Spacer grid element of a spacer grid for nuclear fuel assemblies, spacer grid and nuclear fuel assembly

Abstract

A spacer grid element defining a grid (17) for receiving nuclear fuel rods (4) extending along an extension axis (A) and presenting a polygonal cross section, comprising at least three support sides (20) distributed around the extension axis (A), wherein each support side (20) comprises an inwardly protruding corrugation (24) on which at least one spring (32) for supporting a fuel rod (4) extending through the spacer grid element is formed.

Description

Technical Field

[0001] This invention relates to a spacer grid element for a spacer grid of a nuclear fuel assembly. Background Technology

[0002] Nuclear fuel assemblies typically consist of fuel rods containing fissile material and a protective shell for supporting the fuel rods. The protective shell typically includes a lower nozzle and an upper nozzle spaced apart along the assembly axis, a guide sleeve (also called a guide tube) connecting the lower nozzle to the upper nozzle, and a spacer grid distributed along the guide sleeve. The fuel rods are positioned between the lower and upper nozzles, with the guide sleeve extending through the spacer grid, which is configured to support the fuel rods axially and laterally while maintaining a laterally spaced relationship.

[0003] Each spacer grid can be formed from multiple tubular spacer grid elements assembled together to form a spacer grid, each spacer grid element being configured to receive a fuel rod accordingly.

[0004] RU2138861C1 discloses a spacer grid formed by multiple tubular spacer grid elements. Each spacer grid element has a hexagonal profile and fuel rod support features distributed at 120°.

[0005] One problem that may be encountered with spacer grids is that micro-vibration wear occurs on the fuel rods at the contact points between the fuel rods and the spacer grids, which can lead to fuel rod failure. Summary of the Invention

[0006] One of the objectives of this invention is to provide a spaced grid element that can better support the fuel rod, thereby improving micro-vibration wear robustness and preventing fuel rod failure.

[0007] To this end, the present invention provides a spacer grid element for a nuclear fuel assembly spacer grid, the spacer grid element defining a grid for receiving nuclear fuel rods extending along an extension axis, the spacer grid element having a polygonal cross-section including at least three support sides distributed around the extension axis, wherein each support side includes an inwardly projecting corrugated portion on which at least one spring is formed for supporting fuel rods extending through the spacer grid element.

[0008] The spring positioned on the inwardly protruding corrugated portion has the following advantages: the spring height can be easily adjusted to the grid and fuel rod size. Furthermore, the corrugated portion restricts the movement of the fuel rods within the grid. Additionally, it provides flow channels to improve fuel rod cooling.

[0009] In other embodiments, the spacer grid element includes one or more of the following optional features, either individually or in any technically feasible combination:

[0010] - The spaced grid element includes three supporting sides distributed at 120° around the extending axis;

[0011] - The spaced grid element includes six supporting sides distributed at 60° around the extending axis;

[0012] - The spacer grid element includes at least one non-supported side;

[0013] - At least one supporting side or each supporting side is located between two non-supporting sides.

[0014] - At least one unsupported side or each unsupported side is flat or includes inwardly projecting corrugations;

[0015] - Each spring extends along the extension axis and / or forms a bridge shape;

[0016] - At least one spring or each spring is configured to make a strip-shaped contact with the fuel rod;

[0017] - At least one spring or each spring is configured to make point contact with the fuel rod at at least one contact point;

[0018] - At least one spring or each spring is configured to make point contact with the fuel rod at one contact point or at two contact points spaced apart from each other along the spring;

[0019] - Each spring has a non-linear cross-section in each plane perpendicular to the extension axis;

[0020] - Each spring includes two adjacent wings that extend side by side and are inclined relative to each other, the wings including a contact wing for contacting the fuel rod and a side wing that extends the contact wing laterally;

[0021] - The side wings are flat;

[0022] - The side wings have a width that varies along the length of the spring;

[0023] - The contact wing has a convex outer surface that defines a contact line suitable for contacting the fuel rod;

[0024] - The contact wing has a substantially constant width;

