KR20210038523A - Spacer grid of a nuclear fuel assembly - Google Patents

Abstract

The present invention relates to a space lattice of a nuclear fuel assembly which can be manufactured using three-dimensional printing with high degree of freedom in design, excluding sheet metal processing and welding processing. The space lattice of the nuclear fuel assembly has hollow lattice cells (110) having an inner wall (111) arranged in a lattice structure to be connected to each other in a circumscribed manner, wherein the lattice cell (110) comprises: a plurality of elastic support units (112) curved inward from an inner wall (111) to be formed to protrude and having at least three or more thereof arranged at an equal angle to elastically support a fuel rod (10); and a plurality of inner mixing vanes (113) formed to protrude by allowing an upper tip unit to be turned in a spiral along the upper inner wall of the elastic support unit (112).

Description

Spacer grid of a nuclear fuel assembly

The present invention relates to a support grid of a nuclear fuel assembly that can be manufactured using 3D printing with high design freedom, excluding sheet metal processing and welding processing.

Nuclear fuel used in nuclear reactors is manufactured as fuel rods by molding enriched uranium into cylindrical sintered pellets of a certain size and then loading a number of sintered bodies into a cladding tube, and a number of these fuel rods constitute a nuclear fuel assembly and loaded into the core of the nuclear reactor. After being burned through nuclear reaction.

In general, a nuclear fuel assembly includes a plurality of fuel rods arranged in the axial direction, a plurality of support grids provided in the transverse direction of the fuel rods to support the fuel rods, and a plurality of guide tubes fixed to the support grids to constitute the skeleton of the assembly, It is composed of an upper fixing body and a lower fixing body each supporting the upper and lower ends of the guide tube.

The support grid is one of the important parts of the nuclear fuel assembly that maintains the arrangement of the fuel rods by restraining the lateral movement of the fuel rod and suppressing the axial movement by frictional force. These support grids differ in shape and number depending on the reactor type and design, but are divided into a protective support grid, a lower support grid, an upper support grid, and an intermediate support grid according to the assembly position with the fuel rod, and are assembled vertically. The structure of providing a grid cell in which a fuel rod is inserted is the same as that of a plurality of grid plates.

In particular, the intermediate support grid is arranged between the lower support grid and the upper support grid, occupying most of the support grid, and forms the skeleton of the nuclear fuel assembly to maintain the mechanical properties of the nuclear fuel and support the fuel rod, and from the uranium sintered body. It performs the function of mixing so that the generated heat can be well transferred to the primary coolant through the fuel rod (covered pipe). In addition, the intermediate support grid is an important component that determines the seismic performance of nuclear fuel, and the dynamic impact strength of the intermediate support grid is a major factor included in the calculation of the seismic performance of nuclear fuel.

Specifically, the support grid is provided with a grid spring for elastically supporting the fuel rod in the grid cell and a dimple for limiting the horizontal behavior of the fuel rod. These lattice springs and dimples are formed by sheet metal processing the support lattice plates constituting each lattice cell, and in general, lattice springs are provided on each of the four lattice cells facing each other, and a plurality of dimples are provided on the other two sides. It is prepared.

The manufacturing process of the support grid is to assemble and fix each of the sheet metal-processed inner and outer grids on a separate welding jig, and then the base material is melted by irradiating a laser beam to the cross-welded part of the inner grid, the junction of the inner/outer grid, and the sleeve joint. The laser welding is performed by welding, and then, it is manufactured through a series of processes of grinding and processing the weld bead generated during the welding process of the external grating plate.

Meanwhile, the supporting grid is provided with a mixing vane protruding in the downstream direction of the coolant flow, and the mixing vane has a shape surrounding the fuel rod and serves to promote heat transfer through mixing of the coolant around the fuel rod. In general, the mixing blade extends at the top of the grating plate and has a predetermined shape to change and mix the cooling water direction, and the cooling water mixing performance is determined according to the size, shape, bending angle and position.

