Debris filtering grid for a nuclear fuel assembly

Abstract

Debris filtering grid for a nuclear fuel assembly The debris filtering grid has flow channels (34, 36) extending through the debris filtering grid, each flow channel (34, 36) having a cross-section exhibiting a cross-sectional shape and a cross-sectional area, the flow channels (34, 36) including first flow channels (34) having a first cross-section and second flow channels having a second cross-section differing from the first cross-section by the cross-sectional shape and / or the cross-sectional area, wherein the debris filtering grid comprises at least one region including first rows (44) of first flow channel (34) aligned in a first direction (D1) and second rows (46) of second flow channels (36) aligned in the first direction (D1), the first rows (44) alternating with the second row (46) in a second direction (D2) perpendicular to the first direction (D1).

Description

[0001] Debris filtering grid for a nuclear fuel assembly

[0002] The invention relates to a debris filtering grid fora nuclear fuel assembly.

[0003] Some nuclear fuel assemblies (or “fuel assemblies”) comprise nuclear fuel rods (or “fuel rods”) arranged in a bundle and a skeleton supporting the fuel rods.

[0004] Each fuel rod comprises a tubular cladding containing nuclear fuel (e.g. UO2 pellets), the two ends of the tubular cladding being closed by respective end plugs. Generally, a fuel rod spring is inserted in the fuel rod cladding and applies a compression force on the nuclear fuel to avoid movement of the nuclear fuel inside the fuel rod.

[0005] The skeleton comprises, for example, a bottom nozzle and a top nozzle spaced along a longitudinal axis, guide thimbles (or “guide tubes”) extending along the longitudinal axis between the bottom nozzle and the top nozzle connecting the bottom nozzle and the top nozzle together, and spacer grids attached to the guide thimbles. The fuel rods extend between the bottom nozzle and the top nozzle passing through the spacer grids. The spacer grids support the fuel rods longitudinally and transversely.

[0006] In use, fuel assemblies are arranged side-by-side inside the vessel of the nuclear reactor, the longitudinal axis of each fuel assembly extending vertically, and a coolant fluid is circulated vertically upwards in the vessel, through the fuel assemblies. The coolant fluid moderates the nuclear reaction and collects heat from the fuel rods of the fuel assemblies. In each fuel assembly, the coolant fluid enters via the bottom nozzle, circulates along the fuel rods and exits via the top nozzle.

[0007] In view of ensuring an appropriate heat exchange and of preserving the mechanical integrity of the fuel assembly (e.g. by limiting the risk of fretting) along with limiting pressure losses, it is necessary to control the flow of the coolant fluid in the fuel assembly.

[0008] One of the aims of the invention is to ensure efficient filtering of debris and an improved coolant flow in the fuel assembly.

[0009] To this end, the invention proposes a debris filtering grid for a nuclear fuel assembly, the debris filtering grid having flow channels extending through the debris filtering grid, each flow channel having a cross-section exhibiting a cross-sectional shape and an cross-sectional area, the flow channels including first flow channels having a first cross-section and second flow channels having a second cross-section differing from the first crosssection by the cross-sectional shape and / or the cross-sectional area, wherein the debris filtering grid comprises at least one region including first rows of first flow channel aligned in a first direction and second rows of second flow channels aligned in the first direction, thefirst rows alternating with the second row in a second direction perpendicular to the first direction.

[0010] In some examples, the debris filtering grid comprises one or several of the following optional features, taken individually or in any technically feasible combination:

[0011] - the first flow channels of each first row are offset with respect to the second flow channels of each adjacent second row along the first direction;

[0012] - the first flow channels of each first row are regularly spaced along the first direction and / or the second flow channels of each second row are regularly spaced along the first direction;

[0013] - the spacing of the first flow channels in the first rows and the spacing of the second flow channels in the second rows are equal;

[0014] - the first flow channels are aligned in first columns in the second direction and / or the second flow channels are aligned in second columns in the second direction;

[0015] - the first rows are regularly spaced in the second direction and / or the second rows are regularly spaced in the second direction;

[0016] - the spacing of first rows along the second direction and the spacing of second rows along the second direction are equal;