[0025] - Each support side corrugated portion includes a contact wall and two side connecting walls adjacent to the contact wall and inclined relative to the contact wall;

[0026] - Each spring has a contact wing and a side wing, the contact wing being formed in a contact wall on which a corrugated portion of the spring is formed, and the side wing being formed in a connecting wall on which a corrugated portion of the spring is formed;

[0027] - The spacer grid element includes two springs formed in the corrugations on each support side, and the two springs extend along each other;

[0028] - Two springs formed in the corrugated portion of each support side are formed between at least three slots, the at least three slots including at least one central slot and at least two side slots, each spring being formed between at least one central slot and at least one side slot;

[0029] - The side grooves are D-shaped, C-shaped, I-shaped or S-shaped;

[0030] - Spacer grid elements are manufactured individually and configured to form nuclear fuel assembly spacer grids, which include multiple such spacer grid elements assembled together.

[0031] The present invention also relates to a spacer grid for nuclear fuel assemblies, comprising a plurality of spacer grid elements as defined above, which are assembled together to form a spacer grid.

[0032] The present invention also relates to a spacer grid for nuclear fuel assemblies, comprising a plurality of spacer grid elements as defined above, which are manufactured, for example, as a single material part by additive manufacturing.

[0033] The present invention also relates to a nuclear fuel assembly comprising a bundle of fuel rods and a protective shell for supporting the fuel rods, the protective shell comprising at least one spacer grid as defined above. Attached Figure Description

[0034] The invention and its advantages will be better understood by reading the following description, which is given only as a non-limiting example and with reference to the accompanying drawings, in which:

[0035] Figure 1 This is a schematic side view of a nuclear fuel assembly;

[0036] Figure 2 yes Figure 1 A partial top view of the spacer grid of the fuel assembly;

[0037] Figure 3 yes Figure 2 A partial perspective view of the spacer grid element;

[0038] Figure 4 This is a top view of the spaced grid element according to the second embodiment;

[0039] Figure 5 This is a top view of the spaced grid element according to the third embodiment;

[0040] Figure 6 and Figure 7 This is a schematic side view of the supporting side of the spacer grid element according to different embodiments;

[0041] Figures 8 to 11 This is a front view of the supporting side of a spacer grid element according to different implementation methods;

[0042] Figures 12 to 14 This is a front view of the unsupported side of a spacer grid element with corrugated sections, according to different implementation methods. Detailed Implementation

[0043] Figure 1 The nuclear fuel assembly 2 includes a bundle of nuclear fuel rods 4 and a protective shell 6 for supporting the fuel rods 4. The fuel assembly 2 extends along the assembly axis L.

[0044] The protective shell 6 includes a lower nozzle 8, an upper nozzle 10, multiple guide sleeves 12, and multiple spacer grids 14.

[0045] The lower nozzle 8 and the upper nozzle 10 are spaced apart along the component axis L. Each guide sleeve 12 extends parallel to the component axis L and connects the lower nozzle 8 to the upper nozzle 10. Each guide sleeve 12 opens upward through the upper nozzle 10 to allow a control rod (not shown) to be inserted into the guide sleeve 12.

[0046] Spacer grids 14 are distributed along the guide sleeve 12 and are fixed to the guide sleeve 12, for example, by welding. Each spacer grid 14 extends transversely to the component axis L.

[0047] Each fuel rod 4 includes, for example, a tubular cladding, nuclear fuel pellets stacked within the cladding, and an end plug (not shown) sealing the end of the cladding.

[0048] Each fuel rod 4 extends parallel to the component axis L via a spacer grid 14 and is supported laterally and longitudinally relative to the component axis L by the spacer grid 14. The fuel rods 4 are maintained in a laterally spaced relationship by the spacer grid 14.

[0049] During operation, fuel assembly 2 is placed in the reactor core, with the lower nozzle 8 resting on the core base plate 16 and the assembly axis L being substantially vertical. Coolant flows upward from the inlet of the base plate 16 through the lower nozzle 8, between the fuel rods 4, the spacer grid 14, and the upper nozzle 10, as... Figure 1 As indicated by arrow F, it flows along fuel rod 4.

