KR102460092B1 - 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 is possible to manufacture 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 having an inner grid surface 121 and having polygons assembled with the fuel rod 10; A plurality of sleeve lattice cells 130 having a hollow cylindrical shape assembled with the guide tube 30; including, wherein the fuel rod lattice cells 120 and the sleeve lattice cells 130 are square lattice It is characterized in that the plurality of flow passage cells 140 provided by the remaining space partitioned by the fuel rod grid cells 120 and the sleeve grid cells 130 are integrally formed.

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 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 to constitute the skeleton of the assembly, and the upper and lower ends of the guide tube 30, respectively. It consists 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 restrains the lateral movement of the fuel rod and maintains the arrangement of the fuel rod by restraining the axial movement with frictional force. The spacer grids 21, 22, and 23 have different shapes and numbers depending on the type and design of the reactor, but the upper spacer grid 21 and the upper spacer grid ( It can be divided into a plurality of intermediate spacer grids 22 disposed between 21) and the lower spacer grid 23, and a lower spacer grid 23 arranged at the lowest end, and consists of a plurality of grid plates that are vertically intersected 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 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. , 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 matter 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 is also referred to as a protective spacer (or a spacer for filtering foreign substances). According to such a nuclear fuel assembly, 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 space lattices, and zirconium is widely used in cladding pipes because of its strong corrosion resistance and a 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. Generally, 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. .

In the manufacturing process of the spacer grid, each of the inner and outer grids processed by sheet metal is assembled and fixed on a separately provided welding jig, and then the cross welding of the inner grid, the joint of the inner/outer grid, and the sleeve joint are welded by laser welding or filler metal. It is joined by brazing using

As such, there are many series of processes such as a sheet metal process and a welding process in the manufacturing process of the conventional spacer grid, 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 spacer lattice shape design. In particular, the prior art spacer grid processes the spacer grid plate material to provide grid springs and dimples. Therefore, 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 spacer grid is very low at the end of life (EOL) condition. A technology for securing nuclear fuel seismic performance and mechanical soundness under EOL conditions is inevitably required. As mentioned above, conventional spacer grid manufacturing methods have many restrictions on shape design. 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, and 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 spacer grid and the lower spacer grid of a nuclear fuel assembly that can be secured.

Inconel spacer grid of a nuclear fuel assembly according to the present invention for achieving this object, an outer grid plate consisting of four grid plates in a square; a plurality of fuel rod grid cells having an inner grid surface and having polygons assembled with the fuel rod; a plurality of sleeve lattice cells having a hollow cylindrical shape assembled with a guide tube, wherein the fuel rod lattice cells and the sleeve lattice cells are arranged in a square lattice and are disposed in the fuel rod lattice cells and the sleeve lattice cells It is characterized in that the plurality of flow passage cells provided by the remaining space partitioned by the

Preferably, the fuel rod lattice cell has a diamond shape, and more preferably, the fuel rod lattice cell protrudes on each of the four inner lattice surfaces and further includes a spring for supporting the fuel rod in contact with the fuel rod. supporter.

The Inconel spacer grid of a nuclear fuel assembly according to the present invention includes an outer grid plate, a plurality of fuel rod grid cells having a polygonal shape, and a plurality of sleeve grid cells having a hollow cylindrical shape, wherein the fuel rod grid cells and the sleeve grid cells are square. A plurality of flow passage cells arranged in a square lattice and provided by a residual space partitioned by fuel rod grid cells and sleeve grid cells are integrally formed, thereby excluding sheet metal processing and welding processing and enabling 3D printing with high design freedom. It has an effect suitable for the upper space grid or the lower space grid by securing mechanical strength while simplifying the structure by utilizing it.

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 perspective configuration diagram of a part of Inconel spacer grid according to an embodiment of the present invention;
7 (a) (b) are graphs showing impact test results for Examples and Comparative Examples of the present invention, respectively.

The specific structural or functional descriptions presented in the embodiments of the present invention are merely exemplified for the purpose of describing the 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 only used 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. As used herein, terms such as “comprises” or “have” are intended to designate the presence 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 possibility of the presence 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, excluding the sheet metal processing and welding process in 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, and the present invention is to propose an Inconel spacer suitable as an upper or lower spacer grid. .

