tubular cladding containing nuclear fuel, for example nuclear fuel pellets stacked within the tubular cladding, and end caps closing the ends of the tubular cladding.

[0021] The nuclear fuel assembly 2 includes a support structure 6 that supports the fuel rods 4 longitudinally and transversely.

[0022] The support structure 6 is configured to maintain the fuel rods 4 in a transversely spaced apart relationship. The fuel rods 4 are arranged, for example, in a lattice at the nodes of an imaginary net, preferably a regular net. The transverse separation between the fuel rods allows coolant fluid to flow primarily longitudinally between the fuel rods.

[0023] The support structure 6 of the nuclear fuel assembly 2 includes a bottom nozzle 8, a top nozzle 10, and support grids 12 distributed along the fuel rods 4. The fuel rods 4 extend between the bottom nozzle 8 and the top nozzle 10 through the spacer grids 12. The function of the spacer grids 12 is to maintain the fuel rods 4 in longitudinal and transverse spaced apart relationship.

[0024] The nuclear fuel assembly 2 of FIG. 1 is for use in a boiling water reactor (BWR).

[0025] The armature 6 includes a water channel 14 (or "water rod") that is installed inside the bundle of fuel rods 4 by replacing the fuel rods 4 in the lattice, and a fuel channel 16 that surrounds the bundle of fuel rods 4.

[0026] The water channel 14 and the fuel channel 16 extend between and are connected to the bottom nozzle 8 and the top nozzle 10. The spacer grids 12 are distributed at various locations along and attached to the water channel 14.

[0027] In use, the nuclear fuel assembly 2 is positioned vertically on the lower core plate, with the bottom nozzle 8 receiving a flow of coolant fluid which passes through the bottom nozzle 8 and into the bundle of fuel rods 4, as illustrated by arrow F.

[0028] The nuclear fuel assembly 2 includes a debris filter 18 positioned inside the bottom nozzle 8. The bottom nozzle 8 and the debris filter 18 together define a bottom end portion 20 of the nuclear fuel assembly 2.

[0029] The debris filter 18 is configured to capture debris present in the coolant fluid entering the nuclear fuel assembly 2 via the bottom nozzle 8 .

[0030] As illustrated in FIG. 2, the bottom nozzle 8 includes a lower tie plate 22 and a nozzle portion 24 .

[0031] The lower tie plate 22 is configured, among other things, to have the water channels 14 and the fuel channels 16 attached thereto. The nozzle portion 24 is configured to contain and direct a coolant fluid flow to the water channels 14 and the fuel channels 16.

[0032] The nozzle portion 24 is tubular and extends downwardly from the periphery of the lower tie plate 22. The nozzle portion 24 includes a lower inlet 26 and an upper outlet 28.

[0033] The lower tie plate 22 extends across an upper outlet 28 of the nozzle section 24. The lower tie plate 22 has the shape of a grid. The lower tie plate 22 has fluid flow openings 30 therein to allow coolant fluid to flow therethrough.

[0034] Nozzle portion 24, for example, has an upper section 32 of constant cross section extending downwardly from lower tie plate 22 and a downwardly tapered, conical lower section 34.

[0035] Nozzle portion 24 defines an interior space 36. Interior space 36 is bounded between lower inlet 26 and upper outlet 28 of nozzle portion 24.

[0036] The debris filter 18 is housed inside the lower nozzle 8, more specifically here inside the nozzle portion 24 and below the lower tie plate 22. The debris filter 18 is located upstream of the lower tie plate 22, taking into account the coolant fluid flow during use. The debris filter 18 may be in contact with the underside of the lower tie plate 22. Alternatively, a small gap may be provided between the debris filter 18 and the underside of the lower tie plate.

[0037] The debris filter 18 is preferably manufactured at least in part by additive manufacturing.

[0038] Additive manufacturing refers to a manufacturing method in which the debris filter 18, or at least a portion of the debris filter 18, is manufactured incrementally by adding material to an already manufactured part.

