KR102393587B1 - Inconel spacer grid of a nuclear fuel assembly - Google Patents

Abstract

The present invention relates to an Inconel spacer grid of a nuclear fuel assembly suitable for upper or lower spacer grids because it can be manufactured using 3D printing with a high degree of design freedom, excluding sheet metal processing and welding processing.
The Inconel spacer grid of the nuclear fuel assembly of the present invention includes an outer grid plate 110 in which four grid plates are square; A plurality of fuel rod grid cells ( 120) and the sleeve lattice cells 130 are an Inconel spacer lattice arranged in a square lattice, wherein the fuel rod lattice cells 120 are neighboring fuel rod lattice cells 120 and the sleeve lattice cells 130 ) and at least two or more of the outer grid plate 110 and a plurality of connecting plates 140 extending in an oblique direction are integrally connected.

Description

Inconel spacer grid of a nuclear fuel assembly

The present invention relates to an Inconel spacer grid suitable as an upper spacer grid and a lower spacer grid in a nuclear fuel assembly that can be manufactured using 3D printing with a high degree of design freedom while excluding sheet metal processing and welding processing.

Nuclear fuel used in nuclear reactors is manufactured into fuel rods by charging enriched uranium into cylindrical pellets of a certain size, and then charging a plurality of sintered bodies in a cladding tube. It is then combusted through a nuclear reaction.

1 is a view showing a typical nuclear fuel assembly.

Referring to FIG. 1, in general, a nuclear fuel assembly includes a plurality of fuel rods 10 disposed in the axial direction, and a plurality of spacer grids 21 provided in the transverse direction of the fuel rods 10 to support the fuel rods 10 ( 22 and 23, a plurality of guide tubes 30 that are fixed to the spacer grids 21, 22, and 23 constituting the skeleton of the assembly, and the upper and lower ends of the guide tube 30, respectively. It is composed of an upper fixed body 40 and a lower fixed body (50).

The spacer 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. The spacer grids 21, 22, and 23 have different shapes and numbers depending on the reactor type and design, but the upper spacer grid 21 and the upper spacer grid ( 21) and a plurality of intermediate spacer grids 22 disposed between the lower spacer grid 23, and a lower spacer grid 23 disposed at the lowermost end, and consists of a plurality of grid plates that are vertically crossed and assembled. The structure that provides the grid cell in which the fuel rod is inserted is the same.

Meanwhile, a mixing vane protruding in the downstream direction of the coolant flow may be added to the spacer grid, and this mixing vane has a shape surrounding the fuel rod and serves to promote heat transfer through mixing of the coolant around the fuel rod. , a space lattice having such a function is also referred to as a mixed space lattice.

Also, among the spacer grids, in addition to the function of supporting the fuel rod by being disposed adjacent to the lower fixture, there is provided a spacer grid having a foreign material filtering function that filters foreign matter that may be introduced into the reactor together with the coolant during the circulation process of the coolant. Such a spacer grid is also referred to as a protective spacer grid (or a spacer grid for filtering foreign substances). Depending on these nuclear fuel assemblies, a filtering structure is applied to the lower spacer grid itself, so that the lower spacer grid and the protective spacer grid may be provided as one spacer grid, or a protective spacer grid having a foreign matter filtering function is separately provided from the lower spacer grid. can be provided.

A zirconium alloy (zircaloy) is generally used for these spacer lattices, and zirconium is widely used in cladding pipes and the like because of its strong corrosion resistance and small neutron absorption cross-sectional area.

The spacer grid is provided with a spring that elastically supports the fuel rod in the grid cell and a dimple for limiting the horizontal movement of the fuel rod. The spring and the dimple are formed by sheet metal processing of the spacer grid plate constituting each grid cell, and in general, a grid spring is provided on two surfaces facing each other among the grid cells of four sides, and a plurality of dimples are provided on the other two surfaces. .

The manufacturing process of the spacer grid is performed by assembling and fixing each inner grid plate and the outer grid plate processed by sheet metal to a separately provided welding jig, and then laser welding or filler metal for the cross welding of the inner grid, the joint of the inner/outer grid, and the sleeve joint. It is joined by brazing using , 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 grid.

As such, in the conventional manufacturing process of the spacer grid, there are many series of processes such as a sheet metal process and a welding process, and the shape design technique for securing dynamic impact strength for seismic performance in the design process is quite difficult.

Although the prior art space lattice manufacturing process is a stabilized technology, as described above, it undergoes a multi-step manufacturing process, so that there are many restrictions in the design of the space lattice shape. In particular, in the prior art space grid, a grid spring and dimples are provided by processing a spacer grid plate material. Accordingly, the number of grid springs and dimples that can be designed in each grid cell is limited, thereby limiting the degree of freedom in design.