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 ㎣, making it difficult to manufacture a full-size spacer 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 supply device, selectively irradiating a laser or electron beam according to the design drawing, and then melting and laminating layer by layer 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 design freedom for shape, and has the advantage of excellent mechanical performance because the whole can be manufactured in a single-piece.

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. It is an enlarged view of B, and FIG. 6 is an enlarged isometric configuration diagram 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 polygonal 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 have a square lattice structure. A plurality of flow passage cells 140 provided by the remaining space partitioned by the fuel rod grid cells 120 and the sleeve grid cells 130 are integrally formed.

In the outer grid plate 110 , four grid plates have a square structure and constitute the outer structure of the spacer grid, and a plurality of fuel rod grid cells 120 and sleeve grid cells 130 have a forward grid structure inside the outer grid plate 110 . and the remaining space partitioned by the fuel rod grid cells 120 and the sleeve grid cells 130 constitutes the flow path cell 140 . 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 be added with a separate measurement tube into which the measurement equipment is charged, and this measurement tube may be generally disposed at 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 has a polygonal structure having a plurality of inner grid surfaces 121 , and in this embodiment, the fuel grid cell 120 has a rhombus structure having four inner grid surfaces 121 . . Each inner lattice surface 121 of the fuel rod grid cell 120 may directly contact the fuel rod 10 to support the fuel rod 10, and preferably, is formed to protrude from each of the four inner grid surfaces 121 It may further include a spring 150 that is in contact with the fuel rod 10 to support 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 grating 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 pressure drop reduction effect can be obtained by reducing the height of the spacer grid, and the interior of the fuel rod Since the length can be increased, it can greatly contribute to securing a margin of the rod inner pressure (RIP).

The sleeve grid cell 130 has a hollow cylindrical shape and is assembled with a guide tube (or including a measurement 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.

4 and 5 , in this embodiment, the sleeve grid cell 130 is adjacent to each of the four fuel rod grid cells 120 in the horizontal direction (x-axis) and the vertical direction (y-axis), and the fuel rod grid Four flow passage cells 140 are shown in the diagonal direction forming the remaining space partitioned by the cell 120 and the sleeve grid cell 120 .

Meanwhile, in the present embodiment, the fuel rod lattice cell 120 exemplifies and shows a rhombus structure as a whole, but is not limited thereto, and the planar structure of the flow path cell 140 may vary according to the structure of the fuel rod lattice cell 120 . can be deformed.

In the Inconel spacer grid of the present invention, the fuel rod grid cells 120 have a polygonal (eg, rhombus) structure and are arranged like a honeycomb structure together with the sleeve grid cell 130 so that the spacer grid as a whole has elasticity in the lateral direction. By having it, excellent seismic performance can be expected by securing excellent side impact characteristics.

7 (a) (b) is a graph showing the impact test results for Examples (HIPER17 upper space grid for Westinghouse-type nuclear power plant) and Comparative Examples of the present invention, respectively, (a) is the impact velocity (Impact Velocity) and Impact Force, and (b) shows the relationship between Impact Velocity and Stiffness.

Referring to (a) (b) of FIG. 7 , it can be seen that, in the comparative example, the impact strength and rigidity are sharply reduced due to buckling at the beginning, whereas the impact strength of the present embodiment is greater than that of the comparative example. In particular, the present invention has an advantage in seismic performance because the fuel rod lattice cells constituting the plurality of lattice cells have a polygonal (rhombus) structure, have a certain elastic force, gradually increase the impact strength, and have very low rigidity.

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 are possible 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: euro cell
150: spring

Claims (3)

An outer lattice plate composed of four lattice plates;
A plurality of four springs integrally formed with an inner lattice surface of a closed plane (solid plain) and having a rhombus shape assembled with a fuel rod, and formed to protrude on each of the four inner lattice surfaces to contact the fuel rod and support the fuel rod at four points a fuel rod grid cell;
A plurality of sleeve grid cells having a hollow cylindrical shape assembled with a guide tube; including,
wherein the fuel rod grid cells and the sleeve grid cells are arranged in a lattice, and a plurality of flow passage cells provided by the remaining space partitioned by the fuel rod grid cells and the sleeve grid cells are integrally formed. The inconel spacer of the aggregate.
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