[0039] Additive manufacturing specifically refers to the incremental manufacturing of at least a portion of the debris filter by the incremental addition of successive manufacturing layers.

[0040] The debris filter 18 is at least partially manufactured by additive manufacturing, for example by using one or a combination of the following additive manufacturing methods: powder bed additive manufacturing, in particular melting, sintering or adhesive bonding; deposition additive manufacturing, in particular powder deposition additive manufacturing or wire deposition additive manufacturing; material jet additive manufacturing and binder jet additive manufacturing.

[0041] In one embodiment, the debris filter 18 is only partially manufactured by additive manufacturing.

[0042] In one embodiment, a first portion of the debris filter 18 is manufactured and a second portion of the debris filter 18 is built on the first portion by additive manufacturing.

[0043] The first part is preferably manufactured using a manufacturing method that is not an additive manufacturing method, for example the first part is manufactured by conventional milling or casting of a forged metal sheet.

[0044] In another embodiment, the first and second parts of the debris filter 18 are manufactured separately, each of the first and second parts is manufactured separately by additive manufacturing, and the first and second parts are then assembled together to obtain the debris filter 18.

[0045] In the above embodiments, the first portion is made of, for example, a metal. The second portion is made of, for example, a metal. The metal of the first portion and the metal of the second portion are the same metal or different metals.

[0046] In one embodiment, the debris filter 18 is manufactured entirely by additive manufacturing, thus making the debris filter integrally in a single piece of material obtained by additive manufacturing.

[0047] In one embodiment, the debris filter 18 is manufactured separately from the bottom nozzle 8 and then assembled to the bottom nozzle 8 .

[0048] For example, the method of manufacturing the bottom end portion 20 includes separately manufacturing the nozzle portion 24, the lower tie plate 22 and the debris filter 18 and then assembling them together.

[0049] In one embodiment, the debris filter 18 is built onto the bottom nozzle 8 by additive manufacturing.

[0050] The manufacturing method may include, for example, manufacturing the lower tie plate 22 , then building the debris filter 18 on the lower tie plate 22 by additive manufacturing, and then assembling the nozzle section 24 to the lower tie plate 22 .

[0051] Alternatively, the manufacturing method may include, for example, manufacturing the nozzle portion 24, then building the debris filter 18 on the nozzle portion by additive manufacturing, and then assembling the lower tie plate 22 to the nozzle portion 24.

[0052] As illustrated in FIG. 2, in one embodiment, the debris filter 18 extends along the longitudinal axis L across a majority of the extent E of the interior space 36 of the nozzle portion 24 along the longitudinal axis L.

[0053] By manufacturing the debris filter 18 at least in part by additive manufacturing, it is possible to provide a thick debris filter 18 for improved filtration efficiency while limiting pressure loss of the coolant fluid flowing through the debris filter 18.

[0054] Nozzle portion 24 here includes an upper section 32 and a downwardly tapered lower section 34 .

[0055] In one embodiment, the debris filter 18 extends within an upper section 32 of the nozzle portion 24 down to at least a lower section 34 of the nozzle portion 24 .

[0056] In one embodiment, the debris filter 18 extends into the upper section 32 and into at least a portion of the lower section 34 of the nozzle portion 24 .

[0057] In the particular embodiment illustrated in FIG. 2, the debris filter 18 completely occupies the interior space 36 of the lower nozzle 8 between the lower inlet 26 and the upper outlet 28 of the nozzle portion 24 .

[0058] The debris filter 18 includes an inlet face 18A and an outlet face 18B opposite the inlet face 18A. In use, coolant fluid enters the debris filter 18 via the inlet face 18A and exits the debris filter via the outlet face 18B. The inlet face 18A is adjacent the lower inlet 26 of the nozzle portion 24 and the outlet face 18B faces the lower tie plate 22.