[0050] The bundle of fuel rods 4 in fuel assembly 2 preferably has a hexagonal profile, with the fuel rods 4 being laterally spaced, wherein the fuel rods 4 are located at the nodes of an imaginary hexagonal network.

[0051] The guide sleeve 12 is integrated into the bundle and is received at the node of the imaginary hexagonal network.

[0052] Nuclear fuel assembly 2, for example, is designed for use with VVER (Russian "Vodo-"). (An abbreviation of "EnerguetitcheskiReaktor"). The nuclear fuel assembly 2 of a VVER typically has fuel rods 4 arranged in a bundle with a hexagonal profile.

[0053] exist Figure 1 In the fuel assembly 2 shown, the spacer grids 14 are similar to each other, and will be referred to Figure 2 A spaced grid 14 is further described.

[0054] like Figure 2 As shown, the spacer grid 14 includes a plurality of spacer grid elements 18. Each spacer grid element 18 is tubular and defines a corresponding grid of the spacer grid 14, and each spacer grid element 18 is configured to receive a corresponding fuel rod 4.

[0055] Figure 2 Only a portion of the spacer grid 14 is shown. More specifically, Figure 2 Only seven grid cells formed by seven spaced grid elements 18 are shown.

[0056] The spaced grid elements 18 are disposed at the nodes of the imaginary hexagonal network, and Figure 2 It shows seven grid cells including a central spacer grid element 18 surrounded by six spacer grid elements 18 located at the corners of an imaginary hexagon.

[0057] Figure 2 The spaced grid element 18 is similar, and will be referred to Figure 2 and Figure 3 Further, only one of them will be described.

[0058] The spacer grid element 18 is along a plane perpendicular to the spacer grid 14. Figure 2 The corresponding extension axis A extends along the plane of the component. Extension axis A is substantially parallel to the component axis L. Fuel rods 4, received in each spacer grid element 18, extend along extension axis A through the spacer grid element 18.

[0059] The spaced grid element 18 has a polygonal cross-section and includes at least two supporting sides 20 distributed around the extending axis A.

[0060] More specifically, the spacer grid element 18 has a pseudo-polygonal cross-section, including at least two supporting sides 20 distributed around the extending axis A.

[0061] The term "pseudo-polygon" is used to describe the fact that a cross-section has edges that define an outline of a generally polygonal shape, however, some edges in the cross-section are not straight, but circular or have a shape with wavy parts, which will be explained below.

[0062] Each support side 20 is configured to contact the fuel rod 4 through the spacer grid element 18 used to support the fuel rod 4.

[0063] In one implementation, each side of the polygonal cross-section is a supporting side 20.

[0064] Optionally, the spacer grid element 18 includes at least one unsupported side 22. Each unsupported side 22 is configured not to contact the fuel rods extending through the spacer grid element 18.

[0065] The spacer grid element 18 includes, for example, at least one non-supporting side 22 located between two supporting sides 20.

[0066] The spacer grid element 18 includes, for example, support sides 20 alternating with unsupported sides 22. In such an example, each support side 20 is located between two adjacent unsupported sides 22, and each unsupported side 22 is located between two adjacent support sides 20.

[0067] In a particular embodiment, each spacer grid element 18 has a hexagonal cross-section with six sides, including three supporting sides 20 that are distributed at 120° around the extending axis A, alternating with three unsupported sides 22.

[0068] Each supporting side 20 includes an inwardly projecting central corrugated portion 24 located between two sidewalls 26. Each sidewall 26 connects one edge of the central corrugated portion 24 to the adjacent side. Each adjacent side is either a supporting side 20 or a non-supporting side 22 constructed according to a grid. In the example shown, each adjacent side is a non-supporting side 22.

[0069] Advantageously, the corrugated portion 24 extends along the entire length of the spacer grid element 18, that is, along the extension axis A from one end of the spacer grid element 18 to the other end.