As described above, in the manufacturing process of the conventional support grid, there are many series of processes such as sheet metal process and welding process, and in the design process, shape design technology such as mixing blades for mixing coolant and securing dynamic impact strength for seismic performance is considerably used. Picky.

Although the manufacturing process of the supporting grid in the prior art is a stabilized technology, as described above, since it undergoes a manufacturing process of several stages, many restrictions arise in designing the shape of the supporting grid. In particular, the support grid of the prior art provides grid springs and dimples by sheet metal processing of the support grid plate, and thus the number of designable grid springs and dimples in each grid cell is limited, thereby limiting design freedom.

In this regard, it has been reported that the impact strength of the support grid is very deteriorated at the end of life (EOL) condition. Therefore, in the development of future nuclear fuel and the development of nuclear fuel with an effective fuel area of 14ft in consideration of high combustion and long cycles. A technology for securing nuclear fuel seismic performance and mechanical soundness under EOL conditions is inevitably required. Accordingly, the conventional manufacturing method of the support grid has many restrictions on the shape design as described, so it is sufficiently stable and has high strength under EOL conditions. There is a limit to the implementation.

Patent Document 1: Unexamined Patent Publication No. 2003-0038493 (Publication date: 2003.05.16) Patent Document 2: Registered Patent Publication No. 10-0771830 (Announcement date: 2007.10.30.)

The present invention is to improve the problems of the prior art, and to provide a support grid for a nuclear fuel assembly that can be manufactured using 3D printing that can eliminate sheet metal and welding processes, increase design freedom, and simplify the manufacturing process. .

In the support grid of the nuclear fuel assembly according to the present invention for achieving this purpose, the grid cells in the shape of a hollow cylinder having an inner wall are arranged in a lattice structure and are connected to each other in an circumferential manner. A plurality of elastic support portions which are curved inwardly and protrude from, and at least three or more are disposed at an equal angle to elastically support the fuel rod; Includes a plurality of inner mixing vanes formed by protruding by spirally rotating an upper tip along the upper inner wall of the elastic support, and the inner mixing vane has a lowermost end continuously increasing in the axial direction from the inner wall, but the uppermost end The height of the elastic support is characterized in that it is smaller than the maximum height.

Preferably, the inner mixing vane is rotated by 1/k (k is the number of elastic supports formed in one grid cell) along the inner wall and coincides with the center of the longitudinal direction of the two elastic support portions adjacent to each other at the lowermost end and the uppermost end. Is formed.

In the support grid of the nuclear fuel assembly according to the present invention, hollow grid cells having an inner wall are arranged in a square grid structure and connected circumferentially to each other, and the grid cells are formed to protrude from the inner wall inwardly curved, but at least 3 A plurality of elastic support portions which are disposed at an equal angle to elastically support the fuel rod; Including a plurality of inner mixing vanes protruding by spirally rotating the upper end along the upper inner wall of the elastic support part, excluding sheet metal processing and welding processing, and utilizing 3D printing with high design freedom, while simplifying the structure and mechanical strength. There is an effect that can secure and increase the cooling water mixing effect.

1 is a perspective configuration diagram of a support grid for a nuclear fuel assembly according to a first embodiment of the present invention,
FIG. 2 is a perspective configuration diagram of a support grid for a nuclear fuel assembly cut along the line AA of FIG. 1,
3 is a plan view of a support grid for a nuclear fuel assembly according to a first embodiment of the present invention,
4 is a perspective view of a support grid for a nuclear fuel assembly according to a second embodiment of the present invention,
5 is a perspective configuration diagram of a support grid for a nuclear fuel assembly partially cut along the line BB of FIG. 4,
6 is a plan view of a support grid for a nuclear fuel assembly according to a second embodiment of the present invention,
7 is a partially cut-away perspective view of a support grid for a nuclear fuel assembly showing another modification to the second embodiment of the present invention,
8 to 10 are data showing the flow analysis results for the present invention and a comparative example.