In this regard, it has been reported that the impact strength of the space grid is very low at the end of life (EOL) condition. A technology for securing nuclear fuel seismic performance and mechanical soundness in the EOL condition is inevitably required, and the conventional method of manufacturing a spacer grid has many restrictions on shape design as seen above. There are limitations in implementing it.

Patent Document 1: Korean Patent Publication No. 2003-0038493 (published date: May 16, 2003) 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. It is manufactured by 3D fritting using Inconel as a material, so it cannot be manufactured by the conventional sheet metal process. This is to provide an Inconel spacer grid suitable for the upper space grid and the lower space grid of the nuclear fuel assembly that can be secured.

Inconel spacer grid of a nuclear fuel assembly according to the present invention for achieving this object, the outer grid plate consisting of four grid plates in a square; A plurality of fuel rod grid cells and the sleeve grid cells are formed into a square lattice, including a rectangular fuel rod grid cell having an inner grid surface and assembled with a fuel rod, and a hollow cylindrical sleeve grid cell assembled with a guide tube. A spacer grid of Inconel, wherein the fuel rod grid cells are integrally connected to at least two of adjacent fuel rod grid cells, the sleeve grid cells, and the outer grid plate by a plurality of connecting plates extending in an oblique direction. do it with

Preferably, the fuel rod lattice cell further includes a spring protruding from each of the four inner lattice surfaces to contact the fuel rod to support the fuel rod.

Preferably, the fuel rod grid cell and the sleeve grid cell are respectively connected to neighboring grid cells by at least four connecting plates in an oblique direction.

The Inconel spacer grid of a nuclear fuel assembly according to the present invention is an outer grid, and a plurality of fuel rod grid cells and sleeve grid cells are arranged in a square grid, wherein the fuel rod grid cells are adjacent to each other fuel rod grid cells and sleeve grids. By being integrally connected by at least two or more of the cell and outer grids and a plurality of connecting plates extending in the diagonal direction, sheet metal processing and welding are excluded and the structure is simplified and mechanical strength is achieved by utilizing 3D printing with high design freedom. It has an effect suitable for the upper space grid or the lower space grid.

1 is a view showing a typical nuclear fuel assembly;
2 is a perspective configuration diagram of an Inconel spacer grid according to an embodiment of the present invention;
3 is a plan view of an Inconel spacer grid according to an embodiment of the present invention;
4 and 5 are enlarged views of A and B of FIG. 3, respectively;
6 is an enlarged isometric configuration diagram of a part of an Inconel spacer grid according to an embodiment of the present invention.

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

On the other hand, the terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as "comprises" or "have" are intended to designate the existence of an embodied feature, number, step, action, component, part, or combination thereof, one or more other features or numbers, It should be understood that the existence or addition of steps, operations, components, parts or combinations thereof is not precluded in advance.

The present invention is to provide an Inconel spacer grid that can be produced by metal 3D printing using Inconel as a material by excluding the sheet metal processing and welding process during the manufacturing process of the spacer grid, and supports manufactured by the conventional sheet metal processing and welding process. Restrictions on the shape design of the grid can be eliminated and the manufacturing process can be shortened. Inconel, a nickel-chromium alloy, has a higher neutron absorption than a zirconium alloy, but has an advantage in that it is superior in strength to increase the mechanical strength of the nuclear fuel assembly. In particular, since the upper and lower spacer grids are located at the top and bottom of the nuclear fuel assembly, a material with high neutron absorption may be used. .

In general, various metal 3D printing devices are available, and for example, Germany's CONPCEPTLASER's 3D printing equipment has a maximum production size of 250 × 250 × 280 ㎣, which makes it difficult to manufacture a full-size spacer grid. PBF (Powder Bed) in which a product is manufactured in a way that a powder layer of several tens of μm is laid on a powder bed having a certain area in a powder supply device, a laser or electron beam is selectively irradiated according to a design drawing, and then melted layer by layer and laminated Fusion) method is used. On the other hand, the space grid of the present invention may be employed in a general metal additive manufacturing method employed in general metal 3D printing, and is not limited to a specific method.

Such metal 3D printing has a high degree of freedom in designing the shape, and the whole can be manufactured in a single-piece, so it has the advantage of excellent mechanical performance.

2 is a perspective view of an Inconel spacer grid according to an embodiment of the present invention, FIG. 3 is a plan view of an Inconel spacer grid according to an embodiment of the present invention, and FIGS. 4 and 5 are respectively A of FIG. It is an enlarged view of B, and FIG. 6 is an enlarged isometric configuration view of a part of an Inconel spacer grid according to an embodiment of the present invention.

2 to 6 , the Inconel spacer grid 100 of this embodiment is an outer grid plate 110 in which four grid plates are square, and a fuel rod grid cell 120 of a square structure assembled with the fuel rod 10 . ) and a hollow cylindrical sleeve lattice cell 130 assembled with the guide tube 30, wherein the plurality of fuel rod lattice cells 120 and sleeve lattice cells 130 are formed in a square lattice structure. are placed

The outer lattice plate 110 has four lattice plates having a square structure and constitutes the outer structure of the spacer lattice.