[0070] Preferably, the sidewall 26 of the supporting side 20 extends along the polygonal outline of the spacer grid element 18, and each central corrugated portion 24 is offset inward relative to the polygonal outline of the spacer grid element 18.

[0071] On each support side 20, the central corrugated portion 24 includes, for example, a central wall 28 and two side walls 30, each side wall 30 connecting the contact wall 28 to a corresponding side wall 26 of the support side 20.

[0072] The center wall 28 is offset inward relative to the edge of the polygonal profile of the spacer grid element 18 that corresponds to the supporting side 20.

[0073] like Figure 2 As shown, the contact wall 28 and the two edge walls 26 are substantially parallel.

[0074] Each sidewall 30 extends obliquely relative to the edge of the polygonal profile of the spacer grid element 18 to connect to the corresponding sidewall 26. The two sidewalls 30 extend divergently from the center 28 toward the sidewall 26 relative to each other.

[0075] In a view along the extended axis A of the spacer grid element 18, each side connecting wall 30 is inclined relative to the contact wall 28, for example, at an angle of 45°.

[0076] Since the distance between the extension axis A and the spacer grid element 18 is minimum at each contact wall 28 of the corrugated portion 24, the fuel rod 4 extending along the extension axis A through the spacer grid element 18 only contacts the inwardly protruding corrugated portion 24 of the support side 20 of the spacer grid element 18.

[0077] Preferably, the corrugated portions 24 of the supporting side 20 are identical. Only one of them will be described further.

[0078] At least one spring 32, preferably two springs 32, is formed on the corrugated portion 24, and the springs (one or more) 32 are configured to support the fuel rods 4 extending inside the spaced grid 17.

[0079] Each spring 32 extends, for example, along the extension axis A and is in the shape of a bridge.

[0080] like Figure 3 As shown, each corrugated section 24 is provided with a pair of springs 32, for example. The two springs 32 extend along each other.

[0081] Each pair of springs 32 is formed in the corrugated portion 24, for example, between a central groove 34 and two side grooves 36. The central groove 34 is formed in the contact wall 28, and the two side grooves 36 are each formed in one of the two connecting walls 30 of the corrugated portion 24.

[0082] Each spring 32 is formed at the junction of the connecting wall 30 and the contact wall 28, and more specifically, between a central groove 34 formed in the contact wall 28 and a side groove 36 formed in the connecting wall 30.

[0083] like Figure 3 As shown, in one exemplary embodiment, the central groove 34 is axially longer than the side groove 36.

[0084] Each spring 32 includes, for example, a longitudinal contact wing 38 formed in a contact wall 28 and a longitudinal side wing 40 formed in a connecting wall 30. The contact wing 38 and the side wing 40 extend over the entire length of the spring 32. The side wing 40 is inclined relative to the contact wing 38.

[0085] Advantageously, in one embodiment, each spring 32 has a non-linear cross-section in each plane perpendicular to the extension axis A.

[0086] like Figure 3 As shown, in each plane perpendicular to the extension axis A, the cross-section is arched, wherein the inwardly oriented concave surface provides a convex contact surface on the contact wing 38 for contacting the fuel rod 4.

[0087] In one exemplary embodiment, each contact wing 38 is longitudinally arched. The contact wing 38 is arched along the length of the spring 32. The middle portion of the contact wing 38 is closer to the extension axis A than the end portions of the contact wing 38.

[0088] Optionally, each contact wing 38 is laterally arched. The lateral concave surface of each contact wing 38 points radially outward relative to the extension axis A.

[0089] Alternatively, each contact wing 38 is also arched laterally toward the associated spring 32 of the pair of springs. The springs 32 of each pair are closer together at their middle than at their axial ends.

[0090] Each contact wing 38 preferably has a width that is substantially constant along the length of the spring 32.

[0091] Each side wing 40 is preferably flat and extends laterally from the corresponding contact wing 38 in the plane of the corresponding connecting wall 30.

[0092] In one implementation, such as Figure 3 As shown, the width of the central groove 34 is substantially constant along its length and extends in a straight line.