Specific structural or functional descriptions presented in the embodiments of the present invention are exemplified only for the purpose of describing the embodiments according to the concept of the present invention, and embodiments according to the concept of the present invention may be implemented in various forms. In addition, it should not be construed as limited to the embodiments described in the present specification, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Meanwhile, terms used in the present specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "comprise" or "have" are intended to designate the existence of implemented features, numbers, steps, actions, components, parts, or a combination thereof, and one or more other features or numbers, It is to be understood that the presence or addition of steps, actions, components, parts, or combinations thereof does not preclude the possibility of preliminary exclusion.

The present invention is to provide a support grid that can be manufactured by metal 3D printing, excluding the sheet metal processing and welding process during the manufacturing process of the support grid. Limitations can be lifted and manufacturing processes can be shortened.

In general, various metal 3D printing devices are available. For example, the 3D printing equipment of CONPCEPTLASER of Germany has a maximum production size of 250×250×280㎣, making it possible to manufacture a full-size support grid. PBF (Powder Bed) in which a product is manufactured by laying a powder layer of several tens of µm on a powder bed having a certain area in the powder supplying device and selectively irradiating a laser or electron beam according to the design drawing, and then melting and laminating layer by layer. Fusion) method is being used. Meanwhile, the support grid of the present invention may employ a general metal additive manufacturing method employed in general metal 3D printing, and is not limited to a specific method.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a perspective configuration diagram of a support grid for a nuclear fuel assembly according to a first embodiment of the present invention, FIG. 2 is a perspective configuration diagram of a support grid for a nuclear fuel assembly partially cut along the line AA of FIG. 1, and FIG. 3 is It is a plan view of a support grid for a nuclear fuel assembly according to the first embodiment of the present invention. In the following description, the axial direction refers to the direction of the rotation axis of the lattice cell having a cylindrical shape, and corresponds to the z-axis direction in the drawing.

1 to 3, the support grid 100 of the first embodiment has a hollow cylindrical grid cell 110 having an inner wall 111 having a square lattice (n×n) structure. The plurality of elastic support portions 112 and a spiral inner mixing vane 113 are integrally formed on the inner wall 111 of each grid cell 110 and are connected to each other.

The grid cell 110 has an inner diameter larger than that of the fuel rod 10 and the fuel rod 10 is inserted therein, and the fuel rod 10 is elastically supported by a plurality of elastic support portions 112. Preferably, the elastic support 112 has an elliptical shape having a major axis z1 in the axial direction (z axis) of the grid cell 110.

The inner mixing vane 113 is disposed on the upper inner wall 111 of the elastic support 112 corresponding to the downstream side of the coolant, and the upper end portion is spirally formed along the axial direction (z-axis direction) from the inner wall 111. It is formed protruding by turning. Preferably, the inner mixing vane 113 has a lowermost end (113a) continuously increasing monotonically with respect to the axial direction (z-axis) without a step in the inner wall 111, and the height at the uppermost end (113b) is elastic support 112 ) Does not exceed the maximum height. More preferably, the uppermost end 113b of the inner mixing vane 113 coincides with the upper open end of the grating cell 110.

Specifically, referring to FIG. 3, the grid cell 110 of this embodiment has four elastic supports 112 disposed in a direction perpendicular to each other with respect to the axial direction, and is disposed within a range of a predetermined arc angle (θ). It includes four inner mixing vanes 113. In particular, each inner mixing vane 113 is formed within a range of 90°, which is an arc angle (θ) between two adjacent elastic support units 112, and the lowermost and upper ends of each inner mixing vane 113 are each elastic support unit 112 Coincides with the center of its longitudinal direction. That is, in the present embodiment, each inner mixing vane 113 is spirally rotated 1/4 turn between the two elastic supports 112. As another embodiment, when k (k is a natural number of 3 or more) elastic support portions are formed in the grid cell, the inner mixing vanes provided between the elastic support portions may be formed by rotating 1/k along the inner wall.