[0017] - each second flow channel is arranged inside an imaginary quadrangular polygon having four corners formed by four first flow channels;

[0018] - the first flow channels and the second flow channels are arranged in a repeated pattern comprising one second flow channel arranged inside an imaginary quadrangular polygon having four corners formed by four first flow channels;

[0019] - the first flow channels of the repeated pattern are located at the corners of an imaginary rectangle or square or parallelogram;

[0020] - only one of the shape and / or the area of the first cross-section differs from that of the second cross-section;

[0021] - the area of the first cross-section is greater that the area of the second cross-section; - the first cross-section is circular or polygonal, in particular triangular, quadrangular, pentagonal, hexagonal, heptagonal or octagonal, or star shaped, and / or the second crosssection is circular or polygonal, in particular triangular, quadrangular, pentagonal, hexagonal, heptagonal or octagonal, or star shaped;

[0022] - the cross-sections of the first flow channels and the second flow channels and the distribution of the first flow channels and the second flow channels are configured such that ligaments of the debris filtering separating the first flow channels and the second flow channels have a same constant thickness taken between the flow channels;

[0023] - the inlet face and / or the outlet face of the debris filtering exhibits a 3D shape;- the inlet face and / or the outlet face comprises a plurality of protrusions protruding on the inlet face and distributed over the inlet face, each protrusion including first flow channels and second flow channels, the debris filtering grid being preferably deprived of second flow channels between the protrusions;

[0024] - the inlet face and / or the outlet face comprises at least one 3D shaped region that is shaped to exhibit undulations defining crests alternating with valley, the crests and the valleys being preferably circular and concentric.

[0025] The invention also relates to a nuclear fuel assembly bottom nozzle comprising a lower tie plate and a debris filtering grid as defined above, provided for example on the lower tie plate of the bottom nozzle, in particular below or above said lower tie plate, the lower tie plate and the debris filtering grid being for example manufactured as separate components and assembled or manufactured as a single piece of material, e.g. by additive manufacturing.

[0026] The invention also relates to a nuclear fuel assembly comprising a bottom nozzle and a top nozzle spaced along an longitudinal axis, fuel rods extending longitudinally between the bottom nozzle and the top nozzle, the nuclear fuel assembly comprising a debris filtering grid as defined above or the bottom nozzle being as defined above.

[0027] The nuclear fuel assembly is for example configured for use in a PWR or a BWR or a WER or a HTR or a RNR or a SMR.

[0028] The invention and its advantages will be better understood upon reading the following description that is given solely by way of non-limiting examples and made with reference to the appended drawings, in which:

[0029] - Figure 1 is a side elevation view of a nuclear fuel assembly;

[0030] - Figure 2 is a bottom view of a debris filtering grid;

[0031] - Figures 3 - 9 are partial bottom and / or top views of debris filtering grids;

[0032] - Figure 10 is a perspective view of a portion of a debris filtering grid;

[0033] - Figure 11 is a perspective view of a portion of a debris filtering grid; and

[0034] - Figure 12 is a side elevation view of another nuclear fuel assembly.

[0035] The nuclear fuel assembly 2 of Figure 1 comprises a bundle of nuclear fuel rods 4 (or fuel rods 4”) and a skeleton 6 configured for supporting the fuel rods 4.

[0036] The fuel rods 4 extend parallel to each other and parallel to an assembly axis L. The longitudinal axis L extends vertically when the nuclear fuel assembly 2 is positioned in a nuclear reactor. In operation, a coolant fluid flows through the nuclear fuel assembly 2 in a main flow direction orientated vertically upwards as illustrated by arrow F on Figure 1.In the following, the terms “vertical”, “horizontal”, “bottom”, “top”, “longitudinal”, “transversal”, “upper” and “lower” refer to the position of the nuclear fuel assembly 4 in use in a nuclear reactor, the longitudinal axis being L vertical.

[0037] The skeleton 6 comprises a bottom nozzle 8, a top nozzle 10, a plurality of guide thimbles 12 and a plurality of spacer grids 14.

[0038] The bottom nozzle 8 and the top nozzle 10 are spaced one from the other along the longitudinal axis L.