[0093] In one implementation, such as Figure 3 As shown, each side slot 36 is C-shaped. The width of each side slot 36 increases from its end toward its center. Each side slot 36 has a larger width at its center.

[0094] The free longitudinal edge of each side wing 40 (along the side groove 36) is curved and bends away from the engagement region 44 between the side wing 40 and the contact wing 38. Due to the curvature of the contact wing 38, the engagement region 44 also bends away from the free longitudinal edge of each side wing 40.

[0095] Each side wing 40 has a width that varies along the length of the spring 32 and reaches its maximum width at its center. Each side wing 40 is larger at the center than at its ends.

[0096] In one implementation, such as Figure 2 and Figure 3 As shown, each spacer grid 17 is defined by a corresponding spacer grid element 18, which is assembled to define the spacer grid 14.

[0097] Each spacer grid element 18 defines a corresponding fuel grid 17. Each spacer grid element 18 is a tube extending along the extension axis of the fuel grid 17 and having the cross-section of the spacer grid 17.

[0098] The spacer grid element 18 is preferably made of zirconium alloy. In an alternative embodiment, the spacer grid element 18 is made of Ni-based alloy or another material with high mechanical properties (e.g., Ph13.8Mo).

[0099] like Figure 2 As shown, in order to form the spacer grid 4, each side 20, 22 of each spacer grid element 18 is positioned to contact the side 20, 22 of another spacer grid element 18.

[0100] exist Figure 2 In the exemplary embodiment shown, the spacer grid elements 18 are configured such that for each spacer grid element 18, each supporting side 20 of the spacer grid element 18 that contacts the side of another spacer grid element 18 contacts the non-supporting side 22 of the other spacer grid element 18. Each spacer grid element 18 is manufactured individually, for example, by extrusion or by processing, bending, and welding sheet metal. The spacer grid 14 is then manufactured by welding multiple spacer grid elements 18 together. In an alternative embodiment, the spacer grid elements 18 are made into a single material piece, for example, by additive manufacturing. All the spacer grid elements 18 are manufactured at once to form the spacer grid 14.

[0101] In a preferred embodiment, in each pair of adjacent spacer grid elements 18, the two adjacent sides of the two spacer grid elements 18 are made of a single material.

[0102] Advantageously, when two spacer grid elements 18 are adjacent via two flat, unsupported sides 22, only one flat wall is provided that is shared by the two spacer grid elements 18 and defines the two unsupported sides 22. This allows for material reduction and avoids internal erosion between adjacent sides.

[0103] Advantageously, when two adjacent spacer grid elements 18 are adjacent via the supporting side 20 of one of the spacer grid meshes 17 and the non-supporting side 22 of the other spacer grid element 18, only one wall is manufactured.

[0104] The wall includes a central corrugated portion 24 that protrudes inward relative to one of the two spacer grid elements 18 to define a supporting side 20, and protrudes outward relative to the other spacer grid element 18 to define a non-supporting side 22.

[0105] like Figure 2 and Figure 3 As shown, each unsupported side 22 is, for example, flat. Each unsupported side 22 extends along a corresponding side of the polygonal profile of the spacer grid element 18.

[0106] like Figure 2 As shown, each fuel rod 4 is in contact with each spring 32 of each pair of springs 32 of each corrugated portion 24 of the spacer grid element 18 into which the fuel rod 4 is inserted.

[0107] Spring 32 supports fuel rod 4 laterally and longitudinally through friction between spring 32 and fuel rod 4.

[0108] Providing each spring on the corrugated portion 24 of the spacer grid element 18 allows for the acquisition of a spacer grid 4 with appropriate mechanical features for supporting the fuel rod 4.

[0109] The corrugated portion 24 of each spacer grid element 18 reinforces the spacer grid, forming a box-shaped structure, for example, when the supporting side 20 of one spacer grid element is applied to the non-supporting side 22 or supporting side of another spacer grid element 18.

[0110] Spring 32 has a 3D shape that provides satisfactory support and reduces the risk of micro-vibration wear.