[0059] The debris filter 18 is porous or has openwork and retains debris contained within the coolant fluid while allowing the coolant fluid to pass through the debris filter. The debris filter 18 includes flow openings to allow the coolant fluid to flow through the debris filter 18 from the inlet face 18A to the outlet face 18B. Debris having dimensions larger than the dimensions of the flow openings will be retained by the debris filter 18.

[0060] The debris filter 18 has a retention capacity which corresponds to the size of the smallest debris that can be retained by the debris filter 18. The higher the retention capacity, the smaller the size of the smallest debris that will be retained by the debris filter 18.

[0061] The debris filter 18 will retain debris having a dimension larger than the dimension of the flow openings. The smaller the size of the flow openings, the higher the retention capacity of the debris filter 18.

[0062] In one embodiment, the debris filter 18 has a retention capacity that varies from the inlet face 18A to the outlet face 18B, and more specifically, that gradually increases from the inlet face 18A to the outlet face 18B of the debris filter 18.

[0063] To allow for a gradual increase in retention capacity through the thickness of the debris filter 18, the debris filter 18 has flow openings having dimensions that gradually decrease through the debris filter 18, for example from the inlet face 18A to the outlet face 18B of the debris filter 18.

[0064] As the retention capacity increases, the largest debris is retained adjacent to the inlet face 18A of the debris filter 18 and the smallest debris 18 enters the debris filter 18 but is retained adjacent to the exit face of the debris filter 18.

[0065] One advantage of such a configuration is that layers or portions of the debris filter with lower retention capacity and / or larger size flow openings can be mechanically stronger than layers or portions of the debris filter with higher retention capacity and / or smaller size flow openings. The layers with higher retention capacity can have thinner walls than the walls of layers with lower retention capacity in order to maximize the number of flow openings and limit pressure loss through the debris filter 18.

[0066] Additive manufacturing of the debris filter 18 makes it possible to easily tailor the retention capacity of the debris filter 18, and in particular to provide a debris filter 18 with a retention capacity that varies from the inlet face 18A to the outlet face 18B, in particular a gradual or stepwise increasing retention capacity from the inlet face 18A to the outlet face 18B, while limiting manufacturing costs and limiting pressure loss.

[0067] The retention capacity of the debris filter 18, for example, increases gradually or in steps from the inlet face 18A to the outlet face 18B of the debris filter 18. For example, the debris filter 18 has flow openings with dimensions that vary gradually or in steps from the inlet face 18A to the outlet face 18B of the debris filter 18.

[0068] 2, the debris filter 18 has a gradually increasing retention capacity from the inlet face 18A to the outlet face 18B. For example, the debris filter 18 has flow openings with dimensions that vary gradually from the inlet face 18A to the outlet face 18B.

[0069] The debris filter 18 may, for example, have a number of filtration layers 40, 42, 44 from the inlet face 18A to the outlet face 18B, with each subsequent layer having a higher retention capacity than the previous layer when considering the filtration layers from the inlet face 18A to the outlet face 18B.

[0070] Each filtration layer 40,42,44, for example, has a constant retention capacity through the thickness of the filtration layer 40,42,44.

[0071] Considering the filtration layers from inlet face 18A to outlet face 18B, each subsequent filtration layer has flow openings of smaller size, for example, than those of the preceding filtration layer.

[0072] Thus, the debris filter 18 has at least an inlet filtration layer 40 adjacent the inlet face 18A, which has a lower retention capacity, and an outlet filtration layer 44 adjacent the outlet face 18B of the debris filter 18. The inlet filtration layer 40 has flow openings, for example, of larger dimensions than the flow openings of the outlet filtration layer 44.

[0073] In one embodiment, the debris filter has exactly two filtration layers: an inlet filtration layer 40 and an outlet filtration layer 44 .

[0074] In another embodiment, the debris filter 18 has at least one intermediate filtration layer 42 positioned between the inlet filtration layer 40 and the outlet filtration layer 44 .

[0075] 2, the debris filter 18 has exactly one intermediate filtration layer 42. In a variant, the debris filter 18 has three or more intermediate filtration layers and four or more filtration layers.