[0039] The guide thimbles 12 extend parallel to the assembly axis L and connect the bottom nozzle 8 to the top nozzle 10 with maintaining a predetermined spacing along assembly axis L between the bottom nozzle 8 and the top nozzle 10. The fuel rods 4 are received between the bottom nozzle 8 and the top nozzle 10.

[0040] The spacer grids 14 are distributed along the bundle of fuel rods 4. Each spacer grid 14 is fixedly attached to the guide thimbles 12 which extend through the spacer grid 14.

[0041] Each spacer grid 14 is configured for supporting the fuel rods 4 along the assembly axis L and transversely to the assembly axis L. The spacer grids 14 are configured for supporting the fuel rods 4 in a transversely spaced relationship. The spacer grids 14 are preferably configured for maintaining the fuel rods 4 transversely at the nodes of a regular imaginary network.

[0042] The bottom nozzle 8 comprises a tie plate 16. The tie plate 16 extends perpendicular to the longitudinal axis L, i.e. horizontally in use. The bottom nozzle 8 comprises for example feet 18 extending downwardly from corners of the tie plate 16 for resting on a lower core plate of the nuclear reactor.

[0043] The bottom nozzle 8 comprises a debris filtering grid 32 positioned on or near to the tie plate 16, for example below the tie plate 16 (i.e. upstream the tie plate 16 when considering the main flow direction F of the coolant fluid in use). Alternatively, the debris filtering grid 32 is positioned on top of the tie plate 16 (i.e. downstream the tie plate 16 when considering the main flow direction F of the coolant fluid in use).

[0044] The debris filtering grid 32 is for example manufactured as a component separate from the other components of the bottom nozzle 8, in particular the tie plate 16 and / or the feet 18. Alternatively, the debris filtering grid 32 and the tie plate 16 are manufactured as one single piece of material, e.g. by additive manufacturing. In particular, the bottom nozzle 8 is manufactured as one single piece of material, including the debris filtering grid 32, the tie plate 16 and the feet 18, which are one and unique component, e.g additively manufactured.

[0045] As illustrated on Figure 2, the debris filtering grid 32 is configured for retaining debris.The debris filtering grid 32 has preferably a retention capacity higher than that of the tie plate 16.

[0046] The debris filtering grid 32 extends parallel to an extension plane P corresponding to the plane of Figure 2. When the debris filtering grid 32 is positioned on the tie plate 16, the extension plane P is perpendicular to the longitudinal axis L. In use, the extension plane P is horizontal.

[0047] The debris filtering grid 32 has an inlet face 32A (visible on Figure 2) and an outlet face 32B (hidden on Figure 2). In use, the inlet face 32A faces downwardly and the outlet face 32B faces upwardly. The coolant fluid flows through the debris filtering grid 32 from the inlet face 32A towards the outlet face 32B.

[0048] The debris filtering grid 32 is for example distinct from the tie plate 16 and assembled to the tie plate 16. In such case, the debris filtering grid 32 is manufactured separately form the tie plate 16 and mounted on the tie plate 16. The debris filtering grid 32 is advantageously removable from the tie plate 16. Alternatively, the debris filtering grid 32 is manufactured as a single part of material with the tie plate 16.

[0049] The debris filtering grid 32 comprises a plurality of flow channels 34, 36 extending through the debris filtering grid from the inlet face 32A to the outlet face 32B of the debris filtering grid 32 for allowing the coolant fluid to flow through the debris filtering grid 32.

[0050] The debris filtering grid 32 optionally comprising mounting openings 38 for allowing the guide thimbles 12 or a mounting assembly to extend through the debris filtering grid 32. Each mounting opening 38 has an area strictly larger than that of the flow channels 34, 36. Preferably, when the nuclear fuel assembly 2 is assembled and positioned in the reactor core, the coolant fluid does not flow through the mounting openings 38.

[0051] As illustrated on Figure 3, each flow channel 34, 36 of the debris filtering grid 32 extends along a respective centerline A. The centerline of each flow channel 34, 36 is for example rectilinear and, preferably, perpendicular to the extension plane P of the debris filtering grid 32 (i.e. the plane of Figure 3), or curvilinear. The curvilinear centerline is for example undulated.