[0111] The transversely bent, slender springs 32 provide sufficient bending stiffness to achieve at least one line contact between the fuel rod 4 and each spring 32 over a length sufficient to limit local contact stress. The contact between each pair of springs 32 and the fuel rod 4 must be strong enough to avoid fretting wear, i.e., when the fuel rod 4 vibrates due to high-speed fluid flow during use.

[0112] The side wing 40, which is inclined relative to the contact wing 38, imparts bending stiffness to the spring 32. That is, the bending stiffness of the spring 32 and the deformation of the spring 32 under load depend on the inclination between the wings 38 and 40 and the width of the side wing 40 along the spring 32.

[0113] The fuel rods 4 are additionally clamped by spring 32, which embeds them into each spacer grid element 18, preventing the risk of fuel rod bending. This additional clamping enhances the overall stiffness of the fuel assembly and minimizes sensitivity to fuel assembly bending.

[0114] The central groove 34 and the side grooves 36 of each corrugated section 24 define a number of openings in each spacer grid element 18, which enable hydraulic exchange between different grids of the spacer grid 14.

[0115] This invention is not limited to the examples and variations described above. Other examples and variations are conceivable.

[0116] In the example above, each unsupported side 22 of the spacer grid element 18 is flat or substantially flat.

[0117] In alternative implementations, such as Figure 4 As shown, each unsupported side 22 of the spacer grid element 18 includes an inwardly projecting central corrugated portion 25. This corrugated portion 25 can reinforce the unsupported side 22.

[0118] Advantageously, the corrugated portion 25 extends along the entire length of the spacer grid element 18, that is, along the extension axis A from one end of the spacer grid element 18 to the other end.

[0119] exist Figure 3 In the example shown, the spacer grid element 18 has a polygonal cross-section, particularly a hexagonal cross-section, and includes supporting sides 20 alternating with the non-supporting sides 22.

[0120] In alternative implementations, such as Figure 5 As shown, the spaced grid element 18 has a polygonal cross-section, particularly a hexagonal cross-section, with each side of the polygonal cross-section serving as a supporting side 20.

[0121] In certain implementations, such as Figure 5 As shown, the spaced grid element 18 has a pseudo-hexagonal cross-section, wherein six supporting sides 20 are distributed at 60° around the extending axis A. Each supporting side 20 (i.e., the six sides) is as described above, and in particular includes an inwardly projecting central corrugated portion 24 located between two sidewalls 26 and provided with at least one spring 32.

[0122] Advantageously, such as Figure 6 As shown, each spring 32 is configured to make elongated contact with the fuel rod 4 extending through the spacer grid element 18.

[0123] Specifically, when the spring 32 includes contact wings 38, the contact wings 38 of each spring 32 are configured to contact the fuel rod 4 along at least one contact line 39 between the fuel rod 4 and the spring 32.

[0124] In one embodiment, each spring 32 is configured to make elongated contact with the fuel rod 4 along a single contact line.

[0125] Specifically, when the spring 32 includes contact wings 38, the contact wings 38 of each spring 32 are configured to contact the fuel rod 4 along a single contact line 39 between the fuel rod 4 and the spring 32.

[0126] In another implementation, such as Figure 7 As shown, each spring 32 is configured to make elongated contact with the fuel rod 4 along at least two separate contact lines.

[0127] Specifically, the spring 32 has a W-shaped contact surface (e.g., contact wing 38) such that two portions of the contact surface are closer to the extending axis A than the rest of the spring 32, to define two separate contact lines 39 with the fuel rod 4.

[0128] The central groove 34 located between the two springs 32 on the support side 20 can have different shapes.

[0129] exist Figure 8 In the embodiment shown, the width of the central groove 34 decreases from the axial end of the central groove 34 to the middle of the central groove 34.

[0130] exist Figure 9 In the alternative embodiment shown, the width of the central groove 34 increases from the axial end toward the center of the central groove 34.

[0131] exist Figure 10 In the alternative embodiment shown, the central groove 34 is I-shaped. The central groove 34 has a width that is substantially constant along its length and extends in a straight line.

