Nuclear fuel assembly bottom end debris filter and method of making such a debris filter

Abstract

The debris filter has an inlet face (18A) and an outlet face (18B) opposite to the inlet face (18A) and includes a plurality of filtering structures (50) protruding from the inlet face (18A) of the debris filter (18), each filtering structure (50) having a structure base (52) and a structure top (54) spaced apart along a structure axis (A), each filtering structure (50) including blades (56) distributed circumferentially around the structure axis (A), each blade having one end connected to the structure base (52) and one end connected to the structure top (54), each blade (56) defining a slot (58) with each adjacent blade (56) of the same filtering structure (50).

Description

Technical Field

[0001] The present invention relates to a nuclear fuel assembly for a nuclear reactor, in particular to a nuclear fuel assembly for a light water nuclear reactor. Background Art

[0002] Nuclear fuel assemblies for light water reactors typically include a bundle of fuel rods extending along a longitudinal axis, with the fuel rods supported in a spaced relationship longitudinally and transversely by a support structure.

[0003] In use, multiple nuclear fuel assemblies are positioned vertically and arranged side by side in a reactor vessel to form a reactor core, and a coolant fluid (e.g., water) is passed vertically through the nuclear fuel assemblies. The coolant fluid has the function of slowing down the nuclear reaction and recovering heat from the fuel rods in the nuclear fuel assemblies.

[0004] Debris present in the coolant fluid may damage the fuel rods of the nuclear fuel assembly and to prevent this risk, the nuclear fuel assembly can be provided with a bottom end portion comprising a lower nozzle for receiving the coolant fluid flow and a debris filter, for example, as disclosed in EP2204819A1 and EP2164076A1. Summary of the Invention

[0005] An object of the present invention is to provide a debris filter for the bottom end of a nuclear fuel assembly that effectively captures debris with a low or adaptable pressure loss, and that is preferably easy to manufacture.

[0006] To this end, the present invention proposes a debris filter for the bottom end of a nuclear fuel assembly, which includes a lower nozzle and a debris filter supported by the lower nozzle, the debris filter having an inlet face and an outlet face opposite to the inlet face, wherein the debris filter includes a plurality of filtering structures protruding on 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 distributed circumferentially around the structural axis, each blade having an end connected to the structural base and an end connected to the structural top, and each blade defines a narrow slot with each adjacent blade of the same filtering structure.

[0007] A debris filter comprising a filtering structure made of vanes distributed circumferentially about an axis of the structure may be configured to effectively capture debris while limiting pressure loss.

[0008] A debris filter having such a complex shape can be manufactured at least partially by additive manufacturing, whereby the debris filter can still be easily manufactured.

[0009] In a particular embodiment, the debris filter includes one or more of the following optional features considered individually or in any technically feasible combination:

[0010] - Each blade overlaps circumferentially with each adjacent blade of the same filter structure;

[0011] - each blade of each filtering structure extends helically around the structural axis (A) of the filtering structure;

[0012] - each filtering structure is configured to impart a cyclonic effect or swirl about the axis of the structure to a fluid flowing through the filtering structure;

[0013] - the debris filter comprises a filter section between the inlet face and the outlet face, the filter section having a gradually or stepwise increasing retention capacity;

[0014] - the filter section comprises a plurality of superimposed filter layers arranged one above the other between an inlet face and an outlet face, the filter layers having different retention capacities;

[0015] - When considering the filter layers from the inlet face to the outlet face, each preceding filter layer has a retention capacity that is strictly lower than that of the next filter layer.

[0016] The invention also relates to a nuclear fuel assembly comprising a bottom end portion comprising a debris filter as defined above.

[0017] The invention also relates to a method for producing a debris filter as defined above, the method comprising producing the debris filter at least partially by additive manufacturing.

[0018] In a particular embodiment, the manufacturing method includes one or more of the following optional features considered individually or in any technically feasible combination:

[0019] - constructing a debris filter at least partially on the lower nozzle (8) by additive manufacturing;

[0020] - at least two filter layers of the debris filter are manufactured separately and then assembled together to obtain the debris filter;

[0021] At least two filter layers of the debris filter are produced integrally in a single piece of material by additive manufacturing.

[0022] According to another aspect, the present invention also relates to a method of manufacturing a debris filter for a bottom end portion of a nuclear fuel assembly, the bottom end portion comprising a lower nozzle provided with a debris filter supported by the lower nozzle, the debris filter having an inlet face and an outlet face opposite the inlet face, the method comprising at least partially manufacturing the debris filter by additive manufacturing.

