KR20220032690A - Bottom spacer grid of a nuclear fuel assembly - Google Patents

Abstract

The present invention relates to a bottom spacer grid of a nuclear fuel assembly having a foreign substance filtering function that can be produced by using 3D printing with a high degree of freedom while excluding sheet metal processing and welding processing. The bottom spacer grid (100) of the nuclear fuel assembly has square lattice cells having inner lattice surfaces (111) forming a square lattice. The lattice cells (110) comprise: a spring (120) formed to protrude on each of the four inner lattice surfaces (111) and formed to support a fuel rod; and a foreign substance filtering unit (130) consisting of two or more ribs crossing with each other in each corner.

Description

Bottom spacer grid of a nuclear fuel assembly

The present invention relates to a lower space grid of a nuclear fuel assembly having a foreign material filtering function 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.

In general, a nuclear fuel assembly includes a plurality of fuel rods disposed in the axial direction, a plurality of spacer grids provided in the transverse direction of the fuel rods to support the fuel rods, a plurality of guide tubes fixed to the spacer grid to constitute the skeleton of the assembly; It consists of an upper fixture and a lower fixture that support the upper and lower ends of the guide tube, respectively.

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. These spacer grids have different shapes and numbers depending on the type and design of the reactor, but are divided into a protective spacer grid, a lower spacer grid, an upper spacer grid, and an intermediate spacer grid according to the assembly position with the fuel rod, and assembled vertically crosswise. The structure for 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 lower spacer grid is located at the bottom of the spacer grids and is disposed immediately adjacent to the lower fixed body, and a function of filtering foreign substances introduced into the reactor together with the coolant in the cooling water circulation process may be required.

The coolant circulating in the reactor may contain various kinds of foreign substances, and these foreign substances pass through the flow path of the lower fixture and adhere between the fuel rod and the spacer grid, causing damage to the fuel rod due to vibration and fretting wear. .

As a method of filtering foreign substances mixed in the cooling water, a function to filter foreign substances can be added to the lower space grid, or the size of the flow path of the lower fixture can be limited, Methods using a combination of lower space grids are being used.

The method of limiting the size of the flow path of the lower fixture increases the pressure drop of the coolant due to the reduction of the flow passage area. The pressing force must be increased, the vibration of the fuel rod can be intensified, the lateral flow of the coolant is induced to promote fretting wear, and various problems can occur in that the heat of the fuel rod is not sufficiently absorbed.

The method of adding a filtering function capable of filtering foreign substances to the lower space grid itself has the advantage of increasing the foreign material filtering performance and relatively reducing the pressure drop, but the structure is complicated and manufacturing is difficult.

In general, the lower spacer grid having a filtering function includes a grid spring that elastically supports the fuel rod in the grid cell, a dimple for limiting the horizontal movement of the fuel rod, and a foreign material filtering unit capable of filtering foreign substances mixed in the coolant.

In general, the grid spring, the dimple, and the foreign material filtering unit are formed by sheet metal processing the space grid plate constituting each grid cell, and in general, the grid spring is provided on two surfaces facing each other or adjacent to each other among the grid cells of four sides, A plurality of dimples are provided on the other two surfaces.

Specifically, the manufacturing process of the spacer grid is performed by assembling and fixing each sheet metal-processed inner grid and outer grid to a separately provided welding jig, and then laser welding (Laser Welding) the cross welding of the inner grid, the joint of the inner/outer grid, and the sleeve joint. ) or by brazing using filler metal, 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 described above, in the conventional manufacturing process of the spacer grid, there are many series of processes such as the sheet metal process and the welding process, and since the structure for filtering foreign substances is applied to the lower spacer grid, the shape design technology is quite difficult, and there are many restrictions on the degree of design freedom. This happens.

In general, 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 in the EOL condition is inevitably required. As described above, the conventional method for manufacturing the lower space grid has many restrictions on shape design, so it is sufficiently stable and high strength under the EOL condition. There is a limit to realizing a lower space grid with

Patent Document 1: US Patent No. 4,652,425 (Patent date: March 24, 1987) Patent Document 2: Laid-open Patent Publication No. 10-2010-0076465 (published date: 2010.07.06.)

The present invention is to improve the problems of the prior art, and the lower support of a nuclear fuel assembly having a foreign material filtering function that can be manufactured using 3D printing that can exclude sheet metal and welding processes, increase design freedom, and simplify the manufacturing process It is intended to provide a grid.

In particular, an object of the present invention is to provide a lower space grid of a nuclear fuel assembly capable of minimizing damage caused by foreign substances by including a foreign material filtering structure in which the trapping of foreign substances can be concentrated at the grid edges by guiding foreign substances to the grid edges.

In addition, the present invention provides a lower space grid of a nuclear fuel assembly that can reduce the height of the spacer grid by arranging a spring for elastically supporting the fuel rod and a foreign material filtering structure at the same height or by arranging the foreign material filtering structure under the spring and excluding a separate dimple. is intended to provide.