[0132] The side groove 36 provided along the spring 32 in the support side 20 can take on different shapes.

[0133] exist Figure 8 In the illustrated embodiment, each side slot is C-shaped. It includes a straight edge and an arched edge opposite to the straight edge. The arched edge is, for example, adjacent to the spring 32, and the straight edge is opposite to the spring 32.

[0134] exist Figure 9 In another embodiment shown, each side groove 36 is D-shaped. Each side groove 36 extends along an arc.

[0135] exist Figure 10 In another embodiment shown, each side slot 36 is I-shaped. Each side slot 36 has a substantially constant width along its length and extends in a straight line.

[0136] exist Figure 11 In the alternative embodiment shown, each side groove 36 is S-shaped. It extends along a curve that has two opposite curvatures along its length.

[0137] The present invention is not limited to the embodiments shown, and the different shapes of the central groove 34 and the side grooves 36 shown in the drawings can be combined in different ways.

[0138] like Figures 8 to 11 As shown, each spring 32 is formed between a central groove 34 and a side groove 36.

[0139] In an alternative embodiment, each spring 32 is formed between a plurality of central slots 34 and a side slot 36. Specifically, each spring 32 is formed between two central slots 34 and a side slot 36. This embodiment allows for a connection between two springs 32, thereby forming an H or X shape.

[0140] In an alternative embodiment, each spring 32 is formed between a central slot 34 and a plurality of side slots 36. The side slots 36 are, for example, I-shaped and all aligned with each other.

[0141] The present invention is not limited to the described embodiments, and the different amounts of the described central groove 34 and side groove 36 can be combined in different ways.

[0142] like Figure 3 As shown, the corrugated portion 24 of the supporting side 20 extends in a straight line along the extension axis A.

[0143] The corrugated portions provided on the side of the spacer grid element 18 (i.e., the corrugated portion 24 on the supporting side 20 or the corrugated portion 25 on the non-supporting side 22) define a channel for coolant and can be used to direct the coolant flow at the outlet of the spacer grid.

[0144] In fact, the corrugated portions 24, 25 provided in the supporting side 20 or the non-supporting side 22 of the spacer grid element 18 can be shaped to generate a transverse flow of coolant flowing through the spacer grid 14.

[0145] In this regard, the corrugated portions 24, 25 may extend along the extending axis A, wherein at least one end portion of the corrugated portions 24, 25 (corresponding to the downstream end of the spacer element 18 when considering the flow direction of coolant through the spacer grid 14) is inclined relative to the extending axis A. The inclination angle includes, for example, between 0° and 15°.

[0146] In one example, the corrugated portions 24 and 25 extend along a straight line inclined relative to the extension axis A.

[0147] like Figure 12 As shown, in one example, the corrugated portion 25 of the unsupported side 22 extends along a straight line inclined relative to the extension axis A (“I-shaped corrugation”). The downstream end of the corrugated portion 25 is particularly inclined relative to the extension axis A at the downstream end 25A of the corrugated portion.

[0148] In another example, the corrugated portions 24, 25 extend along a curve inclined relative to the extension axis A at least at their downstream ends.

[0149] like Figure 13 As shown, in one example, the corrugated portion 25 of the non-supporting side 22 extends along an arc (“C-shaped corrugation”).

[0150] like Figure 14 As shown, in one example, the corrugated portion 25 of the unsupported side 22 extends along a curve with two opposite curvatures (“S-shaped” corrugation).

[0151] The above example can be applied to the corrugated section 24 supporting the side.

Claims

1. Spacer grid element of a spacer grid (14) of a nuclear fuel assembly, the spacer grid element (18) defining a grid (17) for receiving fuel rods (4) of a nuclear fuel extending along an extension axis (A), the spacer grid element (18) exhibiting a polygonal cross section comprising at least three support sides (20) distributed around the extension axis (A), wherein each support side (20) comprises an inwardly protruding corrugation on which at least one spring (32) for supporting a fuel rod (4) extending through the spacer grid element (18) is formed.