[0076] In one embodiment of the manufacturing method, the filtration layers 40, 42, 44 of the debris filter 18 with different retention capacities are manufactured integrally in one piece of material by additive manufacturing. In this case, the debris filter 18 is manufactured integrally in one piece of material by additive manufacturing.

[0077] In another embodiment, the at least two filtration layers 40, 42, 44 are manufactured separately and then the at least two filtration layers 40, 42, 44 are assembled together to obtain the debris filter 18. The assembly can be performed, for example, by welding, bonding, screwing, riveting, etc.

[0078] As shown in FIG. 3, in one embodiment, the debris filter 18 has a gradually increasing retention capacity.

[0079] A debris filter 18 with a gradually increasing retention capacity exhibits a retention capacity gradient from the inlet face 18A to the outlet face 18B. The flow openings of the debris filter 18, for example, exhibit a gradient of decreasing size from the inlet face 18A to the outlet face 18B.

[0080] Fabricating the debris filter 18 by additive manufacturing allows for the debris filter 18 to be given complex three-dimensional shapes that may improve filtration while limiting pressure drop through the debris filter.

[0081] Figures 4 to 6 show an embodiment of a debris filter 18 with a complex three-dimensional shape that can be obtained by additive manufacturing.

[0082] As shown in Figures 4-6, the debris filter 18 has an inlet face 18A and an outlet face 18B.

[0083] The debris filter 18 is provided on its inlet face 18A with a plurality of protruding filtering structures 50. Each filtering structure 50 is configured to allow coolant fluid to flow through the filtering structure 50 while trapping debris.

[0084] Each filtering structure 50 is hollow. Each filtering structure 50 has a structural base 52 and a structural top 54 spaced apart along a structural axis A, and a plurality of blades 56 circumferentially distributed about the structural axis A with defining slots 58 therebetween. Each blade 56 has one end connected to the structural base 52 and one end connected to the structural top 54. Each blade 56 is circumferentially positioned between two adjacent blades 56, defining a respective slot 58 with each of the two adjacent blades 56.

[0085] Each blade 56 has two lateral edges that are free. Each blade 56 extends like a bridge between its two ends that are connected to the structural base 52 and the structural top 54, respectively.

[0086] Each filtering structure 50 has an overall shape that tapers from a structural base 52 to a structural top 54. A transverse dimension of each filtering structure 50, taken transverse to a structural axis A, gradually decreases along the structural axis A from the structural base 52 to the structural top 54. Each filtering structure 50, for example, has a generally ogive shape.

[0087] The structural axes A of the filtering structures 50 are preferably parallel. The structural axis A of each filtering structure 50 is preferably substantially perpendicular to the outlet face 18B of the debris filter 18. The structural axis A of each filtering structure 50 is preferably parallel to the longitudinal axis of the nuclear fuel assembly 2 when the debris filter 18 is assembled thereon.

[0088] The structural bases 52 of the filtering structure 50 are coupled together and together define an outlet portion 60 of the debris filter 18 which defines the outlet face 18B of the debris filter 18.

[0089] The filtering structure 50 imparts a three-dimensional shape to the inlet face 18A of the debris filter 18. The outlet face 18A of the debris filter 18 is, for example, substantially flat. The outlet face 18A of the debris filter is provided with an outlet opening 62 for allowing the coolant fluid to exit the debris filter 18.

[0090] Each filtering structure 50 defines a trapping volume that is bounded along a structural axis A by a structural base 52 and a structural top 54 and is bounded laterally by blades 56 .

[0091] Slots 58 defined between the blades 56 allow the coolant fluid to enter the inside of the filtering structure 50, and outlet openings 62 provided in the outlet face 18B allow the coolant fluid to exit the filtering structure 50 and thus the debris filter 18.

[0092] The outlet face 18B of the debris filter 18 presents, for example, a plurality of elongated outlet openings 62 extending in different transverse directions. Advantageously, as shown in FIG. 5, the blades 56 of each filtering structure 50 are distributed about the structural axis A with a circumferential overlap between adjacent blades 56.