The maximum height of each elastic support 112 is located at the same radius on the central axis of the grid cell 110, and if the radius is defined as a diameter'D2', the diameter D2 of the elastic support 112 is the fuel rod 10 ) Is smaller than the outer diameter (D1) (D2 <D1). Accordingly, the fuel rod 10 is elastically supported by the elastic support part 112. Meanwhile, a dimple for limiting the horizontal behavior of the fuel rod may be added to the lattice cell in addition to an elastic spring for elastic support by direct contact with the fuel rod, and this dimple has a larger diameter than the outer diameter D1 of the fuel rod 10. It can have a variety of shapes within the range.

The height of the uppermost end (113b) of the inner mixing vane 113 is located at the same radius on the central axis of the lattice cell 110, and if the radius is defined as a diameter'D3', the uppermost end (113b) of the inner mixing vane 113 The diameter D3 of is larger than the diameter D2 of the elastic support 112 (D2 <D3).

FIG. 4 is a perspective configuration diagram of a support grid for a nuclear fuel assembly according to a second embodiment of the present invention, and FIG. 5 is a perspective configuration diagram of a support grid for a nuclear fuel assembly partially cut along the line BB of FIG. 4, and FIG. A plan view of a support grid for a nuclear fuel assembly according to a second embodiment of the present invention.

4 to 6, in the support grid 200 according to the second embodiment, the grid cells 210 in the shape of a square column having an inner wall 211 are square lattice (n×n). They are arranged in a structure and connected to each other, and a plurality of elastic support portions 212 and a spiral inner mixing vane 213 are integrally formed on the inner wall 211 of each grid cell 210.

The grid cell 210 in the shape of a square column is positioned at which the fuel rod 10 is inserted, and is elastically supported by a plurality of elastic support portions 212 protruding from each inner wall 111. Preferably, the elastic support part 212 has a strip shape curved in the axial direction (z-axis) of the grid cell 110, and holes 212a open to both sides may be formed. For reference, this strip-shaped plate spring structure can be understood as a shape similar to the general lattice spring employed in the support lattice of the prior art, but the support lattice of the prior art is processed by the lattice spring to be processed on the same lattice plate. However, you cannot have grating springs in both directions. On the other hand, in 3D printing, since grating springs can be formed on both sides of the same grating plate, the degree of freedom in designing the grating spring of the support grating can be increased (see FIG. 5).

The inner mixing vane 213 is disposed on the upper inner wall 211 of the elastic support 212 corresponding to the downstream side of the cooling water, and the upper end of the inner wall 211 is spirally formed along the axial direction (z-axis direction). It is formed protruding by turning. Preferably, in the inner mixing vane 213, the lowermost end 213a and the uppermost end 213b are continuously connected without a step at the inner wall 211, and have a spiral shape along a certain radius with respect to the central axis of the grid cell 210 Has. Preferably, the uppermost end 213b of the inner mixing vane 212 coincides with the upper open end of the grating cell 210.

Specifically, referring to FIG. 6, the grid cell 210 of this embodiment has four elastic support portions 212 formed on each inner wall 211 in a direction perpendicular to each other with respect to the axial direction, and a predetermined arc angle. It includes four inner mixing vanes 213 formed at each corner of the lattice cell 210 within the (θ) range. In particular, each inner mixing vane 213 is formed at each corner of the square grid cell 210, and the lowermost and uppermost ends of each inner mixing vane 212 coincide with the central axis of each elastic support 212. That is, each inner mixing vane 213 is spirally rotated 1/4 turn between the two elastic support portions 212.

