KR20210028621A - Spacer grid of a nuclear fuel assembly - Google Patents

Abstract

The present invention relates to a spacer grid of a nuclear fuel assembly, which can be manufactured using three-dimensional printing with a high degree of design freedom, excluding sheet metal processing and welding processing and which can simplify a structure, improve impact strength, and reduce pressure drop. In the spacer grid of the nuclear fuel assembly of the present invention, hollow cylindrical lattice cells (110) having an inner wall (111) are arranged in a lattice structure and are connected to each other in a circumscribed manner, and the lattice cells (110) protrude from the inner wall and spirally rotate in a central axis direction, wherein the lattice cells (110) include an elastic vane (120) having a cross-section with an arc shape and supporting a fuel rod.

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 a nuclear reactor is manufactured as a fuel rod by molding enriched uranium into cylindrical sintered pellets of a certain size and then loading a number of sintered bodies into a cladding tube. After being burned, it is 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 is the same to provide a grid cell in which a fuel rod is inserted, which is composed 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 circumferentially. It is formed by protruding from the wall and rotating in a spiral in the direction of the central axis, and has an arc shape in a cross section and includes an elastic vane that supports the fuel rod.

Preferably, the elastic vane is composed of a free tip protruding from the inner wall in an arc shape and having an arc angle of 270° or more, and more preferably, the axial height of the elastic vane is the same as the height of the grid cell.

Preferably, at least three or more of the elastic vanes are arranged conformally in the axial direction.

In the support grid of the nuclear fuel assembly according to the present invention, grid cells in the shape of a hollow cylinder having an inner wall are arranged in a grid structure and are connected to each other circumferentially, and each grid cell protrudes from the inner wall in a spiral direction in the direction of the central axis. Sheet metal processing and welding including elastic vanes that are formed by turning and have an arc shape in the cross section to support fuel rods are excluded, and 3D printing with high design freedom is used to simplify the structure while improving the impact strength and reducing the pressure drop. There is an effect that can be reduced.

1 is a perspective configuration diagram of a support grid for a nuclear fuel assembly according to an embodiment of the present invention,
2 is a perspective configuration diagram of a support grid for a nuclear fuel assembly cut along line AA of FIG. 1,
3 is a cross-sectional view of the AA line of FIG.
4 is a plan view of a support grid for a nuclear fuel assembly according to an embodiment of the present invention.

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. Restrictions 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 an embodiment of the present invention, FIG. 2 is a perspective configuration diagram of a support grid for a nuclear fuel assembly cut along line AA of FIG. 1, and FIG. It is a cross-sectional configuration diagram of line AA, and Figure 4 is a plan configuration diagram of a support grid for a nuclear fuel assembly according to an 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 4, in the support grid 100 of the embodiment, the grid cells 110 in the shape of a hollow cylinder having an inner wall 111 are arranged in a square lattice structure and connected to each other by circumscribed to each other. The grid cell 110 includes an elastic vane 120 protruding from the inner wall and rotating in a spiral shape along the axial direction, and having an arc shape in a cross section and supporting the fuel rod.

The grid cell 110 has an inner diameter larger than the fuel rod 10 and the fuel rod 10 is inserted therein, and the elastic vane 120 formed in a spiral shape along the inner wall 111 supports the fuel rod 10 while elastically supporting the fuel rod 10. By mixing the surrounding coolant, it promotes heat transfer between the fuel rod and the coolant and reduces the pressure drop.

Preferably, the axial height of the elastic vane 120 is provided to have the same height as the lattice cell 110.

In particular, referring to FIG. 4, the elastic vane 120 is formed of a free tip 121 having a constant arc angle θ1 by protruding from the inner wall 111 in an arc shape in a transverse shape to elastically support the fuel rod. , The maximum height at the inner wall 111 of each elastic vane 120 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 of the elastic vane 120 (D2) is smaller than the outer diameter D1 of the fuel rod 10 (D2 <D1). Accordingly, the fuel rod 10 is elastically supported by the elastic support part 112.

Preferably, each grid cell 110 may be provided with a plurality of elastic vanes 120, and more preferably, the plurality of elastic vanes 120 are rotationally symmetric in the axial direction and disposed at an equal angle. do.

In this embodiment, each grid cell 110 shows that the four elastic vanes 120 are configured to be rotationally symmetric, and the spiral path with respect to the central axis of the grid cell 110 in a plane is a constant arc angle (θ2) It has a spiral within the range, and preferably, its arc angle θ2 does not exceed 360°/k (k is the number of elastic vanes in the lattice cell).

Referring to FIG. 3, the elastic vanes 121 and 122 in the adjacent lattice cells may be formed in opposite directions of rotation.

The support grid of the present invention configured as described above is provided with a spiral elastic vane in the cylindrical grid cell to elastically support the fuel rod and simultaneously perform the function of mixing coolant. The elastic vane of this embodiment is a conventional sheet metal or welding It was not possible to implement it by itself, but it can be easily produced using 3D printing with high design freedom.

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.

100: support grid 110: grid cell
120: elastic vane

Claims (3)

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 circumferentially,
The lattice cell,
It is formed by protruding from the inner wall and rotating in a spiral in the direction of the central axis, and has an arc shape in a cross section and includes an elastic vane that supports the fuel rod,
The elastic vane is a support lattice of a nuclear fuel assembly, characterized in that the elastic vane is configured as a free tip protruding from the inner wall in an arc shape and having an arc angle of 270° or more. The support lattice of claim 1, wherein the height of the elastic vane in the axial direction is the same as the height of the lattice cell. The support grid of a nuclear fuel assembly according to claim 1, wherein at least three or more elastic vanes are arranged at an equal angle in the axial direction.

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