[0023] In a particular embodiment, the manufacturing method includes one or more of the following optional features considered individually or in any technically feasible combination:

[0024] - constructing a debris filter at least partially on the lower nozzle by additive manufacturing;

[0025] - the debris filter comprises at least one filter segment having a retention capacity that increases gradually or stepwise from the inlet face to the outlet face;

[0026] - the debris filter comprises a plurality of superimposed filter layers arranged one above the other between an inlet face and an outlet face, the filter layers having different retention capacities;

[0027] - when considering the filter layers from the inlet face to the outlet face, each preceding filter layer has a retention capacity strictly lower than that of the next filter layer;

[0028] - at least two filter layers are manufactured separately and then assembled together to obtain a debris filter;

[0029] - at least two filter layers are produced integrally as a single piece of material by additive manufacturing;

[0030] - the debris filter comprises a plurality of filtering structures projecting from an inlet face of the debris filter, each filtering structure having a structure base and a structure top spaced apart along a structure axis, each filtering structure comprising vanes distributed circumferentially around the structure axis, each vane having one end connected to the structure base and one end connected to the structure top, each vane defining a slot with each adjacent vane of the same filtering structure;

[0031] - Each blade overlaps circumferentially with each adjacent blade of the same filter structure;

[0032] - Each blade extends helically around the structural axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention and its advantages will be better understood on reading the following description, given by way of example only and with reference to the accompanying drawings, in which:

[0034] - Figure 1 It is a side view of the BWR nuclear fuel assembly;

[0035] - Figure 2 is a cross-sectional view of the bottom end portion of a nuclear fuel assembly;

[0036] - Figure 3 is a cross-sectional view of a bottom end portion according to another embodiment;

[0037] - Figure 4 is a partial side view of a debris filter;

[0038] - Figure 5 yes Figure 4 The debris filter's filtering structure follows Figure 4The cross-sectional view taken from VV:

[0039] - Figure 6 yes Figure 4 A partial top view of a debris filter;

[0040] - Figure 7 is a side view of a debris filter; and

[0041] - Figure 8 This is a side view of a PWR nuclear fuel assembly. DETAILED DESCRIPTION

[0042] Figure 1 The illustrated nuclear fuel assembly 2 is elongated along a longitudinal axis L. In use, the nuclear fuel assembly is positioned in a nuclear reactor core, having the longitudinal axis L extending substantially vertically, with the nuclear fuel assembly resting on a lower core plate.

[0043] In the following, unless otherwise specified, “longitudinal”, “transverse”, “vertical”, “horizontal”, “top”, “bottom”, “upper” and “lower” are all used with reference to the position of use of the nuclear fuel assembly 2 .

[0044] The nuclear fuel assembly 2 comprises a bundle of fuel rods 4 which are elongated and extend along a longitudinal axis L parallel to one another.

[0045] Each fuel rod 4 includes a tubular cladding for receiving nuclear fuel (eg, nuclear fuel pellets stacked in the tubular cladding), and an end cap for closing the end of the tubular cladding.

[0046] The nuclear fuel assembly 2 includes a support structure 6 that supports the fuel rods 4 in longitudinal and transverse directions.

[0047] The support structure 6 is configured to maintain the fuel rods 4 in a spaced relationship in the transverse direction. The fuel rods 4 are arranged, for example, in a grid at the nodes of an imaginary network, preferably a regular network. The transverse spacing between the fuel rods allows the coolant fluid to flow primarily longitudinally between the fuel rods.

[0048] The support structure 6 of the nuclear fuel assembly 2 includes a lower nozzle 8, an upper nozzle 10, and a support grid 12 distributed along the fuel rods 4. The fuel rods 4 extend between the lower nozzle 8 and the upper nozzle 10 through the support grid 12. The function of the support grid 12 is to maintain the fuel rods 4 in a spaced relationship in the longitudinal and transverse directions.

[0049] Figure 1 The nuclear fuel assembly 2 is used in a boiling water reactor (BWR).

[0050] The armature 6 comprises water channels 14 (or “water rods”) incorporated into the bundle of fuel rods 4 by replacing the fuel rods 4 in the grid, and fuel channels 16 surrounding the bundle of fuel rods 4 .