In order to achieve this object, in the lower space lattice of the nuclear fuel assembly according to the present invention, square lattice cells having inner lattice planes form a square lattice, and the lattice cells are arranged on each of the four inner lattice planes. a spring protruding in the direction to support the fuel rod; and a foreign matter filtering unit composed of two or more ribs intersecting each other at each corner.

Preferably, the foreign material filtering unit comprises: a plurality of first ribs provided at each corner to form a concentric circle with the fuel rod; and a second rib protruding in a radial direction from each corner of the four inner lattice surfaces and intersecting the first rib.

More preferably, it further includes a plurality of third ribs protruding from the second ribs with an inclination.

Preferably, the foreign matter filtering unit is formed at each corner adjacent to the lower open end of each grid cell, and each corner together with the grid cell has an inclined end having an inclination in the downstream direction of the cooling water flow.

Preferably, the foreign material filtering unit is formed within the vertical section in which the spring is formed.

In the lower space lattice of the nuclear fuel assembly according to the present invention, square lattice cells having inner lattice surfaces form a square lattice, and the lattice cells are formed to protrude in the longitudinal direction from each of the four inner lattice surfaces. a spring formed to support the fuel rod; Each corner of the lower open end is curved, and includes a foreign material filtering unit composed of two or more ribs that cross each other at each corner. It can be maintained strongly and evenly at the center until the end of the core life (EOL), and foreign substances are concentrated at the corners of each grid cell. Prevents damage (breaking) phenomenon.

1 is a perspective configuration diagram of a lower space grid of a nuclear fuel assembly according to an embodiment of the present invention;
2 is a perspective configuration diagram of a unit lattice cell of a lower space grid of a nuclear fuel assembly according to an embodiment of the present invention;
3 is a bottom perspective view of a unit lattice cell of a lower space grid of a nuclear fuel assembly according to an embodiment of the present invention;
4 is a cross-sectional configuration view of the lower spacer grid of the nuclear fuel assembly cut along the line AA of FIG. 2;
5 is a bottom configuration view of a unit grid cell of a spacer grid for a nuclear fuel assembly according to an embodiment of the present invention.
6 is a perspective configuration diagram of a unit grid cell of a lower space grid of a nuclear fuel assembly according to another embodiment of the present invention;
7 is a perspective configuration diagram of a cross-section taken along line BB of FIG. 6;
Fig. 8 is a cross-sectional view taken along line BB of Fig. 6;

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 a lower spacer grid that can be manufactured by metal 3D printing by excluding the sheet metal processing and welding process during the manufacturing process of the lower spacer grid, and the shape of the lower spacer grid produced by the conventional sheet metal processing and welding process It can eliminate design limitations and shorten the manufacturing process.

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.

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 lower space grid of a nuclear fuel assembly according to an embodiment of the present invention, FIG. 2 is a perspective configuration diagram of a unit grid cell of a lower space grid of a nuclear fuel assembly according to an embodiment of the present invention, and FIG. 3 is a bottom perspective view of a unit lattice cell of a lower spacer grid of a nuclear fuel assembly according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view of the lower spacer grid of the nuclear fuel assembly cut along line AA of FIG. 5 is a bottom configuration diagram of a unit grid cell of a spacer grid for a nuclear fuel assembly according to an embodiment of the present invention.

1 to 5 , in the lower space lattice 100 for a nuclear fuel assembly of this embodiment, the square lattice cells 110 having an inner lattice surface 111 are square lattice (n×n) have a structure Each lattice cell 110 is formed to protrude in the longitudinal direction on each of the four inner lattice surfaces 111 , and a spring 120 formed to support the fuel rod 10 ; Each corner of the lower open end is formed to be curved, and includes a foreign material filtering unit 130 made of two or more ribs that cross each other at each corner.

Each inner grid surface 111 of the grid cell 110 is provided with a spring 120 protruding in the longitudinal direction. In Fig. 2, the unit grid cell 110 shows springs 120 on both the inner and outer surfaces of the four-sided grid surface 111, and the outer surface of each grid surface 111 is the corresponding unit grid cell ( 110) and it should be understood that it corresponds to the inner lattice plane of the lattice cell immediately adjacent to it. In addition, in the present embodiment, each lattice surface constituting the lattice cell 110 may have a window formed through a pair of springs 120 therebetween, but preferably, four The grid plane may be a solid plain plate that is entirely closed. The lattice surface of the closed planar structure can have high impact strength and can improve seismic performance.