The maximum height at the inner wall 211 of each elastic support 212 is located at the same radius on the central axis of the grid cell 210, and if the radius is defined as'D4', the diameter of the elastic support 212 (D4) is smaller than the outer diameter D1 of the fuel rod 10 (D4 <D1). Accordingly, the fuel rod 10 is elastically supported by the elastic support 212. On the other hand, it is the same as the previous embodiment that a dimple for limiting the horizontal behavior of the fuel rod may be added to the lattice cell in addition to an elastic spring for elastically supporting the fuel rod by direct contact with the fuel rod.

The inner mixing vane 213 has a helical shape along the same radius on the central axis of the lattice cell 110, and if the radius is defined as'D5', the diameter (D5) of the inner mixing vane 213 is elastic. It is smaller than the diameter (D4) of the support portion 212 (D4 <D5).

In this embodiment, the diameter D5 of the inner mixing vane 213 is illustrated as being the same as the inner length of one side of the grid cell 210.

7 is a partially cut-away perspective configuration diagram of a support grid for a nuclear fuel assembly showing another modified example from the second embodiment of the present invention, and a redundant description of the same configuration as in the second embodiment will be omitted.

Referring to FIG. 7, in the support grid 300 according to the present embodiment, the grid cells 310 of a square column shape having an inner wall 311 are arranged in a square grid structure to be connected to each other externally, and the inner wall ( In 311), a plurality of elastic support portions 312 and a spiral inner mixing vane 313 are integrally manufactured by 3D printing.

In particular, in this embodiment, the grid cell 310 is a solid plate in which no slots or holes are formed, and an elastic support part 312 protruding from the grid cell 310 to be curved is provided. At this time, the elastic support 312 may be formed to be symmetrical on both sides of the same grating plate.

For reference, in the prior art, the grating spring is formed by sheet metal processing a grating plate, and has a structure in which a grating slot formed through the periphery of the grating spring is inevitably formed. On the other hand, in the present embodiment, it is possible to selectively process the lattice slots as necessary in consideration of the mechanical characteristics of the design of the support lattice, thereby increasing the design freedom of the support lattice.

Experimental example

Flow analysis (CFD) was performed for the first and second embodiments of the present invention, and for comparison, a support grid (HIPER17 type) having a 3×3 grid cell with mixing blades on the top of the conventional type was compared. Flow analysis was performed in the same manner as an example, and the results are shown in [Table 1] below.

[Table 1]

8 to 10 are data showing the flow analysis results for the present invention and the comparative example, and FIGS. 8 and 9 are the x-direction and y-direction at a predetermined height from the top of the mixing vane and the support grid of the comparative example, respectively. The analysis result for the flow velocity of is shown, and FIG. 10 shows the temperature analysis result for one fuel rod.

The present invention described above is not limited by the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope of the technical spirit of the present invention. It will be obvious to those who have the knowledge of. For example, in the present embodiment, the support grid exemplifies a 3×3 grid, but the number of grid cells may increase or decrease within the range of a square grid structure.

100, 200, 300: support grid
110, 210, 310: grid cell
111, 211, 311: inner wall
112, 212, 312: elastic support
113, 213, 313: inner mixing vane

Claims (2)

In the support grid to support the fuel rod of the nuclear fuel assembly,
Hollow cylindrical lattice cells with inner walls are arranged in a lattice structure and are connected to each other by circumscribed,
The lattice cell,
A plurality of elastic support portions which are curved and protruded from the inner wall to the inside, and at least three or more are disposed at an equal angle to elastically support the fuel rod;
And a plurality of inner mixing vanes protruding by spirally rotating an upper tip portion along the upper inner wall of the elastic support portion,
The inner mixing vane is a support grid of a nuclear fuel assembly, characterized in that the lowermost end continuously increases in the axial direction from the inner wall, and the uppermost end is smaller than the maximum height of the elastic support. The method of claim 1, wherein the inner mixing vane coincides with the center of the longitudinal direction of the two elastic support portions adjacent to each other at the lowermost end and the uppermost end, and is 1/k along the inner wall (k is the number of elastic support portions formed in one grid cell). A support grid of a nuclear fuel assembly, characterized in that it is formed by rotation.

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