[0093] Each blade 56 overlaps with each adjacent blade 56 when viewed in a direction that is radial with respect to the structural axis A, as illustrated by arrow V on Figure 5. In other words, the slots 58 are not visible when viewed in a direction that is radial with respect to the structural axis A.

[0094] Preferably, each filtering structure 50 is configured to generate a cyclone effect or vortex about a structural axis A of the filtering structure 50 on the coolant flow passing through the filtering structure 50 .

[0095] Such a filtering structure 50 is particularly efficient in capturing debris in the form of small wires, which are very dangerous for the nuclear fuel assemblies 2 due to the fretting mechanism. Due to the cyclone effect, such debris is likely to be pressed into the filtering structure 50 and thus prevented from exiting the filtering structure 50.

[0096] In one exemplary embodiment, the blades 56 of each filtering structure 50 are configured to create a circulating effect on the coolant flow, generating a cyclone effect or vortex about a structural axis A of the filtering structure 50 .

[0097] 4, advantageously, the blades 56 of each filtering structure 50 extend helically around the structural axis A. This improves the capture of longitudinally oriented elongated debris upon reaching the inlet face of the debris filter 18.

[0098] The helical structure acts like a cyclone, throwing debris outwardly into the filtering structure 50 .

[0099] Moreover, such debris structures 50 tend to deflect the coolant flow, imparting a transverse velocity to the coolant flow downstream of the debris filter 18, thereby enhancing heat exchange between the coolant fluid and the nuclear fuel rods 4.

[0100] The debris filter 18 is highly efficient at filtering debris while limiting pressure drop. The debris filter has a complex shape, but is easily manufacturable by additive manufacturing.

[0101] At least the filtering structure 50 is manufactured by additive manufacturing. In one embodiment, the entire debris filter is manufactured by additive manufacturing. In another embodiment, the plate-shaped portion 60 is provided and then the remaining portions of the filtering structure 50 are built on the plate-shaped portion 50 by additive manufacturing.

[0102] In one exemplary embodiment shown in FIG. 7, the debris filter 18 can incorporate a filtering structure 50 on the inlet face 18A of the debris filter 18, as described in relation to FIGS. 4 and 5, with the retention capacity increasing gradually or stepwise between the filtering structure 50 and the outlet face 18B of the debris filter 18.

[0103] Such a debris filter 18 may, for example, include a filtered inlet section 18C defined by a filtering structure 50 protruding from the inlet face 18A, and a filtered outlet section 18D extending between the filtering structure 50 and the outlet face, and exhibit a gradual or stepwise increasing retention capacity toward the outlet face 18B.

[0104] The outlet section 18D may include, for example, one or more filtration layers positioned between the inlet section 18C and the outlet face 18B of the filtering structure 50, which may define, for example, a single filtration layer of gradually increasing retention capacity or multiple superimposed filtration layers of progressively increasing retention capacity, providing a stepped increase in retention capacity up to the outlet section 18D.

[0105] Furthermore, the debris filter may have a filtering section that exhibits a gradually or stepwise increasing retention capacity associated with another filtering section located upstream or downstream different from the filtering structure 50. In general, the debris filter 18 may include at least a filtering section that exhibits a gradually or stepwise increasing retention capacity from the inlet face 18A side to the outlet face 18B side.

[0106] The present invention is not limited to the embodiments described and illustrated above, other embodiments may be contemplated.

[0107] The above described and illustrated debris filter 18 with its specific debris design (increased retention capacity and / or filtering structure with blades and / or cyclone effect) can be manufactured using other conventional manufacturing methods that do not involve additive manufacturing. Moreover, the present invention is not limited to BWR nuclear fuel assemblies. More generally, it is applicable to light water reactor (LWR) nuclear fuel assemblies. In particular, it is applicable to pressurized water reactor (PWR) nuclear fuel assemblies.