[0052] Each flow channel 34, 36 exhibits a cross-section. The cross-section of each flow channel 34, 36 is taken in a plan perpendicular to the centerline A of this flow channel 3436.

[0053] The cross-section of each flow channel 34, 36 is defined be a shape and an area. At least one region of the debris filtering grid 32 comprises first flow channels having a first cross-section and second flow channels having a second cross-section, the first cross-section being different from the second cross-section.The first flow channels have a first cross-section with the same first shape and the same first cross-sectional area and the second flow channels have a second cross-section with the same second shape and the same second cross-sectional area.

[0054] The first cross-section differs from the second cross-section by the shape and / or the cross-sectional area. The shape of the first cross-section and the shape of the second cross-section are different and / or the area of the first cross-section and the area of the second cross-section are different.

[0055] In some examples, one of the shape and the area of the first cross-section and the second cross-section is identical, the other being different.

[0056] The first flow channels 34 are aligned in a plurality of first rows 44, the first rows 44 being parallel to each other and to a first direction D1 of the extension plane P of the debris filtering grid 32.

[0057] The second flow channels 36 are aligned in a plurality of second rows 46, the second rows 46 being parallel to each other and to the first direction D1.

[0058] The first rows 44 alternate with the second row 46 in a second direction D2 of the extension plan P perpendicular to the first direction D2.

[0059] In some examples, the first flow channels 34 are aligned in a plurality of first columns 54 parallel to each other and to the second direction D2. The first flow channels 34 are arranged in a matrix pattern forming the first rows 44 in the first direction D1 and the first columns 54 in the second direction D2.

[0060] In some examples, the second flow channels 36 are aligned in a plurality of second columns 56 parallel to each other and to the second direction D2. The second flow channels 36 are arranged in a matrix pattern formed by the second rows 46 in the first direction D1 and the second columns 56 in the second direction D2.

[0061] The first flow channel 34 in the first row 44 are staggered with respect to the second flow channels 36 in the second rows 46.

[0062] The first flow channel 34 of each first row 44 are for example regularly spaced with a first spacing S1 that is the same for all the first rows 44 and the second flow channels 36 of each second row 46 are regularly spaced with the first spacing S1 that is the same for all the second rows 46.

[0063] The first flow channels 34 are not aligned with the second fluid channels 36 in the second direction D2. In some examples, the first flow channels 34 of each first row 44 are offset with a first offset 01 with respect to the second flow channels 36 of each adjacent second row 46 along the first direction D1.In some examples, the first flow channels 34 of each first row 44 are offset with a first offset 01 with respect to the second flow channels 36 of each second row 46 along the first direction D1. The first offset 01 is preferably equal to half the first spacing S1.

[0064] When the first flow channels 34 and the second flow channels 36 are provided in first columns 54 and second columns 56, the first flow channels 34 in the first columns 54 are for example staggered with respect to the second flow channels 36 in the second columns 56.

[0065] In some examples, the first flow channels 34 of each first column 54 are regularly spaced with a second spacing S2 that is the same for all the first columns 54 and the second flow channels 36 of each second column 56 are regularly spaced with the second spacing S2 that is the same for all the second column 56.

[0066] The first flow channel 34 are not aligned with the second flow channels 36 in the second direction D2 perpendicular to the first direction D1. In some examples, the first flow channels 34 of each first column 54 are offset with a second offset 02 with respect to the second flow channels 36 of each adjacent second column 56 along the second direction D2.

[0067] In some examples, the first flow channels 34 are of each first column 54 are for example offset with a second offset 02 with respect to the second flow channels 36 of each second column 56 along the second direction D2. The second offset 02 is preferably equal to half the second spacing S2.

[0068] The second flow channels 36 are preferably arranged in quincunx with the first flow channels 34. Each second flow channel 36 is located between four first flow channels 34 arranged at the corner of an imaginary rectangle, preferably an imaginary square.