[0051] The water channel 14 and the fuel channel 16 extend between and connect the lower nozzle 8 and the upper nozzle 10. Spacer grids 12 are attached to the water channel 14 and are distributed at various locations along the water channel 14.

[0052] In use, the nuclear fuel assembly 2 is positioned vertically on a lower core plate having a lower nozzle 8 that receives a flow of coolant fluid through the lower nozzle 8 and into the bundle of fuel rods 4 as indicated by arrows F.

[0053] The nuclear fuel assembly 2 includes a debris filter 18 positioned within the lower nozzle 8. The lower nozzle 8 and the debris filter 18 together define a bottom end 20 of the nuclear fuel assembly 2.

[0054] The debris filter 18 is configured to capture debris present in the coolant fluid entering the nuclear fuel assembly 2 through the lower nozzle 8 .

[0055] like Figure 2 As shown, the lower nozzle 8 includes a lower backing plate 22 and a nozzle portion 24 .

[0056] The bottom plate 22 is configured to attach thereto the water passage 14 and the fuel passage 16 . The nozzle portion 24 is configured to receive and direct the coolant fluid flow to the water passage 14 and the fuel passage 16 .

[0057] The nozzle portion 24 is tubular and extends downward from the outer periphery of the lower pad 22. The nozzle portion 24 includes a lower inlet 26 and an upper outlet 28.

[0058] The bottom plate 22 extends across the upper outlet 28 of the nozzle portion 24. The bottom plate 22 has a grating shape. The bottom plate 22 has fluid flow openings 30 for coolant fluid to flow through the bottom plate 22.

[0059] The nozzle portion 24 has, for example, an upper section 32 of constant cross section extending downward from the lower base plate 22 and a lower section 34 of tapered shape tapering downward.

[0060] The nozzle portion 24 defines an interior space 36. The interior space 36 is defined between the lower inlet 26 and the upper outlet 28 of the nozzle portion 24.

[0061] The debris filter 18 is housed within the lower nozzle 8, more specifically, within the nozzle portion 24 and below the bottom plate 22. In use, the debris filter 18 is located upstream of the bottom plate 22 with respect to coolant fluid flow. The debris filter 18 may be in contact with the underside of the bottom plate 22. Alternatively, a slight gap may be provided between the debris filter 18 and the underside of the bottom plate.

[0062] The debris filter 18 is preferably manufactured at least in part by additive manufacturing.

[0063] Additive manufacturing refers to a manufacturing method that incrementally manufactures the debris filter 18 , or at least a portion of the debris filter 18 , by adding material to an already manufactured portion.

[0064] Additive manufacturing refers in particular to the stepwise manufacturing of at least a portion of the debris filter by successive stepwise additive manufacturing layers.

[0065] 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 fusion, sintering or bonding; deposition additive manufacturing, in particular powder deposition additive manufacturing or wire deposition additive manufacturing; material jetting additive manufacturing; and binder jetting additive manufacturing.

[0066] In one embodiment, the debris filter 18 is only partially manufactured by additive manufacturing.

[0067] In one example, 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.

[0068] The first part is preferably manufactured using a manufacturing method that is not an additive manufacturing method. The first part is manufactured, for example, by conventional milling or casting of a forged metal sheet.

[0069] In another example, the first and second portions of the debris filter 18 are manufactured separately, each of the first and second portions is manufactured separately by additive manufacturing, and then the first and second portions are assembled together to obtain the debris filter 18 .

[0070] In the above example, the first part is made of metal, for example. The second part is made of metal, for example. The metal of the first part and the metal of the second part can be the same metal or different metals.

[0071] In one embodiment, the debris filter 18 is manufactured entirely by additive manufacturing. Thus, the debris filter is integrally made from a single piece of material obtained by additive manufacturing.

[0072] In one embodiment, the debris filter 18 is manufactured separately from the lower nozzle 8 and then assembled to the lower nozzle 8 .

[0073] For example, a method of manufacturing the bottom end 20 includes separately manufacturing the nozzle portion 24, the bottom plate 22, and the debris filter 18 and then assembling them.

[0074] In one embodiment, the debris filter 18 is constructed on the lower nozzle 8 by additive manufacturing.

[0075] The manufacturing method includes, for example, manufacturing the bottom plate 22 , then building the debris filter 18 on the bottom plate 22 by additive manufacturing, and then assembling the nozzle component 24 to the bottom plate 22 .