[0108] FIG. 7, in which reference numbers are the same for elements identical or similar to those in FIG. 1, illustrates a PWR nuclear fuel assembly.

[0109] The nuclear fuel assembly includes a bundle of fuel rods 4 extending along a longitudinal axis L and an armature 6 which supports the fuel rods 4 .

[0110] The armature 6 includes a bottom nozzle 8 and a top nozzle 10 spaced apart along a longitudinal axis L, a guide tube 63 connected to the bottom nozzle 8 and the top nozzle 10, and spacer grids 12 attached to and distributed along the guide tube 63.

[0111] The bottom nozzle 8 is equipped with a debris filter 18. The bottom nozzle 8 has an egg crate plate 64 and legs 66 that extend downwardly from the corners of the egg crate plate 64. In use, the nuclear fuel assemblies 2 rest on the lower core plate via the legs 66.

[0112] The debris filter 18 is attached to the lower nozzle 8 below the egg crate plate 64. The debris filter 18 is thus positioned upstream of the egg crate plate 64. The debris filter 18 is positioned between the legs 66.

[0113] The debris filter 18 may be as per the embodiment described in connection with the BWR nuclear fuel assembly.

[0114] The above-described method of manufacturing the debris filter 18 at least partially by additive manufacturing, and the exemplary embodiments and variants (such as additive manufacturing on the bottom nozzle, layers obtained and assembled by additive manufacturing or integrally formed by additive manufacturing, etc.) are advantageous regardless of the shape of the debris filter.

[0115] In general, therefore, the invention also relates to a method for manufacturing a debris filter for a bottom end part of a nuclear fuel assembly comprising a bottom nozzle with a debris filter supported by the bottom nozzle, the debris filter having an inlet face and an outlet face opposite the inlet face, the method comprising the step of manufacturing the debris filter at least in part by additive manufacturing. [Explanation of symbols]

[0116] 2 Nuclear fuel assembly 4 fuel rods 8 Bottom Nozzle 18 Debris Filter 18A Entrance side 18B Exit surface 40, 42, 44 filtration layer 50 Filtration structure 52 Structural base 54 Structure top 56 Blade 58 Slots A structural axis

Claims

1. A method for manufacturing a debris filter for a bottom end portion of a nuclear fuel assembly, comprising a bottom nozzle (8) and a debris filter (18) supported by the bottom nozzle (8), the debris filter (18) having an inlet face (18A) and an outlet face (18B) opposite the inlet face (18A), the debris filter (18) including at least one filtering section (18D) having a retention capacity that increases gradually or in steps from the inlet face (18A) to the outlet face (18B), comprising: manufacturing the debris filter (18) at least in part by additive manufacturing, the debris filter (18) being built on a bottom nozzle (8) at least in part by additive manufacturing; manufacturing a lower tie plate (22), then building a debris filter (18) on the lower tie plate (22) by additive manufacturing, and then assembling a nozzle portion (24) to the lower tie plate (22); or A method for manufacturing a debris filter (18) comprising the steps of manufacturing a nozzle portion (24), then building the debris filter (18) on the nozzle portion by additive manufacturing, and then assembling a lower tie plate (22) to the nozzle portion (24).

2. 2. The method of claim 1, wherein the debris filter comprises a plurality of superimposed filtration layers (40, 42, 44) positioned one above the other between the inlet face (18A) and the outlet face (18B), the filtration layers (40, 42, 44) having different retention capacities.

3. 3. The method of claim 2, wherein, when considering the filtration layers (40, 42, 44) from the inlet face (18A) to the outlet face (18B), each preceding filtration layer (40, 42) has a retention capacity strictly lower than the retention capacity of the next filtration layer (42, 44).

4. The method of claim 3, wherein at least two of the filtration layers (40, 42, 44) are manufactured separately and assembled together to obtain the debris filter (18).

5. The method of claim 3 or 4, wherein at least two filtration layers (40, 42, 44) are integrally made in a single piece of material by additive manufacturing.

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