[0069] The first flow channels 34 and the second flow channels 36 are distributed over the region of the debris filtering grid 32 according to a repeated pattern of four first flow channels 34 arranged at the corner of an imaginary rectangle, preferably and imaginary square, with a second flow channels 36 located in the imaginary rectangle or square, preferably at the center of said imaginary rectangle or square.

[0070] As illustrated on Figure 3, in some examples, the shape of the first cross-section differs from the shape of the second cross-section and the area of the first cross-section differs from the area of the second cross-section.

[0071] As illustrated on Figure 3, in some examples, the first cross-section is circular and the second cross section is quadrangular, in particular square. The area of the first crosssection is for example greater than the area of the second cross-section.

[0072] The first cross-section may have another shape, such as an elliptical shape or a polygonal shape with three or more sides, such as a triangular shape, a quadrangular shape, a pentagonal shape, a hexagonal shape or an octagonal shape.The second cross-section may have another shape, such as a circular shape or an elliptical shape of a polygonal shape with three or more sides, such as a triangular shape, a quadrangular shape, a pentagonal shape, a hexagonal shape or an octagonal shape.

[0073] As illustrated on Figure 4, the first cross-section is octagonal and the second cross section is quadrangular, in particular square. The area of the first cross-section is greater than the area of the second cross-section.

[0074] As illustrated on Figure 5, the first cross-section is hexagonal and the second cross section is hexagonal. The area of the first cross-section is for example greater than the area of the second cross-section.

[0075] Advantageously, in at least one or in each region provided with alternating rows of first flow channels 34 and second flow channels 36, the cross-sections of the first flow channels 34 and the second flow channels 36 and the distribution of the first flow channels 34 and the second flow channels 36 are configured such that ligaments of the debris filtering grid 32 separating the first flow channels 34 and the second flow channels 36 have a same constant thickness taken between the flow channels.

[0076] Other arrangements of the first flow channels 34 and the second flow channels 36 may be contemplated.

[0077] Each flow channel 34, 36 has an angular orientation around the centerline A of the flow channel 34, 36.

[0078] In some examples, the first flow channels 34 have the same orientation and / or the second flow channels 36 have the same orientation.

[0079] In some examples, the angular orientation of the first flow channels 34 varies along one or more first rows 44 and / or from one first row to the other and / or the angular orientation of the second flow channels 36 may vary along one or more second rows 46 and / or from one second row 46 to the other.

[0080] In some examples, first flow channels 34 of two or more first rows 44 are offset along the first direction D1 and / or the second flow channels 36 of two or more second rows 46.

[0081] As illustrated on Figure 6, the first flow channels 34 exhibit a circular cross-sectional shape of same cross-sectional area and second flow channels 36 exhibit an elliptical cross-sectional shape of same cross-sectional area. The first flow channels 34 of each first rows 44 are offset along the first direction D1 with first flow channels 34 of each adjacent first rows 44. The second flow channels 36 are aligned in second columns 56 in the second direction D2 but the angular orientation of the second flow channels 36 varies from one second row 46 to the next.

[0082] As illustrated on Figure 7, the first flow channels 34 exhibit a circular cross-sectional shape of same cross-sectional area and second flow channels 36 exhibit an elliptical cross-sectional shape of same cross-sectional area. The first flow channels 34 are aligned in first columns 54 in the second direction D2. The second flow channels 36 are aligned in second columns 56 in the second direction D2 but the angular orientation of the second flow channels 36 varies in each second row 46 and also in each second columns 54.

[0083] As illustrated on Figure 8, in some examples, the first flow channels 34 of a first row 44 overlap with the second flow channels 36 of a second row 46 adjacent to the first row 34 in view in the first direction D1. In other words, each second flow channel 36 of the second row 46 located along the first direction D1 between two adjacent first flow channels 34 of the first row 44, extends along the second direction D2 into the interval delimited between said two adjacent first flow channels 34.

[0084] In the example illustrated on Figure 8, the first flow channels 34 have a circular crosssection and the second flow channels 36 have a star-shaped cross-section with four arms, each second flow channel 36 being surrounded by four first flow channels 34 with each arm the cross-section of the second flow channel 36 projecting between two adjacent ones of the four first flow channels 34.