[0076] Alternatively, the manufacturing method includes, for example, manufacturing the nozzle portion 24 , then building the debris filter 18 on the nozzle portion by additive manufacturing, and then assembling the bottom plate 22 to the nozzle portion 24 .

[0077] like Figure 2 As shown, in one embodiment, the debris filter 18 extends along the longitudinal axis L over a majority of the extension E of the interior space 36 of the nozzle portion 24 along the longitudinal axis L.

[0078] Manufacturing the debris filter 18 at least partially by additive manufacturing allows for providing a thick debris filter 18 to improve filtration efficiency while limiting pressure losses of the coolant fluid flowing through the debris filter 18 .

[0079] The nozzle section 24 here comprises an upper portion 32 and a lower portion 34 which tapers downwardly.

[0080] In one embodiment, the debris filter 18 extends in the upper portion 32 of the nozzle portion 24 at least downwardly to the lower portion 34 of the nozzle portion 24 .

[0081] In one embodiment, the debris filter 18 extends through at least a portion of the upper portion 32 and the lower portion 34 of the nozzle portion 24 .

[0082] In a specific embodiment, as Figure 2 As shown, 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 .

[0083] 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 through the inlet face 18A and exits the debris filter through the outlet face 18B. The inlet face 18A is adjacent to the lower inlet 26 of the nozzle portion 24 and the outlet face 18B faces the lower pad 22.

[0084] The debris filter 18 is porous or has a lattice-like structure to allow coolant fluid to pass through the debris filter while retaining debris contained in the coolant fluid. The debris filter 18 includes flow openings for allowing coolant fluid to flow from an inlet face 18A through the debris filter 18 to an outlet face 18B. Debris larger than the flow openings is retained by the debris filter 18.

[0085] The debris filter 18 has a retention capacity corresponding to the size of the smallest debris that can be retained in the debris filter 18. The higher the retention capacity, the smaller the size of the smallest debris retained by the debris filter 18.

[0086] The debris filter 18 retains debris that is larger in size than the flow opening. The smaller the size of the flow opening, the higher the retention capacity of the debris filter 18.

[0087] 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, has a retention capacity that gradually increases from the inlet face 18A to the outlet face 18B of the debris filter 18 .

[0088] In view of the gradually increasing retention capacity throughout the thickness of the debris filter 18 , the debris filter 18 has flow openings that gradually decrease in size throughout the debris filter 18 , for example, from the inlet face 18A to the outlet face 18B of the debris filter 18 .

[0089] As the retention capacity increases, the largest debris is retained near the inlet face 18A of the debris filter 18 , while the smallest debris 18 enters the debris filter 18 but is retained near the outlet face of the debris filter 18 .

[0090] One advantage of this configuration is that layers or portions of the debris filter having lower retention capacity and / or larger flow openings can be more mechanically resistant than layers or portions of the debris filter having higher retention capacity and / or smaller flow openings. Layers with higher retention capacity can have thinner walls than layers with lower retention capacity to maximize the number of flow openings and limit pressure loss across the debris filter 18.

[0091] Additive manufacturing of the debris filter 18 allows for easy adjustment of the retention capacity of the debris filter 18 and, in particular, allows for providing the debris filter 18 with a retention capacity that varies from the inlet face 18A to the outlet face 18B, in particular a retention capacity that gradually or stepwise increases from the inlet face 18A to the outlet face 18B, thereby limiting manufacturing costs and pressure losses.

[0092] The retention capacity of the debris filter 18 increases gradually or stepwise from the inlet face 18A to the outlet face 18B of the debris filter 18. For example, the debris filter 18 has flow openings that change in size gradually or stepwise from the inlet face 18A to the outlet face 18B of the debris filter 18.

[0093] exist Figure 2 In the example shown, the debris filter 18 has a retention capacity that increases gradually from the inlet face 18A to the outlet face 18B. For example, the debris filter 18 has a flow opening that changes in size gradually from the inlet face 18A to the outlet face 18B.

[0094] The debris filter 18, for example, has several filter 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 the filter layers are considered from the inlet face 18A to the outlet face 18B.

[0095] Each filter layer 40 , 42 , 44 has, for example, a retention capacity that is constant over the entire thickness of the filter layer 40 , 42 , 44 .