The spring 120 is fixed at both upper and lower ends in the longitudinal direction (z-axis) of each lattice plane 111 and protrudes from the center to elastically support the fuel rod 10 , preferably, of each lattice plane 111 . placed in the middle The spring 120 includes a contact portion having a curved surface to make surface contact with the surface of the fuel rod in the longitudinal direction (z-axis), and this contact portion includes a fuel rod lifting prevention groove 11 formed in the lower portion of the fuel rod 10 and contact Such a contact portion is in contact with the fuel rod lifting prevention groove 11 to prevent the fuel rod lifting when the fuel rod is lifted by hydraulic power.

For reference, in the prior art, a separate structure (dimple) was required to regulate the position of the dimple other than the spring for elastically supporting the fuel rod. Springs are provided on both inner lattice planes of the dog. Therefore, in the present invention, the fuel rod 10 can be firmly positioned in the center of the grid cell 110 until the end of the careful life (EOL) because the spring can support the fuel rod equally and firmly in four directions.

In addition, the lower spacer grid of the present invention having such a structure has the advantage that the dimple structure as in the prior art can be excluded because the spring can support the fuel rod equally in four directions.

Next, the foreign material filtering unit 130 has each edge 112 of the lower open end in the longitudinal direction (z-axis) within the range h1 at the lower open end has an inclination in the downstream direction of the coolant flow from the corner. An inclined end 112a is formed. The inclined end 112a may be a straight line or a curved slope.

Preferably, it comprises two or more ribs 131 , 132 , 133 intersecting each other at each corner. On the other hand, as shown in FIG. 4 , the foreign material filtering unit 130 may be formed only from the lower opening end to a section lower than the spring 120 .

Preferably, the foreign material filtering unit 130 has a plurality of first ribs 131 provided at each corner to form a concentric circle with the fuel rod 10, and radially protruding from each corner of the three inner lattice planes. A plurality of second ribs 132 intersecting the first rib 131 are included.

The spacing between the first ribs 131 configured as concentric circles and the spacing between the plurality of radially-shaped second ribs 132 may be appropriately determined in consideration of the reduction in pressure drop and the size of the filtered foreign matter. Preferably, it further includes a plurality of third ribs 133 protruding from the second ribs 132 with an inclination.

As described above, the foreign material filtering unit 130 provided at each corner of the lower opening of each grid cell 110 is composed of a plurality of ribs crossing each other, so that the foreign material passing through the lower fixing body is concentrated at the corner of each grid cell 110 . This prevents the fuel rod from being damaged (breaking) by fretting of foreign substances stuck between the fuel rod and the spacer grid, which is a problem occurring in the lower spacer grid in the prior art.

6 is a perspective configuration diagram of a unit lattice cell of a lower space grid of a nuclear fuel assembly according to another embodiment of the present invention, FIG. 7 is a perspective configuration diagram taken along line BB of FIG. 6 , and FIG. 8 is BB of FIG. It is a cross section of a line.

6 to 8, in the lower space lattice 210 of this embodiment, the square lattice cells 210 having the inner lattice surface 211 constitute a square lattice of a plurality of lattice cells. It is composed of 210, and each grid cell 210 is formed to protrude in the longitudinal direction on each of the four inner grid faces 211 and includes a foreign material filtering unit 230 consisting of two or more ribs intersecting each other at each corner. This is the same as the previous embodiment.

In the present embodiment, the vertical section h2 of the foreign material filtering unit 230 is formed within the range of the vertical section L1 in which the spring 220 is formed (h2<L1). As such, by providing the foreign material filtering unit 230 within the vertical section h2 of the spring 220, there is an effect of reducing the pressure drop due to the reduction of the height of the lower spacer as a whole, and it is possible to increase the internal length of the fuel rod, It is advantageous in securing the margin of rod inner pressure (RIP).

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

100: lower space grid 110, 210: grid cell
111: grid surface 120, 220: spring
130, 230: foreign matter filtering unit 131: first rib
132: second rib 133: third rib

Claims (5)

In the lower spacer grid to support the fuel rod of the nuclear fuel assembly,
Square lattice cells with an inner lattice plane form a square lattice,
The grid cell is
a spring protruding from each of the four inner lattice surfaces in the longitudinal direction to support the fuel rod;
A lower spacer grid of a nuclear fuel assembly comprising a foreign material filter consisting of two or more ribs that intersect each other at each corner. According to claim 1, wherein the foreign matter filtering unit,
a plurality of first ribs provided at each corner to form a concentric circle with the fuel rod;
A lower space grid of a nuclear fuel assembly including a second rib that protrudes in a radial direction from each corner of the four inner grid planes and intersects the first rib. The lower spacer grid of claim 2, further comprising a plurality of third ribs inclined and protruding from the second ribs. The method according to claim 1, wherein the foreign matter filtering unit is formed at each corner adjacent to the lower open end of each grid cell, and each corner together with the grid cell has an inclined end having a slope in the downstream direction of the cooling water flow. The lower space grid of the nuclear fuel assembly. The lower space grid of claim 1, wherein the foreign material filtering unit is formed within a vertical section in which the spring is formed.

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