[0085] As illustrated on Figure 9, the debris filtering grid 32 comprises one or more mixed regions 60, each mixed region 60 being provided with first flow channels 34 and second flow channels 36 arranged in alternating rows.

[0086] In some examples, the debris filtering grid 32 comprises one single mixed region 60 provided with first flow channels 34 and second flow channels 36 arranged in alternating rows, said region 60 extending for example over the entire area of the debris filtering grid 32.

[0087] In some examples, the debris filtering grid 32 comprises a plurality of mixed region 60 with being distributed over the debris filtering grid 32.

[0088] In some examples, the debris filtering grid 32 comprises first flow channels 34 distributed over the entire surface of the debris filtering grid 32 and second flow channels 34 provided only in a limited number of mixed regions 60. The debris filtering grid 32 comprises less second flow channels 36 than first flow channels 34.

[0089] In some examples, as illustrated on Figure 9, the debris filtering grid 32 comprises a plurality of mixed region 60 spaced from each other with being distributed over the debris filtering grid 32 in a matrix pattern. In this example, each mixed region comprises 4x4 first flow channels 34 and 3x3 second flow channels arranged between the 4x4 second flow channels 34 in a quincunx.

[0090] In some examples, the inlet face 32A and / or the outlet face 32B of the debris filtering grid 32 is / are flat.

[0091] In some examples, the inlet face 32A and / or the outlet face 32B of the debris filtering grid 32 exhibit(s) a three-dimensional shape (3D shape).In some examples, as illustrated on Figure 10, the inlet face 32A comprises for example a plurality of protrusions 62 protruding on the inlet face 32A and distributed over the inlet face 32A. The protrusion 62 are for example dome-shaped.

[0092] The protrusions 62 are for example distributed over the inlet face 32A in a matrix pattern. Each dome-shaped protrusion 62 corresponds for example to one of the mixed region 60 of the debris filtering grid 32 including first flow channels 34 and second flow channels 36. The debris filtering grid is for example deprived of second flow channels 36 between the protrusions 62.

[0093] In some examples, as illustrated on Figure 11, the inlet face 32A comprises at least one region in which the inlet face 32A is 3D shaped to exhibit undulations defining crests 64 alternating with valleys 66. The crests 64 are for example circular and concentric. The valleys 66 are thus also circular and concentric.

[0094] The debris filtering grid 32 comprises one or more such regions. For example, only one quadrant of the debris filtering grid 32 is represented on Figure 8 and the debris filtering grid 32 comprises for example four regions in which the inlet face 32A is 3D shaped to exhibit undulations defining crests 64 alternating with valley 66, in particular circular and concentric crests 64 alternating with circular and concentric valleys 66.

[0095] In operation, the nuclear fuel assembly 2 is resting on the lower core plate of the reactor vessel, the lower core plate comprising one or more coolant injection holes located in register with the nuclear fuel assembly for injecting coolant into the nuclear fuel assembly 2.

[0096] In some examples, the inlet face 32A is configured to have one respective regions 3D shaped to exhibit circular and concentric undulations defining crests 64 alternating with valleys 66 in register with each coolant injection hole the lower core plate located in register with the nuclear fuel assembly.

[0097] This promotes capturing the debris exiting each coolant injection hole.

[0098] All the examples of 3D shape described here above for the inlet face 32A apply for the outlet face 32B when the outlet face 32B exhibits a 3D shape.

[0099] The debris filtering grid 32 comprising one or more regions combining first flow channels 34 and second flow channels 36 in a stagger pattern allows an efficient filtering of the coolant fluid flowing the debris filtering grid 32, in particular with retaining small debris, whilst limiting the pressure loss of the coolant fluid across the debris filtering grid 32.

[0100] First flow channels 34 and second flow channels 36 in a stagger pattern with first cross-sections and second cross-sections having different shape, area and / or angular orientations promote efficient filtering with allowing a high surface density of flow channels.The inlet face 32A of the debris filtering 32 allow trapping debris hitting the inlet face 32Awith preventing the debris to migrate along the inlet face 32A toward the periphery of the inlet face 32A and prevent elongated debris to orientate in the flow direction which would increase the risk that such elongated debris to pass through a flow channel 34, 36.