[0096] When considering the filter layers from the inlet face 18A to the outlet face 18B, the size of the flow opening of each subsequent filter layer is, for example, smaller than the size of the flow opening of the preceding filter layer.

[0097] Thus, debris filter 18 has at least an inlet filter layer 40 with a lower retention capacity near inlet face 18A and an outlet filter layer 44 near outlet face 18B of debris filter 18. The size of the flow opening of inlet filter layer 40 is larger than the size of the flow opening of outlet filter layer 44, for example.

[0098] In one embodiment, the debris filter has exactly two filter layers, an inlet filter layer 40 and an outlet filter layer 44 .

[0099] In another embodiment, the debris filter 18 has at least one intermediate filter layer 42 between the inlet filter layer 40 and the outlet filter layer 44 .

[0100] exist Figure 2 In the example shown, the debris filter 18 has exactly one middle filter layer 42. In a variant, the debris filter 18 has more than two middle filter layers and more than three filter layers.

[0101] In one embodiment of the manufacturing method, the filter layers 40, 42, 44 with different retention capacities of the debris filter 18 are integrally manufactured as one piece of material by additive manufacturing. In this case, the debris filter 18 is integrally manufactured as one piece of material by additive manufacturing.

[0102] In another embodiment, at least two filter layers 40, 42, 44 are manufactured separately and then assembled together to obtain the debris filter 18. For example, the assembly is performed by welding, bonding, screwing, riveting, etc.

[0103] like Figure 3 As shown, in one embodiment, the debris filter 18 has progressively increasing retention capacities.

[0104] The debris filter 18 with gradually increasing retention capacity has a retention capacity gradient from the inlet face 18A to the outlet face 18B. The flow openings of the debris filter 18 have a decreasing size gradient from the inlet face 18A to the outlet face 18B, for example.

[0105] Fabricating the debris filter 18 by additive manufacturing allows for imparting complex three-dimensional shapes to the debris filter 18 that may improve filtration while limiting pressure loss across the debris filter.

[0106] Figures 4 to 6 An example of a debris filter 18 is shown having a complex three-dimensional shape obtainable by additive manufacturing.

[0107] like Figures 4 to 6 As shown, the debris filter 18 has an inlet face 18A and an outlet face 18B.

[0108] 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 capturing debris.

[0109] 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 distributed circumferentially around the structural axis A, with slots 58 defined between the blades. 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 located between two adjacent blades 56 and defines a corresponding slot 58 with each of the two adjacent blades 56.

[0110] Each blade 56 has two free lateral edges. Each blade 56 extends like a bridge between its two ends connected to the structure base 52 and the structure top 54 respectively.

[0111] Each filtering structure 50 has an overall shape that tapers from a structure base 52 to a structure top 54. The transverse dimension of each filtering structure 50 considered transverse to the structure axis A decreases gradually from the structure base 52 to the structure top 54 along the structure axis A. Each filtering structure 50 has, for example, an overall oval shape.

[0112] The structural axes A of the plurality of filter structures 50 are preferably parallel. The structural axis A of each filter structure 50 is preferably substantially perpendicular to the outlet face 18B of the debris filter 18. When the debris filter 18 is installed on the nuclear fuel assembly 2, the structural axis A of each filter structure 50 is preferably parallel to the longitudinal axis of the nuclear fuel assembly 2.

[0113] The structural bases 52 of the filtering structures 50 are connected together. The structural bases 52 together define an outlet portion 60 of the debris filter 18 which defines the outlet face 18B of the debris filter 18.

[0114] 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 coolant fluid to exit the debris filter 18.

[0115] Each filtering structure 50 defines a capture volume delimited along a structure axis A by a structure base 52 and a structure top 54 and laterally delimited by vanes 56 .

[0116] Slots 58 defined between vanes 56 allow coolant fluid to enter the interior of the filtering structure 50 , and outlet openings 62 provided in the outlet face 18B allow coolant fluid to exit the filtering structure 50 and, therefore, the debris filter 18 .

[0117] The outlet face 18B of the debris filter 18 has a plurality of elongated outlet openings 62 extending, for example, in different transverse directions. Figure 5 As shown, the vanes 56 of each filtering structure 50 are distributed about the structure axis A with circumferential overlap between adjacent vanes 56 .

[0118] like Figure 5 As shown by arrow V on the top, each blade 56 overlaps with each adjacent blade 56 when viewed in a radial direction relative to the structural axis A. In other words, when viewed in a radial direction relative to the structural axis A, the slot 58 cannot be seen inside.