2. Spacer grid element according to claim 1, comprising three support sides (20) distributed at 120° around the extension axis (A).

3. Spacer grid element according to claim 1 or 2, comprising six support sides (20) distributed at 60° around the extension axis (A).

4. The spacer grid element of claim 1, wherein, The spacer grid element (18) comprises at least one non-support side (22).

5. The spacer grid element of claim 4, wherein At least one support side or each support side (20) is located between two non-support sides (22).

6. The spacer grid element of claim 4 or 5, wherein At least one non-support side or each non-support side (22) is flat or comprises an inwardly protruding corrugation.

7. The spacer grid element of claim 1, wherein, Each spring (32) is elongated along the extension axis and / or is bridge-like.

8. The spacer grid element of claim 1, wherein, At least one spring (32) or each spring (32) is configured for an elongated contact with the fuel rod.

9. The spacer grid element of claim 1, wherein, At least one spring (32) or each spring (32) is configured for a point contact with the fuel rod at at least one contact point.

10. The spacer grid element of claim 1, wherein, At least one spring (32) or each spring (32) is configured for a point contact with the fuel rod at one contact point or at two contact points spaced apart from each other along the spring (32).

11. The spacer grid element of claim 1, wherein, Each spring (32) has a non-straight cross section in each plane perpendicular to the extension axis (A).

12. The spacer grid element of claim 1, wherein, Each spring (32) comprises two adjacent wings extending side by side along a spring axis (B) and being inclined with respect to each other, the wings comprising a contact wing (38) for contacting the fuel rod (4) and a flank wing (40) laterally extending the contact wing (38).

13. The spacer grid element of claim 12, wherein, The flank wing (40) is flat.

14. The spacer grid element of claim 12 or 13, wherein The flank wing (40) has a width that varies along the length of the spring (32).

15. The spacer grid element of claim 12, wherein, The contact wing (38) has a convex outer surface defining a contact line (39) adapted to contact the fuel rod (4).

16. The spacer grid element of claim 12, wherein, The contact wing (38) has a substantially constant width.

17. The spacer grid element of claim 1, wherein, The corrugation of each support side (20) comprises one contact wall (28) and two flank connection walls (30) adjacent to and inclined with respect to the contact wall (28).

18. The spacer grid element of claim 17, wherein, Each spring (32) has a contact wing (38) formed in the contact wall (28) on which the corrugation of the spring (32) is formed, and a lateral wing (40) formed in one of the connecting walls (30) on which the corrugation of the spring (32) is formed.

19. The spacer grid element according to claim 1, comprising two springs (32) formed in the corrugation of each support side (20), the two springs (32) extending along each other.

20. The spacer grid element of claim 19, wherein, The two springs (32) formed in the corrugation of each support side (20) are formed between at least three slots, the at least three slots comprising at least one central slot (34) and at least two lateral slots (36), each spring (32) being formed between the at least one central slot (34) and at least one lateral slot (36).

21. The spacer grid element of claim 20, wherein, The lateral slots (36) are D-shaped, C-shaped, I-shaped or S-shaped.

22. The spacer grid element according to claim 1, manufactured individually and configured for forming a spacer grid (14) of a nuclear fuel assembly, the nuclear fuel assembly spacer grid comprising a plurality of such spacer grid elements (18) assembled together.

23. A spacer grid for a nuclear fuel assembly, comprising a plurality of spacer grid elements (18) according to claim 22, the plurality of spacer grid elements (18) being assembled together to form the spacer grid (14).

24. A spacer grid for a nuclear fuel assembly, comprising a plurality of spacer grid elements (18) according to claim 1, the plurality of spacer grid elements (18) being made in a single piece of material by additive manufacturing.

25. A nuclear fuel assembly, comprising a bundle of fuel rods (4) and a protective sheath (6) for supporting the fuel rods (4), the protective sheath (6) comprising at least one spacer grid (14) according to claim 23 and / or at least one spacer grid (14) according to claim 24.

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