[0101] The nuclear fuel assembly 2 as illustrated in Figure 1 is configured for a Pressurized Water Reactor (PWR).

[0102] The debris filtering grid 32 can be configured for use in any type of nuclear fuel assembly provided with a bottom nozzle for any type or nuclear reactor, such as a Boiling Water Reactor (BWR), a water-water energetic reactor (WWER or also VVER from russian “Vodo-Vodianoi' Energuetitcheski Reaktor”), a High Temperature Reactor (HTR), a Rapid Neutron Reactor (RNR) or a Small Modular Reactor (SMR).

[0103] In some examples, the debris filtering grid 32 is configured for use in a nuclear fuel assembly for use in a WER.

[0104] A nuclear fuel assembly 2 for a VVER is illustrated on Figure 12 on which elements similar to that of Figure 1 bear the same numeral reference.

[0105] The nuclear fuel assembly 2 comprises a bundle of nuclear fuel rods 4 and a skeleton 6 comprising a bottom nozzle 8, a top nozzle 10, a plurality of guide thimbles 12 and a plurality of spacer grids 14.

[0106] In the nuclear fuel assembly 2 of Figure 1, the fuel rods are maintained at the nodes of an imaginary rectangular network.

[0107] The nuclear fuel assembly 2 of Figure 12 differs of that of Figure 1 in that the fuel rods are maintained at the nodes of an imaginary hexagonal network.

[0108] The bottom nozzle 8 of the nuclear fuel assembly 2 of Figure 12 comprises a tie plate 16 and is provided with a debris filtering grid 32.

[0109] In some examples, the debris filtering grid 32 is configured for use in a nuclear fuel assembly for a Boiling Water Reactor (BWR).

[0110] Such a nuclear fuel assembly differs from that of Figure 1 in that the nuclear fuel assembly is deprived of guide thimbles but comprises a fuel channel encasing the bundle of fuel rods and a water channel provided inside the bundle of fuel rods. The bottom nozzle and the top nozzle of the fuel assembly are for example mechanically connected by the fuel channel and / or the water channel. Spacer grid may be provided with being attached to the channel and / or the water channel or not.

[0111] In some examples, the nuclear fuel assembly is not configured for receiving nuclear fuel rods but is configured for receiving nuclear fuel particles, such as tri-structural isotropic fuel particles (or TRISO fuel particles), or nuclear fuel plates, each nuclear fuel plate comprising tablets of fissile material received in cells of a planar honeycomb substratesandwiched between to closure panels. The nuclear fuel particles or the nuclear fuel plates are for example encased in a tubular water channel provided with a bottom nozzle at an inlet extremity of the water channel.

[0112] All the statements made in relation to the debris filtering grid 32 of the nuclear fuel assembly 2 of Figure 1 apply to that of the other types of nuclear fuel assembly.

[0113] The debris filtering grids described according to the invention can be manufactured by any known manufacturing processes such as but not limited to machining, molding and / or 3D printing / additive manufacturing.

Claims

CLAIMS1. A debris filtering grid for a nuclear fuel assembly, the debris filtering grid (32) having flow channels (34, 36) extending through the debris filtering grid, each flow channel (34, 36) having a cross-section exhibiting a cross-sectional shape and an cross-sectional area, the flow channels (34, 36) including first flow channels (34) having a first cross-section and second flow channels having a second cross-section differing from the first cross-section by the cross-sectional shape and / or the cross-sectional area, wherein the debris filtering grid comprises at least one region including first rows (44) of first flow channel (34) aligned in a first direction (D1) and second rows (46) of second flow channels (36) aligned in the first direction (D1 ), the first rows (44) alternating with the second row (46) in a second direction (D2) perpendicular to the first direction (D1 ).

2. Debris filtering grid as in claim 1, wherein the first flow channels (34) of each first row (44) are offset with respect to the second flow channels (36) of each adjacent second row (46) along the first direction (D1).

3. Debris filtering grid as in claim 1 or 2, wherein the first flow channels (34) of each first row (44) are regularly spaced along the first direction (D1 ) and / or the second flow channels (36) of each second row (46) are regularly spaced along the first direction (D1).