[0119] Preferably, each filtering structure 50 is configured to impart a cyclonic effect or swirl about a structural axis A of the filtering structure 50 to a coolant flow flowing through the filtering structure 50 .

[0120] Due to the mesh structure, this filter structure 50 is particularly effective for capturing wire-shaped debris that is very dangerous for the nuclear fuel assembly 2. Due to the cyclone effect, these debris are likely to be pressed into the filter structure 50 and thus prevented from leaving the filter structure 50.

[0121] In an exemplary embodiment, the vanes 56 of each filtering structure 50 are configured to create a circulation effect, thereby imparting a cyclonic effect or swirl to the coolant flow about the structural axis A of the filtering structure 50 .

[0122] like Figure 4 As can be seen in FIG, advantageously, the vanes 56 of each filtering structure 50 extend helically about the structure axis A. This improves the capture of longitudinally oriented elongated debris upon reaching the inlet face of the debris filter 18.

[0123] The spiral structure acts like a cyclone and throws debris outwardly into the filter structure 50 .

[0124] Additionally, such debris structures 50 tend to deflect the coolant flow, thereby imparting a transverse velocity to the coolant flow downstream of the debris filter 18. This can enhance heat exchange between the coolant fluid and the nuclear fuel rods 4.

[0125] The debris filter 18 is very effective at filtering debris while limiting pressure loss. The debris filter has a complex shape but can be easily manufactured by additive manufacturing.

[0126] At least the filter structure 50 is manufactured by additive manufacturing. In one embodiment, the entire debris filter is manufactured by additive manufacturing. In another embodiment, a plate-like portion 60 is provided and then the remainder of the filter structure 50 is constructed on the plate-like portion 50 by additive manufacturing.

[0127] exist Figure 7 In one exemplary embodiment shown, the debris filter 18 may incorporate a plurality of components related to the debris filter 18 on the inlet face 18A. Figure 4 and Figure 5 The described filtering structure 50 has a gradually or stepwise increasing retention capacity between the filtering structure 50 and the outlet face 18B of the debris filter 18 .

[0128] Such debris filter 18 includes, for example, a filter inlet section 18C defined by a filter structure 50 protruding from the inlet face 18A and a filter outlet section 18D extending between the filter structure 50 and the outlet face, the filter outlet section 18D having a gradually or stepwise increasing retention capacity toward the outlet face 18B.

[0129] Outlet section 18D includes, for example, one or more filter layers between inlet section 18C, filter structure 50, and outlet face 18B, such as defining a filter layer with progressively increasing retention capacity or multiple superimposed filter layers with progressively increasing retention capacity, thereby imparting progressively increasing retention capacity to outlet section 18D.

[0130] Additionally, the debris filter may include a filter segment having a gradually or stepwise increasing retention capacity associated with another filter segment located upstream or downstream from the filter structure 50. In general, the debris filter 18 may include at least a filter segment having a gradually or stepwise increasing retention capacity from the inlet face 18A side to the outlet face 18B side.

[0131] The present invention is not limited to the examples described and illustrated above. Other examples can be envisaged.

[0132] The debris filter 18 having the specific debris design described and illustrated above (enhanced retention capacity and / or a filter structure with vanes and / or a cyclonic effect) can be manufactured using other conventional manufacturing methods that do not involve additive manufacturing. Furthermore, 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.

[0133] Figure 7 A PWR nuclear fuel assembly is shown, wherein the same or similar elements are numbered as in Figure 1 The same.

[0134] The nuclear fuel assembly comprises a bundle of fuel rods 4 extending along a longitudinal axis L and an appendage 6 holding the fuel rods 4 .

[0135] The attachment 6 includes a lower nozzle 8 and an upper nozzle 10 spaced apart along the longitudinal axis L, a guide pipe 63 connected to the lower nozzle 8 and the upper nozzle 10 , and a spacing grid 12 distributed along the guide pipe 63 and attached to the guide pipe 63 .

[0136] The lower nozzle 8 is provided with a debris filter 18. The lower nozzle 8 has an egg crate plate 64 and legs 66 extending downwardly from the corners of the egg crate plate 64. In use, the nuclear fuel assembly 2 rests on the lower core plate by the legs 66.

[0137] The debris filter 18 is attached to the lower nozzle 8 below the egg crate plate 64. The debris filter 18 is therefore located upstream of the egg crate plate 64. The debris filter 18 is located between the legs 66.