Preferably, the fuel rod grid cell 120 is a plurality of connecting plates 140 extending in an oblique direction with at least two or more of the adjacent fuel rod grid cells 120 , sleeve grid cells 130 , and outer grid plates 110 . ) is integrally connected with

In the present invention, each of the outer grid plate 110 , the fuel rod grid cell 120 , and the sleeve grid cell 130 is a closed solid plate.

On the other hand, the nuclear fuel assembly may have a separate measuring tube in which the measuring equipment is charged, and such a measuring tube may be generally disposed in the center of the spacer grid. It is collectively described as Also, the arrangement or number of guide tubes may be variously modified according to the nuclear fuel assembly.

The fuel rod grid cell 120 may support the fuel rod 10 by directly contacting the fuel rod 10 with four inner grid surfaces 121 , and preferably, the four inner grid surfaces 121 protrude from each of the four inner grid surfaces 121 . It may further include a spring 150 for supporting the fuel rod 10 in contact with the fuel rod 10 .

For reference, in the prior art, a separate structure (dimple) was required to regulate the position of the fuel rod other than the spring for elastically supporting the fuel rod. Springs are provided on both inner lattice planes to eliminate dimples.

In addition, since the Inconel spacer grid of the present invention having such a structure can exclude a dimple structure for regulating the position of the fuel rod as in the prior art, the height of the upper and lower sections of the spring 150 can be reduced, so that the entire spacer grid There is an effect of reducing the pressure drop by reducing the height of the fuel rod, and since the internal length of the fuel rod can be increased, it can greatly contribute to securing the margin of the rod inner pressure (RIP).

In addition, since the fuel rod grid cell 120 is connected to the neighboring fuel rod/sleeve grid cells by a plurality of connecting plates 140 that extend diagonally, it is possible to elastically support the fuel rod without the need for a separate spring/dimple. Due to the shape characteristics of the connected grid, the space grid may have flexible rigidity as a whole. In addition, if necessary, when the diagonal connecting plate is configured in the shape of a curved bulkhead, the cooling water mixing effect can be enhanced.

The sleeve grid cell 130 has a hollow cylindrical shape and is assembled with a guide tube (or a measuring tube) 30 . On the other hand, the sleeve grid cell 130 may be assembled by welding or bulge processing with the guide tube 30, or may be fastened by screwing to each other.

In particular, referring to FIGS. 4 and 5 , the connecting plate 140 integrally connects the neighboring fuel rod grid cells 120 , the sleeve grid cells 130 , and the outer grid plate 110 in the diagonal direction θ.

In FIG. 4 , the sleeve grid cell 130 is connected to four adjacent fuel rod grid cells 120 by a connecting plate 140 , so that one sleeve grid cell 130 has four connecting plates 140 . .

The fuel rod grid cell 120 disposed at the corner in FIG. 5 is connected to the outer grid plate 110 and two connecting plates 141 and 142, and the fuel rod grid cell and two connecting plates 143 and 144 immediately adjacent to each other. ) to show that it has four connecting plates 141, 142, 143, and 144.

On the other hand, in this embodiment, the fuel rod grid cell 120 and the guide tube sleeve grid cell 130 have been described by exemplifying that they are connected to neighboring grid cells by four connecting plates, respectively, but all grid cells are integrated in the outer grid. The number and angle of the connecting plates connecting each fuel rod/sleeve grid cell within the range connected by

The present invention described above is not limited by the above-described embodiments and the accompanying drawings, and it is common in the technical field to which the present invention pertains that various substitutions, modifications and changes can be made within the scope without departing from the technical spirit of the present invention. It will be clear to those who have the knowledge of

10: fuel rod 30: guide tube
110: outer grid 120: fuel rod grid cell
130: sleeve grid cell 140: connecting plate
150: spring

Claims (3)

An outer lattice plate composed of four lattice plates;
A plurality of fuel rod grid cells and the sleeve grid cells are formed into a square lattice, including a rectangular fuel rod grid cell having an inner grid surface and assembled with a fuel rod, and a hollow cylindrical sleeve grid cell assembled with a guide tube. As a space grid of Inconel to be disposed,
The fuel rod grid cells are integrally connected to at least two of the adjacent fuel rod grid cells, the sleeve grid cells, and the outer grid plate by a plurality of connecting plates extending in an oblique direction. . The inconel spacer grid of a nuclear fuel assembly according to claim 1, wherein the fuel rod grid cell further comprises a spring protruding from each of the four inner grid surfaces to contact the fuel rod to support the fuel rod. The inconel spacer grid of a nuclear fuel assembly according to claim 1, wherein the fuel rod grid cell and the sleeve grid cell are respectively connected to neighboring grid cells in an oblique direction by at least four connecting plates.

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