4. Debris filtering grid as in claim 3, wherein the spacing of the first flow channels (34) in the first rows (44) and the spacing of the second flow channels (36) in the second rows (46) are equal.

5. Debris filtering grid as in any one of the preceding claims, wherein the first flow channels (34) are aligned in first columns (54) in the second direction (D2) and / or the second flow channels (36) are aligned in second columns (56) in the second direction (D2).

6. Debris filtering grid as in any one of the preceding claims, wherein the first rows (44) are regularly spaced in the second direction (D2) and / or the second rows (46) are regularly spaced in the second direction (D2).

7. Debris filtering grid as in claim 6, wherein the spacing of first rows (44) along the second direction (D2) and the spacing of second rows (46) along the second direction (D2) are equal.

8. Debris filtering grid as in any one of the preceding claims, wherein each second flow channel (36) is arranged inside an imaginary quadrangular polygon having four corners formed by four first flow channels (34).

9. Debris filtering grid as in any one of the preceding claims, wherein the first flow channels (34) and the second flow channels (36) are arranged in a repeated patterncomprising one second flow channel (36) arranged inside an imaginary quadrangular polygon having four corners formed by four first flow channels (34).

10. Debris filtering grid as in claim 9, wherein the first flow channels (34) of the repeated pattern are located at the corners of an imaginary rectangle or square or parallelogram.

11. Debris filtering grid according to any one of the preceding claims, wherein only one of the shape and / or the area of the first cross-section differs from that of the second cross-section.

12. Debris filtering grid according to any one of the preceding claims, wherein the area of the first cross-section is greater that the area of the second cross-section.

13. Debris filtering grid according to any one of the preceding claims, wherein the first cross-section is circular or polygonal, in particular triangular, quadrangular, pentagonal, hexagonal, heptagonal or octagonal, or star shaped, and / or the second cross-section is circular or polygonal, in particular triangular, quadrangular, pentagonal, hexagonal, heptagonal or octagonal, or star shaped.

14. Debris filtering grid according to any one of the preceding claims, wherein the cross-sections of the first flow channels (34) and the second flow channels (36) and the distribution of the first flow channels (34) and the second flow channels (36) are configured such that ligaments of the debris filtering separating the first flow channels (34) and the second flow channels (36) have a same constant thickness taken between the flow channels.

15. Debris filtering according to any one of the preceding claims, wherein the inlet face (32A) and / or the outlet face (32B) of the debris filtering (32) exhibits a 3D shape.

16. Debris filtering according to claim 15, wherein the inlet face (32A) and / or the outlet face (32B) comprises a plurality of protrusions (62) protruding on the inlet face (32A) and distributed over the inlet face (32A), each protrusion (62) including first flow channels (34) and second flow channels (36), the debris filtering grid being preferably deprived of second flow channels (36) between the protrusions (62).

17. Debris filtering grid according to claim 15, wherein the inlet face (32A) and / or the outlet face (32B) comprises at least one 3D shaped region that is shaped to exhibit undulations defining crests (64) alternating with valleys (66), the crests (64) and the valleys (66) being preferably circular and concentric.

18. Nuclear fuel assembly bottom nozzle (8) comprising a lower tie plate (16) and a debris filtering grid (32) as in any one of the preceding claims, provided for example on the lower tie plate (16) of the bottom nozzle (10), in particular below or above said lower tie plate (16), the lower tie plate (16) and the debris filtering grid (32) being for examplemanufactured as separate components and assembled or manufactured as a single piece of material, e.g. by additive manufacturing.

19. Nuclear fuel assembly comprising a bottom nozzle (8) and a top nozzle (10) spaced along an longitudinal axis (L), fuel rods (4) extending longitudinally between the bottom nozzle (8) and the top nozzle (10), the nuclear fuel assembly comprising a debris filtering grid (32) as in any one of the claims 1 - 17 or the bottom nozzle (32) being as in claim 18.

20. Nuclear fuel assembly as defined in claim 19, configured for use in a PWR or a BWR or a VVER or a HTR or a RNR or a SMR.

Images