[0138] The debris filter 18 may be according to the examples described with reference to the BWR nuclear fuel assembly.

[0139] The method of manufacturing the debris filter 18 at least partially by additive manufacturing and the exemplary embodiments and variants described above (additive manufacturing on the lower nozzle, obtained by additive manufacturing and assembled or forming an integral layer by additive manufacturing, . . . ) is advantageously independent of the shape of the debris filter.

[0140] Thus, generally speaking, the present invention also relates to a method of manufacturing a debris filter for a bottom end portion of a nuclear fuel assembly, the bottom end portion comprising a lower nozzle provided with a debris filter supported by the lower nozzle, the debris filter having an inlet face and an outlet face opposite the inlet face, the method comprising manufacturing the debris filter at least partially by additive manufacturing.

Claims

1. A debris filter for a bottom end portion of a nuclear fuel assembly, the bottom end portion of the nuclear fuel assembly comprising a lower nozzle (8) and the debris filter (18) supported by the lower nozzle (8), the debris filter having an inlet face (18A) and an outlet face (18B) opposite the inlet face (18A), wherein the debris filter (18) comprises a plurality of filtering structures (50) protruding from the inlet face (18A) of the debris filter (18), each filtering structure (50) having a structure base (52) and a structure top (54) spaced apart along a structure axis (A), each filtering structure (50) comprising blades (56) distributed circumferentially around the structure axis (A), each blade having one end connected to the structure base (52) and one end connected to the structure top (54), each blade (56) defining a slot (58) with each adjacent blade (56) of the same filtering structure (50), in, The vanes of each filtering structure define a debris capture volume, the debris capture volume of each filtering structure being axially defined between the structure base and the structure top and laterally bounded by the vanes; The outlet face of the debris filter is provided with an outlet opening for allowing coolant fluid to exit the debris filter; The slots defined between the vanes allow coolant fluid to enter the interior of the filtering structure, and the outlet openings provided in the outlet face allow coolant fluid to exit the filtering structure and thereby the debris filter.

2. The debris filter according to claim 1, wherein Each vane (56) circumferentially overlaps each adjacent vane (56) of the same filtering structure (50).

3. The debris filter according to claim 1, wherein Each blade (56) of each filtering structure (50) extends helically about a structural axis (A) of the filtering structure (50).

4. The debris filter according to claim 1, wherein Each filtering structure (50) is configured to impart a cyclonic effect or swirling flow about the structure's axis (A) to fluid flowing through the filtering structure (50).

5. The debris filter according to claim 1, wherein The debris filter (18) includes a filter section (18D) between the inlet face (18A) and the outlet face (18B), the filter section (18D) having a gradually or stepwise increasing retention capacity.

6. The debris filter according to claim 5, wherein The filter section (18D) includes a plurality of superimposed filter layers (40, 42, 44) stacked one above the other between the inlet face (18A) and the outlet face (18B), the filter layers (40, 42, 44) having different retention capacities.

7. The debris filter according to claim 6, wherein When considering the filter layers (40, 42, 44) from the inlet face (18A) to the outlet face (18B), each preceding filter layer (40, 42) has a strictly lower retention capacity than the next filter layer (42, 44).

8. A nuclear fuel assembly comprising a bottom end portion comprising the debris filter according to claim 1.

9. A method for manufacturing a debris filter (18) according to claim 1, the method comprising manufacturing the debris filter (18) at least in part by additive manufacturing.

10. The method according to claim 9, wherein: The debris filter (18) is at least partially constructed on the lower nozzle (8) by additive manufacturing.

11. The method according to claim 9, wherein The debris filter (18) includes a filter section (18D) between the inlet face (18A) and the outlet face (18B), the filter section (18D) having a gradually or stepwise increasing retention capacity.

12. The method according to claim 11, wherein The filter section (18D) includes a plurality of superimposed filter layers (40, 42, 44) stacked one above the other between the inlet face (18A) and the outlet face (18B), the filter layers (40, 42, 44) having different retention capacities.

13. The method according to claim 12, wherein: At least two of the filter layers (40, 42, 44) are manufactured separately and then assembled together to obtain the debris filter (18).

14. The method according to claim 12, wherein: At least two filter layers (40, 42, 44) are produced integrally in a single piece of material by additive manufacturing.

Images